The soils that one finds in wetland areas differ significantly from the soils of upland areas. Referred to as hydric soils, technically they include any soil that is covered or inundated with water for two weeks or more during the growing season. This somewhat vague definition is difficult to utilize from a regulatory perspective and, in its stead, hydric soil field indicators are most often used. These rely on the presence of properties most often associated with hydric soils such as thick organic deposits near the surface, mottled soils and even smell (hydrogen sulfide from decomposition can cause a “rotten egg” odor.)

The U.S.D.A. Natural Resources Conservation Service provides an impressive amount of material on soil field indicators that may be accessed by at http://soils.usda.gov/.