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Hydric Soils Wetland Delineation Certification Refresher General Information • Soils consist of unconsolidated, natural mineral that supports, or is capable of supporting, plant life. • Components that make up soil include: – Sand; – Silt; – Clay; and – Organic matter. General Information • Most soils have 2 or more identifiable horizons, described from the surface downward. • A soil horizon is a layer oriented approximately parallel to the soil surface, and is usually differentiated from contiguous horizons by characteristics that cam be seen or measured in the field (e.g. color, structure, texture, etc.). Typical Soil Horizons Surface Organic Layer O horizon Area of primary interest A Horizon Surface Mineral Layer For delineation purposes. Subsoil B Horizon Underlying C Horizon Material Bedrock R Horizon A horizon Bw horizon C horizon A horizon E horizon Bh horizon Bs horizon Soil Horizons • A horizon – Surface soil or topsoil: – Zone in which organic matter is usually being added to the mineral soil. – Zone from which both mineral and organic matter are being moved slowly downward. – Defined as having a value of 3 or less and a chroma of 2 or less. Soil Colors • Munsell Soil Color Book, 7.5YR page. A horizon (Value 3 or less and Chroma 2 or less) Influencing Factors in Soil Formation • Climate • Parent Material • Relief • Organisms • Time • Hydrology – overriding factor for hydric soils. Soil Color • Soil colors are described as a combination of: – Hue (e.g. 10YR); – Value (e.g. 4/); and – Chroma (e.g. /1). Written as 10YR 4/1 Hue Red 0 2.5R 5R 7.5R 10R Yellow-Red 0 2.5YR 5YR 7.5YR 10YR Yellow 0 2.5Y 5Y 7.5Y 10Y Value • 10/0 - Pure White The Lightness or Darkness of • 5/0 - “Gray” Color • 0/0 - Pure Black Chroma “Neutral” “Pure” Color Color /0 /2 /4 /6 /8 Increasing strength of color Increasing grayness Coloring Soils • Optimum conditions – Natural light; – Clear, sunny day; – Midday; – Light at right angles; – Soil moist. Describing Redox Features • Matrix (predominant) color; • Redox colors; • Redox contrast, abundance, and size. Describing Redox Features • Contrast • Abundance – Faint -- evident only – Few -- less than 2% on close examination – Common -- 2 to 20% – Distinct -- readily seen – Many -- more than 20% – Prominent -- contrast strongly • Size – Fine -- < 5 mm – Medium -- 5 to 15 mm – Coarse -- > 15 mm Hydric Soils • The hydric soil definition and criteria published in the 1987 Corps Manual are obsolete. Current hydric soil definition, criteria, and lists are available from the USDA at: http://soils.usda.gov/use/hydric/ Hydric Soil Definition • A soil that formed under conditions of saturation, flooding or ponding long enough during the growing season to develop anaerobic conditions in the upper part. • Hydric soils support, or are capable of supporting, the growth and regeneration of hydrophytic vegetation. Hydric Soil Definition • Hydric soils include those soils that are artificially wet. • Hydric soils include those soils that are artificially drained, if the natural soil was hydric. Hydric Soil Definition • Some series, designated as hydric, have phases that are not hydric depending on water table, flooding, and ponding characteristics. Criteria for Hydric Soils • Four broad hydric soil criteria are: 1. Organic soils; 2. Mineral soils with high water tables; 3. Ponded soils; 4. Flooded soils. • Hydric soil criteria were designed to generate a list of hydric soils from the national database. • Except for criteria 3 and 4, they were not intended for field identification purposes. Criteria for Hydric Soils Hydric Soil Criteria: 1. All Histels except Folistels, and Histosols except Folists; 2. Soils in Aquic suborders, great groups, or subgroups, Albolls suborder, Historthels great group, Histoturbels great group, Pachic subgroups, or Cumulic subgroups that are: Criteria for Hydric Soils 2a. Somewhat poorly drained with a water table equal to 0.0 foot (ft) from the surface during the growing season, or This criterion is an artifact of the