Ngerikiil Watershed Resource Assessment

United States Department of Agriculture Natural Resources Conservation Service Pacific Basin Area February 2005 Ngerikiil Watershed Resource Assessment Ngerikiil Watershed Resource Assessment Sponsored by: Palau Natural Resources Council & Airai Community, Republic of Palau Prepared by: United States Department of Agriculture Natural Resources Conservation Service Pacific Basin Area Technical report written by: Dr. Robert T. Gavenda - NRCS Soil Scientist & Assessment Team Leader Anthony H. Ingersoll - NRCS Conservation Agronomist Sherman L. White - NRCS Civil Engineer Nicole Caruso - Peace Corps Volunteer, Palau Conservation Society Robin A. DeMeo - Resource Conservationist, NRCS Palau Field Office Paul Zellmer - NRCS Natural Resource Specialist, Guam John H. Lawrence - NRCS State Resource Conservationist February 2005 The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, and marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at 202-720-2600 (voice and TDD). I ACKNOWLEDGEMENTS The Ngerikiil Watershed Resource Assessment was conducted under the direction of the United States Department of Agriculture, Natural Resources Conservation Service (USDA-NRCS). The project manager for the Ngerikiil Watershed project is Robin A. DeMeo, Resource Conservationist, Palau NRCS Field Office. The local Palau sponsorship for the assessment was provided jointly by the Honorable Governor of Airai, Tmewang Rengulbai, and the Palau Natural Resource Council. The assessment sponsors and authors wish to acknowledge the following individuals and groups for their contribution to the Ngerikiil Watershed Resource Assessment and the watershed planning process: To the many farmers and landowners who graciously allowed us access to their property and answered our many questions, including but not limited too: Kenjiro Dengokl Uwai Ikesakes Meresebang Ngiralmau John Oiph Victor Yano Lazarrenna Yosinawo We also like to thank the following Chiefs, groups, agencies, members and individuals: Koichi Watanabe, Chief Ngirachitei in Oikull Alan Seid, Chief Adelbai ra Irikl in Oikull Risao Rechirei, Chief Iyechad ra Odelomel in Oikull James Orak, Chief Recheyungel in Ngermid Donald Dengokl, Ngerikiil Watershed Working Group Member Portia Franz, Palau Community College, Cooperative Research and Extension (CRE) Charles Guard, Warning Coordination Meteorologist, NOAA Weather Forecast Office, Guam Terangue “Tiger” Gillham, Executive Officer, Environmental Quality Protection Board (EQPB), Republic of Palau Yimnang Golbuu, Palau International Coral Reef Center Gillian Johanes, Palau Conservation Society and Chief Aderdei in Oikull John Kintaro, National Inspector for the Compact Road, Environmental Quality Protection Board (EQPB), Republic of Palau Ann Kitalong, Biologist, Private Consultant with The Environment Inc., Palau Rick Mangham, Manager of Capital Improvement Program, Ministry of Resources & Development, Republic of Palau Jack Master, Airai State Legislature Henriette Merei, Ngerikiil Watershed Working Group Member II Ubei Nakamoto, Pesticide Inspector, EQPB, Republic of Palau David Orrukem, Ngerikiil Watershed Working Group Member Judy Otto, former Director of the Palau Conservation Society (PCS) Kelly Raleigh, Project Manager, Office of the Palau Automated Land and Resource Information System, Ministry of Resources & Development Kashgar Rengulbai, Forester, Bureau of Agriculture, Republic of Palau Techur Rengulbai, Chief of Water, Republic of Palau Ivan Rudimch, Ngerikiil Watershed Working Group Member Ebais Sadang, Forester, Bureau of Agriculture, Republic of Palau Belhaim Sakuma, Director of Palau Conservation Society (PCS) Melwat Telei, Chairman Ngerikiil Watershed Working Group Jon Vogt, Environmental Inspector, U.S. Army Corps of Engineers, Compact Road Project, Palau Cover Photo: Aerial photo overlooking Airai Bay, Palau. Photo: USDA-Natural Resources Conservation Service. III TABLE OF CONTENTS EXECUTIVE SUMMARY __________________________________________________________________ 1 SECTION 1: 1.1 1.2 1.3 1.4 ASSESSMENT OVERVIEW ____________________________________________________ 7 INTRODUCTION _____________________________________________________________________ 7 PURPOSE ___________________________________________________________________________ 8 OBJECTIVE _________________________________________________________________________ 9 DESCRIPTION OF THE ASSESSMENT___________________________________________________ 9 PROJECT AREA ____________________________________________________________ 10 SECTION 2: 2.1 PHYSICAL DESCRIPTION ____________________________________________________________ 10 2.2 DEVELOPED LAND AREAS __________________________________________________________ 13 2.3 AGRICULTURAL AREAS ____________________________________________________________ 13 2.4 CLIMATIC CONDITIONS_____________________________________________________________ 15 2.5 GEOLOGY _________________________________________________________________________ 16 2.6 HYDROLOGY ______________________________________________________________________ 16 2.6.1 Groundwater ___________________________________________________________________ 17 2.6.2 Surface Water __________________________________________________________________ 17 2.6.3 Rainfall _______________________________________________________________________ 19 2.6.4 Water Use _____________________________________________________________________ 25 2.6.5 Water Quality __________________________________________________________________ 25 2.6.6 Recommendations _______________________________________________________________ 26 2.7 SOILS _____________________________________________________________________________ 27 2.7.1 Soil Classification _______________________________________________________________ 27 2.7.2 Soil Mapping Concepts ___________________________________________________________ 29 2.7.3 Soil Survey Procedures ___________________________________________________________ 29 2.7.4 Soil Formation __________________________________________________________________ 36 2.7.5 Soil Properties__________________________________________________________________ 37 2.7.6 Soil Inventory __________________________________________________________________ 39 2.7.7 Soil Interpretations ______________________________________________________________ 41 2.8 VEGETATION AND PLANT COMMUNITIES ____________________________________________ 43 SECTION 3: CRITICAL RESOURCE CONCERNS___________________________________________ 48 3.1 SOIL EROSION & SEDIMENTATION ___________________________________________________ 48 3.1.1 Effects of Soil Erosion on Water Quality _____________________________________________ 49 3.1.2 Causes of Soil Erosion ___________________________________________________________ 50 3.1.3 Erosion Rates __________________________________________________________________ 51 3.1.4 Roads_________________________________________________________________________ 60 3.1.5 Development ___________________________________________________________________ 64 3.1.6 Agriculture ____________________________________________________________________ 67 3.1.7 Burning of Savanna Areas_________________________________________________________ 81 3.1.8 Stream Bank Erosion_____________________________________________________________ 83 3.2 NUTRIENT, PESTICIDE & OTHER POLLUTION__________________________________________ 85 3.2.1 Animal Manure _________________________________________________________________ 85 3.2.2 Chemical Fertilizer Runoff ________________________________________________________ 87 3.2.3 Pesticide Leaching ______________________________________________________________ 89 3.3 SOLID WASTE DISPOSAL ____________________________________________________________ 90 3.4 INVASIVE SPECIES _________________________________________________________________ 91 3.5 WILDLIFE HABITAT IMPACTS _______________________________________________________ 93 SECTION 4: RECOMMENDATIONS & FUTURE CONDITIONS ______________________________ 95 4.1 SOIL EROSION & SEDIMENTATION ___________________________________________________ 96 4.1.1 Roads_________________________________________________________________________ 96 4.1.2 Development ___________________________________________________________________ 98 4.1.3 Agriculture ___________________________________________________________________ 101 IV 4.1.4 Burning & Land Clearing ________________________________________________________ 102 4.1.5 Stream Bank Erosion____________________________________________________________ 102 4.2 NUTRIENT & PESTICIDE POLLUTION ________________________________________________ 103 4.2.1 Animal Manure ________________________________________________________________ 103 4.2.2 Chemical Fertilizer Runoff & Nutrient Over-Enrichment________________________________ 106 4.2.3 Pesticide Leaching _____________________________________________________________ 107 4.3 SOLID WASTE DISPOSAL ___________________________________________________________ 108 4.4 INVASIVE SPECIES ________________________________________________________________ 109 4.5 WILDLIFE HABITAT IMPACTS ______________________________________________________ 110 APPENDIX A: APPENDIX B: APPENDIX C: WORKS CITED ____________________________________________________________ 1 GENERAL REFERENCES___________________________________________________ 1 LIST OF ACRONYMS USED_________________________________________________ 1 V EXECUTIVE SUMMARY The Ngerikiil Watershed area covers 28.5 square kilometers (11 square miles or 7,040 acres) of Airai State, Babeldaob Island. The sub-watersheds of Ngerikiil include the Ngerikiil, Ikoranges, Kmekumel, Edeng, Oikull, and Airai (Map 1). The watershed has been an area of importance to Palau as a major water source (water intake built in 1985) and therefore, of interest for a watershed protection project for many years. In July 2002, the Palau Natural Resources Council (PNRC) and Governor of Airai, Mr. Tmewang Rengulbai, requested United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) assistance for the Ngerikiil Watershed Resource Assessment. NRCS responded to the request with a field inventory of the watershed and a literature review. The findings are presented in this report as a comprehensive resource assessment of the Ngerikiil Watershed. The primary objectives were to identify pollution sources, sustainable and unsustainable land uses within the watershed, and to make recommendations addressing natural resource concerns, especially those affecting water quality within the Ngerikiil Watershed of Airai State, Palau’s critical drinking water source. The Resource Assessment is designed to help the stakeholders better understand the resource problems by helping to find solutions for maintaining and/or improving surface and near-shore water quality while sustaining healthy habitats. The document is divided into four sections: the first section provides an overview of the assessment with the purpose and objectives; the second section covers the project area description reviewing the natural resources in the watershed; the third section covers an in-depth look at the critical resource concerns; and the fourth section covers the recommendations for solving the resource concerns. Critical Resource Concerns and Recommendations Five critical resource concerns were identified through the resource assessment. In order of their level of threat to the main watershed objectives the critical resource concerns are: • • • • • Soil Erosion and Sedimentation Nutrient, Fertilizer and Pesticide Pollution Solid Waste Disposal Invasive Species Wildlife Habitat Loss Soil Erosion and Sedimentation Sediment-laden runoff, reaching the river and ultimately the ocean, is presently the most serious resource concern within the Ngerikiil Watershed. This often-unrecognized pollutant is affecting both Palau’s primary drinking water source and coral reef health within Airai Bay. There are five primary sources: 1 • • • • • Sediment-laden runoff from unprotected roads Sediment-laden runoff from housing and other development Erosion from agricultural land lacking conservation practices Erosion from burned savanna areas Stream bank erosion Soil erosion is a natural process. Human activity, however, can increase the rate of erosion within the landscape. The soils on Babeldaob Island contain a large percentage of clay particles that remain suspended when in water and are transported long distances in runoff until they settle out. They are very acidic, low in nutrients and organic matter, and high in soluble aluminum. These properties create marginal conditions for plant growth resulting in fragile soil-plant communities that, once disturbed, are very difficult to re-establish. The amount of soil eroding from particular sloped landscapes was estimated. Some deposition of the eroded soil occurs as the soil travels between the particular landscape source and the downslope body of water, therefore, these estimations do not represent the amount of soil entering the tributaries or river as sediment,. The eroding landscapes assessed were: • • • • • Unpaved, non-graveled roads Construction sites (bare soil, no conservation and sites with mulch and/or cover) Agricultural lands (traditional Palauan farming practices and cropland on various slopes without conservation practices) Undisturbed forest Savanna (frequently burned and unburned) The estimated erosion values are used for comparisons to predict soil loss under different site and management conditions. A soil loss tolerance, or the maximum amount of erosion at which the plant growth can be maintained within the soil, is estimated based on the soil properties for each soil series. This tolerance level, determined to be 11.2 metric tons per hectare per year (5 tons/acre/year) for the Aimeliik and Palau soil series, represents the amount of soil created each year and therefore, is equal to the maximum soil loss tolerated to maintain sustainability of the soil and landscape. 2 Map 1: Location of Ngerikiil Watershed and its sub-watersheds and streams 3 Roads and Development The development of the new United States Compact Road will cause significant land use changes by opening up the watershed to more roads and development. While the Compact Road is being constructed under relatively high environmental scrutiny and protection, other National and State roads have not been installed with either close inspection or environmental standards. New farms, housing and other development within the Ngerikiil Watershed currently lack measures to protect against soil running off the construction site. Unless strict environmental codes and laws are passed and enforced for development and road construction, serious impacts to the watershed’s water quality can be expected to increase with the opening of the Compact Road. Roads in the watershed, all of which are unpaved, produce the highest estimated rate of erosion of any land use, 1,070.3 metric tons per hectare per year (477.4 tons/acre/year), over 100 times the tolerance level. Along many roads, drainage routes are much too steep and as a result, contain numerous gullies. Paving of these roads would reduce this erosion to virtually nothing. Runoff from roads should be captured in such a manner to reduce velocities allowing for infiltration and/or direct flow to wetland areas or non-erosive areas. Unprotected construction sites are vulnerable to soil erosion and contribute to sediment-laden runoff reaching the Ngerikiil River. Calculations indicate that erosion from construction sites within the watershed can be reduced by 85 percent if conservation efforts including mulching and other types of soil cover are used at these sites. Agriculture Poor farming practices detach large amounts of soil and allow them to be transported by wind and surface runoff into streams and lagoons. Soil fertility may be lost because large percentages of a farm field are not vegetated, eliminating the soil nutrient source and exposing the more nutrient-rich topsoil to erosion (particularly erosion caused by the heavy and frequent rains). Soil losses not only cause soil infertility but also degrade water supplies and impacts aquatic life. Erosion rates were estimated from agricultural fields with various agricultural practices, including detrimental practices such as clean tillage, farming up and down slope, burning, and conservation practices such as cross-slope farming, crop rotation, and mulching. The estimates indicate that the combination of tilling the soil and leaving the soil bare or unvegetated in the farm fields causes the highest amount of erosion. This practice, called high tillage or clean tillage, causes erosion in excess of 669 metric tons per hectare per year (298.4 tons/acre/year) from farm fields on steep slopes. This exceeds the tolerance goal of 11.2 metric tons per hectare per year (5 tons/acre/year) by nearly 6,000 percent. The average annual rainfall for Airai State is about 370.8 centimeters per year (146 inches/year). At this volume and the intensity at which rain comes down, tilling soil on any slope and leaving it bare for even short periods of time will lead to significant erosion. The resource assessment team observed some crop fields in Palau to be tilled up and down the slope instead of across slopes. The steepness of the slopes gives the water enough energy to severely erode these straight bare-earth channels. The application of just one or two conservation techniques is not enough, particularly on moderate (six to12 percent) and steep (greater than12 percent) slopes, in Palau. Because the soil 4 here is so vulnerable to erosion, it is crucial to incorporate several conservation techniques that include cross-slope, low-till farming with mulching, grass cover, vegetated drainage ways and crop rotations or agroforestry. Agroforestry is the traditional Palauan farming practice of multistoried crops (fruit trees, medicinal plants or shrubs, and food crops) planted intermixed or in small patches. Agroforestry minimizes the disturbance of the soil and maximizes the input of organic matter. Estimated erosion from areas farmed using the traditional Palauan method of agroforestry occurs at rates below the soil erosion tolerance level of 11.2 metric tons per hectare per year (5 tons/acre/year) annually. “Heavy use areas” are areas of the farm that are subjected to large amounts of foot or machine traffic, for example, access roads, footpaths, and areas beneath water spigots. The assessment team observed heavy use areas and access roads on farms in Palau to be eroding massively in many cases. These areas should be covered by vegetation, gravel, pavement or some type of erosion control; maintenance of cover is also critical. Burning of Savanna Areas Savanna or grassland areas, covering nine percent of the watershed, are often subjected to human-induced burning for purposes of producing ash for plant fertilizer. While ash itself is an excellent fertilizer containing important plant nutrients particularly potassium, ash produced in this manner is typically washed away from heavy rains, causing a net loss of nutrients in the soil. This process leaves the soils less fertile and creates increased soil erosion leading to lower fertility in a cycle of increasing soil degradation. Burning is a serious concern as a contributing factor to the erosion problem on the island of Babeldaob. Erosion on frequently burned savannas occurs at upwards of 223 metric tons per hectare per year (99.5 tons/acre/year), while healthy unburned grassland was estimated to erode at an annual rate of only 3.1 metric tons per hectare per year (1.4 tons/acre/year). Instead of burning fields to produce ash for fertilizer, ash from cooking fires should be used as fertilizer, applied by digging and mixing the ash into the soil to reduce the likelihood of it being washed away. Additionally, important plant nutrients can be obtained from nitrogen-fixing legume plants. Legumes should be rotated into croplands every year during a three-month fallow period, the approximate time it takes for them to start to flower. As soon as the legume plants flower, they should be cut back and this plant matter should be incorporated into the soil, providing nutrients for the next plantings. Stream Bank Erosion The final source of sediment affecting water quality in the Ngerikiil Watershed is from failing stream banks. Many of these may be the naturally occurring results of stream meander in the upper portions of the watershed where no development is taking place. Streams naturally migrate as one side of the bank is built up and the other side erodes away. Human-induced stream bank erosion is also present. There exists nearly 3,000 meters (9,842.5’) of riverbank along the Ngerikiil River where agricultural tillage is being practiced close to the river’s edge. This practice has removed the natural forest and plant cover buffer in some places next to the stream. The roots of these buffer species hold the bank together protecting it from slippage and erosion. Removal of these buffer areas leaves the river’s banks vulnerable to eroding and slumping. 5 A major stream bank failure was observed during the assessment, resulting from loss of buffer species that previously anchored the bank in place. This failure caused the river to encroach approximately 4.6 meters (15’) into this farm field, for a length of about 12.2 meters (40’) along the river. The danger with this vertical cut bank is that the river will continue to undercut that bank, which leads to further bank failure, erosion and encroachment into the farmer’s field. A riparian buffer of between 10.7 to 19.8 meters (35’ to 65’) should be maintained along the banks of the river and all tributaries in the watershed. Nutrient, Fertilizer, and Pesticide Pollution The Ngerikiil Watershed presently does not appear to be seriously threatened by either point or non-point source pollutants. However, the likelihood for pollutants to appear in the environment will dramatically increase with development. Potential future sources include point or direct discharges from gasoline stations (leaking storage tanks) or laundry facilities (phosphates from washing machines or solvents from dry cleaners) and non-point or diffuse sources such as runoff from roads and parking lots (automobile oils). Three existing pollution sources within the watershed have been identified as specific concerns that, if left unchecked, will become problems adversely affecting water quality and the environment. The sources are animal manure from confined animal feeding operations, runoff of excess fertilizers, and pesticide leaching and runoff. Runoff, overflowing from open manure storage structures at concentrated animal areas was observed by the assessment team. Algae growth in drainage ditches at several farms indicates excess nutrients from either over-fertilization or poor manure management practices. Excess nutrients (particularly nitrogen, phosphorus and potassium), contained in fertilizer and animal manure, are very toxic to aquatic wildlife and can be a major human health hazard. Development of a nutrient management plan for animal manure that minimizes the pollution and utilizes the nutrients is critical for each confined animal feeding operation. Proper application of fertilizers that incorporates the fertilizer into the soil so that it becomes chemically bound to the soil particles and does not leach or volatize is very important. Additional recommendations for nutrient management are provided in the Recommendations Section at the end of this report. Pesticides and herbicides are sometimes illegally imported into Palau in unidentifiable packaging. Use of harmful, illegal pesticides and herbicides can have long-lasting deleterious affects on soil fertility, water quality and natural habitats. Rigorous enforcement is imperative. 6 SECTION 1: ASSESSMENT OVERVIEW 1.1 INTRODUCTION “In the old days, the population of Palau was larger than today. However, they were aware of conservation and the environmental impacts of our natural resources. In that regard, the people kept their establishments away from the watersheds especially. [Today] the development is taking place at a pace that we may not be able to control around the Ngerikiil Watershed areas. Nevertheless, the development is part of our community improvement. Yet we must explore better ways to improve, protect, preserve, with a sound management plan.” Koichi Watanabe, Chief Ngirachitei in Oikull. The Ngerikiil Watershed project is a cooperative watershed project sponsored by the Honorable Governor of Airai, Tmewang Rengulbai, the Palau Natural Resource Council (PNRC) and the members of the PNRC Watershed Committee. The Palau Natural Resource Council Watershed Committee members include: Ann Kitalong, The Environment Inc. (TEI); Portia Franz, Palau Community College – Cooperative Research Extension (PCC-CRE); David Hinchley, The Nature Conservancy (TNC); Kascar Rengulbai, Republic of Palau Bureau of Agriculture (BOA); Kimie Ngirchechol, Republic of Palau Bureau of Marine Resources (BMR); Tarita Holm, BOA; Kelly Raleigh, Palau Automated Land and Resource Information System (PALARIS); Alma Ridep-Morris, BMR; and Robin DeMeo, United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS). The Ngerikiil Watershed has been an area of importance to Palau as a major water source (water intake built in 1980) and therefore of interest for a watershed protection project for many years. The Environmental Quality Protection Board completed an initial Ngerikiil Watershed Inventory in 1993, which calls, “for a more in depth assessment of the areas physical characteristics and potential environmental impacts resulting from current activities.” (Elliott and Franz, 1993). In 1998, the Palau Community College conducted the Ngerikiil River Project focusing on water quality testing (Rengiil, 1999). In the 1998 Unified Watershed Assessment process under the Clean Water Action Plan, Palau participants identified the Ngerikiil Watershed as a priority watershed in, “need of restoration and preventative action to sustain water quality and aquatic ecosystems.” The Palau Natural Resource Council identified the importance of a watershed project for the Ngerikiil since 2000 and formulized the Watershed Committee in August of 2001. The Palau Natural Resources Council Watershed Committee has had over 26 meetings since it was formed. In July 2002, the PNRC council and Governor of Airai, Tmewang Rengulbai, requested NRCS assistance for the Ngerikiil Watershed Resource Assessment. In August 2002, the Governor of Airai also appointed a State Working Committee to help facilitate communication between the technical groups and the community and help facilitate implementation of planning recommendations in the watershed. In 2003, the Palauan Traditional Leaders of the Ngerikiil Watershed area provided their support for watershed protection during scoping meetings with local working groups. Ngirachitei, Koichi Watanabe, said, “We must protect Ngerikiil Watershed for it is very important for our water supply today and for the future generations to come.” Adelbai ra Irikl, Allen Seid, said, “In general, we the traditional chiefs of Oikull village, where Ngerikiil Watershed is located are all 7 in a consensus that the watershed must be protected at all costs.” Aderdei, Gillian Johanes, said, “The traditional chiefs of Oikull are currently working with the conservation programs in the community to develop a conservation plan for the Ngerikiil Watershed.” Iyechad ra Odelomel, Risao Rechirei, said, “Today I am working for the public water works. I see the housing developments, commercial, and farm activities encroaching beyond the Ngerikiil Watershed areas. We need to promulgate some local laws to specifically spell out the importance of conservation and protection of our natural resources today and for the future.” The Natural Resources Conservation Service responded to the request for assistance with the technical Resource Assessment Team, which conducted a field inventory of the watershed in March of 2003, a comprehensive literature review, and coordinated input from numerous local and regional agencies and persons. NRCS made a commitment of time and resources to the completion of the Ngerikiil Watershed Resource Assessment over the past year. 1.2 PURPOSE The purpose of the Ngerikiil Watershed Resource Assessment is to conduct a comprehensive resource assessment of the Ngerikiil Watershed with the objective of maintaining and/or improving surface and near-shore water quality. The Resource Assessment is designed to help the stakeholders (i.e. natural resource managers, farmers, and landowners) better understand the resource problems and help find solutions. The assessment area, the Ngerikiil Watershed, is located on the southeast shore of Airai State on the island of Babeldaob (Map 1). The Ngerikiil Watershed is a major potable water supply area for Airai State and city of Koror, supplying seventy-five percent of the population of Palau with fresh water. This area was selected because of its vulnerability to water quality impairment from commercial and subsistence agriculture, road and residential construction, deforestation through cutting and fire, and other environmental and social impacts. Moderate development, road construction, and increased commercial agriculture contribute to erosion and sedimentation in the area, particularly along the lower Ngerikiil River tributaries and into its estuarine system in Airai Bay. According to some local residents, the estuarine system of Arial Bay was, at one time, a productive fishery. The coral reef protects the shoreline from storm high-tide surges and protects its near-shore fisheries. The mangrove forest acts as a nursery that enhances the fishery and provides a great abundance of food items. This fishery has now declined, likely due to increased sedimentation in the estuary and bay system. The watershed, mangrove forest, and reef conditions all relate to this decline in the fishery and local abundance of food items.1 Therefore, the purpose of this assessment is to identify present and future natural resource concerns that affect water quality at the Ngerikiil Pump Station, in Airai Bay, and beyond to the marine environment. 