A hydric soil is a soil that is saturated, flooded or ponded long enough during the growing season to develop anaerobic conditions in the upper part of the soil profile that favor the growth and regeneration of hydrophytic vegetation (USDA - SCS, 1991). A soil is inundated when the water table is at or above the soil surface. A soil is flooded if the water is moving across the soil surface as in a slough or on a floodplain.
A soil is ponded if the water is sitting on top of the soil with no movement to an outlet, as is the case with some depressions. A soil is saturated if the water table is within 6 inches of the soil surface for sandy textured soils or within 12 inches for loamy or clayey textured soils. These water table depths for each textural category will support a capillary rise of water to the soil surface. If the duration of saturation or inundation is long enough (greater than several weeks during the growing season), the oxygen content in the in the topsoil water will be exhausted. The subsequent anaerobic conditions in the soil result in an accumulation of organic matter and the reduction and movement of iron which produce a soil morphology that is identifiable in the field (hydric soil indicators).
The USDA - NRCS recognizes four (4) of the hydric soil indicators that are evidence of a water table at or above the soil surface for more than several weeks during the growing season. The hydric soil indicators are muck, mucky texture, gley colors, and sulfidic odor. A complete description of these indicators plus additional criteria needed for each indicator can be found in Soil and Water Relationships of Florida's Ecological Communities.
(Florida Soil Conservation Service, Staff, 1992). The remaining hydric soil indicators, shown in the table below, are recognized as evidence of saturatioof the top layer of soil for more than several weeks. These hydric soil indicators are also discussed in detail in the FL - SCS publication previously mentioned.
Hydric Soil Indicators of Saturation
Polychromatic Matrix (matrix stripping)
Iron and Manganese Concretions1
Distinct and Prominent Mottles1
Notes:1 For loamy and clayey soil textures only.
March 8, 2019 - 12:04pm
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