way the soils database was populated over the years; artificially drained PD and VPD soils were called SWP in previous years. Criteria for Hydric Soils 2b. Poorly drained or very poorly drained and have either: i. Water table equal to 0.0 ft from the surface during the growing season if textures are coarse sand, sand, or fine sand in all layers within 20 inches, or for other soils ii. Water table at less than or equal to 0.5 ft from the surface during the growing season if permeability is equal to or greater than 6.0 inches / hr in all layers within 20 inches, or iii. Water table at less than or equal to 1.0 ft from the surface during the growing season if permeability is less than 6.0 inches / hr in any layer within 20 inches, or Criteria for Hydric Soils 3. Soils that are frequently ponded for long duration or very long duration during the growing season; or 4. Soils that are frequently flooded for long duration or very long duration during the growing season Hydric Soil Criteria • Frequently – flooding, ponding, or saturation likely to occur often under usual weather conditions (>50 in 100 years). • Ponded – water stands in closed depression. • Flooded – soil surface temporarily covered with flowing water from any source. • Long Duration – innundation for a single event ranges from 7 days to 1 month. • Very Long Duration – innundation for a single event is greater than 1 month. Hydric Soil Lists • A hydric soil list is an interpretative rating which must be confirmed by on-site investigation. • Types of hydric soil lists: – National – State – Local or field office Local or field office lists have precedence over state and national lists. 87 Manual Wetland Indicators (Non-Sandy Soils) • Indicators in descending order of reliability. a. Organic soils (Histosols); b. Histic epipedons; c. Sulfidic material; d. Aquic or peraquic moisture regime; e. Reducing soil conditions; f. Soil colors; g. Soils appearing on hydric soils lists; and h. Iron and manganese concretions. 87 Manual Wetland Indicators (Non-Sandy Soils) • Organic Soils (Histosols) – more than 50% of upper 32 inches is organic material; or any organic material resting on bedrock. 87 Manual Wetland Indicators (Non-Sandy Soils) • Histic epipedon – an 8-16 inch layer of organic material at, or near, the surface of a mineral hydric soil. 87 Manual Wetland Indicators (Non-Sandy Soils) • Sulfidic material – when mineral soils emit an odor of rotten eggs, hydrogen sulfide is present. Sulfides are produced only in a reducing environment. 87 Manual Wetland Indicators (Non-Sandy Soils) • Order of reducing reaction (fastest to slowest) Redox Potential Element Reaction +350 mV Oxygen O2 + 4H+ = 2H2O +220 mV Nitrogen 2NO3- + 12H+ = N2 + 6H2O +200 mV Manganese MnO2 + 4H+ = Mn2+ + 2H2O +120 mV Iron Fe(OH)3 + 3H+ = Fe2+ + 3H2O -150 mV Sulfur SO42- + 10H+ = H2S + 4H2O -250 mV Carbon CO2 + 8H+ = CH4 + 2H2O 87 Manual Wetland Indicators (Non-Sandy Soils) Subgroup - Great Group, Suborder, Order • Aquic or peraquic 4 3 2 1 moisture regime – An aquic moisture Vertic Udifluvent regime is a reducing one; a peraquic • 4 – Vertic subgroup: High clay, shrink- swell. moisture regime is one • 3 – Udi(c) great group: Humid climate. characterized by the • 2 – Fluv(ic) suborder: Alluvial. presence of ground • 1 – Ent(isol) order: Minimal soil water always at or development. near the surface. Moisture regime information is found in the Suborder Soil Taxonomy Nomenclature 4 3 2 1 Typic Fluvaquents •4 – Typic subgroup. •3 – Fluv(ic) great group. •2 – aqu(ic) suborder. •1 – Ent(isol) order. Typical4 Entisols1 with aquic2 moisture regimes that occur on floodplains3. Soil Taxonomy Nomenclature 4 3 2 1 Mollic Fluvaquents •4 – Mollic subgroup. •3 – Fluv(ic) great group. •2 – aqu(ic) suborder. •1 – Ent(isol) order. Entisols1 with aquic2 moisture regimes that occur on floodplains3 and have thick, dark surface layers4. 87 Manual Wetland Indicators (Non-Sandy) • Reducing soil conditions – reducing soil conditions as evidence by colorimetric field test, typically α,α’-dipyridl. Reduced iron reacts with the dye and results in a red coloration. 