1 Personal communication with Airai resident 8 1.3 OBJECTIVE The objective of this resource assessment is to identify and make recommendations to address natural resource concerns, especially those affecting water quality within the Ngerikiil Watershed of Airai State, Palau’s critical drinking water source. Water quality, both above the water pump plant and that entering Airai Bay by the Ngerikiil River, is the principle resource concern communicated by the sponsors to the assessment team. However, the team also evaluated other natural resource issues within the watershed. 1.4 DESCRIPTION OF THE ASSESSMENT The Republic of Palau is closely affiliated with the United States (U.S.), having been a part of the Trust Territory of the United States until it became an independent country on October 1, 1994. The Compact of Free Association, under Article II Section 222, provides the authority for the Natural Resources Conservation Service to assist individual landowners, states, local governments, and other non-federal entities. The United States Department of Agriculture Natural Resources Conservation Service is a U.S. Federal agency that is charged with working with private landowners to help them protect their natural resources. Traditionally, NRCS conservationists spend most of their time on agriculture land working in close cooperation with local soil and water conservation districts. The agency emphasizes voluntary, science-based assistance, partnerships, and cooperative problem solving at the community level. The Natural Resources Conservation Service has a long history of providing technical assistance to Palau including publishing the Soil Survey of Islands of Palau in 1983. The Republic of Palau, Ministry of Resource and Development and the NRCS formalized a working relationship with the signing of a Mutual Agreement on December 7, 2000. The Mutual Agreement establishes a basis for cooperation and assistance to achieve common natural resource conservation goals and objectives. The Republic of Palau recognizes the need for NRCS technical assistance to aid in its efforts to improve agriculture and forestry while protecting the natural resource base, and has requested that such service be provided. The Ngerikiil Watershed Resource Assessment was funded by the USDA - Natural Resources Conservation Service, Pacific Basin Area Office through the Conservation Technical Assistance program. A six-person NRCS team conducted the fieldwork for the Resource Assessment of the Ngerikiil Watershed on March 10-14, 2003. Robert T. Gavenda, Team Leader & Soil Scientist; John H. Lawrence, State Resource Conservationist; Anthony H. Ingersoll, Conservation Agronomist; Sherman L. White, Civil Engineer; and Cynthia B. Ingersoll, NRCS Earth Team Volunteer; and Robin A. DeMeo, Resource Conservationist, NRCS Palau Field Office. Members of the Palau Bureau of Agriculture and others participated by gathering data and also by sharing their experiences and knowledge of the Ngerikiil Watershed with the assessment team. The Geology and Hydrology sections of this report were consolidated and written by Nicole Caruso, a hydro-geologist and Peace Corps Volunteer with Palau Conservation Society, assigned to the Ngerikiil Watershed project. 9 SECTION 2: PROJECT AREA A watershed is defined as the area of land that is drained by a particular stream or river system. In some cases, such as the Ngerikiil Watershed it is all of the area that drains into a common receiving water-body, bay, or ocean. It is usually called by the name of the principle stream or river that it contains. The Ngerikiil Watershed, therefore, is the area draining into Airai Bay including the Ngerikiil River, its tributaries (i.e. Ikoranges stream, Kmekumel stream, Edeng stream, and Oikull stream) and the Ngerikiil sub-watershed drainage areas (Map 2). 2.1 PHYSICAL DESCRIPTION The Ngerikiil Watershed covers over 28,466 hectares (70,341 acres) of Airai State, Babeldaob Island. The sub-watersheds of Ngerikiil include the Ngerikiil, Ikoranges, Kmekumel, Edeng, Oikull, and Airai (Table 1 and Map 2). The Koror-Airai water system dam is in the Ngerikiil Watershed just downstream of where the Edeng and Kmekumel streams enter the Ngerikiil River. The dam provides a barrier that prevents salt-water intrusion from tidal waters into the drinking water pump. The southwestern part of the Oikull Peninsula and the area southeast of the airport, identified as Airai sub-watershed, are considered part of the Ngerikiil Watershed because runoff from these areas drains into Airai Bay and influences the mangrove forest and coral reef areas. The geomorphology (i.e. surface land features including topography, vegetation and hydrology) of the watershed reveal three distinct zones: upper, middle and lower. The upper zone is characterized by high relief, undisturbed natural forest, and deeply incised tributaries. The middle zone consists of lower relief, river floodplains, and the vast majority of development in the watershed. The lower zone contains mangrove forest at sea level. Successful management of the watershed should address each zone separately with an understanding of how use of each affects the other zones. Table 1: Ngerikiil sub-watersheds and area Sub-Watershed Ngerikiil Ikoranges Kmekumel Edeng Oikull Airai Totals Square Miles 1.8 1.3 1.6 4.1 1.8 0.4 11.0 Square Meters 4,526,270 3,333,970 4,020,960 10,716,500 4,748,790 1,119,550 28,466,040 Acres 1,118 824 994 2,648 1,173 277 7,034 % of Total 16% 12% 14% 38% 17% 4% 100% 10 Map 2: Ngerikiil Watershed sub-watersheds and streams 11 Ngerikiil River Sub-Watershed This is the central watercourse located in the river floodplain and mangrove areas of the watershed. The river itself, under tidal influence, has a calm flow before it drains into Airai Bay. There a short concrete lined channel behind the dam and the stream banks where the U.S. Compact Road crosses the Ngerikiil River are stabilized with a concrete, rock, and masonry revetment. Ikoranges Sub-Watershed The Ikoranges stream is north of the airport and the smallest of the three sub-watersheds that drain into the Ngerikiil River. It has, however, one of the highest percentages of housing, farm, and road development of all the sub-watersheds in the Ngerikiil basin. Kmekumel Sub-Watershed The Kmekumel stream flows off the eastern slopes of Mount Ngetchum (Map 1). The old Japanese road runs along the western ridge bordering the watershed. Most of this sub-watershed consists of primary forest; there are only a few structures and bare eroded areas along this ridge. Edeng Sub-Watershed The Edeng stream forms the largest sub-watershed in the Ngerikiil Watershed. The Edeng Stream has four major branches feeding it. The sub-watershed reaches from the ridge of the Ngchesar range and includes the western slopes of Rois Berg, Ormuul, Ngeraod, and Ngerbekebekur, and the eastern slope of the Kedam range (Map 1). The land coverage is primarily forest vegetation, mostly primary forest, with small areas of savanna in the upper area, with residential and agricultural uses confined to the road along the southeast part of the subwatershed. The Edeng sub-watershed ends just downstream of the Koror-Airai water intake. Oikull Sub-Watershed The Oikull sub-watershed covers the western slopes of Oikull and drains directly into Airai Bay. There is a road along the ridge and several smaller roads to farms. There are bare soil areas in the Oikull basin where soil erosion is evident. This area contains several registered historical sites including the remains of five traditional villages (i.e. Medal, Klouloikull, Iuang, Mengloi, and Ngerduais) which consist of large stone features, terraces, docks and large scattered shards in the village areas. A Yapese quarry site containing a complete limestone rock disk is also reported in this area (Blayok, 1993 and Olsudong, 1997). Airai Sub-Watershed The Airai sub-watershed area drains off the east end of the airport runway into Airai Bay. The registered historic traditional village of Airai, Ordomel, exists in this sub-area, and includes the remains of Chad ser a Mechorei Causeway, stone platform, Yapese stone money quarries, historic cave sites and the Airai Bai (Blayok, 1993 and Olsudong, 1997). 12 2.2 DEVELOPED LAND AREAS The water intake and pumps on the Edeng tributary were installed in 1985. Electrical power was introduced into the area the same year. Only one house and the Palau Mission Academy (built 1970) existed in the watershed at this time. An increase in farm and land development occurred in the watershed in the 1990s. Land development includes construction sites, roads and associated affected areas (e.g. eroded areas). Nearby residential areas, include the Ngerusar, Yelch, and Airai. Land development and commercial agriculture on approximately nine percent of the Ngerikiil Watershed have increased the potential impacts of erosion and sedimentation on water quality (Table 2 and Map 3). Table 2: Land use types and total area Land Type Agriculture Developed and Bare Areas Road Savanna Forest Totals Square Miles 0.54 0.33 0.15 0.98 8.99 11.0 Square Meters 1,405,353 840,041 388,498 2,533,910 23,294,852 28,466,040 Acres 347 208 96 626 5,756 7,034 % of Total 5% 3% 1% 9% 82% 100% 2.3 AGRICULTURAL AREAS A significant land use of the Ngerikiil Watershed is farming. Farming is evident along the floodplains of the Ngerikiil in the 1976 aerial photographs. The number and size of farms in the watershed has increased since this time. A comparison of the area farmed along the floodplains in 1976 and 1992 is presented in Figure 1. Previous German, Japanese, and American occupations, as well as the present Chinese, Bangladesh, and Philippine influence, have introduced new commercial agricultural practices and techniques. Agricultural areas are expected to grow in Palau as the population expands and the demand for fresh, high-quality produce and other farm products increases. The Ngerikiil Watershed contains several commercial farms which are growing multiple, nontraditional crops for market sale. Farming, formerly located primarily on the flat flood plains, is moving up to steeper, marginal land (Map 3). This trend is exacerbating the resource problem of increased sedimentation reaching the Ngerikiil River, Airai Bay, and the ocean beyond. The increased use of commercial fertilizers and pesticides is further increasing the potential of pollutants reaching the river. The number and size of confined animal operations is increasing within the watershed. This, too, will put increased pressure on the water quality of the Ngerikiil Watershed. 13 Along with this growth, there needs to be regulation and monitoring of these activities in order to assure sustainable and environmentally sound development (Elliott & Franz, 1993). Map 3: Land Use Types 14 Figure 1: Aerial photographs of Ngerikiil River, 1976 and 1992, agricultural area 2.4 CLIMATIC CONDITIONS The climate of the Ngerikiil Watershed varies only slightly from Koror, where there is the National Weather Station that has collected weather data for over 30 years. The following was based on the long-term data from Koror, provided by the NOAA Weather Forecast Office, Guam. The climate is tropical with a mean annual rainfall of around 375.9 centimeters (148”) (Koror averages). The heaviest rains are due to monsoonal storms that generally occur between the middle of June through August. The highest daily rainfall occurred in April 1979 with 43 centimeters (16.95”). There averages 263 days with rainfall greater than 0.025 centimeter (0.01”). The average monthly rainfall for July is 45.8 centimeters (18.04”). Pre-WWII Japanese Forestry rainfall records show a slightly higher rainfall amount than the 30 years of Koror records. Prevailing winds in the Ngerikiil Watershed are the northeastern trade winds, with a mean wind speed of 9.65 kilometer per hour (6 mph or 5.2 knots) (Koror averages). Maximum winds recorded were during typhoon events that approached within 144.8 kilometers (90 miles) of the Ngerikiil Watershed. The major typhoons include: Gelda, December 15, 1959 with 140-knot winds (161.1 mph); Louise, November 16, 1964, with 100-knot winds (115 mph); Opal, 15 December 11, 1964, with 140-knot winds (161.1 mph); and Mike, November 10, 1990, with 135 knot winds (155.4 mph) (NOAA National Weather Service, Guam). The average annual temperature in Koror is 27.6 degrees Celsius (81.7°F). The average annual maximum temperature is 30.9 degrees Celsius (87.7°F) and the average annual minimum temperature is 24.2 degrees Celsius (75.6°F) at Koror. The lowest temperature occurred in January 1998 at 20.6 degrees Celsius (69°F) and the highest was 35 degrees Celsius (95°F) on June 1976. There are approximately 72 days where the temperature goes above 32.2 degrees Celsius (90°F). Palau has moderate levels of sunshine. There is a 30-year average of 6.5 cloudless, 79.3 partially cloudy and 275.6 cloudy days per year in Koror. The number of cloudless days may be fewer in the Ngerikiil Watershed due to its mountainous terrain. The normal relative humidity averages 85 percent. June is slightly higher with 86 percent and April being the driest with 83 percent. 2.5 GEOLOGY Babeldaob Island formed from raised volcanic material of tuff and breccia. Limestone from ancient coral reefs and marine terraces are found at the eastern Oikull Peninsula of the watershed. The bedrock of the rest of the Ngerikiil Watershed is of the same origin as the bedrock of the entire island of Babeldaob. It consists of deeply weathered basaltic and andesitic volcanic breccias and tuffs erupted and deposited between 58 and 22.5 million years ago up to 609.6 meters (2,000’) thick (USGS, 1984; Corwin, 1952). In areas of low relief, the bedrock is overlain by up to 45.7 meters (150’) of Airai clay. This clay originated from highly weathered breccia at higher elevations and deposited between 22.5 and 2 million years ago, at a time of higher sea levels, in estuaries and swamps (U.S. Army, 1956). The clay unit consists of interbedded white, light brown and gray clays, silty clays and lignite (i.e. decayed plant material and clay), and is mapped as occurring in the floodplains of the Ngerikiil River and along the Ikoranges tributary within the watershed (U.S. Army, 1956). Inter-tidal mangrove areas are underlain by 150 centimeters (5’) or more of peat or highly organic soils, very poorly drained with rapid permeability (SCS, 1983). The middle and upper watershed areas are largely covered with 150 centimeters (5’) or more of silt loam and silty clay loam that is well drained with moderately rapid permeability (SCS, 1983). 2.6 HYDROLOGY The Ngerikiil Watershed provides the majority of drinking water for approximately 75 percent of the people of Palau. Waters from the Ngerikiil Watershed drain into Airai Bay. The bay is a small (3 square kilometers or 1.2 square miles), semi-enclosed, mangrove-fringed coral lagoon on the southeast coast of Babeldaob. Until the 1970s, the land was largely undisturbed in the watershed. However, construction of the Koror airport, extensive land clearing for agriculture in the lowlands, destruction of mangroves and riparian buffer zones along the banks of the Ngerikiil, and most recently construction of the Compact Road and residential developments, has caused significant sediment loads into the river and the bay. Due to the decline of water quality as a result of increased development and environmentally destructive land use practices, much of the patch reef in Airai Bay has been smothered, and hence, the fisheries in the bay have collapsed. At present, Palau does not have land use planning or required controls in place to prevent erosion, sedimentation into riverine systems, and the resulting loss of marine diversity or 16 habitats due to this sedimentation. The Ngerikiil Watershed provides a poignant example of what will happen throughout Babeldaob if land use controls are not instituted parallel with construction of the Compact Road. Suspended fine sediment into the bay exceeds 1500 mg/l (0.2 oz/gallon); the river sediment plume is about 2 meters thick (6.6’) (Golbuu, 2003). Should land development and land use practices continue unchecked, sustainability of this drinking water source and suitability of the soils for farming will be jeopardized. The following sections provide a summary of available data of past and current conditions of water resources of the Ngerikiil Watershed that should serve as a baseline for future monitoring and management options. 2.6.1 Groundwater No records have been retained in Palau of well logs or pumping tests of the eight or more test wells that were drilled in Airai in the 1970s and 1980s that would indicate the water bearing properties of the bedrock and overburden. According to Richard Mangham of Ministry of Resources and Development - Capital Improvement Project (CIP), wells located near surface waters yield as much as 227.1 liters per minute (50 gpm). But due to the naturally high levels of iron and manganese that occur, anaerobic bacteria forms in such numbers in the wells that the efficiency of the pumps is reduced by up to eighty percent in just a few months. Therefore, maintenance of pumps and pipe stems becomes costly. Due to the composition and structure of the volcanic bedrock with scattered and concealed joints (U.S. Army, 1956), these wells were likely drawing water from the nearby surface sources. Groundwater sources in Babeldaob are not likely significant. 2.6.2 Surface Water Due to the abundance and largely continuous availability of surface water in Palau, this source has been the more viable and cost effective option for drinking water. The Ngerikiil River is fed by three main tributaries. They are the Edeng, the Kmekumel and the Ikoranges tributaries (Figure 2). The headwaters of the Edeng begin near Rois Beng, Ormuul and Kedam (Figure 2). The main Edeng channel is approximately 5.3 kilometers (3.3 miles) and, according to the USGS Topographic Map of Oreor 1983, have 12 small tributaries off its main channel. The headwaters of the Kmekumel begin near Ngetchum (Figure 2). The main Kmekumel channel is approximately 3.7 kilometers (2.3 miles) and has two small tributaries feeding into it. The Ikoranges tributary of the Ngerikiil has its headwaters east of the Ngerimel reservoir (Figure 2). Its main channel length is approximately 2.7 kilometers (1.7 miles) and has five small tributaries feeding into it, according to the United State Geological Services (USGS) Topographic Map of Oreor 1983. The Ngerikiil River, from its mouth at Airai Bay to the fork of Edeng and Kmekumel tributaries, has a main channel length of 3.7 kilometers (2.3 miles). The total of these main channel lengths is 15.4 kilometers (9.6 miles). In total, including the small tributaries feeding into these main channels, the total stream length in the watershed is approximately 43 kilometers (27 miles) (NRCS, 2003). 17 Figure 2: Ngerikiil Watershed water source attributes Two USGS stage-gauging stations exist in the watershed (Figure 2). United States Geological Survey has published continuous monthly total discharge data (based on daily averages) for the gage on the Edeng for the period of 1969 through September 1981, and reported 1982 and 1983 data in USGS Water Resources of the Palau Islands, 1984. The USGS has a partial record of discharge data for the Kmekumel gage for the period from 1970 to September 1993. Table 3 lists the average, minimum and maximum discharges of the two tributaries from USGS data of these gages. The average discharge of the Kmekumel is 0.27 cubic meter per second (9.59 ft3/sec) or 6.2 million gallons per day. The average discharge of the Edeng is 0.9 cubic meter per second (33 ft3/sec) or 21 million gallons per day. Recurrence intervals for high flows and low flows of the Edeng are presented in the USGS Water Resources of the Palau Islands, 1984. Low flow rates of the Kmekumel were determined by correlation to the Edeng. A summary of these results is presented in Table 4. These results show a large resource of water available from these tributaries to the Ngerikiil. The lowest daily discharge with a recurrence interval of 10 years for the Edeng tributary is one cubic feet second or 0.65 million gallons per day. 18 Table 3: Flow rates for periods of record for tributaries Flow (cfs) Edeng Tributary Discharge Average Minimum Maximum 33.0 1.2 1,850 Flow (gpm) 14,811.4 560 830,336 Flow (Mgd) 21 0.8 1,195.7 Kmekumel Tributary Discharge Average Minimum Maximum 9.59 0.18 1,880 4,304.3 80.8 843,800 6.2 0.12 1,215.1 Table 4: Flow rates for Edeng tributary High Flow Number of Consecutive Days 30 7 3 1 1 Low Flow Number of Consecutive Days 30 14 7 7 1 1 Instantaneous Annual Peak Flow (cfs) Flow (gpm) Flow (Mgd) Recurrence Interval (Years) 900 403,900 581.6 1.1 2,300 1,032,300 1486.5 2 3,000 1,346,500 1939.0 5 Notes: 1,800 gpm or 2.6 Mgd currently being pumped from Edeng tributary pump station. Flow (cfs) 100 150 300 1,000 100 Flow (gpm) 44,900 67,300 134,600 448,800 44,900 Flow (Mgd) 64.6 96.9 193.9 646.3 64.6 Recurrence Interval (Years) 6.5 2 2 6 1 Flow (cfs) 3 6 3 5 1 17 Flow (gpm) 1,350 2,690 1,360 2,240 450 7,630 Flow (Mgd) 1.9 3.9 2 3.2 0.65 11 Recurrence Interval (Years) 5 2 5 2 10 1 2.6.3 Rainfall The source of this significant amount of surface water is rainfall. Figure 3 presents rainfall data from the Koror gage station, located at the National Weather Service Office, for the period from July 1947 through November 2003. The average annual rainfall for this time-period is 375.72 centimeters (147.92”). The average monthly rainfall for this period is 31.29 centimeters (12.32”). The greatest average monthly rainfall occurs between June and August, with the greatest monthly totals occurring in July of 1962 (88.44 cm or 34.82”) and June of 1990 (85.93 cm or 33.83”). The lowest average monthly rainfall occurs between February and April; the lowest monthly totals for this time-period occurred in February 1983 (1.6 cm or 0.64”) and March 1998 (1.27 cm or 0.50”). Comparison of data from both islands, where available for the same timeperiods, indicates that there is not a great difference in rainfall totals between Babeldaob and Koror (USGS, 1984). Incomplete monthly total rainfall data is available for a USGS rain gage in 19 Airai located near the dam on the Ngerikiil River from November 1978 through September 2002. This data is presented in comparison to the Koror rainfall data in Figure 4 for this time period. On average for the Edeng tributary (as well as for the other river gage stations in Babeldaob), approximately 70 percent of the rainfall becomes channel flow and runs into the ocean (USGS, 1984). All available data begins in October 1969 and runs through September 1993. Figure 5 illustrates the direct relationship between precipitation and discharge of both the Kmekumel and Edeng from, July 1981 through July 1993. Two major storm events - July/August 1981 and June 1990 are presented in Figures 6 and 7. Analysis of the daily precipitation and discharge for these events indicates the volume of base flow or groundwater contribution of the tributaries, total runoff, and direct runoff or surface flow caused by excess rainfall of the storm event. The total precipitation for the July/August 1981 storm event was 50.42 centimeters (19.85”) over 31-day period, between July 24 and August 21. The discharge data for this period indicates that the average base flow of the Edeng tributary is approximately 0.51 cubic meters per second (18 ft3/sec). The total runoff of this flood period, including base flow, was 58.76 cubic meters per second per day (2,075 ft3/sec/day). The direct runoff, determined from subtracting base flow from total runoff, was 43.98 cubic meters per second per day (1,553 ft3/sec/day) or 34.44 centimeters (13.56”) (68 percent of rainfall). The total precipitation for the June 1990 storm event was 42.39 centimeters (16.69”). The discharge data for this event indicates that the average base flow of the Kmekumel tributary is 0.12 cubic meter per second (4.35 ft3/sec). The storm event lasted for 15 days from June 23 through July 7. The total runoff of annual flood during this period, including base flow, was 11.83 cubic meters per second per day (417.8 ft3/sec/day). The direct runoff was 9.98 cubic meters per second per day (352.55 ft3/sec/day) or 23.1 centimeters (9.1”) for this storm event (55 percent of rainfall). 20 July 1947 through November 2003 40 34.82" Jul 33.83" Jun Jul Aug Jul Jul Jun Jan Apr Jun Jul Jul Jun Jun Mar Oct Feb Jul Jul Dec Jul Aug Jun Jul Oct Apr Sep Jun Jul Jan Jul Dec Nov Sep Feb Aug Jan Jun Jul Jun Jul Jul Sep Feb Aug Jul 35 30 May Aug Jan Jul Jun May Nov Aug Sep Aug Sep May Precipitation (Inches) 25 May May 20 15 10 5 Feb Apr 0 Jul-47 Jul-49 Jan Jan Nov Feb Mar Feb Apr Mar Feb Mar Jul-53 Jul-55 Jul-57 Jul-59 Apr Jul-61 Jul Jul-63 Apr Feb Feb Feb Jul-65 Jul-67 Mar Apr Jan Jul-69 Jul-71 Mar Feb Jul-73 Feb Jul-75 Apr Mar Jul-77 Mar Apr Sep Jul-79 Jul-81 Jan Apr Apr Sep Feb Mar Apr Feb 0.64" Dec Jul-83 Jul-85 Jul-87 Jul-89 Feb Apr Jul-91 Jul-93 Jan Sep OctAug Nov Feb Apr Sep Apr Mar0.50" Jul-95 Jul-97 Jul-99 Jul-01 Feb Jul-51 Date Figure 3: Koror monthly precipitation totals 21 Jul-03 40.00 35.00 30.00 November 1978 through September 2002 Precipitation (In) 25.00 20.00 15.00 10.00 5.00 0.00 1 8 5 0 7 9 4 6 3 2 3 1 8 6 2 1 9 5 4 0 8 9 7 0 -7 v-7 v-8 v-8 v-8 v-8 v-8 v-8 v-8 v-8 v-8 v-8 v-9 v-9 v-9 v-9 v-9 v-9 v-9 v-9 v-9 v-9 v-0 v-0 o o o o o o o ov o o o o o o o o o o o o o o o o N N N N N N N N N N N N N N N N N N N N N N N N Koror Figure 4: Koror and Airai monthly precipitation totals Airai Date 22 Edeng and Kmekumel Discharge (ft3/sec) Koror Precipitation (in.) Edeng and Kmekumel Discharge (ft3/sec) Koror Precipitation (in.) Edeng and Kmekumel Discharge (ft3/sec) Koror Precipitation (in.) Figure 5: Direct relationship between precipitation and discharge of both the Kmekumel and Edeng from, July 1981 through July 1993 23 g 8 7 6 Precipitation (In) y g 600 500 400 300 200 100 0 5 4 3 2 1 8/1 8/3 8/5 8/7 7/16 7/18 7/20 7/22 7/24 7/26 7/28 7/30 8/9 8/11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 8/27 8/29 8/31 0 DateEdeng Tributary Koror Rainfall Figure 6: Koror rainfall, Edeng tributary, July and August 1981 storm events 9 8 7 Precipitation (In) 200 180 160 140 120 100 80 60 40 20 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 Date Koror Rainfall Kmekumel Tributary 6 5 4 3 2 1 0 Discharge of Kmekumel Discharge of Edeng (ft /s) 3 Figure 7: Koror rainfall, Kmekumel tributary, June 1990 storm event (ft /s) 24 3 2.6.4 Water Use The Ngerikiil River dam provides a barrier that prevents salt water intrusion from tidal waters into the drinking water pump on the Edeng tributary. According to David Dengokl of the Bureau of Public Works, approximately 6,814 liters per minute (1,800 gpm) or 9.8 million liters per day (2.6 million gallons/day) are pumped from the pumping station located approximately 80 meters (263’) upstream from the USGS Edeng gage (Figure 2). This water is pumped directly to the water treatment plant. An additional 2,839 liters per minute (750 gpm or 1 million gallons/day), approximately, is piped to the treatment plant via gravity flow from the Ngerimel Reservoir. These two sources provide the drinking water treated at the water treatment plant in Ngeruluobel hamlet in Airai and then distributed throughout Airai and to Koror. The water treatment plant has maintained hourly records of the amount of water being treated and discharged into the distribution system since 1998. However, the amount of water pumped from the Edeng tributary and Ngerimel Reservoir is not recorded. As part of the census collected by the Office of Planning and Statistics of the Ministry of Finance, every occupied housing unit is surveyed as to whether it is connected to piped water, not differentiating between treated and untreated piped water. These results show that the total number of housing units in Koror and Airai served by piped water has increased from 1,632 units to 2,516 units between 1986 and 2000. The 2000 census results indicate that only three housing units in Airai were not connected to piped water in 2000. An exponential increase in development is possible following the completion of the Compact Road and, therefore, it is not appropriate to predict future growth based on this census data. Currently, 99 percent of the homes in Koror State and the hamlets of Airai, Ked, Ngerusar, Ngeruluobel, Ngetkib, and parts of Chochelochol (excluding Ngerikiil) in Airai are served by the Koror/Airai Public Water Treatment System (K/A PWS). Current withdrawals exceed some low flow conditions for the Edeng tributary (see Table 4). 