A hydric soil is a soil that is saturated, flooded, or ponded long enough during the growing season to develop anaerobic conditions. This lack of oxygen in the soil can lead to the formation of certain observable characteristics in wetland soils, such as a thick layer of organic matter (non-decomposed plant materials) in the upper part of the soil column.  Other observable features include oxidized root channels and redoximorphic features (concentrations and depletions of Iron and other elements, i.e., mottling, gleying).

In Michigan, the state's legal definition of wetland makes no mention of soils. However, the administrative rules do direct the use of soils as an indicator of the presence of water under abnormal circumstances or when signs of hydrology are not conclusive.   Many different types and textures of soils are found in wetlands including mucks, peat, loams, clays, and sands. Mucks and peat are obvious wetland soils, but even loam, clay, and sandy soils can be wetland soils if they are frequently saturated or inundated. Soil scientists can interpret soils in a way that describes the history of water exposure.

Short of hiring someone to do detailed borings across a site, an excellent overview of the types of soils likely to be found on site can usually be obtained through the use of a Modern Soil Survey produced by the U.S. Department of Agriculture, Natural Resources Conservation Service (NRCS). Soil surveys are available for most counties in Michigan and those unavailable will be completed soon.

Modern Soil Surveys have been produced by detailed field work translated into coded areas on aerial photographs. Each major soil series is identified throughout the county and described in text. Reviewing descriptions for soils on a parcel can provide a great deal of information about the likely presence or absence of wetland conditions. Descriptions, such as "poorly," "somewhat poorly," or "very poorly" drained soils, "unsuitable for building because of wetness," etc., should provide immediate flags that wetlands are likely to be present. Other useful information is seasonal depth to groundwater, typical vertical profiles, suitability of the soil for various purposes, etc.

To assist in identifying soils developed under conditions sufficiently wet to support wetlands, the NRCS, along with other federal agencies, developed a definition and listing of those soils termed "hydric."  If the name of a soil series or subgroup is included on this list, it should be considered to be a wetland soil. Other useful information included with the listing is the drainage class, high water table depth, likelihood of flooding, and permeability.

There are several limitations to using soil surveys and lists of hydric soils. First, they generally do not map "inclusions" of different soil types if the map units are less than 2 acres in size. These inclusions can be wetland soils within an upland soil series. Sometimes, the description will include the types of soils that are the most common inclusions in the series. Also, as for all information sources, there are occasional errors. Finally, as noted above, having a wetland soil present is not a legal requirement for an area to be a wetland. There are wetland soils that have been historically drained so that they no longer have wetland characteristics, and conversely, there are non-wetland soils that now support wetlands because of additional flow into the water table.

The following websites provide a wealth of information on how to identify hydric soils in the field and through use of Soil Surveys. The presence of a hydric soil confirms that the necessary hydrology has been present, at least for an extended period in the past. These websites also provide extensive information on the soils that are classified as hydric, and the physical indicators used in the field to identify hydric soils.

Hydric Soils of the United States

Field Indicators of Hydric Soils in the United States

Michigan Soil Survey Information

List of Published Soil Surveys