What Are Hydric Soils?

One of the indicators of a wetland is hydric soil. This, along with hydrology and vegetation, is what helps to determine a wetland from other waters. When surveying, or delineating a wetland area, wetland soils must be present, otherwise, it cannot be declared a wetland. But what makes a soil hydric? The definition for hydric soil is that soil that has been saturated by flooding or ponded water for a sufficient period to create an anaerobic, or oxygen poor, area in its upper section.

Hydric soils can have a top layer of varying thicknesses of organic matter or plant material. Some other characteristics of hydric soil are roots or the channel left by decomposed roots. Another feature is called redoximorphic, which means iron in the soil is depleted, leaving a reddish area or mottle. To help out in determining soils for an area, there are national lists available from the US Department of Agriculture or the Natural Resource Conservation Service (NRCS). These lists are filed by county and give maps and descriptions of the different soils that are found within that county. It's easier to go into the field having some idea what to look for, so it's a good idea to study the list first.

The lists can also assist developers by stating whether or not a particular area has sufficient soil to enable building sites. It lists which soils would be poor due to wetness or poorly drained conditions. Since it lists the hydric soils, it would also show at a glance which areas are probably wetlands. From soil data, a site can be studied to determine if periodic flooding has occurred and how easily it might drain due to the permeability of the soil. As good as the soil survey maps are, they should not be completely relied upon, because they could be out of date or may not include enough detail. They are supposed to be used as a general overview. Sometimes an area can change. Where there once wasn't a wetland or creek channel, there could be over time. Flooding, fire or landscaping can change the morphology of streams and the frequency of flooding, thereby creating hydric soils after a while.

Drought, while a natural occurrence, can alter the environment and change the soil characteristics. However, when there are hydric soils, it assures that the necessary water, or hydrology, is there. So, if you find hydric soil, you really only need to look for wetland vegetation to determine if an area is indeed a wetland.