2.6.5 Water Quality Water quality data was previously collected in the watershed Pesticide analysis, was also conducted by Environmental Quality Protection Board (EQPB) in April of 2000, of water collected upstream of the Edeng tributary intake. The complete laboratory results from this analysis could not be located by EQPB; however, the results were reportedly below detection limits for all parameters. Additionally, the Daewoo turbidity data, discussed below, is not included, but is available through the U.S. Army Corps of Engineers. The USGS water quality samples were collected from the gage locations on the Edeng and Kmekumel tributaries (Figure 2). The location of the USGS Airai well is also identified in Figure 2. The results were compared to United States Environmental Protection Agency (USEPA) National Drinking Water Standards for the applicable parameters and confirm the naturally high concentrations of iron and manganese previously discussed. These results, along with the Palau Community College, Cooperative Research and Extension (PCC-CRE) results (PCC1 through PCC5), indicate good water quality in regards to important indicators such as dissolved oxygen, pH, turbidity values, total suspended solids and nitrate. The K/A PWS records hourly measurements of turbidity from mixed intake waters from both the Edeng tributary intake and the Ngerimel Reservoir intake. According to David Dengokl, these values approach 100 25 Nephlometric Turbidity Units (NTU) during heavy rains but generally decrease within two to three hours time to normal levels. Dengokl reported an extreme and rare turbidity value of 1400 NTU occurred in either 2001 or 2002. Fecal coliform results from the PCC-CRE study approach exceptionally high values, especially the 15,700 number fecal coliform per100 milliliters from river sample near Evergreen Farm in October 1998. The presence of fecal coliform bacteria indicates that the water may be contaminated with human or animal wastes. Disease-causing pathogens in these wastes can cause health risks to susceptible humans and biota. While the water treatment process kills these bacteria, high levels in the river pose threats to riverine and estuarine ecosystems and potentially to recreational river users. The heavy metal results from EQPB sample just upstream of the Edeng tributary intake are below USEPA drinking water standards for all parameters except aluminum (Al). Aluminum (along with iron and manganese) occurs at high levels in the soils and, as a result, is a natural leachate from the soils. Aluminum poses a health risk when water reaches acidic levels. Consequently, due to these naturally occurring high levels in the soils, once vegetation is removed, regrowth is extremely slow to occur. Daewoo Company, contractors for the Compact Road, analyze turbidity, pH, temperature, and dissolved oxygen from river water samples along drain lines (DL) 3 and 7 (Figure 2) once a week and near the bridge in Airai once a month. Because of the infrequency and randomness of the collection times, these results do not relate to rainfall, runoff, or river discharge, and have not been included in this report. These results show significant turbidity at DL 7, up to 450 NTU, which has been one of the biggest problem areas for erosion along the Compact Road (Jon Vogt, United States Army Corps of Engineers). High turbidity is also recorded near the bridge, up to 305 NTU; brown, muddy waters thick with sediment are visible after any rainfall at this site. 2.6.6 Recommendations Stream flow in the Ngerikiil Watershed and rainfall are directly correlated. The abundance of both indicate that with appropriate water storage management, withdraw efficiency (e.g. fix existing leaks in the distribution system), and land use management that conserves key watershed areas and sustains water quality, the Ngerikiil Watershed will be able to provide for strategic future development. Evidence, in the form of currently measured sedimentation rates in the bay (Golbuu et al., 2003) and surveys of local fishermen, suggests that a large portion of the reefs in Airai Bay has already been degraded due to sedimentation resulting from construction and poor farming practices within the Ngerikiil Watershed. Sustainable land use within the watershed is the goal for rehabilitation of the reef and to ensure a clean and plentiful drinking water source from the streams and river. Development and land use restrictions should be developed for primary protection zones surrounding stream banks, particularly near the drinking water intake. Furthermore, a comprehensive and holistic land use management plan that conserves upland forests and mangrove forests should focus on sustaining the health of the river and reef. An emergency management plan should be developed that details instructions to take in the event of a pollution release to the watershed waters; the appropriate persons should be educated regarding their roles in public notification and cleanup of the release. 26 2.7 2.7.1 SOILS Soil Classification Soils are classified based on measured and inferred properties following Soil Taxonomy (Soil Survey Staff, 1999). Most of the extensive soils in Palau have at least one set of lab data from analyses performed at the USDA National Soil Survey Laboratory to support the classifications. Many soil observations were made during the soil mapping process to document the range in variation in soil profiles and properties. Table 5 lists the classifications of the Ngerikiil Watershed soils at the Subgroup level of taxonomy as published in Smith (1983). Changes in Soil Taxonomy since the publication of the Palau soil survey necessitate the reclassification of most soils in Palau. The proposed classifications of the Ngerikiil Watershed soils according to the latest edition of Soil Taxonomy are also presented in Table 5. Table 5: Classification of the soils in the Ngerikiil Watershed Soil Name Aimeliik Babelthuap Dechel Ilachetomel Mesei Ngardmau Ngatpang Ngedebus Ngersuul Palau Peleliu Tabecheding Typic Troporthents Subgroup classification (Smith, 1983) Oxic Humitropepts Haplic Acrorthox Tropic Fluvaquents Typic Sulfihemists Terric Troposaprists Typic Troporthents Tropeptic Haplorthox Typic Tropopsamments Aquic Dystropepts Tropeptic Haplorthox Lithic Eutropepts Aquic Tropudults Typic Troporthents Proposed Subgroup classification (Soil Taxonomy 2nd Edition, 1999) Typic Haploperox Typic Kandiperox Fluvaquentic Endoaquepts Typic Sulfihemists Terric Haplosaprists Oxic Dystrudepts Typic Haploperox Typic Udipsamments Fluvaquentic Dystrudepts Typic Haploperox Lithic Haprendolls Aquic Kandiperox Typic Udorthents Soil classification groups soils with similar properties. Soil taxonomy uses soil characteristics reflecting soil properties and behavior that are important for particular agricultural and engineering interpretations. These groupings of similar soils for the most part, are classified as soil series, the lowest and most specific level of soil taxonomy. The soils identified as any one series will have similar appearance and properties and will interpret the same for various engineering and agricultural uses. Soil series are given local geographic names from where they are originally established but are mapped wherever soils with those properties are found. As an example, soils identified as the Peleliu series are mapped on the Island of Babeldaob. This is because soil scientists found soils on Babeldaob with properties similar to those already identified as the Peleliu series, which was first described on the island of Peleliu. The Ngedebus 27 series, also first described on Peleliu, is mapped on most islands in Micronesia and in American Samoa. Map 4: Soils Groups 28 2.7.2 Soil Mapping Concepts Soil mapping employs concepts apart from taxonomy. Map units are designed to represent areas of soils on landscape segments. A map unit commonly consists of many delineations shown on a soils map. Map units commonly consist of phases of soil series based on surface texture and the slope of the land. Phases identify important soil features not part of the taxonomic system but important for management. An example of a map unit based on a phase of a soil series is Ngatpang silty clay loam, six to 12 percent slopes. Some areas may have two or more soils and/or land types so intricately distributed across a landscape that it is not possible to map the different soils separately. In this situation, map units are designed as complexes with two or more named components. An example of a map unit based on a complex of two named components is Aimeliik-Palau complex, six to 12 percent slopes. The amount and geographic distribution of named components is stated in the map unit description. Regardless of the number of named components in a map unit, unnamed minor components are included in map units. A map unit description lists the more likely unnamed components that may be included within delineations. These unnamed components or inclusions may be similar to the named components, but could be dissimilar and have properties quite different than the named components. A soil survey is made at a particular scale depending on the intricacy of the soil patterns and the expected intensity of soil use. The Palau soil survey was published at a large scale of 1:10,000 or 10 centimeters (3.9”) on the map equals one kilometer on the ground (3,280.8’). The smallest delineation at this scale is about 4000 square meters (0.4 hectares or about one acre). A survey of this kind is useful for watershed planning but not appropriate for site-specific interpretations. Field verification of soils is needed for site-specific interpretations. 2.7.3 Soil Survey Procedures The most recent soil survey of Palau (Smith, 1983) was partially based on earlier geology and soil investigations (US Army, 1956; Vessel and Simonson, 1958). Soil mappers looked at major divisions in geologic parent materials affecting soil properties. They analyzed and correlated landforms and vegetation with soils. After establishing the relationships among the factors controlling soil formation (parent material, landform, relief, climate, vegetation and time available for soil formation), they developed a model to predict the location of soils across the landscape. They examined soils to test hypotheses regarding soil distribution and soil properties, and modified the model as field observations increased knowledge of soil distribution. The soil mappers could predict with reasonable accuracy the occurrence of certain soils based on landform, geology and vegetation, and therefore did not need to examine every soil delineation, especially in areas where access was difficult. The Aimeliik (forested) and Palau (savanna) series are typically on side slopes but may also occur on vegetated ridgetops and valley bottoms (Photos 1 and 2). Babelthuap and Ngardmau series make up the remainder of the volcanic soils and comprise nine percent of the total watershed (Photo 3). Bottomlands consist primarily of the saltwater mangrove organic soils of the Ilachetomel series (71 percent of bottomlands, or almost 11 percent of the total watershed). The agriculturally productive Dechel (Photo 4) and Ngersuul mineral soils, along with smaller 29 amounts of the organic Mesei series, comprise nearly all the remaining bottomlands soils and account for only about 4.5 percent of the watershed area. Photo 1: Aimeliik series profile Photo 2: Palau series profile Photo 3: Babelthuap series profile, note high water table and oxidized root channels Photo 4: Dechel series profile, note the presence of ironstone fragments (dark red) and nodules concentrated on the soil and within the soil profile Photo 5 shows the landscape distribution of soil complexes on volcanic uplands. The Babelthuap and Ngardmau series are on ridgetops that may be bare ground or sparsely vegetated with ferns and other 30 plants that are indicators of poor soil fertility. The Dechel, Ngersuul and Mesei series are in low wet areas in the landscape. Aimeliik-Palau complex Babelthuap -Ngardmau complex Dechel-Mesei complex Photo 5: Landscape distribution of soil complexes on volcanic uplands 31 Marine terraces have the Ngatpang and Tabecheding series soils of the watershed. The Ngatpang series comprises 43 percent of marine terraces and covers four percent of the total area (Photo 6). Tabecheding soil (Photo 7) comprises 57 percent of marine terraces and covers six percent of the total area of the watershed. Photo 6: Ngatpang series profile, the red iron concentrations indicate seasonal wetness Photo 7: Tabecheding series profile Limestone soils are in the Peleliu series (Photo 8), which is in a complex with Rock Outcrop, and accounts for only 2.5 percent of the watershed area. Photo 8: Peleliu series profile 32 Miscellaneous land has been highly modified by urbanization. It is concentrated around the airport and accounts for about one percent of the watershed. Photo 9: Steep hillside on Ngatpang series (marine terraces), recently cleared and burned and vegetation starting to grow back Photo 10: Close-up of bare ground, GPS unit is about five inches (12.5 cm) long Soils on steep slopes have a high potential to erode if vegetation is removed (Photo 9 & 10). Landscapes with slopes greater than 12 percent account for 72 percent of the watershed (Map 5) and those of 30 percent or more (Map 6) account for 44 percent of the watershed. Volcanic and marine terrace soils are on the large majority of these steep landscapes. Limestone soils within the watershed remain under forest due to their occurrence on highly permeable, inaccessible, steep landscapes that makes them unsuitable for homesite or agricultural development. 33 Map 5: Ngerikiil Watershed soil groups on greater than twelve percent slopes 34 Map 6: Ngerikiil Watershed soil groups on greater than thirty percent slopes 35 2.7.4 Soil Formation The island of Babeldaob is one of the high volcanic islands in the western Pacific Ocean. The island formed from volcanic accumulation along the crest of the Palau ridge (US Army, 1956). Numerous emergences and submergences, and marine and stream erosion later modified the volcanic rocks. The resulting landscape is rounded and highly dissected by streams. Soils in the Ngerikiil Watershed formed primarily in four of the five major parent materials in Palau: bottomlands, marine terraces, volcanic uplands and limestone. High year-round temperatures combined with abundant rainfall have caused extensive chemical decomposition of rock minerals into soil minerals with the accompanying loss of soil nutrients. The volcanic bedrock has been significantly altered to great depth within the Ngerikiil Watershed. The majority of Ngerikiil Watershed Area soils formed from highly weathered volcanic bedrock. The Aimeliik, Palau, Babelthuap and Ngardmau soil series are the major soils on volcanic uplands. Several soil scientists who have worked in Palau (Smith and Babik, 1988; Ford, 1982) believed these soil series were essentially the same soil before humans arrived in Palau and cleared land of forest. Fire used to clear land has caused loss of organic matter and nutrients and has disrupted the nutrient cycle. Removal of vegetation by fire has also led to erosion on ridge tops where the Babelthuap and Ngardmau soils are located. These soils are nutrient poor and vegetation has difficulty becoming established and thriving on them. These soils are the most degraded of the soils in the Ngerikiil Watershed. The Palau soil series has a lesser degree of degradation and supports savanna vegetation. Aimeliik soils are forested and most fertile of the volcanic soils in the watershed because the nutrient cycling has been least disrupted. Marine terraces formed as sediment from upslope accumulated in near-shore environments and formed bedded marine clay. Subsequent emergence of the terraces either by tectonic uplift of the Palau landmass or by lowering of sea level left the terraces high and dry and subject to erosion and soil formation. The terraces are generally slightly sloping planar surfaces but dissected by stream erosion. Ngatpang and Tabecheding soil series are mapped on terraces. Bottomlands are located on valley bottoms where water cannot drain freely into streams or the ocean. The soils developed in bottomlands are generally wet and saturated for at least part of the year, influencing their formation. Bottomland soils can be mineral soils such as the Dechel and Ngersuul series, which formed from water deposited sediment. Organic soils formed in vegetation that accumulated because saturation inhibited decomposition. The bottomland organic soils are Mesei series in fresh water environs and the Ilachetomel series in brackish water. The Mesei series is mapped as a complex with the Dechel series and occurs in low spots in the landscape where water accumulates. Small areas of soil developed on limestone occur on hills in the southeast Ngerikiil Watershed on the Oikull Peninsula. Soils on these hills are mapped as the Peleliu series, which is shallow and rocky and is complexed with Rock Outcrop. These soils are on steep landscapes under forest. At the southern tip of the Oikull Peninsula small areas of sandy soils formed in alluvium from water and wind-deposited coral sand. These soils are mapped as the Ngedebus series. These soils are next to beaches and are vegetated mainly with coconut trees and atoll forest. 36 Small areas of fill land for urban development and otherwise highly modified lands are around the airport and within the mangrove swamp. These areas are mapped as Typic TroporthentsUrban Land complex in the soil survey but are referred to in this report as “miscellaneous land.” Table 6 summarizes the management properties of the soils in the Ngerikiil Watershed. Table 6: Management properties of the soils in the Ngerikiil Watershed * Soil Name Crops Agroforestry: coconut, mango, banana, papaya, guava, cassava, yams pineapple, dryland taro and vegetable crops Suitable for crops only if special management used Wetland taro, rice Not suitable for crops Wetland taro, rice Suitable for crops only if special management used Agroforestry: coconut, mango, banana, papaya, guava, cassava, yams pineapple, dryland taro and vegetable crops Coconuts; suitable for some other crops only if special management used Bananas, cassava, coconuts, guava, mangosteens, sweet potatoes, and dryland taro Agroforestry: coconut, mango, banana, papaya, guava, cassava, yams pineapple, dryland taro and vegetable crops Suitable for crops only if special management used Suitable for some crops only if special management used Not suitable for crops Pasture Building Site Development Limited by slope, high clay content and low strength Limited by slope, high clay content and low strength Not suitable Not suitable Not suitable Not suitable Septic Tank Absorption Fields Aimeliik Good pastureland if cattle rotated with legume planting Limited by slope Babelthuap Dechel Ilachetomel Mesei Ngardmau Not suitable Not suitable Not suitable Not suitable Not suitable Suitable in nonerosive areas where cattle rotated with legume planting Limited by slope Not suitable Not suitable Not suitable Not suitable Ngatpang Limited by slope, high clay content and low strength Not suitable Ngedebus Not suitable Not suitable Not suitable Ngersuul Not suitable Not suitable Not suitable Palau Good pastureland if cattle rotated with legume planting Limited by slope, high clay content and low strength Limited by slope Peleliu Not suitable Not suitable Limited by wetness, shrink-swell, slope and low strength Not suitable Tabecheding Typic Troporthents Not suitable Not suitable Not suitable Soil series consists of fill material; use suitability depends on type of fill *See Soil Survey of Islands of Palau, Smith, 1983 for more details 2.7.5 Soil Properties Table 7 summarizes ranges in some important soil properties by major soil group (Map 4). There is wide variation in topsoil organic matter in Palau. This variation occurs because of the kind and 37 amount of vegetation the soil supports, agricultural practices, the degree of degradation the soil has experienced, and the degree of soil wetness. Organic matter variation in upland volcanic soils is discussed in detail by Smith and Babik (1988). Organic matter is an indicator of soil health in Palau. Organic matter in volcanic upland and marine terrace soils promotes stronger soil structure, and increased permeability and aeration. Organic matter provides nutrients when converted to humus, and it increases a soil’s capacity to retain both water and nutrients. Organic compounds may complex with aluminum and lower the amount of soluble aluminum in the soil. Bottomlands have relatively high amounts of organic matter because wet soil conditions slow the rate of decomposition. Limestone soils are under forest vegetation that produces large amounts of organic matter. Minimal disturbance of these soils allows organic matter to accumulate. The majority of soils in the Ngerikiil Watershed formed in highly weathered volcanic materials. The clays remaining after long periods of soil formation in a hot humid climate have a low capacity to retain nutrients and most plant nutrients have been leached from the soil. The variation in nutrient holding capacity shown in Table 7 is primarily due to the amount of organic matter in the soil. Low organic matter content results in low nutrient holding capacity. Smith and Babik (1988) describe in detail how the volcanic upland soils differ. The Aimeliik series has an intact nutrient cycling system (i.e., forest) that maintains a surface layer relatively high in organic matter and nutrients. Clearing forest from upland volcanic soils disrupts the nutrient cycling system and lowers biomass production. Organic matter, which can provide a substantial amount of a soil’s ability to hold nutrients, is commonly burned off allowing further topsoil depletion of plant nutrients via leaching or through erosion. The Palau series found under savanna grasses and ferns have lower organic matter and nutrients at the surface. The Babelthuap series represents further degradation of volcanic soil where there is no effective nutrient cycling and low biomass accumulation under the sparse fern vegetation. Sparse vegetation leads to soil erosion and low soil fertility causes difficulty in re-establishing vegetation on these soils. Table 7: Soil property ranges for major soil groups Soil Group Volcanic uplands Marine Terraces Bottomlands Limestone * Al = aluminum Soil Layer topsoil subsoil topsoil subsoil topsoil subsoil topsoil subsoil Organic Matter low – high low low very low - low high – very high low - moderate high moderate Nutrient Capacity low – very high low - moderate very low – low low – high high – very high moderate - high high moderate Al-toxicity* low – very high low - very high mod – very high low - very high low – moderate low - moderate none none 38 Loss of topsoil and organic matter lowers soil productivity, but this can be compensated for by using synthetic fertilizers. However, fertilizer application needs to be carefully managed to avoid leaching and runoff. In general, the Volcanic Uplands soils have little capacity to hold nutrients and over-fertilizing is likely. Excess fertilizer will either be leached through the soil, and potentially to groundwater, or will be removed from the site by erosion and runoff. Pollution of downstream waters is a distinct possibility in this situation. The Marine Terrace soils and the large majority of the area covered by Volcanic Upland soils have halloysitic mineralogy. Halloysite is a soil mineral commonly formed from volcanic rocks in humid tropical environments. In the wet conditions of Palau, halloysite forms very fine tubes that can hold water. Soils in which halloysite dominates have low bearing strength and can cause severe problems for roads. Pressure applied to the soil by vehicle wheels can cause the release of water held by the mineral and result in muddy conditions and poor traction. Aluminum becomes soluble under acidic conditions. At pH values less than 5.2, the solubility of aluminum increases greatly. Aluminum complexes with phosphate, which plants need for nutrition. Aluminum toxicity stunts root growth, effectively reducing the volume of soil that roots can exploit for water and nutrients. Stunted roots are not efficient at extracting nutrients from nutrient-poor soils. Aluminum toxicity is not a problem on limestone soils with high pH levels. Soils on Bottomlands have favorable pH levels so aluminum toxicity is not a concern. Soils on Volcanic Uplands and Marine Terraces generally have high acidity and potential aluminum toxicity problems. Some volcanic soil layers with large amount of organic matter and deep layers below the active zone of mineral weathering are in the “low” range of aluminum toxicity. Extensive data sets for a number of sampled soils, but not all of Palau’s soils, can be found at the NRCS web site www.soils.usda.gov under “characterization data.” Querying by soil series name is the easiest way to access the database. Ranges of soil properties and a number of agricultural and engineering interpretations based on those properties are listed in the tables in the published soil survey (Smith, 1983). 2.7.6 Soil Inventory During the week of March 10-14, 2003, the field team examined soils in the southern part of the Ngerikiil Watershed to assess the accuracy of the soil maps in the Soil Survey of the Islands of Palau (Smith, 1983). Forty-five locations were examined by the USDA-NRCS, Pacific Basin Area Soil Scientist (Gavenda). These locations consisted of a number of map units representative of the watershed. In all instances, the soil maps accurately identified the soils at a given location given the ranges of characteristics of the soil series and map unit variability. The conclusion drawn from the field examination is that the soil maps can confidently be used as to make extrapolations on a watershed basis. The soils in the Ngerikiil Watershed represent four of the five major groupings of soils in Palau. These soils are on bottomlands, marine terraces, volcanic uplands, and limestone (Photos 1-8). These major groupings characterize landscapes that differ in geologic materials and drainage, which affect soil formation and therefore the properties and distribution of soils. Twenty-six soil map units based on thirteen soil series and two miscellaneous land types are used to group soils 39 on detailed soils maps (Smith, 1983). The soil map units found in the watershed are listed in Table 8. Table 8: Soil legend for soils in the Ngerikiil Watershed (Smith 1983) Symbol 400 401 402 403 404 405 406 408 409 411 418 419 420 421 422 423 424 426 431 434 435 436 437 438 439 441 Soils Map Unit Name Aimeliik-Palau complex, 6 to 12 percent slopes Aimeliik-Palau complex, 12 to 30 percent slopes Aimeliik-Palau complex, 30 to 50 percent slopes Aimeliik-Palau complex, 50 to 75 percent slopes Babelthuap-Ngardmau complex, 2 to 6 percent slopes Babelthuap-Ngardmau complex, 6 to 12 percent slopes Babelthuap-Ngardmau complex, 12 to 30 percent slopes Dechel-Mesei complex, 0 to 2 percent slopes Ilachetomel peat, 0 to 1 percent slopes Ngardmau-Babelthuap complex, 30 to 50 percent slopes Ngatpang gravelly clay loam, 2 to 12 percent slopes, severely eroded Ngatpang gravelly clay loam, 12 to 50 percent slopes, severely eroded Ngatpang silty clay loam, 2 to 6 percent slopes Ngatpang silty clay loam, 6 to 12 percent slopes Ngatpang silty clay loam, 12 to 30 percent slopes Ngatpang silty clay loam, 30 to 50 percent slopes Ngedebus sand, 0 to 3 percent slopes Ngersuul silt loam, 0 to 2 percent slopes Palau-Aimeliik complex, 2 to 6 percent slopes Rock outcrop-Peleliu complex, 80 to 150 percent slopes Tabecheding silty clay loam, 2 to 6 percent slopes Tabecheding silty clay loam, 6 to 12 percent slopes Tabecheding silty clay loam, 2 to 12 percent slopes, severely eroded Tabecheding silty clay loam, 12 to 30 percent slopes Tabecheding silty clay loam, 12 to 30 percent slopes, severely eroded Typic Troporthents-Urban land complex, 0 to 1 percent slopes The volcanic soils, which are primarily under forest and savanna vegetation, occupy the greatest part (71 percent) of the Ngerikiil Watershed. Bottomland soils are the most agriculturally productive lands but they cover only 15 percent of the watershed. Soils on marine terraces cover 10.5 percent of the watershed; these landscapes are in forest, savanna and agriculture. Areas of limestone soils (2.5 percent) occur on steep forested hills in the southeast part of the watershed. Miscellaneous urban land comprises only a minor area (one percent) of the watershed. The Aimeliik and Palau series account for about 62 percent of the area in the Ngerikiil Watershed and 87 percent of the area covered by volcanic soils (Photos 1 & 2). The following photos show profiles for a number of the soils founds in the Ngerikiil Watershed. The scale in all photos is in centimeters. 40 Bottomlands consist primarily of the saltwater mangrove organic soils of the Ilachetomel series (71 percent of bottomlands or almost 11 percent of the total watershed). The agriculturally productive Dechel (Photo 4) and Ngersuul mineral soils, along with smaller amounts of the organic Mesei series, comprise nearly all the remaining Bottomlands soils and account for only about 4.5 percent of the watershed area. Photo 5 shows the landscape distribution of soil complexes on volcanic uplands. The Aimeliik (forested) and Palau (savanna) series are generally on sideslopes but may also occur on vegetated ridgetops and valley bottoms. The Babelthuap and Ngardmau series are on ridgetops that may be bare ground or sparsely vegetated with ferns and other plants that are indicators of poor soil fertility. The Dechel, Ngersuul and Mesei series are in low wet areas in the landscape. Marine terraces have the Ngatpang and Tabecheding series soils. The Ngatpang series comprises 43 percent of marine terraces and covers four percent of the total area (Photo 6). Tabecheding soil (Photo 7) comprises 57 percent of marine terraces and covers six percent of the total area. Limestone soils are in the Peleliu series (Photo 8), which is in a complex with Rock Outcrop, and account for only 2.5 percent of the watershed area. Miscellaneous land has been highly modified by urbanization. It is concentrated around the airport and accounts for about one percent of the watershed. Landscapes with slopes greater than 12 percent account for 72 percent of the watershed (Map 5) and those of 30 percent or more (Map 6) account for 44 percent of the watershed. Soils on steep slopes have a high potential to erode if vegetation is removed (Photo 9 & 10). Volcanic and marine terrace soils are on the large majority of these steep landscapes. Limestone soils also occur on steep landscapes but they remain under forest because of their unsuitability for home site or agricultural development. 