Institute for Wetland & Environmental Education & Research
Wetland Primer What Is Hydric Soil?
Frequently flooded and/or waterlogged soils associated with wetlands are called hydric soils, while lake and river bottoms have hydric substrates (since they don't support free-standing vegetation). Technically, any soil that is inundated (covered by water) for two weeks or more during the growing season in most years is considered a hydric soil. Most hydric soils have distinct properties that help separate them from better driained soils of uplands (drylands). These properties include thick organic deposits in the upper part of the soil (anaerobic conditions slow down oxidation of organic matter), grayish subsoils (due to lack of iron oxides), mottled soils (grayish subsoil with orangish, yellowish, or reddish mottles, reflecting a fluctuating water table, but prolonged saturation), a rotten egg odor coming from the upper part of the soil (hydrogen sulfide from organic matter decomposition), black sands (due to heavy organic coatings - muck - of sand grains), and blotchy sandy soils (with organic streaking or variable coloring of the sand due to differences in the amount of organic coatins of sand grains).
The U.S.D.A. Natural Resources Conservation Service has published a detailed listing of hydric soil field indicators. Contact your NRCS county or state office for a copy. They also have lists of "hydric soil map units" that can be used to help identify possible wetlands on their published county soil survey reports. These reports include large-scale maps showing soil types on the landscape.
Figure 4. Organic Soil composed of decomposed
leaves and stems.
Figure 5. Hydric mineral soil showing predominant gray
Figure 6. Dark-colored, hydric
soil of the Midwestern Prairies.
Figure 7. Soils from a meadow in
showing gray colored hydric soil from wet meadow and orange colored
subsoil of upland (non hydric) soil.