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Effects of the Suwannee River Sill on the Okefenokee Swamp Hydrological Environment Cynthia S. Loftin USGS-BRD Maine Cooperative Fish and Wildlife Research Unit University of Maine, Orono Wiley M. Kitchens USGS-BRD Florida Cooperative Fish and Wildlife Research Unit University of Florida, Gainesville Georgia Atlanta Macon Savannah Tallahassee Jacksonville Okefenokee National Wildlife Refuge Project Objective: Has the Suwannee River sill affected the Okefenokee Swamp hydrological environment and vegetation distributions? Water Control Structures Main Channel Suwannee River Sill Aquatic Prairie Forested Swamp Herbaceous Prairie Smilax spp. and shrubs Upland Pine Forest Sill Area Average Conditions Sill Area, Dry Conditions Main Channel, Suwannee River Sill Ditch, Dry Conditions Processes Affecting the Okefenokee Landscape and the Scale of those Effects 1cm 1m 1km 1000km 4 10,000 years landscape 3 1000 years forest 2 Drought 100 years patch stand Logging Duration of 1 10 years Disturbance 0 canopy or Landscape leaf Hydrology Change Year Component -1 Fire Month (Log Years) -2 Hurricanes Day -3 Thunderstorms Hour -4 -5 Minute -6 -4 -2 0 2 4 Space (Log Kilometers) Hydrological Physical Vegetation Features Environment History Species’ Manipulative Hydrological Processes Environment Comparisons: HYDRO-MODEL Map Overlays Species’ Models Landscape Patterns Suwannee Sill and Processes Effects Hydrological Features Weather, Water Level, Flow Physical Environment Topography, Peat Thickness Vegetation 1952 BW Photos History Pre-logging Surveys 1990 Imagery 1977 CIR Photos Species’ Hydrological Environments Manipulative Processes 1891-1897 Suwannee Canal 1889-1942 Logging 1950s Peat Mining 1960-1962 Suwannee Sill Construction Flow Features and Directions During Average Conditions Suwannee River Sill Daily Water Depths in Swamp Basins (1993) 2.25 1.75 West Water 1.25 Depth East Central (m) 0.75 Northeast 0.25 Southeast -0.25 JAN MAR MAY JULY SEPT NOV Month Swamp Topographic Surface and Hydrologic Basins HYDRO-MODEL Steps Water Depth + Rain + Inflow - Outflow - Evapotranspiration + Ground Surface Elevation/Roughness Flow Direction Calculation Amount of Water to Move Water Movement Model Simulations 2.25 Northeast 1.75 1.25 0.75 Water Depth (m) 0.25 no sill with sill -0.25 no outflow 2.5 West 75% ET 150% ET 2 1.5 1 0.5 0 1980 1985 1990 1994 Year Annual Average Water Depth 1941-1995 SCFSP Water Depth (m) SCRA Year Areas Affected by Model Manipulations Inflow Outflow ET Sill ET Sill (upper basin) Outflow ET ET Areas Affected by Sill Operation Extended hydroperiod in high water conditions Flow direction Extended hydroperiod reversal in in low water very high water conditions level conditions Reduced hydroperiod Increased outflow in very high water level conditions 70 Vegetation Composition 60 of Okefenokee 50 National Wildlife Refuge Percent 40 1890-1990 30 20 Upland Pine 10 Wet Forest 0 Shrub 1890 1952 1977 1990 Prairie Year Vegetation Type in 1990 Vegetation Type Sill South- East- North- Regional Comparison in 1952 Area west Central North east of Changes in Vegetation Types, Wet Forest WF WF, S WF, S WF WF (WF) Before and After Shrub WF S, WF S WF S, WF Sill Construction (S) Prairie WF S S WF S (P) Proportion and Size of Wildfires by 5-Year Intervals (1855-1993) 60 50 40 30 20 10 0 210000 180000 150000 Area (ha) 120000 Sill Construction 90000 60000 30000 0 ~ ~ 55 25 35 45 55 65 75 85 95 18 19 19 19 19 19 19 19 19 5-Year Interval Vegetation Succession in Okefenokee Swamp Prairie Prairie-Shrub-Swamp Prairie- Shrub- Shrub-Swamp Cypress Shrub-Cypress-Swamp Bay-Shrub-Swamp Cypress- Bay- Mixed Blackgum Swamp Blackgum Bay-Swamp Swamp no fire moderate fire severe fire + logging 1977 1990 Summary Points • The Suwannee River sill is increasing flooding depth and duration in 18% of the refuge, primarily during periods of abundant precipitation. • Although fire management may be affecting fire distributions, the sill has little effect of the swamp fire regime. Summary Points (continued) • The observed changes result from logging, fire management, hydrologic manipulations, and vegetation succession. • The role of these processes as the primary driver of change is influenced by the location within the swamp. Acknowledgements Okefenokee National Wildlife Refuge, USFWS-Region 4, USGS-BRD, N. Ansay, J. Aufmuth, J. Brookshire, C. Depkin, D. Evenson, J. Kitchens, J. Loftin, D. O’Neill, P. Owen, L. Pearlstine, B. Rasberry, K. Williges
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