2.7.7 Soil Interpretations Topsoil is generally only 10 to 15 centimeters (four to six inches) thick in Palau soils. Topsoil has the most favorable physical and chemical properties within a soil profile. Keeping the topsoil intact maintains soil quality and productivity. Subsoil properties of Volcanic Upland and Marine Terrace soils are undesirable for agriculture because of low fertility and high potential for soluble aluminum contents that are toxic to plants. Subsoil soil structure is not as favorable for water infiltration, therefore greater runoff and erosion can be expected if topsoil is removed. Furthermore, once the topsoil is eroded it may be difficult to re-establish trees or produce acceptable crop yields without considerable addition of fertilizer and/or liming amendments. Smith (1983) discusses soil fertility issues and crop and pasture management for Palau soils. Limestone soils and landscapes are generally not suitable for development. The good Bottomlands soils in the Ngerikiil Watershed have already been cleared and developed for agriculture and home sites. These two soil groups have high resilience, that is, they resist erosion and degradation well. These soil groups have low sensitivity to disturbance. That is, they only suffer degradation under very poor management and persistent mismanagement (Stocking, 2003). Volcanic Upland and Marine Terrace soils are the most likely soils to be exposed to new development pressure in the Ngerikiil Watershed. Both of these soil groups have low resilience 41 and high sensitivity to disturbance, making them the least desirable soils to develop. The soils are easy to degrade through fire or mechanical disturbance. Disturbance brings noticeable adverse effects on agricultural productivity through loss of nutrients, lower available water holding capacity and decreased permeability. These soils are also difficult to restore to their original condition. They are best left in a forested condition. The soil scientists who conducted the soil survey rated soils for various uses. These evaluations were based on topsoil and subsoil properties. The interpretations for various uses are in tables in the soil survey (Smith, 1983). Each component of each map unit is rated separately and the principal limitations are listed. Smith (1983) summarizes the rating system as follows: The limitations are considered slight if soil properties and site features are generally favorable for the indicated use and limitations are minor and easily overcome; moderate if soil properties or site features are not favorable for the indicated use and special planning, design or maintenance is needed to overcome or minimize the limitations; and severe if soil properties or site features are so unfavorable or so difficult to overcome that special design, significant increases in construction costs, and possibly increased maintenance are required. Special feasibility studies may be required where the soil limitations are severe. A summary of generalized soil management interpretations is provided in Table 9 below. Note that these interpretations are based on soil series, not map units as in the soil survey, and are only for the soils are they are found in the Ngerikiil Watershed. Terminology differs from language used for official NRCS interpretations. The Soil Survey of Islands of Palau, Republic of Palau (Smith, 1983) should be consulted for official interpretations. For dwellings without basements, in general the Volcanic Uplands soils are rated as having moderate to severe limitations primarily because of steep slopes. Marine Terrace soils have slight to severe limitations depending on slope steepness and degree of wetness. Bottomlands soils have severe ratings because of flooding, ponding and low strength. Limestone soils are rated severe because of the shallow depth to hard bedrock and some map units are very steep. For septic tank absorption leach fields, the Volcanic Uplands soils generally rate slight to severe depending on slope steepness. Marine Terrace soils rate severe primarily because of slow permeability, but some map units are too steep and other are too wet. Bottomlands soils also rate severe because of slow permeability, flooding and ponding. Limestone soils rate severe because of depth to hard bedrock and presence of large stones. All soils in the Ngerikiil Watershed rate as poor for road fill because of low soil strength, and some map units are too steep while others are too wet. 42 Table 9: Generalized management interpretations of the soils in the Ngerikiil Watershed Soil Name Suitable Crops Agroforestry: coconut, mango, banana, papaya, guava, cassava, yams pineapple, dryland taro and vegetable crops Suitable for crops only if special management used Wetland taro, rice Pasture Good pastureland if livestock rotated with legume planting Suitable for pasture only if special management used Not suitable; limited by wetness and flooding Not suitable; limited by wetness and flooding Not suitable; limited by wetness and flooding Suitable for pasture only if special management used Suitable in nonerosive areas where livestock rotated with legume planting Limited by low fertility and droughtiness Not suitable; limited by wetness and flooding Good pastureland if livestock rotated with legume planting Not suitable; limited by slope and rockiness Not suitable; limited by wetness Not suitable Building Site Development Limited by slope, high clay content and low strength Limited by slope, high clay content and low strength Not suitable; limited by wetness and flooding Not suitable; limited by wetness and flooding Not suitable; limited by wetness and flooding Limited by slope, high clay content and low strength Limited by slope, high clay content and low strength Not suitable; limited by flooding Not suitable; limited by wetness and flooding Limited by slope, high clay content and low strength Not suitable; limited by slope Septic Tank Absorption Fields Aimeliik Limited by slope Babelthuap Limited by slope Not suitable; limited by wetness and flooding Not suitable; limited by wetness and flooding Not suitable; limited by wetness and flooding Limited by slope Dechel Ilachetomel Not suitable for crops Mesei Wetland taro, rice Suitable for crops only if special management used Agroforestry: coconut, mango, banana, papaya, guava, cassava, yams pineapple, dryland taro and vegetable crops Coconuts; suitable for some other crops only if special management used Bananas, cassava, coconuts, guava, mangosteens, sweet potatoes, and dryland taro Agroforestry: coconut, mango, banana, papaya, guava, cassava, yams pineapple, dryland taro and vegetable crops Suitable for crops only if special management used Suitable for some crops only if special management used Not suitable for crops Ngardmau Ngatpang Not suitable; limited by slow perc rate and wetness Ngedebus Not suitable; limited by flooding Not suitable; limited by wetness and flooding Ngersuul Palau Limited by slope Peleliu Not suitable; limited by slope and shallow to bedrock Tabecheding Typic Troporthents Limited by wetness, Not suitable; limited by shrink-swell, slope and slow perc rate and wetness low strength Soil consists of fill material or subsoil; use suitability depends on type of fill, subsoil properties and slope The Soil Survey of Islands of Palau, Republic of Palau (Smith, 1983) should be consulted for official interpretations 2.8 VEGETATION AND PLANT COMMUNITIES The Ngerikiil Watershed area is covered with forest, secondary vegetation, agroforest, and non– forested areas (Map 7). Forested areas may be divided into interior upland, mangrove, and swamp forest, with a few Rock Island limestone forest in Airai bay. Table 10 provides a listing of common vegetation in each of the vegetation communities. 43 Upland forest is on volcanic soils in the hilly interior of the watershed and consists of a speciesrich mixed broadleaf forest that occupies flat or sloping sites as well as river and stream banks. Palauan upland forest is the most diverse vegetative community in Micronesia. The vegetative structure is divided into an upper and lower canopy. Of the species listed in Table 10, understory communities of plants include Pinanga insignis, Pandanus aimiriikensis, and Ixora casei. Along ravines and streams, Barringtonia racemosa, Semecarpus venenosus and the palm Pinanga insignis are common. Found along the lower portions of rivers and on coastal mudflats, the mangrove forests in Palau are the most species-rich in Micronesia. Well-developed stands can become 15 to 20 meters (49.2’ to 65.6;) tall. On the seaward side, Rhizophora stylosa and Sonneratia alba dominate; at larger river mouths or bay indentations, Rhizophora apiculata and R. stylosa can become pure stands or occur with Sonneratia alba and Bruguiera gymnorrhiza; landward, Heritiera littoralis, Lumnitzera littorea and Xylocarpus granatum are included in the mix; and where the estuary becomes river-like, Bruguiera, Lumnitzera, Sonneratia and Xylocarpus species are common, but Rhizophora spp. becomes uncommon. The palm Nypa fruticans is fairly common along the lower portions and mouths of rivers. Other woody species include Avicennia marina, Ceriops tagal and Scyphiphora hydrophyllacea (Cole et al., 1987). Often found just inland of mangrove forest, where the soils are inundated with fresh or slightly brackish water, coastal swamp forests in Palau are today generally degraded and covered with Hibiscus tiliaceus; other suitable habitat has been replaced by taro cultivation. Tree species include Barringtonia racemosa, Calophyllum soulattri, Cynometra ramiflora, Heritiera littoralis, Horsfieldia irya, Samadera indica and Terminalia catappa (Cole et al., 1987). Limestone forests are unique to limestone outcrops and coralline limestone islands and are susceptible to any disturbance. These forests are generally untouched by development because of inaccessibility and landscape/soil characteristics. The rock island forest in the Airai area covers over 192 hectares (472 acres). Agroforests generally appear along the coasts or near dwellings. They typically contain coconuts, often in extensive plantations, breadfruit, mangos, bananas, betelnut and java plum. On Babeldaob, an extensive savanna dominated by an herbaceous flora of grasses, herbs, and sedges can be found. Scattered throughout are woody shrubs and small trees of Alphitonia carolinensis, Decaspermum raymundii, Fagraea ksid, Melastoma malabathricum, Pandanus spp., Rhus taitensis and Symplocos racemosa var. palauensis. On recently disturbed sites or fallow lands, a variety of fast-growing small trees and shrubs quickly fill in. On the islands with volcanic soils, this secondary vegetation commonly consists of Macaranga carolinensis, Bambusa spp. and Hibiscus tiliaceus in wetter sites. On the limestone islands, Macaranga carolinensis and Timonius timon, an introduced species, are pioneers (Cole et al., 1987). 44 Table 10: Common vegetation species in the Ngerikiil Watershed Vegetation Community U R, FWS U U U, R U U U, S U U U U U U U U U, L U U U U, A U U, L U U, S M M FWS M FWS M, FWS FWS M M M Scientific Name Alphitonia carolinensis Barringtonia racemosa Calophyllum inophyllum var. wakamatsui Calophyllum pelewense Campnosperma brevipetiolata Cerbera floribunda Cyathea Iunalata Fagraea ksid Glochidion macrosepalum, Glochidion ramiflorum Gmelina palawensis Horsfieldia palauensis, Ixora casei Manilkara udoido Myristica insularis, Osmoxylon oliveri Pandanus aimiriikensis Parinari corymbosa Parinari laurina Pinanga insignis Pterocarpus indicus Rhus taitensis Semecarpus venenosus Serianthes kanehirae Symplocos racemosa var. palauensis Avicennia marina var. alba Bruguiera gymnorrhiza Calophyllum soulattri Ceriops tagal Donax canniformis Heritiera littoralis Horsfieldia amklaal Lumnitzera littorea Nypa fruticans Rhizophora apiculata Family Name (Common English Name) Rhamnaceae Lecythidaceae Clusiaceae Clusiaceae Anacardiaceae Apocynaceae Cyatheaceae Gentianaceae Euphorbiaceae Euphorbiaceae Verbenaceae Myristicaceae Rubiaceae Sapotaceae Myristicaceae Araliaceae Pandanaceae Rosaceae Rosaceae Arecaceae Fabaceae Anacardiaceae Anacardiaceae (Poison Tree) Fabaceae Symplocaceae Verbenaceae Rhizophoraceae (oriental mangrove) Clusiaceae Rhizophoraceae (mangrove) Marantaceae Sterculiaceae Myristicaceae Combretaceae Arecaceae Rhizophoraceae (mangrove) Kesiamel Chertochet Bkau Cheritem Demailei Ias Choes Tonget Ukall Chebtui Dadaiit Kodenges Olebtaches Biut Temring Chebicheb Chemeklachel Mekekad Touechel Bngaol Ngolem Blacheos Chersachel Kerdeu Udeuid Palauan Name Chelebiob Koranges Chesemolech Chesemolech Kelelacharm Chemeridech Cheluu Ksid 45 Vegetation Community M FWS M M FWS M L L L L L L L L L A A A A A A A A A A S S S S S S S S S S Scientific Name Rhizophora mucronata var. stylosa Samadera indica Scyphiphora hydrophyllacea Sonneratia alba Stemonurus ammui Xylocarpus granatum Bikkia palauensis Clerodendrum inerme var. oceanicum Cordia spp. Dracaena multiflora Gulubia palauensis Intsia bijuga Premna obtusifolia Psychotria spp. Ptychosperma palauensis Areca catechu Artocarpus spp. Cocos nucifera Eugenia cuminii Garcinia mangostana Mangifera indica Musa spp. Nephelium lappaceum Swietenia mahagoni Swietenia macrophyllla Bambusa spp. Decaspermum spp. Eurya japonica var. nitida Gleichenia linearis Hibiscus tiliaceus Ischaemum spp. Macaranga carolinensis Melastoma malabathricum Miscanthus floridulus Wikstroemia elliptica Family Name (Common English Name) Rhizophoraceae (mangrove) Simaroubaceae Rubiaceae Sonneratiaceae Icacinaceae Meliaceae (Cannonball Fruit Tree) Rubiaceae Verbenaceae Boraginaceae (Geiger Tree) Tiliaceae Arecaceae (Rock Island Palm) Fabaceae (Ironwood) Verbenaceae Rubiaceae Arecaceae (Palau Palm) Arecaceae (Betelnut) Moraceae (Breadfruit) Arecaceae (Coconut) Myrtaceae (Java Plum) Clusiaceae (Mangosteen) Anacardiaceae (Mango) Musaceae (Banana) Sapindaceae (Rambutan) Meliaceae (Mahogany) Meliaceae Poaceae (Bambuu) Myrtaceae Theaceae Gleicheniaceae (False Staghorn) Malvaceae (Hibiscus) Poaceae Euphorbiaceae Melastomataceae Poaceae Thymelaeaceae Palauan Name Cheskeam Kuat Churur Ngmui Meduulokeb ong Rur Emrert Kelau, Baderirt Orredakl Bochelaucher erak Dort Chosm Chesebuuch Buuch Meduu Lius Mesekerrak Mangosteen Iedel Bengeltuu, Tuu, Blantalos Rambotang Mahongani Kertaku Cheskiik Itouch Chermall Tametaml Bedel Matakui Banga ruchel Rao Cole et al. 1987, Fosberg and Mueller-Dombois, 1998 Note: A=Agroforest; FWS=Fresh Water (or slightly brackish) Swamp; L=Limestone Forest; M=Mangrove Forest; R=Riverine; S=Savanna/Secondary Vegetation; U=Upland Forest 46 Map 7: Forested and non-forested areas 47 SECTION 3: CRITICAL RESOURCE CONCERNS Five critical resource concerns were identified through the resource assessment. These concerns provide the basis for recommended actions to resolve and/or improve the identified concerns (see Section 4 for Recommendations). The five natural resource concerns, listed in order of their level of threat to the main watershed objectives, are: soil erosion and sedimentation; nutrient, fertilizer and pesticide pollution; solid waste disposal; invasive species; and wildlife habitat loss. The first concern, soil erosion and sedimentation, is subdivided into five categories: roads, development, agriculture, burning of savanna areas, and steam bank erosion. The second concern, nutrient, fertilizer and pesticide pollution, is subdivided into three categories: animal manure, chemical fertilizer runoff, and pesticide leaching. These natural resource concerns are described in detail below following a brief introduction to soil erosion and the way it is measured in the field. 3.1 SOIL EROSION & SEDIMENTATION Sediment-laden runoff reaching the river and ultimately the ocean is presently the most serious resource concern within the Ngerikiil Watershed. This often-unrecognized pollutant is affecting both Palau’s primary drinking water source and coral reef health within Airai bay. There are five primary sources of this runoff: • • • • • Sediment-laden runoff from unprotected roads Sediment-laden runoff from housing and other development Erosion on agricultural land lacking any conservation practices Erosion on burned savanna areas Stream bank erosion Soil erosion is the detachment and transport of soil by water, wind, gravity or any combination of these conditions. It is part of the natural process of geologic aging that is always happening as geographic areas evolve. Babeldaob Island has been eroding ever since a marine volcano was uplifted from the ocean floor to form the island. Erosion is what has made the island look as it does today and has contributed to the development of the estuarine system. Problems arise when an unusually large amount of erosion happens to upset this balance and begins to destroy or reduce the quality of any part of the area’s natural resource base. Human activity can increase the rate of erosion within the landscape or ecosystem. Damage can be caused by a few large-scale activities or the cumulative effect of many seemingly insignificant actions or combinations of the two. Many environmental problems can occur when a population becomes concentrated enough in a given area to outstrip the environment’s ability to absorb their impacts; e.g., if only one family lived on Babeldaob Island they could probably do anything they liked and not adversely affect the environment, but thousands of people living together on a small island cannot. In this situation, people must live sustainably within the natural systems in order to preserve the resources that provide life and comfort. By utilizing the many existing conservation practices 48 available such as the traditional Palauan practices, a population can develop with the necessities and quality of life they desire indefinitely. The soils on Babeldaob Island contain a large percentage of clay particles that remain in suspension in water and are transported over long distances until they settle out. The soils on Babeldaob Island are very acidic, low in nutrients and organic matter, and high in soluble aluminum. These properties create marginal conditions for plant growth resulting in fragile soilplant communities that, once disturbed, are very difficult to re-establish. In their 1993 report on the Ngerikiil Watershed Inventory and Management Recommendations Project, Elliott and Franz state on page 30 that “Sediment loss measurements are needed in order to determine the actual amount of soil loss that is occurring as a result of road building, field burning and other disruptive activities.” The NRCS assessment team took some of those soil loss measurements. Tables in the Erosion Rates section below, show sheet and rill erosion values on various land uses within the watershed. The numbers for bare-soil areas on several land uses clearly show accelerated sedimentation within the Ngerikiil Watershed. Uncontrolled or improperly managed land development activities conducted by man, therefore, can easily disrupt the natural soil-plant balance and result in dramatic increases in soil erosion and decreases in environmental quality. 3.1.1 Effects of Soil Erosion on Water Quality Poor farming practices and irresponsible construction practices are detaching large amounts of soil, allowing them to be transported by wind and surface runoff into streams, river and bay in the watershed. The immediate concern should be the current and future increase of erosion in the watershed. This sedimentation can severely impact aquatic life, water quality and human health and safety. Sediments from land runoff can decrease water clarity, smother sensitive bottom habitats such as seagrass beds and reef as well as transport toxins and nutrients (Boesch, 2003). Suspended sediment increases the turbidity of the water, thus allowing less sunlight penetration for aquatic plants, and deposited sediment can fill in natural pools, which are habitat for aquatic animals. Most upland soils located in the watershed are classified as silt loam, or silty clay loam in texture. This means the soil particles are very small and stay in suspension in the water for long periods. Once in suspension, these soil particles may take several days or even weeks to settle out and fall to the bottom of the water body. Some will even be re-suspended with currents, tides, and inflows from rivers and streams. Some of the sediment from upstream of the intake station is pumped to the Airai State water treatment plant where it must be settled out. Photo 11 shows one week’s worth of sediment awaiting removal. Photo 12 is a close-up of that sediment where clear delineations of rainfall events are visible on the sediment profile. The extra work to deal with all this sediment creates additional cost and strain on Palau’s water treatment facilities. Most sediment ultimately reaches Airai Bay and the ocean beyond. Approximately 69 percent of terrigenous mud from the Ngerikiil River, a sediment plume typically two meters (6.6’) thick following a storm, settles in Airai Bay (Golbuu et al., 2003). Sediment is clearly a diffuse pollutant of concern in the Ngerikiil Watershed, threatening both the drinking water and the coral reef resource. Suspended soil particles are not traveling alone. Other pollutants such as pesticides and nutrients are attached to the soil particles and are thus carried into the water along with them. The fine clay and silt particles in the soils have a high nutrient holding capacity, which means that very large 49 amounts of nutrients and other chemical pollutants can stay adsorbed on the particles and thus be carried into the surface water. Diffuse pollutants such as nutrients and pesticides are addressed in Section 3.2 below. Photo 11: One week’s worth of sediment Photo 12: Close-up of the sediment awaiting removal 3.1.2 Causes of Soil Erosion Water erosion is the principal problem in the Ngerikiil Watershed. When raindrops hit exposed earth at a velocity of approximately seven to nine meters per second (15.7 to 20.1 mph), they detach particles from direct impact of raindrops. The dislodged particles are now available to be transported by surface runoff. As soil particles are carried away, runoff concentrates into rills up to several inches deep that eventually develop into large gullies. In the process, sediment particles are carried for a while and then deposited as the transporting capacity of the flow is exceeded. The next storm to come along may pick up the deposited particles and carry them further down in the watershed. Sediment is transported incrementally in this way until it reaches its final destination in the mangroves, bay, reef or ocean. The classical forms of erosion by water are sheet and rill, and gully erosion. Sheet erosion, also called interrill erosion, is almost imperceptible soil movement from raindrop splash resulting in the breakdown of soil surface structure and surface runoff. It occurs rather uniformly over the slope and may go unnoticed until most of the productive topsoil has been lost. Rill erosion results when surface runoff concentrates forming numerous small yet well-defined channels that can be obliterated by tillage. Although sheet erosion is not obvious, rills, typically up to six inches wide and four inches deep, are very obvious (Foster, 1986). Gully erosion occurs where runoff tends to collect and concentrate in a few major natural waterways or swales before leaving the field, and eventually, most water and sediment discharge from fields through them. Gully areas are clearly channelized and recur in the same area each year. Gullies may be short-lived if they are plowed and tilled or if these areas are vegetated. However, if not addressed, they will form channels too deep to cross with farm equipment, 50 removing portions of fields from production. Once established, these gullies are permanent unless the concentrated runoff and runoff velocity that caused the gully are addressed and the gully is filled with soil moved with heavy equipment. Several factors determine the erosion potential of a particular site: • Soil Erodibility: Soil structure, texture and percentage of organic matter influence a soil’s propensity for erosion. Silt and fine sand typically indicate a very erodible soil; the presence of organic matter generally reduces the erodibility. Vegetative Cover: Vegetation is the most important factor in minimizing erosion. Plants and trees shield the soil from raindrop impacts, hold soil together with their root masses, and slow the velocity of surface runoff promoting water infiltration into the soil. Babeldaob has lost extensive plant cover through fires, development and farming. Surface Cover: Surface cover includes crop residue, rocks, moss, algae, and other nonerodible material that is in direct contact with the soil surface. Surface cover affects erosion by reducing the transport capacity and velocity of runoff water, increasing water infiltration into the subsurface, and by decreasing the soil surface area susceptible to raindrop impact (Renard and Foster, 1992). Topography: Longer slopes deliver more runoff to the bottom of the slope and steep slopes increase the velocity of runoff. The upper watershed is mostly mountainous terrain with long, steep slopes. Climate/Season (Erosivity): The more frequent, intense and lengthy the rainfall events are, the higher the erosion risk. Frequent storms give higher runoff because the land stays saturated for long periods and has less chance to infiltrate between storms. Palau not only gets a very large amount of annual precipitation, but much of this rain is concentrated in the summer months (rainy season). Erosion Rates • • • • 3.1.3 Erosion rates for sheet and rill erosion can be predicted using the Revised Universal Soil Loss Equation (RUSLE), which is an improved method of the Universal Soil Loss Equation (USLE) developed, by Wischmeier and Smith, 1978. RUSLE is an empirical equation, derived from field observations, that gives an estimate of soil erosion rates. The RUSLE equation was developed from over 40 years of research and data collection from small plots throughout the United States. It is useful in determining the adequacy of conservation measures for controlling soil erosion and to predict sediment movement and resultant non-point source pollution. Despite the simplification of many of the variables involved, RUSLE is the most widely accepted method of estimating sheet and rill soil erosion. The revised equation uses a computer model to calculate revised values used in the equation. RUSLE provides a means of comparison to evaluate various resource management options primarily for cropping systems. Therefore, the equation is a planning tool and not an exact measurement of soil erosion. The RUSLE model uses English units and is reported in tons of soil 51 per acre per year. To convert to the metric system: tons/acre/year X 2.242 = metric ton/hectare/year. The RUSLE equation is: A = R x K x (LS) x C x P where: A = Average Annual Soil Loss, expressed in tons per acre per year (metric tons/hectare/year). R = Rainfall Erosivity Factor, based on intensity and frequency of rainfall as well as the average annual precipitation. An R-factor range of 1450 to 1550 was determined for Airai State. K = Soil Erodibility Factor, or how resistant the soil is to water energy. The K-factors for each soil type can be found in the Soil Survey of Islands of Palau, USDA, SCS (NRCS), pages 115-117. L = Slope Length, measured from the point of erosion to the point of soil deposition or concentrated flow. S = Slope Steepness, expressed in percent and is the measure of feet of vertical fall in 30.5 meter (100’) of horizontal distance. The L and S are used together to derive an LS value from one of three LS tables. C = Cover Management Factor, is based on the amount of live cover, crop or plant residue on the soil surface, and amount and intensity of soil disturbance throughout the year. P = Practice Factor, a value of 1.0 is used for nonagricultural land or cropland without installed and properly maintained conservation practices. The P value is reduced when conservation practices, such as terraces, are applied that shorten or modify the slope length of a field. A soil loss tolerance, or the maximum amount of erosion at which the plant growth can be maintained within the soil, was estimated based on the soil properties of the soils in the watershed. This tolerance level or erosion conservation goal, determined to be 11.2 metric tons per hectare per year (5 tons/acre/year) for the Aimeliik and Palau series, represents a goal for the maximum annual soil loss for each land use type within the watershed. The slope of the landscape is an important consideration in the RUSLE calculation. In Table 11, the percent of slope has been grouped into four categories: floodplain, gentle, moderate and steep (Map 8). Slope is expressed in percent, meaning the number of units the land falls (or rises) in 100 units of horizontal distance. The higher the percent, the steeper the slope. For example, a slope that drops ten vertical feet in one hundred horizontal feet is a 10 percent slope (vertical drop/horizontal distance times 100). 