87 Manual Wetland Indicators (Non-Sandy) • Soil colors – Soil color is often the most diagnostic indicators and include the following: – Gleyed soils – pronounced reduction of iron, managnese, and other minerals producing grayish, blueish, or greenish colors; – Soils with bright mottles and/or low matrix chroma. • Matrix of 2 or less in mottled soils; • Matrix of 1 or less in unmottled soils. 87 Manual Wetland Indicators (Non-Sandy) Gleyed Mottled Unmottled 87 Manual Wetland Indicators (Non-Sandy) • IMPORTANT NOTE: ! The statement in the 87 Manual that gleyed and low-chroma colors must be observed "immediately below the A-horizon or 10 inches (whichever is shallower)" is intended as general guidance. ! Certain “problem soils” may differ. Problem Soils • Problem Soils as identified in 1992 Clarification. – Mollisols; – Spodosols; – Entisols; – Red parent material. 87 Manual Wetland Indicators (Non-Sandy) • “Problem Soils” may not exhibit typical soil color characteristics. Care must be taken when making hydric soil determinations in these areas. • If a problem soil is present, follow the procedures outlined in: “Guidelines for Submitting Wetland Delineations to the St. Paul District Corps of Engineers and Local Units of Government in the State of Minnesota, (96-01078-SDE, April 17, 1996).” 87 Manual Wetland Indicators (Non-Sandy) • Soils appearing on hydric soils lists – Using the criteria for hydric soils, the NTCHS has developed a list of hydric soils. Be sure that the mapped soil description matches the sampled soil. 87 Manual Wetland Indicators (Non-Sandy) • Iron and Manganese concretions – Concretions >2mm in diameter and within 7.5cm of the surface are evidence that the soil is saturated for long periods near the surface. 87 Manual Wetland Indicators (Sandy Soils) • Not all indicators can be applied to sandy soils, in particular, soil color should not be used as an indicator in most sandy soils. • Additional indicators for sandy soils: – High organic matter content in surface horizon; – Streaking of subsurface horizons by organic matter; and – Organic pans. 87 Manual Wetland Indicators (Sandy Soils) • High organic matter content in surface horizon: prolonged inundation or saturation creates anaerobic conditions that greatly reduce oxidation of organic matter causing it to accumulate above or in the surface horizon. 87 Manual Wetland Indicators (Sandy Soils) • Streaking of subsurface horizons by organic matter: Organic matter is moved downward through sand as water table fluctuates. Sandy soil appears vertically streaked with darker areas. 87 Manual Wetland Indicators (Sandy Soils) • Organic pans: As organic matter is moved downward through sandy soils, it tends to accumulate at the point representing the most commonly occurring depth to water table. 87 Manual Wetland Indicators (Sandy Soils) • In recently deposited sandy material (i.e. Entisols), it may be impossible to find any of these indicators. In such cases, consider this as a natural atypical situation. • Entisols are identified as a “Problem Soil”. • If a problem soil is present, follow the procedures in the St. Paul District Corps of Engineers guidelines. Additional Materials to Review • In addition to the 87 Manual, delineators must also be familiar with the following publications: – Questions & Answers on 1987 Manual (CECW-OR, October 7, 1991); – Clarification and Interpretation of the 1987 Manual (CECW-OR, March 6, 1992); and – Guidelines for Submitting Wetland Delineations to the St. Paul District Corps of Engineers and Local Units of Government in the State of Minnesota (96-01078-SDE, April 17, 1996). Common Pitfalls • Not sampling below the A horizon. • Inconsistent hydric soil determinations. • Calling drained hydric soils non-hydric. • Using NRCS Field indicators in place of 87 Manual criteria. • Forgetting criteria 3 and 4 for hydric soils. • Not recognizing and adjusting for problem soils (mollisols, entisols, and red parent material).
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