Hydric Soils as a Part of Water Treatment in Wetland Systems

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Hydric Soils as a Part of Water Treatment in Wetland Systems

Most basically, a hydric soil is defined as "A soil that is saturated, flooded, or ponded long enough during the growing season to develop anaerobic conditions in the upper part (Kent, 1994, p. 26)." Included by this definition in the United States Department of Agriculture/Soil Conservation Service's list Hydric Soils of the United States are all of the poorly drained and very poorly drained soils and most of the somewhat poorly drained soil series.

Hydric soils are further categorized into two major groups: mineral soils and organic soils. Histosols (organic soils) typically contain at least 46 cm of organic matter in the upper part of the soil profile. They are
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Organic soils are readily identifiable by the relatively high percentage of poorly decomposed organic matter in the soil matrix. Frequently organic soils can be recognized by their color - very dark chromas and dark hues (10 YR 2/1, etc.).

Thick organic surface layers (20-40 cm) called histic epipedons that overly hydric mineral soils develop as a result of prolonged saturation in the root zone. Aquic and peraquic moisture regimes are characterized by elevated groundwater levels. Peraquic moisture regimes occur when groundwater is always at or near the soil surface. Aquic moisture regimes are reducing and because of saturation are nearly free of dissolved oxygen during the growing season. The presence of sulfidic material is indicative of permanently saturated soil conditions. Reducing conditions are recognizable in the field using a test kit.

Color is a most useful indicator for hydric mineral soil. Soils with water at or near the surface for most of the year may become gleyed, taking on a dull gray, bluish, or greenish color as oxidized (ferric) iron is reduced to ferrous and removed from the soil. Mottling occurs where the water table fluctuates periodically. Longer periods of soil saturation and anaerobic conditions, followed by aerobic conditions, turns manganese ions into oxides which are deposited as concretions. Streaking of subsurface horizons occurs as organic matter is

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