52 Table 11: Slope types used in sheet and rill erosion calculations Slope Type Nearly level/floodplain Gently sloping Strongly sloping Moderately steep Steep Very steep Extremely steep Slope(%) 0-2 2-6 6-12 12-20 20-50 50-75 >60 Taken from the Soil Survey of Islands of Palau, Smith, 1983 Gully erosion is estimated directly in the field via cross section measurements and flow estimates. Any bare and steep area is likely to produce gullies, which are significant sources of sedimentation. Sedimentation from soil erosion can have a detrimental impact on water quality. As erosion occurs on a disturbed or bare soil, sediment is transported both within a field or area and off-site. The soil loss computed by RUSLE is the amount of sediment lost from the landscape profile represented by the particular RUSLE computation, not the amount of sediment leaving a field or watershed. Sediment yield to a receiving water body is influenced by rainfall intensity, distance to the water body, groundcover between the point of erosion and the receiving water body, and topography. RUSLE calculations do not quantify sediment yield to the Ngerikiil River or Airai Bay, or whether sediment reaches those water bodies. The following tables represent soil loss values computed from RUSLE which may be used for comparisons to predict relative soil loss under different site and management conditions. Management decisions such as conservation areas, reduced or no tillage to retain residue, planting of cover crops, elimination of burning, mulching of bare soil sites can lessen the impact of soil erosion and sediment and thus improve water quality. “ID” is the RUSLE run identifier. “WP” is the GPS Waypoint Number for the site where the data was collected. Values for “A” (average annual soil loss) are in tons per acre per year. Values in parentheses are average annual soil losses in metric tons per hectare per year. Slope is provided in percent slope per length of distance (feet) that the slope was measured. The following Tables 12 through 19 represent soil loss values computed from RUSLE, which may be used for comparisons to predict relative soil loss under different site and management conditions. Management decisions, such as conservation areas, reduced or no tillage to retain residue, planting of cover crops, elimination of burning, vegetating and mulching bare soil sites, can lessen the impact of soil erosion and sediment and thus improve water quality. Values for “A” (average annual soil loss) are in tons per acre per year. Values in parentheses are average annual soil losses in metric tons per hectare per year. Slope is provided in percent slope per length of distance that the slope was measured, in feet. 53 Table 12: Roads (unpaved) sheet and rill erosion Roads, sheet and rill erosion ID 1 WP 43 Slope (%/ft) 12/25 R 1550 x K 0.17 x LS x 0.70 C 1.0 x P= 1.0 A 184 (412.5) Notes non-graveled, bladed with dozer Gully Erosion Eroded Cross Section (sq ft) Length Soil Wt. Total 1 2 3 (ft) lbs/cu.ft. lbs lbs/ton years {[(24.38 + 13.94 + 13.56) / 3] x 470} x 74.9 = (608,787 / 2000) / 1 = Tons/ ac/yr 304 (273.6) ____________________________________________________________________________________________________ Total Road Erosion: 184 tons (sheet & rill erosion) + 304 tons (gully erosion) = 488 tons (1,094.1 metric tons) Notes: Gully erosion calculations from Revised Universal Soil Loss Equation Field Handbook for the Pacific Basin, USDA NRCS Pacific Basin Area, Field Office Technical Guide, Section I, December, 1999, Page 13. Table 13: Construction sites sheet and rill erosion Construction sites sheet and rill erosion ID 2 WP 44 Slope (%/ft) 8/60 R 1500 x K 0.15 x LS x 0.79 C 0.43 x P= 1.0 A Notes 76 bare soil site, no conservation (170.4) 178 3 13 12/50 1550 0.10 1.15 1.0 1.0 borrow areas next to road (399.1) Notes: Construction sites include housing areas during the construction phase with no soil erosion protection on site. Barrow areas refer to several bare soil areas found along the road where people were loading soil for use elsewhere. Like the home construction sites, no soil erosion protection practices were in place. Table 14: Cropland, moderately steep to steep slopes (13-30 percent), sheet and rill erosion Cropland, moderately steep to steep slopes (13-30 percent), sheet and rill erosion ID 4 WP 33 Slope (%/ft) 24/127 R 1550 x K 0.20 x LS x 4.85 C 0.20 x P= 0.85 A Notes 256 bare soil, cross-slope farming (574) 230 5 17 23/100 1500 0.17 3.93 0.23 1.0 bare soil, taro & cassava (515.7) 325 6 30 16/80 1550 0.20 2.28 0.46 1.0 bare, tilled up & down slope (728.7) 111 7 27 13/110 1500 0.17 2.17 0.20 1.0 fallowed cropland, tilled (248.9) Notes: These four samples on steeper cropland are on sites with few or no conservation practices in place. Run number four (4) was cross-slope but with intensive tillage and bare soil. The other three runs represent intensively tilled steep cropland with no conservation practices. It is clear that cropping steep slopes without conservation creates serious soil erosion. 54 Table 15: Cropland, strongly sloping slopes (6-12 percent), sheet and rill erosion Cropland, strongly sloping slopes (6-12 percent), sheet and rill erosion ID 8 WP 30 Slope (%/ft) 12/110 R 1550 x K 0.17 x LS x 1.88 C 0.46 x P= 1.0 A Notes 230 bare, tilled up & down slope (515.7) 12 9 36 8/60 1450 0.05 0.81 0.20 1.0 fallowed cropland burned (26.9) 90 10 34 8/200 1550 0.20 1.45 0.20 1.0 peppers, up & down slope (201.8) Notes: These three RUSLE runs are on more moderate slopes. Runs number eight (8) and 10 demonstrate that cropping even moderate slopes without conservation results in serious sheet and rill erosion. Run number nine (9) is a field that had been in grass fallow a number of years then burned off. This run represents its present state prior to tillage. Table 16: Cropland, nearly level to gently sloping slopes (0-5 percent), sheet and rill erosion Cropland, nearly level to gently sloping slopes (0-5 percent), sheet and rill erosion ID WP Slope (%/ft) R x K x LS x C x P= A Notes 0.1 11 20 0.5/15 1500 0.10 0.07 0.01 1.0 wetland taro cover, low tillage (0.2) 21 12 28 2/135 1500 0.24 0.29 0.20 1.0 beans, no cover, high tillage (47.1) 25 vegetable crops in rotation 13 49 4/60 1500 0.17 0.43 0.23 1.0 (56.1) heavy till 51 14 22 5/80 1500 0.17 0.59 0.34 1.0 bare, tomatoes in rotation (114.3) Notes: Runs number 12-14 indicate that sheet and rill erosion can be elevated even on gentle to nearly level ground without protective conservation measures. The flat wetland taro fields do not experience the erosion of adjacent dryer fields, as seen in run number 11. Table 17: Agroforestry sheet and rill erosion Agroforestry sheet and rill erosion ID 15 16 WP 16 49 Slope (%/ft) 25/26 6/200 R 1500 1500 x K 0.17 0.17 x LS x 2.17 0.90 C 0.01 0.01 x P= 0.80 0.80 A 4.4 (9.9) 1.8 (4.0) Notes betel-nut, full ground cover coconut, betel-nut, cover Table 18: Forestland sheet and rill erosion Forestland sheet and rill erosion ID 17 WP 58 Slope (%/ft) 10/75 R 1550 x K 0.10 x LS x 1.18 C 0.01 x P= 1.0 A Notes 1.8 healthy, undisturbed forest (4.0) Notes: Forestland includes native and re-growth forest and jungle on upland slopes. 55 Table 19: Savanna areas sheet and rill erosion Savanna areas sheet and rill erosion ID 18 WP 29 Slope (%/ft) 16/124 R x K 0.17 x LS x 3.37 C 0.11 x P= 1.0 A Notes 98 woody & fern, little cover (219.7) 76 19 47 18/65 1500 0.20 2.30 0.11 1.0 woody & fern, little cover (170.4) 16 20 25 30/115 1500 0.17 5.31 0.012 1.0 fern & grass, low-med cover (35.9) 13 fern & pitcher plant, low 21 42 17/300 1500 0.17 0.79 0.012 1.0 (29.1) cover 1.4 22 41 8/200 1450 0.10 0.99 0.10 1.0 healthy, unburned grassland (3.1) Notes: These savanna or “ked” areas vary greatly over the landscape and from site to site. Some are burned often making them more vulnerable to erosion (runs number 18 and 19), while other savanna areas have filled in with thick grass cover offering good protection from erosion (run number 22). 1550 The tables above clearly show that the highest erosion rates are produced from exposed bare soil on strongly sloping, moderately steep and steep slopes. Bare exposed soil at a borrow area on a 12 percent slope produces erosion at an estimated rate of 399.1 metric tons per hectare per year (178 tons/acre/year). This exceeds the conservation goal of 11.2 metric tons per hectare per year (5 tons/acre/year) by over 35 times. These estimated rates also show us that sustainable erosion rates (rates near 5 tons/acre/year) occur in vegetated areas on nearly level or strongly sloping slopes where conservation is being practiced. Table 20 below indicates the estimated contribution of soil erosion within the watershed for each land use type presently existing in the watershed. These totals are based on the range of values estimated above in Tables 12 through 19 and the total area of each land use type (see Table 2). This table very clearly indicates that intact, forested areas produce by far the least amount of erosion, even though forested land covers 82 percent of the watershed. These results also indicate that the quantity of erosion contribution by other land uses is dependent on whether or not conservation management is occurring (consciously or unconsciously). While these other land uses – unpaved roads, developed and bare areas, agriculture, and savannas, only cover 18 percent of the watershed, they potentially contribute nearly 23 times (275,538 metric tons or 236,948 tons annually) the amount of erosion that comes from the forested area annually. Should these percentages of land use areas increase in developed areas and a decrease in forested areas, with the continued lack of implementation of erosion conservation practices, damages to the land and seas could become irreversible. 56 Table 20: Total area of land use types and estimated range of annual erosion Land Use Type Roads (All Unpaved) Developed and Bare Areas Agricultural Land Savanna Forest % of Total Watershed Land Area 1% 3% 5% 9% 82% Acres 96 208 347 626 5,756 Estimated Range of Total Annual Erosion (tons/year) 46,848 (42,451 metric tons/year) 2,500 - 16,000 (2,250 – 14,400 metric tons/year) 1,900 - 112,800 (1,710 – 101,520 metric tons/year) 900 - 61,300 (810 – 55,170 metric tons/year) 10,400 (9,360 metric tons/year) 57 Map 8: Slope types in the Ngerikiil Watershed 58 Map 9: Slope breaks and land use types in the major farming area of the Ngerikiil Watershed 59 3.1.4 Roads With the development of the new Compact Road, significant land use changes will occur. The majority of sediment-laden runoff reaching the Ngerikiil River above the pump plant appears to be coming from bare exposed dirt roads that service the Compact Road as it undergoes construction, and some from the Compact Road itself. These are mainly short term concerns that will presumably be addressed during or at the completion of the Compact Road construction. Of greater concern are the long term effects of opening up the watershed to more roads and development and the future of the watershed as a source of drinking water. While the Compact Road construction has had relatively high environmental scrutiny and protection, other roads have not been constructed with such close inspection or strict environmental standards. Likewise, ongoing development within the watershed is being carried out with little or no environmental standards. Even where the roads are not too steep, significant amounts of sediment are sheet flowing down the hillsides. The team observed several alluvial fans beginning at the road edge and stretching hundreds of meters over barren and cleared land. A representative stretch of road approximately 143.3 meters (470’) long with seven to 12 percent slopes was measured by the team. The team found that this stretch of road lost about 230 cubic meters (8,122 ft3) of soil. Photo 13: Stick fences used as a sediment control measure along the Compact Road Drainage routes along the roadsides are often eroded 60 or more centimeters (two or more feet) deep, well into the saprolite. Saprolite is made up of highly weathered unconsolidated residual material, red clay to lava in this case, underlying the soil and grading to hard bedrock. Runoff water carrying loads of sediment exits the roads via deliberate cutouts or natural breaches in the side berms that have led to the formation of deep gullies along the roads. An average gully along the side of the road was measured and found to have lost approximately 1.5 cubic meters (53 ft3) over about a 3 meters (10’) length. The team observed some primitive sediment control measures such as the stick fences (Photo 13). These structures, whether overloaded in 10 weeks or 10 months are an indication of a very large amount of sediment coming off the land in Ngerikiil. 60 The assessment team observed a state road on a 12 percent slope installed to serve a new development with virtually no mitigation standards applied (Photo 14). A bulldozer operator simply dropped the blade and cut a road straight down a 12 percent slope. Annual erosion was measured at this site and found to be 1,094 metric tons per hectare per year (488 tons/acre/year) (Table 12). This is nearly 100 times the conservation goal. Serious erosion was evident throughout this and other road cuts. The estimated total annual erosion from roads based on this calculation and total area of unpaved roads in the watershed 38.8 hectare (96 acres) is 42,451 metric tons per hectare (46,848 tons/acre). Photo 14: Airai State road installed on a twelve percent (12%) slope to serve a new development While roads cover only one percent of the watershed, they erode over four times as much as the forested lands (9,360 metric tons or 10,400 tons annually) that cover 82 percent of the watershed (Table 20). 61 Photos 14, 15, 16, 17, 18, and 19 illustrate what is currently happening on the road system in the Ngerikiil Watershed. Photo 15: Massive sediment flow into forest Photo 16: Erosion on unimproved roads Photo 17: Massive sediment flow into forest Photo 18: Erosion on unimproved roads Roads in the Ngerikiil Watershed are generally unpaved and highly eroded. Many are in areas much too steep for unpaved roads and as a result contain numerous gullies from eroding soils. 62 Very little in the way of sediment control was observed. Common practice appears to be the application of crushed coral on top of eroding roads. This, however, does little in the way of protection and ultimately contributes more sediment to runoff as the coral fill simply washes away and exposes the soil once again. The result of this practice can be seen in Photo 19. Photo 19: Crushed coral fill on top of eroding road As roads branching off the newly opened Compact Road are installed, with little or no environmental protection measures, sediment-laden runoff entering the Ngerikiil River above the pump plant can be expected to increase significantly if conservation measures are not required during road construction. 63 3.1.5 Development New farms, housing and other development within the Ngerikiil Watershed lack measures toprevent sediment runoff from construction sites (Photos 20 and 21). These sites are major sources of sediment reaching the river. The erosion rates at two construction sites, one incorporating the use of mulch or other cover over the exposed soil and the other without any type of cover over the exposed soil, were estimated. The site with soil cover was estimated to erode at a rate of 26.9 metric tons per hectare per year (12 tons/acre/year), while the bare exposed soil construction site eroded at an estimated rate of 170.4 metric tons per hectare per year (76 tons/acre/year) (Table 13). Based on the area of developed and/or bare lands within the watershed 84.2 hectares (208 acres), this source erodes between 2,250 and 14,400 metric tons (2,500 and 16,000 tons) of soil annually (Table 20). Bare areas, formerly borrow areas for road construction, were estimated to erode at up to 399.1 metric tons per hectare per year (178 tons/acre/year) (Table 13). Unless strict environmental codes and laws are passed and enforced on development and road construction, serious impacts to the watershed’s water quality can be expected to increase with the opening of the Compact Road. Photo 20: Erosion from construction Photo 21: Erosion from construction activity When a new structure is built, it affects not only drainage patterns within the construction site but also alters the natural pattern of water flow over the surrounding areas. As development continues, the hydrology of the watershed changes. More cleared and paved areas allow water to runoff more quickly. This can result in higher water velocities, peak discharges and stream flows, which all contribute to increased erosion. Runoff water will always seek the path of least resistance through and around a developed area. If left uncontrolled, this often leads to gully erosion. The solution is to control the water flow by manipulating its direction and velocity until it can be released to a stable outlet. A stable outlet is one that releases the water after dissipating enough energy (slowing it down) so that it theoretically cannot erode any surface it will run over until reaching the river, bay or ocean. The most important factors to consider when trying to minimize erosion at a construction site are the material that the water is running over, the water velocity, and the slope of the land. Channels are one way to control surface runoff and minimize erosion at construction sites. The steeper the slope, the faster the water will move, but different channel linings will also affect the flow velocity to varying degrees. Channel linings also have varying degrees of erosivity, for example, 64 a concrete channel is far less erosive than a natural earth channel, so care should be taken when deciding what type of lining to use. Although there will most likely be situations in the Ngerikiil Watershed that require high water velocities and concrete linings, vegetated earth should be used whenever possible as it slows the velocity of runoff, allows for infiltration, is the less costly, and usually accepted as more aesthetic than concrete. Generally speaking, grass lined channels should not be designed for velocities greater than 1.5 meters per second (5 ft/sec). Some examples of good species of grass to use are Zoysia sp. (Japanese), Axonopus sp. (carpet), Cynodon dactylon (Bermuda), Eremochloa opiuroides (centipede), and Brachiaria decumbens (signal) grass. Photo 22 (below), while not taken in the watershed, illustrates the many landslips observed by the team. Because Palau soils are very prone to landslides and slips, all cut slopes should have a stable grade to prevent these failures. The following Table 21 is a “rule of thumb” list of safe slope values for various natural materials in the absence of site-specific data. Although it may be possible to use steeper slopes for road cuts, finding the steepest safe slope may require taking core samples and performing proper soil analyses on each particular site. Table 21: Material and safe side slope Figure 8: Example of 3:1 slope for silt soil 3’ Steepness Steepest Material Rock Gravel Sand Clay Least Steep Silt Safe Side Slope 1:1 – 1:1.5 1.5:1 – 2:1 2:1 – 2.5:1 2.5:1 – 4:1 3:1 – 4:1 Example for Silt Slope 1’ ↓ Photo 22: Landslip on a grassed road-cut slope 65 Development of land for construction of buildings, roads, or farm facilities typically necessitates the disturbance of the natural system. Usually, land must be cleared of vegetation and soil must be excavated. Observations of new neighborhoods being constructed in the watershed yielded evidence of large amounts of erosion caused by poor construction practices. Soil is generally excavated, indiscriminately thrown to the side and consequently washed away with every rain. Some major hazards associated with development are: • • Exposure of soil to erosion from wind and water More water runoff, soil movement, sediment accumulation and peak flows due to removal of plant cover streets, buildings, sidewalks, etc, decreasing the area of soil that can absorb water changes in drainage areas caused by grading operations, diversions and streets changes in volume and duration of water concentrations caused by altering steepness, distance and surface roughness heavy equipment compacting the soil and thereby reducing its water intake by as much as 90 percent prolonged exposure of unprotected soil to the elements, particularly rainfall • • • • • Alteration of the groundwater regime that can affect the drainage system, slope stability, survival of existing vegetation and establishment of new plants Exposure of soil underneath the topsoil that may be unfavorable to plants Obstruction of stream flows with structures Improper timing and sequence of construction activities Abandonment of sites before completion of construction Development does not have to be irresponsible. Responsible construction practices do a very good job of controlling pollution from disturbed areas and protecting the resource base. The overall environmental and economic benefits provided far outweigh the relatively small cost of the extra energy required for implementation. The lower reaches of the Ikoranges tributary, the Ngerikiil River, and the Oikull streams and most of the farming area within the watershed lie on flat valley bottom or floodplain that is rarely flooded. While the frequency of flooding of the entire floodplain has not been documented, local residents have reported that the Ngerikiil River in this floodplain area exceeds bank full flow 66 approximately every seven to 10 years. Construction within the floodplain should be conducted with precaution to flooding, considering such measures as buildings on stilts instead of slabs. 3.1.6 Agriculture Modern and foreign-developed methods of agriculture cause a significant amount of land degradation, in contrast to traditional Palauan methods that used to be more common. Traditional and sustainable farming practices in the watershed produce erosion at rates between 0.2 and 9.9 metric tons per hectare per year (0.1 and 4.4 tons /acre/year) (Tables 16 and 17). In addition, unsustainable techniques cause erosion at rates of over 515.7 and 728.7 metric tons per hectare per year (230 and 325 tons/acre/year) (Tables 14 and 15). With 140.4 hectares (347 acres) of agricultural land currently existing in the watershed, annual erosion could reach upwards of 102,330 metric tons (112,800 tons) annually (Table 20). This is over 10 times the amount of erosion produced by forested lands that cover 16 times more land area than agriculture. Presented in the following sections are the unsustainable methods that were observed in the watershed and some sustainable methods. 67 Unsustainable Farming Practices Clean Till Clean till is the practice of plowing a field and removing all vegetation except for planted crops. The average annual rainfall for Airai State is about 370.8 centimeters per year (146”/year). At this volume and the intensity at which it comes down, tilling soil on any slope and leaving it bare for even short periods of time will lead to significant sheet and rill erosion. This was confirmed during our field observation and data collection. Photo 23, for example, shows a newly planted cassava (tapioca) field on a 23 percent slope. The average annual sheet and rill erosion on this field with its present crop rotation as measured by the Revised Universal Soil Loss Equation (RUSLE, see section 3.1.3 for a description of this tool) is about 515.7 metric tons per hectare per year (230 tons/acre/year). Conservation planning aims to keep soil erosion at a maximum of 11.2 metric tons per hectare per year (5 tons/acre/year). This erosion, 208.7 metric tons (230 tons), exceeds that goal by 4,600 percent. The cassava in this field is planted across the slope, which is a recommended conservation practice, yet it provides little benefit on this bare exposed steep field. Photo 23: Newly planted cassava (tapioca) field on a 23 percent slope Photo 24 shows another clean-tilled cassava field plowed up and down a nine percent slope. The erosion rate calculated for this field in its present rotation is 134.5 metric tons per hectare per year (60 tons/acre/year), 12 times the tolerance objective. Photo 25 shows a five percent slope tomato field in the Ngerikiil Watershed with a rotation that includes long beans, pumpkin, radish 68 and chili peppers. Erosion on this relatively flat field was calculated at about 112.1 metric tons per hectare per year (50 tons/acre/year) due to the intensive tillage associated with this rotation and the large areas of bare exposed soil. Even fields on the flat floodplain soils, if left exposed, contribute significantly to the sediment load in the Ngerikiil River. Photo 26, for example, is of a flat two percent slope of newly planted beans. This field is losing soil at the rate of about 44.8 metric tons per hectare per year (20 tons/acre/year.). Clean-tillage in the tropics is a formula for high erosion and sediment-laden runoff, regardless of slope steepness. Even a mature stand of cassava and other crops, if clean-tilled, as seen in Photo 27, will lead to very high erosion rates and sediment-laden runoff. Photo 24: Young cassava planted up and down a nine percent (9%) slope Photo 25: This tomato field has a five percent (5%) slope and a crop rotation of long beans, pumpkin, radish and chili peppers. Erosion on this relatively flat field was calculated at about 112 metric tons per hectare per year (50 tons/acre/year) Photo 26: These newly planted beans with no cover on a two percent (2%) slope is still eroding at 45 metric tons per hectare per year (20 tons/acre/year) Photo 27: Even a mature stand of cassava and other crops, if clean-tilled, as seen in this photo, will lead to very high erosion rates 69 Photo 28 reveals the underlying saprolite visible between two heavily tilled crop rows, evidence of severe soil erosion and loss of productivity. A profile of this soil (Photo 29) shows thin, fragile topsoil with unproductive saprolite below. Once the topsoil is eroded off it will be very difficult to sustain a protective plant cover and the erosion cycle will continue. Photo 28: The underlying saprolite visible between two heavily tilled crop rows is evidence of severe soil erosion and loss of productivity Photo 29: Soil profile shows a thin, fragile topsoil with unproductive saprolite below Farming Up and Down Slope The resource assessment team visited farms on steep, converted savanna areas within the Ngerikiil Watershed. On some of these farms we found extreme amounts of soil erosion, both sheet and rill and ephemeral gully erosion. Photo 30 is of a highly cultivated, bare-soil field on a 12 percent slope. The tillage is up and down the slope. Using the RUSLE tool we calculated the average annual erosion on this field to be in excess of 504.5 metric tons per hectare per year (225 tons/acre/year). On another steeper (18 percent) field close by, the erosion rate was determined to be in excess of 717.4 metric tons per hectare per year (320 tons/acre/year), 6,400 percent over the recommended conservation goal. That rate is sheet and rill erosion only; if the ephemeral gully and other erosion were included in our calculation this value would be higher yet. In Photo 31 we see two clean-tilled fields cultivated up and down a steep savanna slope (upper slope is 16 percent, lower slope is 12 percent). Notice the drainage ditch cut between the fields and the large quantity of sediment building up behind the log at the edge of the field. The erosion estimate on the field above the drainage ditch is 403.6 metric tons per hectare per year (180 tons/acre/year) and below is 246.6 metric tons per hectare per year (110 tons/acre/year). 70 The sheet and rill erosion rate on the 10 percent slope seen in Photo 32 is 177.1 metric tons per hectare per year (79 tons/acre/year). As mentioned previously, conservation planning aims to keep soil erosion at a maximum of 11.2 metric tons/hectare/year (5 tons/acre/year). Photo 30: Cultivated bare soil field with average annual erosion in excess of 504 metric tons per hectare per year (225 tons/acre/year) Photo 31: Two clean-tilled fields cultivated up and down a 14% slope with soil erosion well in excess of 247 metric tons per hectare per year (110 tons/acre/year) Photo 32: The sheet and rill erosion rate on this 10% slope tilled up and down the slope is 177 metric tons per hectare per year (79 tons/acre/year) Improper Fertilization In some instances, as soils lose fertility as a result of being heavily tilled, often up and down the slope, farmers have to apply large amounts of synthetic fertilizers to maintain production. This then has the potential to adversely affect water quality. A manifestation of this over-fertilization 71 is algae growth in furrows (Photo 33) and can lead to eutrophication of downstream waters. Timing, method and amount of fertilizer applied are key factors to fertilizer application. Applying fertilizer to a field should be avoided just prior to a rain event, if at all possible. Additionally, fertilizer should be incorporated or dug into the soil. Avoid over-fertilization by applying only in areas accessible by the crop roots. White fertilizer (10-30-10, representing percent of nitrogen-phosphorus-potassium respectively) pellets can be seen on the soil surface of the field in Photo 34. This field lies adjacent to a drainage ditch similar to the one seen in Photo 35 that leads ultimately to the Ngerikiil River. Photo 34 shows poor application of fertilizer: broadcasting fertilizer pellets on top of tilled soil without mixing it into the soil. As much of the agriculture in the watershed is found in the fertile flats next to the river, it is very easy for these exposed pellets to be washed off the fields into the water nearby. Photo 33: Algae growth in furrows 72 Photo 34: Bare soil field, notice the pellets of chemical fertilizer broadcast on surface Photo 35: Drainage ditch carrying fertilizer and pesticides to downstream areas Bare-Earth Furrows and Drainage Channels Furrows are shallow trenches between crop rows plowed to elevate crop rows and keep them dry. Furrows oriented up and down slopes, compounded by the lack of vegetative cover between rows, leads to serious erosion of the topsoil as the furrows become drainage ways for field water runoff, the velocity of which is far too great for a non-engineered and non-vegetated ditch. The steepness of the slopes gives the water enough energy to severely erode these straight bare-earth channels. This is evidenced by the miniature alluvial fans observed by the team at the bottoms of furrow rows (Photo 36). In some cases the furrows had been eroded into little gullies between the crop rows (Photo 37). Field drainage ditch networks on Palauan farms were, almost without exception, observed to be bare-earth channels with steep side slopes that ultimately emptied into the Ngerikiil River. In some cases the channels had reached depths and widths of 1.5 meters (5’) by the time they reached the river. Over time, the drainage water carries not only sediment from the eroding ditch, but also sediment and excess nutrients and pesticides running off the cropland, straight into the river. This may be clearly seen in Photos 38 and 39 of poorly designed drainage ditches. 73 Photo 36: Large sediment plumes caused by erosion of bare rows tilled up and down the slope. Photo 37: Furrows eroded into little gullies between the crop rows 74 Photo 38: Example of a poorly designed drainage ditch. Photo 39: Another example of a poorly designed drainage ditch Neglected and Un-vegetated Heavy Use Areas “Heavy use areas” are areas of the farm that are subjected to large amounts of foot or machine traffic, for example, access roads, foot paths, areas beneath water spigots, etc. Farms contain many of these, particularly access roads, which were observed in Palau to be eroding tremendously in many cases. These areas are frequently neglected, as they lose their vegetation and begin eroding very quickly and thus should be covered and maintained to minimize erosion. See Section 4.1.3 for recommendations for these areas. Photo 40 shows an abandoned access road that is greatly eroded. Photo 40: A greatly eroded abandoned access road 75 Sustainable Farming Practices The application of just one or two conservation practices is not enough to reduce erosion significantly, particularly on moderate (six to 12 percent) and steep (greater than 12 percent) slopes, in Palau. The soil here is so vulnerable to erosion, it is crucial to incorporate all conservation techniques that include cross-slope farming or terracing, low-till farming with mulching, grass cover, vegetated drainage ways and crop rotations or agroforestry. Agroforestry The traditional Palauan farming method of agroforestry has proven to be sustainable, causing insignificant soil erosion. This method involves planting of multi-storied crops – fruit trees, medicinal plants or shrubs, and food crops – intermixed or in small patches. Agroforestry involves minimal disturbance of the soil and maximum input of organic matter into the soil. Photo 41 and 42 shows traditional Palauan and Pacific island agroforestry. Photo 41: Traditional Palauan agroforest with taro, cassava, betel nut, brak, lemon, and onion Photo 42: Traditional forest garden of taro, banana, papaya, coconut, and breadfruit 76 Cross-Slope Farming “Contour” farming is the practice of planting crop rows along equal elevation, perpendicular to the direction of slope (horizontal). Due to the heavy and frequent rains in Palau, erosion across contoured row crops occurs readily. Therefore, “cross-slope” farming is recommended. Crossslope farming is planting crop rows at a slight angle from contour so that excess runoff water is directed off the field toward grass-lined drainage ways. The furrows between crop rows that direct the water should also be grassed to minimize erosion. Cross-slope farming may be used on land with slopes of up to about 20 percent to reduce sheet and rill erosion, nutrient loss and water loss by decreasing water velocity and increasing the time of concentration for the runoff (i.e., increasing infiltration). Photo 43 shows an example of cross slope farming; this field would be improved with grass cover between crop rows to restrict soil erosion in these areas. Photo 43: Cross-slope farming; arrows show direction of slope Minimum-Till or No-Till Farming Minimum-till farming involves plowing only crop rows and maintaining vegetation, such as grass, in furrow areas next to crops. This minimizes disturbance to soil and therefore, decreases the potential for erosion. The most highly recommended, low erosion farming technique for the climatic conditions here is planting crops in individual holes, leaving surrounding soils undisturbed and grass-covered. Photo 44 shows a good example of minimum till agriculture. This field could be improved with grass cover surrounding the crop rows, in addition to the existing grass cover around the field. 77 Photo 44: Minimum till field with surrounding grass and fruit tree cover for soil stability Mulching Using leaves from trees for mulching around crops is a valuable technique that is traditionally used in Palau. Mulching minimizes soil erosion, decreases the temperature of the farm fields by providing shade to underlying roots, holds or stores nutrients, as well as adds nutrients to the soil. Photo 45 shows an examples of grass-cover between and around crops. Photo 46 shows an example of mulching in a taro patch. These are great examples of keeping the soil covered, thereby reducing soil erosion well below current rates. These techniques will have important application for most agriculture systems in Palau. Photo 45: Grass cover in and around a cassava field 78 Photo 46: Mulching and grass cover in and around a taro patch Crop Rotation “Crop rotation” is growing crops in a recurring sequence on the same field. Including nitrogenfixing legume crops in the rotation, such as sun hemp, at least once a year helps rebuild nutrients, organic matter, texture and structure in the soil. After the legume crops have grown for two to three months, the plants should be cut down and incorporated into the soil to naturally degrade. Photo 47 is a picture of sunnhemp, an excellent rotating crop for soil nutrient supplements. Photo 47: Sunhemp, an excellent crop for rotation and soil nutrient supplements 79 Grassed Drainage Ways Drainage for a particular field is provided with systems of diversions and grassed or stone waterways. These waterways are channels lined with grass or stones and designed for stability that carries runoff from crop rows down the slope for discharge at a stable outlet. Water may enter these channels directly from the crop rows or from a diversion. A diversion is a grass-lined channel constructed across the slope for the purpose of collecting water from crop rows and directing it to a grassed waterway or irrigation network. Photo 48 is an example of a stone-lined drainage way through farm fields. This photo also shows an extensive area of bare, exposed soil, an unsustainable farming practice. Photo 48: Stone-lined drainage way reduces runoff velocity, encouraging infiltration of water and eroded soil Terracing Slopes, too steep for contour farming may require “terracing”. Terraces are constructed benches along the contour lines that generally perform the same basic functions as contour farming but on a more intense level. This is a very effective tool for preserving soil on any slope. Again, the down slope areas between the terraced benches where the crops are planted should be grasscovered to minimize erosion. Since terracing is very labor intensive, it should only be undertaken if the benefits are certain to outweigh the costs. It is typically used when there is no other available land to farm. Photo 49 shows an example of terrace farming in the Himalayas. Photo 49: Terrace farming in Nepal 80 3.1.7 Burning of Savanna Areas Savanna or grassland covers nine percent of the Ngerikiil Watershed (Photo 50). The savanna cover is primarily grasses (areas not recently burned are established in Ischaemum) and a low growing fern Gleichenia linearis (more prevalent in areas recently or regularly burned and tolerant of high soluble aluminum levels in the soil) with scattered Pandanus trees. The fern is quite extensive on degraded soils and appears to be the primary pioneer species after fires or soil disturbance (Kuhn and Bautista, 1996). Many professionals employed in resource management and native to the area believe the bare areas are a result of frequent fires set by hunters for the purpose of driving game out or simply to exit an area after hunting. Some of the savannas are the result of mining or land clearing for agriculture, timber production or development purposes (Cole et. al., 1987). These areas very likely were forested at one time (Kuhn and Bautista, 1996). These savannas are often subjected repeatedly to human-induced burning for purposes of producing ash for plant fertilizer. While ash itself is an excellent fertilizer containing important plant nutrients particularly potassium, ash produced in this manner is typically washed away by heavy rains, causing a net loss of nutrients to the soil. This process leaves the soil less fertile and creates increased soil erosion leading to lower fertility in a cycle of increasing soil degradation. The cycle of burning and erosion results in the depletion of vegetation (Photo 51). This, in turn, results in rain-caused erosion and high sedimentation down slope with deleterious effects in lowlying areas, mangrove forests, and reefs. Burning vegetation also allows invasive species a foothold. Photo 52 depicts a site where fire has been used repeatedly on an 11 percent slope. Repeated burning of a site leaves little organic material on the surface. Photo 53 is a close-up of the ground seen in the previous photo. It reveals little or no protective cover over a bare soil surface. The assessment team calculated sheet and rill erosion on this untilled slope at 100.9 metric tons per hectare per year (45 tons/acre/year). Healthy, unburned savannas on low and moderate slopes with full cover erode at rates of approximately 3.1 metric tons per hectare per year (1.4 tons/acre/year) (Table 19). If all 253.3 hectares (626 acres) of savanna in the watershed were maintained with cover, they would produce less than 816.5 metric tons (900 tons) of eroded soil annually in the watershed (Table 20). Frequently burned savannas on moderately steep slopes erode at rates of up to 219.7 metric tons per hectare per year (98 tons/acre/year) (Table 19). Such land use on all savanna land in the watershed will save over 54,431 metric tons (60,000 tons) of soil annually (Table 20) or nearly six times the contribution of soil eroded on forested lands in the watershed. 81 Photo 50: Savanna areas within the watershed constitutes nine percent(9%) of the total watershed Photo 51: A burned field Photo 52: Repeated burning of site leaves little organic material on surface Photo 53: Close-up of soil surface in Photo 52 showing little organic material to protect the soil from erosion 82 3.1.8 Stream Bank Erosion The final source of sediment affecting water quality in the Ngerikiil Watershed is from failing stream banks along the Ngerikiil and Edeng rivers and other streams within the watershed. Stream bank erosion due to stream meander in the upper portions of the watershed occurs naturally where no development is taking place. The eroded stream banks of concern are the ones caused by or interfering with human activities in lower portions of the watershed. Streams are dynamic and complex parts of a “living” system. In natural stream meandering, the flow velocity is higher at the outside of the curve and lower on the inside. This results in scouring of the outside and sediment deposition on the inside. In this way, streams naturally migrate as one side of the bank is built up and the other side erodes away. Responsible development means interfering as little as possible with the natural system. Erosion of the banks is a natural process that happens when the frictional forces of the flowing water overpower the resisting forces of the bank lining, whether soil or vegetation. A change in either force (an increase in frictional force due to faster stream flow or a decrease in resistive force due to vegetation removal) can transform a relatively stable stream into a highly eroding one. When streamside vegetation is cut down, burned off or otherwise killed, resisting force is lost and increased erosion occurs. Likewise, if normal or peak flows are increased (due to development in the watershed, for example) flowing water forces are increased and cause more erosion. Our team observed many areas along the Ngerikiil River where intensive agricultural tillage is being practiced too close to the river’s edge. This practice typically removes the natural forest and plant cover buffer. The roots of these buffer species provide valuable armoring to the river’s banks protecting it from slippage and erosion. Removal of these riparian species leaves the river’s banks vulnerable to eroding and slumping. An example of this is seen in Photo 54 that was taken in March 2003. It shows a major stream bank failure along the Ngerikiil River, as a result, the buffer species that previously anchored the bank in place was also lost. The eroded areas observed are in locations where all trees have been cleared all the way up to the river’s edge. The river has encroached approximately 4.6 meters (15’) into this farm field, for a length of about 12.2 meters (40’) along the river. The danger with this vertical cut bank is that the river will continue to undercut that bank which leads to further bank failure and erosion. This eroded bank problem appeared to be compounded by a fallen tree that had redirected the water flow. Large objects in a stream can affect the direction of the erosive forces and thus the erosion of the bank. A tree that has fallen into the river can act as a jetty and redirect water more toward the bank and cause failure. No stream, however, should be indiscriminately cleared of debris. Most rocks, logs and other debris in the stream are naturally providing animal habitat as well as the energy dissipation that helps protect the bank. The problem only comes when a large object falls in and significantly changes the flow of the water. The individual farmer should be vigilant but only remove an object if it is causing obvious bank erosion. We see in Photo 55 the same site two months later. The soil has been tilled and cassava has been planted to within 0.6 meter (2’) of the river. There is little protective buffer to armor this cut bank and further steam bank failure and erosion can be expected. This photo was taken just after some strong rains earlier in the day. Notice the brown heavily sediment-laden Ngerikiil River water flowing past. 83 Failing steam banks often lead to new, straighter river courses. This results in increased river velocity which has greater eroding potential than the original meandering river. The increased energy results in more steam bank failures thus exacerbating and perpetuating the problem and increasing the likelihood of flooding. Photo 54: Stream bank erosion along the Ngerikiil River in March 2003: Approximately 3.7 meters (12’) of soil profile has been lost along about 15 meters (50’) of river bank Photo 55: Same site as in Photo 54 but two months later: Notice the newly planted cassava right up to the river’s edge at the eroded area 84 3.2 NUTRIENT, PESTICIDE & OTHER POLLUTION Pollution occurs when a substance (i.e., gas, liquid or solid), an organism, or energy (e.g., sound or heat) is released into the environment by human activities and produces an adverse effect on organisms or the environmental processes on which they depend. (Boesch et al., 2003) Marine pollution comes in many forms and from many sources. Some pollutants, in sufficient concentrations, are toxic to marine organisms. These include both naturally occurring chemicals present in much higher concentrations as a result of human activities (e.g., trace metals and oil), as well as compounds that did not exist in nature until manufactured by humans (e.g., pesticides such as DDT). (Boesch et al., 2003) Other pollutants are harmful not because they are toxic but because they stimulate biological activity or alter habitats. The addition of large amounts of organic matter in the form of sewage or fish-processing wastes, for example, supports the growth of decomposer microbes that can exhaust the available oxygen supply. Naturally occurring concentrations of nutrients, particularly nitrogen and phosphorus, are responsible for the rich biological productivity of many coastal waters. However, human-induced inputs of these nutrients can stimulate the production of more organic matter than an ecosystem can assimilate. Turbid waters, depletion of oxygen, and blooms of noxious algae may result. Sediments from land runoff, as discussed in previous sections, or from dredging can decrease water clarity and smother sensitive bottom habitats such as reefs and seagrass beds. (Boesch et al., 2003) Pollution emanates from either direct discharges such as pipe (point) or diffuse (non-point) sources. Examples of point source discharges are land-based industrial and municipal outfalls of wastewater into coastal waters or rivers, discharges from vessel operations and at sea waste disposal. Pollutants from diffuse sources include those released into the atmosphere by fossilfuel and waste combustion; and land runoff of pesticides, toxic waste products, nutrients, and sediments (Boesch et al., 2003). Phosphates from laundry detergents are a potentially significant threat to the health of rivers and reefs, as laundry effluents in Palau are discharged without treatment. The Ngerikiil Watershed at present, does not appear to be seriously threatened by either point or non-point pollutants but our team did find areas of concern that, if left unchecked, will become problems adversely affecting water quality and the Palauan environment. Three specific concerns, all interrelated, were identified: animal manure from confined animal feeding operations, runoff of excess fertilizers, and pesticide leaching and runoff. 3.2.1 Animal Manure Often, animal wastes are the most significant source of nutrient pollution from agriculture. Manure management also presents a risk of pollution if holding facilities (Photos 56 and 57) fail or do not function properly (Mallin, 2000). Frequently too much manure is produced within a geographic area for it to be applied to nearby land without overloading soils with nutrients (NRC, 2000). At present, confined animal feeding operations are few within the Ngerikiil Watershed relative to the overall land area. Geraldine Rengiil’s Water Quality report from 1999, however, indicates that there are some water quality concerns stemming from animal operations, 85 primarily below the pump plant. There is also a possible public health concern regarding any development (particularly farms) upstream of the drinking water intake station. Proper handling of pig and poultry manure and other byproducts is required to ensure the safety and health of everyone and everything around. The team visited three swine facilities having 10 to 25 pigs each, two duck facilities having 20 to 30 ducks each, and one poultry farm having approximately 8,000 laying hens and 6,000 chicks. Generally speaking, the observed livestock operations had inadequate management of wastes. Manure storage tanks and open storage pits were seen overflowing. There also appeared to be excess nutrients running off at least four of these farms as evidenced by the presence of algae growth in the drainage ditches and river. The source of excess nutrients is likely either commercial fertilizer or poor manure management practices. Large amounts of nutrients—particularly nitrogen (N), phosphorus (P) and potassium (K)—are contained in fertilizer and animal manure. Animal wastes pose serious health and environmental hazards when they are allowed to reach the water system. Excess nutrients in the rivers can be very toxic to aquatic wildlife and stimulate algae growth and lead to eutrophication. There is also the potential for a major human health hazard if farms develop upstream of intake stations for water treatment plants and local wells used for drinking water. Nitrate is one of the very common forms of nitrogen and the most dangerous. Excess nitrates in water are known to cause methemoglobinemea or “Blue Baby Syndrome,” which causes babies to turn blue from oxygen deprivation. Nitrates can also cause miscarriages and still births in people and livestock. Photo 56: Confined chickens of a poultry farm Photo 57: Confined pigs on concrete slab Animal manure also contains large amounts of disease-causing pathogens that can injure humans, livestock and other animals if allowed to contaminate crops and/or drinking water. Some common agents that can cause a wide range of problems—from mild diarrhea to fatal illnesses—are: bacteria such as Salmonella, Shigellae, Cholerae, E. coli, Leptosporidia, Encephalitis, Chlamydia, Gangrene and those causing botulism; Protozoa such as Giardia, Cryptosporidia and Balantidium coli; and Helminths such as large roundworms. Disease outbreaks happen often all over the world due to improper containment of animal manure and 86 human sewage. However, the danger can be greatly reduced through intelligent waste management practices. (See Section 4.2.1 Animal Manure for application recommendations.) 3.2.2 Chemical Fertilizer Runoff Eutrophication, an increase in plant nutrient minerals and organisms causing a decrease in oxygen, has become more extensive in many of the world’s water bodies due to increased loadings of mineral nutrients, particularly nitrogen and phosphorus. These stimulate the production of organic matter within the marine and freshwater ecosystems. Among the harmful consequences of this increased organic production is hypoxia, or stressfully low dissolved oxygen, reductions of seagrass beds and corals, and potentially noxious or toxic blooms of algae (Boesch et al., 2003). Nutrient pollution has been increasingly recognized as a key threat to coastal environments over the past 20 years because of both new scientific understanding and declining trends in water quality (Nixon, 1995). Nutrient pollution has also resulted in loss of coral reef habitat and seagrass in U.S. tropical regions (Bell, 1992; Lapointe, 1999). Large-scale eutrophication is a problem that has developed during the last half of the 20th century with expanded use of chemical fertilizers (Vitousek et al., 1997). Coral reef degradation is of major concern in the Ngerikiil Watershed. Excess sediment and nutrients are typically the main culprits when it comes to the killing of any coral reef. Under natural circumstances coastal mangroves do the job of intercepting sediment and nutrients that runoff of the watershed. Irresponsible land development includes: • • • Not controlling erosion and sedimentation Not containing excess nutrients Removing upland forests, riparian buffers, and mangrove forests Irresponsible land development leads to a greater amount of pollutants reaching the reefs than they are able to endure. Sediment from deforestation, construction and farming activities flows past the mangroves as their capacity is exceeded (especially if they are being cut down) and collects on the corals instead. This gathering of sediment is one thing that acts to shade and smother the corals and causing death of the reef. Eutrophication leads to coral reef and surface water degradation. Nutrients from sewage, farm runoff and other urban development stimulate algae growth on the corals. These algae communities vigorously strip the excess nutrients from the water as they grow much faster than the corals. As they get larger they help trap even more sediment and ultimately cause coral bleaching and death. When a body of surface water becomes overburdened with nutrients (particularly nitrogen and phosphorus) algae blooms begin to thrive and take over. As old algae dies off and decays, it is consumed by bacteria. The decaying process consumes oxygen and eventually depletes the dissolved oxygen supply in the water. Low dissolved oxygen kills off fish, crabs, shrimp and the living reef. It converts the water to anoxic conditions leading to objectionable odors and a generally nasty body of water. Algae growth also blocks out sunlight and thereby chokes out aquatic plant life. 87 Sea grasses, seaweeds, and coral reefs create important habitats that provide food and shelter for a rich diversity of marine organisms, but are very sensitive to nutrient pollution. Reductions in available light caused by the increased phytoplankton density and the proliferation of microscopic and macroscopic algae growing on seagrass blades that result from high nutrient loads adversely affect marine plants (Duarte, 1995). Sea grasses sometimes give way to fast growing macroalgae. Ultimately, conditions may become too turbid to support any macroscopic plants. As seagrass beds are lost, sediments are more easily eroded, causing the pace of loss to accelerate. Significant seagrass losses caused by excessive nutrient loadings have been observed in bays and coastal lagoons all over the world (Bricker et al., 1999; Duarte, 1995). Partial recovery of seagrass beds in some areas has been observed as a result of efforts to abate nutrient pollution (Boesch et al., 2003). Reef-building corals have a symbiotic relationship with algae (zooxanthellae) that live in coral tissue and efficiently recycle available nutrients. This relationship allows corals to build reefs in clear waters with low nutrient levels. Even small increases in nutrient loads can stimulate phytoplankton growth and reduce light availability for zooxanthellae in the deeper parts of the reef. Elevated nutrient levels or reduced light availability may make already temperature-stressed corals more prone to expelling zooxanthellae, producing a “bleaching” effect (Brown, 2000). Increased availability of nutrients can shift an ecosystem dominated by corals and coralline algae toward dominance by algal turf and macroalgae (Bell, 1992; Lapointe, 1999). Over enrichment may also contribute to environmental stresses that make corals susceptible to diseases that appear to be increasing in distribution and virulence (Harvell et al., 1999). The use of chemical fertilizers by farmers and homeowners in Palau appears to be relatively low at this time. The worldwide use of chemical fertilizers, however, is growing and projected to increase substantially to support an expanding world population and increased meat consumption (Forsberg, C.,1998). As the population of Palau increases the use of chemical fertilizers within the Ngerikiil Watershed will also likely increase. The river flats are crossed by a series of drainage ditches and canals (Photo 58) that ultimately lead to the Ngerikiil River. Photo 59 shows a main canal draining many acres of agricultural land emptying into the Ngerikiil River. This creates a situation conducive to chemical fertilizer runoff and nutrient over enrichment. This report is not an indictment of the farmers within the watershed. Overall, most growers seemed to be practicing good management techniques with regards to fertilizer use. Furthermore, farmers are not the only users of chemical fertilizers. Other users include homeowners, resorts and hotels, municipalities, etc. This report is rather a call to the people of Palau to be proactive in dealing with the use of chemical fertilizers within this relatively vulnerable watershed. Refer to Section 4.2.2 for suitable application practices. 88 Photo 58: At the confluence of a main canal with the Ngerikiil River, this canal drains many acres of farm fields Photo 59: Example of a farm ditch draining fields directly into the Ngerikiil River 3.2.3 Pesticide Leaching In their report on the Ngeremeduu Watershed in 1996, authors Kuhn and Bautista made several statements about pesticides that are applicable today to the Ngerikiil Watershed. They report that pesticide use is minimal in Palau although the more intensive agriculture operations are beginning to use herbicides to control grasses and weeds, and insecticides to control insects. If properly selected and applied, pesticides can improve harvest and economic returns on certain crops. One concern is that some pesticides are being imported in containers labeled in foreign languages. Inspectors and agriculture specialists, therefore, do not know what is in the containers. Although Palau has laws that make this illegal, it appears they are not being adequately enforced since containers with such labeling are presently in use. The Ngerikiil Resource Assessment Team also found unidentified pesticide containers, with labeling entirely in a foreign (Chinese) language, on farms within the watershed. According to Palau’s Environmental Quality Protection Board, some pesticides that have been banned by the United States and other countries are still imported and used illegally in Palau. These pesticides have been banned because they are suspected to cause cancer in animals or are persistent in the environment. It is possible that some pesticides are entering Palau that can cause degradation to receiving water bodies, poison wildlife, or increase the chance of cancer in humans who work in and around application areas as well as consumers who eat treated produce. The chemical properties and predicted environmental reaction of pesticides registered for use in the United States can help determine which pesticides should be restricted from environmentally sensitive areas or drinking water sources, and handling and disposal instructions are readily available. There are many pesticides on the market which, when used as directed on the label, pose minimal risk to human health and the environment, and can be readily obtained (Kuhn and Bautista, 1996). Refer to Section 4.2.3 for guidance. 89 3.3 SOLID WASTE DISPOSAL Solid waste means any garbage, or refuse, sludge from a wastewater treatment plant, water supply treatment plant, or air pollution control facility and other discarded material, including solid, liquid, semisolid, or contained gaseous material resulting from industrial, commercial, mining, and agricultural operations, and from community activities (U.S. EPA, 2004). Approximately 108 metric tons (120 tons) of commercial and domestic waste each week are produced in the urban areas of Koror and Airai (Golder Associates Pty Ltd, 1999). Airai state does not have a public trash collection system. Residents and businesses in Airai transport their own garbage at the dump located next to the old Japanese building next to the Ked Community Center in Airai. This dump is not lined and is not regulated. Without regulation, it is likely that trash is dumped in other locations throughout the state as well. Solid waste reaches our oceans via storm water runoff, storm drains, sewer overflows, landfills or dumps, rivers and streams, and trash discarded by boats. Typical debris from these sources includes medical waste, street litter and sewage. Each year millions of seabirds, sea turtles, fish, and marine mammals become entangled in marine debris or ingest plastics that they have mistaken for food or ingest them while feeding on natural food. Plastic and toxic substances present in plastics constricts the animals’ movements, causes reproductive failure, or kills the marine animals through starvation, exhaustion, or infection from deep wounds caused by tightening material (U.S. EPA, 2003). Additionally, marine debris and their associated toxins can injure swimmers, divers, and beach users; result in lost tourism revenues; damage boats; suffocate marine plants and coral communities; make fish unsafe for consumption; and contaminate waters with pathogens (U.S. EPA, 2003). As space is very limited in Palau and, as discussed above, disturbance of vegetation and soil significantly impacts the land and waters here, it is very important that minimization of waste disposal is taken seriously. While solid waste disposal is not yet a serious pollution concern within the Ngerikiil Watershed itself, population pressures and the increased use of plastics and other non-biodegradable throw-away items will result in this being a growing issue for Palau. Typically, a combination of waste management occurs in a community. Waste management should be approached by setting preference to source reduction then recycling then composting then incineration and landfilling. Source reduction is waste prevention or consuming and throwing away less. Source reduction includes purchasing durable, long-lasting goods and seeking products and packaging that are as free of toxics as possible (U.S. EPA, 2004). Recycling is a series of activities that includes collecting recyclable materials that would otherwise be considered waste, sorting and processing recyclables into raw materials then using these raw materials to make new products. Using recovered or recycled material generates less solid waste, helps to reduce the energy used and pollution caused by the extraction and processing of virgin materials (U.S. EPA, 2003). Composting is the collection and natural decomposition of organic waste for purposes of saving landfill space and producing a nutrient rich soil amendment. Composting requires: 90 • Carbon rich woody materials, such as coconut fronds, coconut shells, paper, or branches • • • Nitrogen rich materials, such as kitchen scraps, weeds, and manures Moisture (composting pile should be kept damp, not wet) Air (by turning the pile frequently, it will decompose faster and will not smell) Incineration, or the burning of waste to produce energy, can provide energy in the form of electricity or processed steam, while reducing the volume of waste that must be landfilled by a significant fraction (U.S.EPA, 2004). 3.4 INVASIVE SPECIES Invasive species are non-native plants and animals that have been introduced into an environment in which they did not evolve and thus usually upset ecosystem stability by invading habitats in which they have no natural predators allowing them to reproduce at high rates. Invasive species are considered the second greatest threat to biodiversity, next to habitat destruction. They are of particular significance in small island countries, such as Palau. Invasive species may be introduced via natural pathways - wind, water currents, and other forms of dispersal in which a specific species has developed morphological and behavioral characteristics to employ, or by man made pathways. Humans introduce non-native species intentionally, such as living seeds, whole plants, or pets. Introduction pathways include ballast water discharge, soil associated with the trade of nursery stock, importation of fruits and vegetables, and the international movement of people, automobiles and equipment. In these and countless other unintentional pathways, the movement of species is an indirect byproduct of our activities. Once introduced, these species can change the dynamics of an environment forever and can be extremely difficult to eradicate. Tables 22 and 23 list the more common invasive plants and animals, respectively, in Babeldaob that threaten the Ngerikiil Watershed and their associated negative impacts. 91 Table 22: Common invasive plant species of Babeldaob Common English Name Scientific Name Palauan Name Negative Impact Small shrub that forms dense stands that prevent establishment of other species, including crops, both due to competition and allelopathic (suppression due to release of toxins) effects. Extremely aggressive grass species, that is resistant to fire and competes with wide variety of vegetation, including crops. Four hectares (10 acres) found near airport. Unknown whether native or early introduction, but recent road construction has allowed its proliferation. This smothering vine grows at edges of roads then climbs over trees, shading them. This vine grows very fast – up to one foot a day – in shade and sun, taking over farms and natural environments. Thorny climbing shrub that establishes in farmlands and along roadsides. Climbing vine that smothers individual plants and groups of trees. Chromolaena odorata Siam-weed Ngesngesil Imperata cylindrica Cogon-grass Kasoring Merremia peltata Merremia Kebeas Mikania micrantha Mile-a-minute weed Teb el yas Mimosa invisa Thunbergia grandiflora Giant-sensitive plant Blue-trumpet vine Mechiuaiuu Bungel etiu DeMeo et al., 2002; Space et al., 2003 Table 23: Common invasive animals of Babeldaob Common English Name African Snail Chestnut Manakin Cockatoo Domestic Cat Domestic Dog Fruit fly Macaque Monkey Pig Rat Holm and Michaels, 2003 Negative Impact Possible threat to biodiversity; crop pest. Spreads grass seeds; could potentially assist in spreading of Imperata cylindrical. Eats the heart of endemic palm, reducing population of these to endangered status. Eats bird eggs and other local species; however, positively, reduces rat population. May have leptospirosis, have bitten people, and uncontrolled dogs are public nuisance. Damage agriculture, high economic and health costs to Palau. Damage crops and native vegetation, potential human health problem, public nuisance. Damage crops, damage native vegetation. Spread diseases, including leptospirosis, damage property and food supplies. 92 3.5 WILDLIFE HABITAT IMPACTS While wildlife was not identified as a resource concern to be specifically addressed for this assessment, it is, nevertheless, an important natural resource within the Ngerikiil Watershed. There are several species listed as threatened or endangered in Palau. The one species of note by the assessment team within the watershed is the endangered estuarine crocodile (Crocodylus porosus (Schneider, 1801)), also known as the saltwater crocodile. Photos 60 and 61 shows a small estuarine crocodile caught in the Ngerikiil River above the new Compact Road bridge. Formerly widespread, the estuarine crocodile was almost exterminated in the Palau Islands by Australian hunters (due to an official program of extermination that occurred from 1966 to 1981 resulting in this species becoming extremely endangered) following an incident in which a tourist was injured. However, the species is now recovering under protection, although most of the individuals are small and extremely secretive (Scott, D.A., 1993). Typically, its habitat occurs in brackish waters, inhabiting large river estuaries and deltas with associated coastal mangrove swamp-forest, but also extends into deep rivers far above tidal influence. It can also be found in freshwater pools and swamps. Additionally, the watershed provides habitat for fruit bats, Pteropus marianus pelewensis, that feeds on fruit trees throughout the watershed. The fruit bat is declining in numbers because of excessive hunting and is endangered in many other places in the world. The watershed also provides habitat to a number of birds, some endemic. Table 24 is a list of many of the birds that live in the watershed. Photo 60: Live crocodile captured along the Ngerikiil River Photo 61: Caged crocodile captured along the Ngerikiil River 93 Table 24: Birds with habitats in the Ngerikiil Watershed Scientific Name Anous minutus Anous stolidus Aplonis opaca Artamus leucorhynchus Caloenas nicobarica Caprimulgus indicus Cettia annae Coracina tenuirostris Ducula oceanica Gallicolumba conifrons Gygis alba Halcyon cinnamomin Halcyon chloris Ixobrychus sinesis Lonchura Malacca Myagra erythrops Myzomela cardinali Phaethon lepturus Phalacrocorax melanoleucos Pitohui tenebrosa Poliolimnas cinereous Porphyrio phorphyrio Ptilinopus pelewensis Pyrroglaux podargina Rallina eurizonoides Rallus phillippensis Rhipidura lepida Zosterops cinereus Zosterops conspicillatus Common English Name black noddy brown noddy Micronesian starling white-breasted wood swallow Nicobar pigeon jungle nightjar Palau bush warbler cicadabird Micronesian pigeon Palauan ground dove white tern Micronesian kingfisher collared kingfisher yellow bittern chestnut manniki Palau flycatcher cardina honeyeater white-tailed tropicbird little pied cormorant Palau morningbird white-browed rail purple swamphen Palauan fruit dove Palau owl slaty-legged crake banded rail Palau fantail dusky white-eye bridled white-eye Tutau Palauan Name Bedaoch Mechadelbedaoch Kiuid Mengaluliu Laib Chebacheb Wuul, Esisbasech Kiuidukall Belochel Omekrengukl Sechosch Cherosech Ongelmadech Tengadidik Cheloteachel Kanaria Charmelachull Chesisebangiau Dudek Habitat Community M, R U M, S, U S L, U L, M, R, U L, U U U L, U U L, U M, S, U FWS, S S M, U U, S U M, R U FWS, S FWS L, U L, M, U FWS, L, S, U S, FWS U U U, S Sngorch Uek Biib Chesuch Ulerratel, Kok, Och Terriid Melimdelebteb Chetitalial Charmbedel Engbring, 1988 Note: A=Agroforest; FWS=Fresh Water (or slightly brackish) Swamp; L=Limestone Forest; M=Mangrove Forest; R=Riverine; S=Savanna/Secondary Vegetation; U=Upland Forest 94 SECTION 4: RECOMMENDATIONS & FUTURE CONDITIONS Observations and analysis made by the assessment team during the Rapid Assessment of the Ngerikiil Watershed resulted in the following recommendations. They are meant to be general guidelines and directions to help solve the soil erosion and other problems identified in Section 3 Critical Resource Concerns. The terrestrial watershed collects, concentrates and delivers rainfall runoff to the tributaries, river and bay (Photo 62). The majority of the coral reef in Airai Bay is smothered by sediment and dying, if not already dead (Photo 63). Terrigenous (originating from the land) mud is responsible for this coral death and the transformation from coral to algal dominance in the bay (Golbuu et al., 2003). Mean suspended sediment concentrations (SSC) for reefs not subjected to humaninduced sedimentation are less than 10 milligrams per liter (0.001 oz/gallon) (Rogers, 1990). The 2003 study of sedimentation into Airai Bay by Golbuu et al. measured suspended sediment concentrations over about a 100-day period at the mouth of the river by the mangroves and at the mouth of the bay in the main channel near the ocean. The results indicate SSC of between 30 and 50 milligrams per liter (0.004 and 0.006 oz/gallon) in the absence of runoff at the mouth of the river. During river floods, SSC values exceeded 1500 milligrams per liter (0.2 oz/gallon), the limit for the meter. SSC values at the mouth of the bay were commonly 20 milligrams per liter (0.003 oz/gallon), peaking at 60 milligrams per liter (0.008 oz/gallon). This report indicates that only approximately one percent of the terrigenous mud entering the bay reaches the ocean, an estimated 30 percent is trapped in the mangroves, while 69 percent is deposited in the bay itself. Because the bay is protected from oceanic storms and has restricted water circulation, it does not experience significant flushing from wave energy. However, it is possible that if sedimentation into the bay is decreased through land use management, in time the reefs and seagrass ecosystems could recover. Photo 62: Sediment moving out into Airai Bay Photo 63: Sediment smothering coral in Airai Bay If left unchecked, erosion and sediment from developing areas may cause considerable economic and irreparable environmental damage to land, stream and bay water quality and coral reefs located downstream. As a minimum, a primary protection zone surrounding targeted water bodies, such as the drinking water source, the rivers, and bay, should be delineated and management measures targeted for implementation. No high-intensity activities such as mining 95 and quarries, large confined animal operations, or chemical storage facilities should be allowed within the primary protection zone (to be determined by local consensus) and activities outside this primary zone but within the watershed should be required to adhere to strict measures designed to minimize runoff and erosion during and after disturbance. Management of future development and land use in the watershed should prohibit potential pollution sources upstream of the water intake in order to protect the drinking source, as well as downstream areas that could contaminate the bay. The zone of influence includes land areas surrounding the stream bank where groundwater infiltration supplies the stream during periods of low stage or where surface runoff during flood events when the soil is saturated contributes runoff to the drinking source surface water. Restrictions to land use within this primary protection zone should be a minimum of watershed management. A comprehensive and holistic approach to watershed management designates conservation areas and sets environmental guidelines for development and agricultural practices. A comprehensive and holistic watershed management plan can also help to guide and control growth and development to prevent wasteful and haphazard development. This plan is developed based on criteria set up by the local community according to their objective that may involve subjects such as the best agricultural land, historic, scenic and natural beauty, open spaces and parks; and attractive developed areas. Developed areas should be constructed with erosion prevention measures and sustainability of biodiversity in mind. 4.1 4.1.1 SOIL EROSION & SEDIMENTATION Roads The entire road system should be designed so that runoff water is caught at the roadway and controlled until it may be discharged at a stable outlet and with a non-erosive velocity. The storm water management methods used depends primarily on the topography. Water may be drained through an open channel along the roadside or it may be caught in a catch basin on the uphill side of the road and run through a culvert to the other side before being discharged over an energy dissipating structure. It may be able to sheet flow directly off the side of a flat road surrounded with vegetated buffer strip. Areas used as a borrow site for road maintenance should be re-established back to permanent vegetation once disturbance activity has stopped. The Compact Road construction contains some good examples of proper storm water management practices as seen in Photos 64 and 65. 96 Photo 64: A culvert carrying water from a catch basin across to a chute Photo 65: The chute with energy dissipation at the bottom Erosion Control Measures for Road Construction • Do not place a road on greater than seven percent slope. Where the slope of a hillside is greater than seven percent, the road should be constructed cross slope, maintaining a minimal grade. Roads also should not be located close to stream banks. The road should be placed a sufficient distance from any stream or river with a vegetated buffer strip wide enough to filter out sediment carried by runoff. A natural buffer zone between the road and stream is recommended as a filter for sediment carried by water running off the road. Table 25 gives a general guideline for the width of this buffer. Table 25: General guidelines for buffer width between a road and stream % Slope Between Road and Stream 0 10 20 30 40 50 60 70 Buffer Strip Width 15.2 meters (50’) 27.4 meters (90’) 39.6 meters (130’) 51.8 meters (170’) 64.0 meters (210’) 76.2 meters (250’) 88.4 meters (290’) 100.6 meters (330’) • • • Where roadside slopes are too steep producing high runoff velocities, engineered controls such as rock lined diversion ditches, may be required to manage runoff. As exposed soil and gravel washes away quickly in this Palauan climate, roads should be covered and paved as soon as possible to minimize erosion. 97 For more information on effective erosion control measures that may be used in site-specific road construction activities please see NRCS and EQPB. 4.1.2 Development Effective Erosion Control Planning for Land Development • Plan the development to fit the site. Analyze the site to determine how to develop it with the least impact on the environment. Utilize existing topography as much as possible to minimize excavation and maintain vegetative buffers between disturbed areas and offsite areas. Determine limits of clearing and grading. Disturb only what is necessary to accommodate construction and pay particular attention to critical areas like steep slopes, highly erodible soils and surface water borders. Clearing and grading should be staged and not done all at once! Divide the site into natural drainage areas. Consider how much erosion is to be controlled in each small drainage area before planning for the whole site. It is better to control erosion at the source and not rely solely on perimeter sediment trapping measures. Select erosion and sediment control practices. Vegetative controls are the first line of defense for preventing erosion and catching sediment. Structural controls should be used where vegetative control is not adequate for the particular situation. Local building codes should exist and call for an erosion and sediment control plan for any land development and construction activities that may degrade the environment if not controlled. These codes should also include the necessary penalties to enforce compliance. An erosion control plan should include a map of existing topography and proposed grading, provisions for erosion and sediment control, time schedule of activities and implementation and maintenance phasing. • • • • Main Principles for Erosion and Sediment Control • Disturb as little land as possible in the first place. Do not clear a large piece of land at once if only a small part will be constructed. Clear only the land that is needed for immediate construction and use responsible practices all the way through on that land. Only when ready to start another project phase should the land then be cleared for that phase. Allow the least water possible to enter and exit the disturbed areas. Runoff water coming down from above a construction site should be diverted around excavations. If it is necessary to allow runoff to go through the site because of the topography it must be contained in a stable channel all the way through the site and discharged safely. Protect detached soil as much as possible from being transported. Bare earth areas should be protected in the interim by spreading mulch over them. Mulch helps protect bare soil from raindrop impacts and decreases runoff velocity. However, it is not a substitute for real vegetation. 98 • • • Catch the sediment that does detach and keep it onsite. Sediment that becomes loosened and washes away should be caught before it leaves the site with structures such as silt fences and sediment basins. Establish vegetation on disturbed areas as soon as possible. Disturbed areas must be reseeded immediately with appropriate grasses, bushes and trees. The Army Corps of Engineers has developed a hydro-seed mixture that appears to be working very well on the Compact Road. Implement proper management practices on the construction site. Educate workers on the importance of erosion control, clearly mark off limits of land disturbance, make one person responsible for implementing the plan and perform daily inspections. Last but certainly not least, MAINTENANCE. Whether it is keeping grassed waterways mowed, sediment basins cleaned out, or silt fences intact, aggressive maintenance of erosion and sediment control measures throughout construction is critical to their success. For more information on effective erosion control measures that may be used in site-specific construction activities please see NRCS and EQPB. • • • • Flood Control Flood control technologies continue to improve in Airai and elsewhere and techniques should address other watershed-related principles, while maximizing public safety. • • Improve storm water management practices to include more than concrete-lined channels that increase the speed and volume of storm water flows, and thus the flood hazard. Minimize the use of impermeable concrete in the construction of flood control and other structures. Traditionally, flood control in Airai State has equated to the construction of lined trapezoidal or box-shaped channels that convey storm waters through the landscape. These structures were built with little regard for the needs of native aquatic species, pedestrian access by citizens who live near the streams, or the function of natural stream courses in filtering impurities and regulating water temperature. Aesthetic enhancement of the watersheds is a principle compatible with many of the aforementioned subjects, and should be combined with improving flood control management practices, increase in stewardship of the watershed, and promotion of native species habitats, among others. An attractive watershed is usually synonymous with a healthy watershed. • Septic Systems As the new Compact Road is completed, an increase in land use and residential dwellings is expected. • Measures should be taken to insure all new dwellings have properly designed and installed sanitation facilities. 99 • Some soils are suited for septic systems with leach fields and should be encouraged over other cheaper and less effective treatment systems. The Soil Survey of Palau identifies soil suitability for septic systems. Composting toilets could be another viable option in areas not suited for septic systems. • Contact NRCS for more information and technical assistance. Water Quality Accurate assessments of surface water quality in the watershed provide a key indicator of the overall health of the watershed. • The high costs of comprehensive water quality monitoring have precluded the compiling of a complete data record that could be used for a variety of watershed related programs, including water quality and sediment control, native species habitat enhancement, and recreational opportunities such as tourism, boating, swimming, and fishing. Operation and Maintenance It is important to remember that no system lasts forever or functions by itself. The fact is all things deteriorate over time and demand attention for upkeep and repairs. Whether it is a waste management/utilization system, erosion control measures, a riparian zone or any farming practice, ongoing effort and expenditure are always required to assure proper functioning and maintain safe conditions. • It is essential that a long-term serious commitment be made from the very beginning of any project or conservation practice to implement and carry out an effective operation and maintenance (O&M) plan for the life of the project. If an O&M plan is not carried out properly then the project will likely become a waste of everyone’s time, energy and money. Operation includes administration, management, and performance of non-maintenance actions needed to keep a completed practice safe and functioning; compliance with federal, state, and local laws; minimal negative impact on environment; and keeping commitments made in O&M agreement. The purpose of maintenance is to prevent deterioration of practices, repair damage and replace components as needed due to normal deterioration, flooding, vandalism, etc. It includes both routine work and more complex and costly work. An O&M plan lists steps that need to be followed for smooth operation, items that need to be checked and frequency for checking and parties responsible for operation and maintenance. It should typically include the following: general description of project, location, measures, life of project, responsible party • • • 100 description of the operation and maintenance required to ensure the practice functions as planned inspection and reporting schedule and requirements designated responsible parties and authorities requirements of all applicable laws and regulations consequences of not adhering to O&M • O&M are unequivocally the responsibility of the owners and users of the resources. This means that the people who are benefiting from the conservation of the island’s environment and natural resource base are the ones who must take responsibility for it. If the population as a collective is to reap the rewards of conservation then EVERYONE must pitch in and do their part. Agriculture 4.1.3 Due to the excessively high amount of soil erosion and soil degradation occurring on agricultural lands within the watershed, it is imperative that Best Management Practices (BMPs) for agriculture be used to control sediment-laden runoff. Best Management Practices to Control Erosion • Examples of well-established BMPs include: agroforestry cross-slope farming or terracing low-till farming with mulching grass cover vegetated drainage ways crop rotations returning marginal farmland to riparian buffer zones in order to intercept the drainage from farm fields and prevent steam bank erosion removing land vulnerable to high rates of erosion and nitrogen loss from production • • • Restrictions should be placed on intensive farming and steep slope farming. All highly erodible farm fields should be required to have a conservation farm plan. Agroforestry (the practice of crops inter-planted under tree canopies) is highly recommended as a sustainable farming practice. A producer could be required to develop and implement a conservation plan designed to minimize soil erosion, maintain water quality, and manage natural resources on the farm. 101 Access Roads Well-designed access roads help control the flow of water as an integral part of the farm drainage system while reducing erosion. • In general, these roads should run as closely to the natural contours of the land as possible to minimize disturbance of the natural drainage patterns. They should generally be designed with proper crowns, grass-lined lined ditches as part of the overall drainage plan and grades less than 10 percent. Surface drainage systems with proper side slopes of at least 3:1 and lined with grass or other suitable material will protect the channels themselves from eroding and help catch sediment and other pollutants running off crop fields. Channels should be protected from excessive traffic, particularly livestock. Uncontrolled animals can destroy the banks of any ditch, waterway or river and cause more erosion. Some systems may require water control structures to control erosion at the point of discharge into the river. • • For more information on how to protect heavily used areas and proper surface drainage techniques please contact NRCS. 4.1.4 Burning & Land Clearing Intentionally set fires are a major disturbance activity in the watershed causing excessive erosion and sedimentation. Fire Control and Prevention • • • A fire protection ordinance should be in effect and the ordinance regularly enforced. The means necessary to effectively enforce fire control should be provided. Begin community education campaign to stress the damage fire causes to the ecosystem and marine fisheries as a result of soil erosion. A reforestation program should be diligently pursued and supported by the state and national government. Trees maintain the vital and delicate balance for plant establishment and subsequent erosion control. Reforestation of eroded areas is a long- term endeavor and will take a long-term commitment and technical assistance. Field trials are needed to identify quick-establishing vegetation on disturbed sites to control erosion until other natural or volunteer species can become established. Stream Bank Erosion 4.1.5 The first rule for protecting streams from bank erosion and water pollution is to stay away from the river’s edge as much as possible. Riparian forest buffers naturally shield the stream from excess amounts of sediment, organic material, nutrients, pesticides and other pollutants in runoff water. They also provide habitat for land and aquatic wildlife and protect the steam bank from 102 excessive erosion. While many parts of the Ngerikiil River were observed to have healthy riparian buffer zones of various types of trees, they were generally not adequate in the middle agricultural and floodplain areas of the watershed. An ideal riparian area will be made up of three different zones, each having its specific function. However, these zones may be mixed and matched according to the needs of the site. The width of a zone is always measured on a horizontal line perpendicular to the direction of flow. Zone 1 is at least 4.6 meters (15’) of permanent forest vegetation right on the stream bank. The deep roots of these trees help hold and stabilize the soil to protect the bank from being eroded. Next is Zone 2, which is a minimum of 6.1 meters (20’). This area is generally made up of nonpermanent vegetation designed for the harvesting of forest products. Zone 3 is essentially a grass filter strip between Zone 2 and the developed land. This filter strip helps remove sediment and other pollutants from runoff water by filtration, deposition, infiltration, absorption, adsorption, decomposition and volatilization. Riparian Forest Buffers • A wide, diverse riparian buffer zone is critical for protection against stream bank failure. While these zones will not guarantee that banks along rivers will not fail – a stream or river’s natural meander sometimes results in bank failure and new river courses regardless of measures taken – they will greatly reduce the likelihood of “unnatural” stream bank erosion. Cease all farming activity to within at least 10.7 meters (35’) of any river or stream bank within the Ngerikiil Watershed. Designate a riparian buffer exclusion zone of 10.7 to 19.8 meters (35’ to 65’) along the entire length of the Ngerikiil and Edeng rivers and other smaller rivers and streams flowing into these two rivers. Width can vary to reduce the economic impact of existing farms but 10.7 meters (35’) should be a minimum. Replant these 10.7 to 19.8 meters (35’ to 65’) wide riparian buffer zones with a diverse mix of trees, shrubs, ground cover, and other species with their anchoring roots designed to armor the bank. Follow the USDA NRCS, Field Office Technical Guide, Section IV, Riparian Forest Buffer Practice Standard for implementation of above. • • • • For more information on how to build riparian zones please contact NRCS. 4.2 4.2.1 NUTRIENT & PESTICIDE POLLUTION Animal Manure The effects of pollution are reversible and respond to pollution abatement. Runoff from developed and agricultural lands is now the predominant pathways for toxic contaminants entering many coastal ecosystems. Abating these sources will require major commitments and innovative approaches. Nutrients leaking from our land-based economy are having profound effects over larger scales than imagined 30 years ago (Boesch et al., 2003). 103 Reducing nutrient pollution should be a national priority for Palau. Effective control of multiple sources of nutrients and contaminants on watershed scales would require a mix of voluntary and mandatory approaches. Incentives and disincentives included in statutes and management practices can be very important in promoting and shaping voluntary actions involving agriculture and land uses (Boesch et al., 2003). Several Best Management Practices (BMPs) that will address confined livestock operations and the animal manure source of diffuse pollution are: Management of Animal Manure • Development of a nutrient management plan for animal manure that minimizes pollution and utilizes the nutrients by balancing the amount of manure produced with the amount of nutrients needed by the plants (see also recommendations for fertilizer in next section). Soil testing for nutrient concentration. Matching the volume of manure produced on a farm with the land area and crop or vegetation available to utilize that volume. Education of livestock operators of the fertilizer value of their manure. Proper engineering of animal manure utilization systems. • • • • Measures to Apply for Safe Application of Animal Manure • Due to the potential for microbial contamination of produce from raw waste, it is important to apply the manure in the crop area of lowest risk. Use of untreated (raw) manure on food crops carries a greater risk of contamination compared with the use of manure that has been treated to reduce pathogens. Applying raw manure or leachates from raw manure, to produce fields during the growing season prior to harvest is not generally recommended. Animal waste, liquid or solid, should be applied on orchard crops (citrus, papaya, banana, guava, betel nut, etc.) and trees. This typically does not pose much risk of microbial infection of produce. If liquid waste volume is excessive for orchard crops and trees, apply to vegetable crop fields at least two weeks prior to planting and incorporate into the soil. Do not apply just before or during a rainstorm to avoid splash and runoff. Do not apply animal waste (liquid or solid) to any vegetables or fruits which are normally eaten raw (e.g., carrots, radishes, watermelon), or to any leafy vegetables (e.g., petchay, cabbage, lettuce). Do not apply liquid waste to low-growing vegetables that could easily come in contact with the raw liquid waste. Waste should not be applied near surface waters, concentrated surface runoff, slopes greater than 10 percent or fields prone to erosion. Compost all solids and incorporate into the soil prior to planting. Avoid contact between produce and any animal waste. Thoroughly clean all surfaces where produce is processed, stored, or handled. While there is some utilization of the manure in Airai for fertilization, there could be much more. Since animal manure contains large amounts of the nutrients that plants need, by far the most preferable method of managing waste is to use it as fertilizer. If the nutrients in the manure can be consumed by crops as food great benefits can be had. The problem of disposal is solved, money may be saved on fertilizer, water quality is protected, and the soil is • 104 enriched. Crop farms can even import manure from local animal farms to be used as fertilizer (the team did observe one farm buying manure from the poultry operation). • Different crops require different amounts of nitrogen, phosphorus, and potassium (N-P-K) while different animal manures contain different amounts of these nutrients. This information is readily available and care must be taken to apply the proper amounts of nutrients so as not to over fertilize. A properly planned waste utilization system should be part of an overall nutrient management system and is based upon the calculation of the nutrient needs of the particular crops being grown vs. the nutrient value of the manure being generated and matching them to come up with the correct application rate. If the crops grown are not enough to handle the manure generated on a farm, there is nothing wrong with planting, for example, an extra patch of banana or breadfruit trees to maximize the farm’s profitability and eliminate the waste disposal problem. There are many ways to apply manure to crops and plenty of room for creativity. It may be hauled and shoveled by hand, run through irrigation channels, spread with perforated pipes carried behind a tractor, etc. However, because of its pathogen content, animal waste must be handled very carefully and, as always, worker safety should be a priority. Boots and gloves should always be used when handling manure and bodies should be thoroughly cleaned afterward. Another very effective method of utilizing nutrients from farm and household organic wastes—including dead animals—is composting. This enables farmers to save on fertilizer costs and reduce pollution while improving soil fertility, tilth and water holding capacity. Most people are aware of composting to some extent but may not necessarily understand how much science is involved. Proper composting is much more than just throwing garbage into a pile and letting it rot. Since it converts ammonia nitrogen into a more stable organic form in an aerobic biological process, the correct recipe is essential for optimum success. The most critical component is the ratio of carbon (coconut husks, leaves, grass, wood chips, shredded paper, etc.) to nitrogen (manure, animal carcasses, crop residue, etc.) which should be calculated from available data. The system also must have sufficient moisture and oxygen as well as a pH around six to eight. Manure may be handled as either liquid (less than five percent solids), slurry (five to15 percent solids), semi-solid (10 to 22 percent solids) or solid (less than 20 percent liquid). Each method has its advantages and disadvantages but handling manure in the most solid form possible may be preferable for water conservation. Ideally, a farmer should use the least amount of water necessary for cleaning animal pens. For example placing a slotted floor (for livestock to walk on) over a sloped concrete floor is a very effective way of separating animals from their feces. The waste falls through the slots and may be easily scraped up from underneath for collection. If a liquid system is used the wash-down water should be utilized for irrigation of appropriate crops. • • • For more information on utilizing manure for fertilization please see Fertilizing with Pig Waste, A Guidebook for Pacific Island Farmers (available from NRCS) and e-FOTG Practice Standards Manure Transfer, Waste Storage Facility, Composting Facility and Waste Utilization. 105 4.2.2 Chemical Fertilizer Runoff & Nutrient Over-Enrichment Significant reduction in nutrient pollution may be achieved by approaches that reduce the use of nutrients, control the losses to the environment at the point of release (e.g., farm field, animal feeding operation, lawn, subdivision, golf course), and sequester or remove pollutants as they are transported to the sea. Various agricultural practices affect nitrogen and phosphorus runoff and losses to surface and ground water (Boesch et al., 2003). The Republic of Palau should require the use of Best Management Practices for agriculture and development to control polluted runoff. By combining the following approaches and practices a significant portion of the edge-of-field nitrogen and phosphorus losses can be reduced, regardless of the land use source. 106 Control of Polluted Runoff • Identify and publicize regionally appropriate non-point source BMPs that include those employed to reduce soil erosion, such as cross-slope farming and conservation tillage (reduced or no till). Develop a program for certifying their implementation. Monitor their effectiveness. Remove land vulnerable to high rates of erosion and nutrient loss from production. Establish and maintain wooded riparian buffer zones for steam bank protection. Incorporate grazing management. Establish grassed waterways. Test soils to precisely match fertilizer applications to crop nutritional needs (many farmers still over apply to ensure maximum crop yields). Applying fertilizer only at the time the crop needs it. Incorporate fertilizer into the soil directly around plants only so that it becomes chemically bound to soil, but does not leach or volatize out of field. Practice a soil building crop rotation. Use soil and manure amendments (compost). Utilize mulching to protect bare soil. Establish buffer strips between cultivated fields and nearby streams. Moderate excessive drainage by ditches and tile lines. Retain healthy river floodplains and wetlands. Construct and restore wetlands and vegetative buffers to intercept drainage from farm fields. Construct catchment basins where applicable. Pesticide Leaching • • • • • • • • • • • • • • • • • 4.2.3 Whenever pesticides are used, there is a potential for leaching and water contamination, particularly in this climate of frequent and heavy rains. There are ways water quality can be protected using pesticides effectively. 107 Proper Application of Pesticides for Protection of Water Quality • Use Integrated Pest Management (IPM) practices to avoid unnecessary pesticide use. IPM includes cultural (such as crop rotation and agroforestry), biological use of pest’s natural enemies, physical barriers such as screens or traps, chemical pesticides, and legal control to stop the spread of invasive pests and to certify pesticide applicators of restricted-use pesticides (Goodman, 2000). Choose pesticides that have less potential or for surface runoff. Use the lowest effective rate of a pesticide for the type of soil and pest conditions. Keep all pesticide preparation areas and storage units at least 46 meters (150’) from any surface water or well. Plant vegetative covers as buffer zones around surface water. If rain is predicted or if there are strong winds do not apply pesticides. Control erosion to prevent runoff water from carrying pesticides attached to soil particles. Minimize drift during application by spot spraying on targets only. Minimize pesticide waste by using less pesticide. Report all spills to EQPB. Use fire prevention practices to avoid fires involving pesticides. • • • • • • • • • • For a list of legal pesticides and more information on application of pesticides, contact EQPB. 4.3 SOLID WASTE DISPOSAL Reducing the amount of waste generated on land and disposing of it properly is critical to the longevity and sustainability of a healthy watershed. Solid Waste Disposal and Reduction • • • • Dispose of trash properly at designated landfills. Consolidation of trash minimizes its impact to the natural environment. Reduce the amount of trash generated. Reuse products. For example, reuse plastic bags when shopping. Recycle. Recycling can significantly reduce the amounts of trash being generated and disposed. 108 • • Cut the rings of plastic six-pack holders. This lowers the risk of entanglement to marine animals if the holders do make it out to sea. Compost. Table 26 provides a list of what to compost and what not to compost. Table 26: What to compost Yes Grass clippings, garden trimmings Green weeds, dry weeds, and leaves Coffee grounds, tea bags Kitchen scraps, liquids Cardboard, paper Seaweed Banana leaves Nutshells Iron wood needles Coconut fronds and shells Telengtungd leaves Hair clippings No Meat, grease, or dairy products Dog, cat or other meat eating animal manures Diseased plants Weeds with seeds Toxic materials, such as herbicides, pesticides and paper with toxic ink Charcoal ashes Metals Glass Plastics • • • • Participate in local beach, river or stream clean ups. Practice good housekeeping. Look for alternative materials or avoid excessive packaging when deciding on purchases. Educate others about solid waste. For more information on solid waste disposal, recycling and composting, contact EQPB, Bureau of Public Works and NRCS. 4.4 INVASIVE SPECIES Protect and restore the native forest. This will address other watershed issues such as erosion reduction and increased infiltration, and the perpetuation of species that rely on a native ecosystem. This also increases the cultural resource base as native forests supply materials that are traditional in Palau culture. Recently the USDA Forest Service released their recommendations, Report to the Republic of Palau on Invasive Plant Species of Environmental Concern, 2003. In this report they made the following general recommendations: General Recommendations to Reduce Invasive Species 109 • • • • Discourage offsite dumping and encourage onsite composting of garden waste and cuttings to avoid spreading of noxious weeds. Infrequent mowing or slashing may actually spread weed species that reproduce vegetatively. Limit burning and extinguish fires promptly. Disturbance of ecosystems, removal of competition and the exposure of mineral soil favor many invasive species. Undisturbed ecosystems are much more resistant to invasion. Limiting land clearing helps to prevent the establishment and spread of invasive plant species. The interception of invasive species is addressed through decontamination (such as fumigation, water immersion, heat and cold treatment, and irradiation) of suspected carriers, inspection, and legal constraints to importation of high-risk commodities. WILDLIFE HABITAT IMPACTS • 4.5 Tropical forests are sometimes referred to as “green deserts” as they grow on extremely poor soils in conditions of extreme heat and rain (Stone, 1997). When the forests are cleared, the nutrients in the soils, and eventually the soil itself, are washed away by the torrential rains, leaving a barren landscape capable of supporting only a greatly degraded ecosystem (Stone, 1997). The climate of Palau encourages prolific growth of biological diversity of plants, insects, and animals within its rainforests. However, the interconnectedness of the soils, water quality of surface waters, groundwater, and the bay, vegetation and wildlife, is extremely fragile. By protecting and preserving the wildlife habitat of Palau’s forests, the future of all ecosystems from ridge to reef is ensured. Crocodiles There appears to remain a fear among many Palauan as to the danger of crocodiles. An attitude prevails to exterminate this reptile from the waters of Palau. While the danger to mankind cannot be ignored, it can be managed in such a way as to provide protection to both the crocodile and human. The estuarine crocodile represents yet another wildlife species that ranks the Republic of Palau as unique in the world. Protecting this species and its habitat should be an important goal for Palau, both for its ecosystem diversity and its tourist value. • Develop a wildlife habitat management plan for the estuarine crocodile within the Ngerikiil Watershed. This plan should include re-establishment of a riparian forest buffer along the river to provide critical habitat to the animal Educate the public on the value of this wildlife species and on ways to avoid contact with these animals in their habitat Encourage a conservation program that sets aside and protects habitat, and restricts or controls the hunting of this species • • 110 • Take advantage of the opportunities the crocodile provides to draw and educate tourists to Palau "Conservation is the foresighted utilization, preservation and/or renewal of forests, waters, lands and minerals, for the greatest good of the greatest number for the longest time."-Gifford Pinchot Photo 66: Ngerikiil River outlet into Airai Bay 111 APPENDIX A: WORKS CITED Bell, P.R.F., 1992. Eutrophication and coral reefs – some examples in the Great Barrier Reef lagoon, Water Research 26:553-568. Blayok, Vince, 1993. Draft Reconnaissance Survey of Airai State, Division of Cultural Affairs, Republic of Palau. Boesch, D.F, R.H. Burroughs, J.E. Baker, R.P. Mason, C.L. Rowe, and R.L. Siefert, 2003. Marine Pollution in the United States, A report prepared for the Pew Oceans Commission. Bricker, S.B., Clement, C.G., Pirhalla, D.G., Orlando, S.P., and Farrow, D.R.G., 1999. National Estuarine Eutrophication Assessment: Effects of Nutrient Enrichment in the Nation's Estuaries, National Ocean Service, Special Projects Office and the National Centers for Coastal Ociean Science, Silver Spring, Maryland. Cole, T.G., M.C. Falanruw, C.D. MacLean, C.D. Whitesell, and A.H. Ambacher, 1987. Vegetation Survey of the Republic of Palau, Resource Bulletin PSW-22, U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station. Corwin, 1952. Demeo, Robin, Holme, Tarita, Sengebau,Fred, Miles, Joel, 2002. Invasive Plants of Palau, Palau Natural Resources Council, USDA NRCS, Koror, Palau. Duarte, C.M., 1995. Submerged Aquatic Vegetation in Relation to Different Nutrient Regimes, Ophelia 41: Dinamarca 41: 87-112. Elliott, S.R., and P. Franz, 1993. The Ngerikiil Watershed Inventory and Management Recommendations Project Report, University of Oregon Micronesia and South Pacific Technical Assistance Program and the Palau Environmental Quality Protection Board. Engbring, John, 1988. Field Guide to the Birds of Palau, Conservation Office, Bureau of Education, Koror, Palau. Ford, Alan R., 1982. Soil Formation by Geomorphic Units, Unpublished paper, US Department of Agriculture, Soil Conservation Service. Forsberg, C., 1998. Which policies can stop large scale eutrophication?, Water Science and Technology 37:193-200. Foster, G.R., 1986. Understanding Ephemeral Gully Erosion, Soil Conservation: An Assessment of the National Resources Inventory, Volume 2, The National Academy of Sciences, National Academy Press, Washinton, D.C. Golbuu, Yimnang; Victor, Steven; Wolanski, Eric; Richmond, Robert H., 2003. Trapping of fine sediment in a semi-enclosed bay, Palau, Micronesia, Estuarine Coastal and Shelf Science 57: 941-949. 1 Golder Associates Pty Ltd, September 1999. National Landfill Project, Comparative Evaluation of Two Proposed Sanitary Landfill Sites; Submitted to Design Engineering Office, Bureau of Public Works, Koror, Palau. Goodman, Nancy, ed. 2000. Private Pesticide Applicator’s Training Manual, 18th edition, University of Minnesota Extension Service and Minnesota Department of Agriculture, Internet address, http://www.extension.umn.edu/pesticides/pat/ppatman/ppatmanual.html. Harvell, C.D., K. Kim, J. M. Burkholder, R. R. Colwell, P. R. Epstein, D. J. Grimes, E. E. Hofmann, E. K. Lipp, A. D. M. E. Osterhaus, R. M. Overstreet, J. W. Porter, G. W. Smith, G. R. Vasta, 1999. Emerging Marine Diseases--Climate Links and Anthropogenic Factors, Internet address: Science -- Harvell et al. 285 (5433): 1505 Holm, Tarita; Michaels, Pua, February 2003. National Report on Invasive Alien Species, Office of Environmental Response and Coordination and Bureau of Agriculture, Republic of Palau. Kuhn, J. and P. Bautista, 1996. Rapid Assessment of the Ngeremeduu Watershed of the Republic of Palau, U.S. Department of Agriculture, Natural Resources Conservation Service. Lapointe, B.E., 1999. Simultaneous topo-down and bottom-up forces control microalgal blooms on coral reefs, Limnology and Oceanography 44:1586-1592. Mallin, M.A., 2000. Impacts of industrial animal production on rivers and estuaries, American Scientist 88:26-37. Mueller-Dombois, D. and F. R. Fosberg, 1998. Vegetation of the tropical Pacific islands, Springer-Verlag, New York. NOAA, 2004.National Oceanic and Atmospheric Administration, National Weather Service, Guam. NRCS, 2003. United States Department of Agriculture, Natural Resources Conservation Service. Nixon, S.W., 1995. Coastal marine eutrophication: a definition, social causes, and future concerns, Ophelia 41:199-219. Olsudong, Rita, 1997. Draft Inventory of Cultural Sites and Oral History of Melekeok and Airai States, Division of Cultural Affairs, Republic of Palau. Renard, K.G., G.R. Foster, G.A. Weesies, D.K. McCool, and D.C. Yoder, 1992. Predicting Soil Erosion: A Guide to Conservation Planning with the Revised Universal Soil Loss Equation (RUSLE), Agriculture Handbook No. 703, U.S. Department of Agriculture, Agricultural Research Service. Rengiil, G., 1999. The Water Quality Program Report, Department of Cooperative Research and Extension, Palau Community College and the Palau Environmental Quality Protection Board. Rogers, Caroline S., 1990. Responses of coral reefs and reef organisms to sedimentation, Marine Ecology Progress Series 62: 185-202. SCS, 1983. United States Department of Agriculture, Soil Conservation Service. 2 Scott, D.A., 1993. A Directory of Wetlands in Oceania, Compiled for the International Waterfowl and Wetlands Research Bureau (IWRB), Asian Wetland Bureau (AWB), South Pacific Regional Environment Programme (SPREP), and the Ramsar Bureau. Smith, C.W., 1983. Soil Survey of Islands of Palau, Republic of Palau, U.S. Department of Agriculture, Soil Conservation Service. Smith, Christopher W. and Neil R. Babik, 1988. Properties and Management Considerations of Some Acid Soils of Palau, Third (3rd) International Soil Management Workshop, Management and Utilization of Acid Soils of Oceania, Belau, February 2-6, 1987, 39-62 p. Soil Survey Staff, 1999. Soil Taxonomy. A Basic System of Soil Classification for Making and Interpreting Soil Surveys, USDA Natural Resources Conservation Service, Agricultural Handbook 436, Second edition. Space, James C., Waterhouse, Miles, Joel E., Tiobech, Joseph and Rengulbai, Kashgar, 2003. Report to the Republic of Palau in Invasive Plant Species of Environmental Concern, USDA Forest Service, Pacific Southwest Research Station, Institute of Pacific Islands Forestry, Honolulu, Hawaii, USA, Internet address, Report on invasive plant species in Palau. Stocking, M.A., 2003. Tropical Soils and Food Security: The Next 50 Years, Science 203:13561359. Stone, David, 1997. Biodiversity of Indonesia, Tien Wah Press/Archipelago Press, Singapore, 208 p. U.S. Army, 1956. Military Geology of Palau Islands, Caroline Islands, Engineer Intelligence Dossier, Strategic Study: Carolines, Subtitle: 19 Analysis of the Natural Environment. U.S. Environmental Protection Agency, 2004. Basic Facts about Waste, Office of Solid Waste and Emergency Response, Mail Code 5103T, 1200 Pennsylvania Avenue, N.W. Washington, DC 20460, Internet address, http://www.epa.gov/epaoswer/osw/facts.htm. U.S. Environmental Protection Agency, 2003. Marine Debris Abatement, Office of Wetlands, Oceans and Watersheds, Ocean and Coastal Protection Division, Mail Code 4504T, 1200 Pennsylvania Avenue NW, Washington, DC, Internet address, http://www.epa.gov/owow/oceans/debris/. Unified Watershed Assessment, 1998. Process under the Clean Water Action Plan for Palau to prioritize watersheds in the state. United States Geological Services, 1984. Vessel, A.J. and R.W. Simonson,1958. Soils and Agriculture of the Palau Islands, Pacific Science 12:281-298. Vitousek, P.M., J.D. Aber, R.W. Howarth, G.E. Likens, P.A. Matson, D.W. Schindler, W.H. Schlesinger, and D.G. Tilman, 1997. Human alteration of the global nitrogen cycle: sources and consequences, Ecological Applications 7:737-750. Vogt, Jon, United States Army Corps of Engineers, 2003. 3 Wischmeier, W.H. and D.D. Smith., 1978. Predicting Rainfall Erosion Losses, A Guide to Conservation Planning, Agriculture Handbook No. 537, U.S. Department of Agriculture, Science and Education Administration. 4 APPENDIX B: GENERAL REFERENCES Ballendorf, Dirk A., 1989. Tactile Accomplishments of the German Administration on the Eastern Carolines, 1900-1910, from Official German Sources, Presentation made to the Ninth Annual College of Arts and Sciences Research Conference, University of Guam, April 1989, Internet address, http://www.uog.edu/faculty/ballendo/german.html. Dellberg, R.A., 1982. Road Building Guide for Small Private Roads, California Association of Resource Conservation Districts and the U.S. Department of Agriculture, Soil Conservation Service. Kellogg, Robert L.; Nehring, Robert; Grube, Arthur; Goss, Don W.; Plotkin, Steve, 2000. Environmental Indicators of Pesticide Leaching and Runoff from Farm Fields, Presented at a Conference on "Agricultural Productivity: Data, Methods, and Measures", March 9-10, 2000, Washington DC, Internet address, http://www.nrcs.usda.gov/technical/land/pubs/eip_pap.html. Kocsis, J.J., M.E. Stransky, R. Wescom, R. Drew., 1992. Resource Assessment and Conservation Study Plan for Ngchesar State, Republic of Palau, Technical Report, U.S. Department of Agriculture, Soil Conservation Service. MacLean, C.D., T.G. Cole, C.D. Whitesell, and K.E. McDuffie, 1988. Timber Resources of Babelthuap, Republic of Palau, Resource Bulletin PSW-23, U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station. Mayo, Herald M., circa 1972. Palau Islands Plant Relocation Survey and Agricultural History,Trust Territory of the Pacific Islands, Micronesian Area Research Center, University of Guam. McGrath, W.A., circa 1971. The Effects of Urban Drift in the Palau District of Micronesia, The Pacific Collection, Micronesian Area Research Center, University of Guam. National Research Council, 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution, National Academy Press, Washington, D.C. ROP ROERC, 2002. National report to the United Nations Convention to Combat Desertification, R. O. P. Office of the President of the Republic of Palau, Office of Environmental Response and Coordination. Siefert, R.L., 2003. Marine Pollution in the United States, A report prepared for the Pew Oceans Commission. UNRP, 2002. United Nations Environment Programme, Chemicals, Regionally Based Assessment of Persistent Toxic Substances, Pacific Islands Regional Report, United Nations Global Environmental Facility, Chatelaine, GE, Switzerland, Internet address, http://www.chem.unep.ch/pts/regreports/PacificIslands.pdf. U.S. Army, circa 1949. Military Geology of Palau Islands, Caroline Islands, U. S. Army, Corps of Engineers, Internet address, http://www.geocities.com/ctrlburn/introduction.html. 1 U.S. Environmental Protection Agency, 1991. Applying Pesticides Correctly, A Guide for Private and Commercial Applicators, U.S. EPA, USDA Extension Service and University of Guam, Pesticide Applicator Training program, Cooperative Extension Service, Mangilao, Guam. University of Guam, 2003. Farm & Garden Pesticide Use, U.S. EPA, USDA Extension Service and University of Guam, Pesticide Applicator Training program, Cooperative Extension Service, Mangilao, Guam. 2 APPENDIX C: LIST OF ACRONYMS USED The following lists acronyms used in this assessment: BMP CFS COE CPRD CRM CWRM CZARA CZMP DPW DWSRF EIS EPA EQPB GWPP HEER MGD NAWQA NPDES NWA NOAA NRCS NRCS PBAO NRCS PFO PCS PCC-CRE PL RANW SCS SDWA TMDL USDA USFWS USGS USN Best management practice Cubic feet per second U.S. Army Corps of Engineers Coastal Protection and Restoration Division (NOAA) Concrete, rock, masonry Commission on Water Resource Management (State) Coastal Zone Act Reauthorization Amendments Coastal Zone Management Program (State) Department of Public Works Drinking Water State Revolving Fund Environmental Impact Study Environmental Protection Agency Environmental Quality Protection Board Ground Water Protection Program Hazard Evaluation and Emergency Response (DOH) Million gallons per day National Water Quality Assessment (USGS) National Pollutant Discharge Elimination System Ngerikiil Watershed Area National Oceanic and Atmospheric Administration Natural Resources Conservation Service Natural Resources Conservation Service - Pacific Basin Area Office Natural Resources Conservation Service – Palau Field Office Palau Conservation Society Palau Community College - Cooperative Research & Extension Public Law Rapid Assessment of the Ngerikiil Watershed Soil Conservation Service (former name for the USDA - NRCS) Safe Drinking Water Act Total Maximum Daily Load United States Department of Agriculture United States Fish & Wildlife Service United States Geological Survey United States Navy 1