Hydric conditions and hydromorphic properties within a mollisol catena in Southeastern Minnesota

Wetlands are characterized by wetland hydrology, hydrophytic vegetation, and hydric soils. The multiparameter approach to wetland identification and delineation requires independent evaluation of all three diagnostic characteristics. Hydric soils can be determined from data collected under saturated and anaerobic soil conditions or by using accepted field indicators. The objectives of this research were to: (i) evaluate the presence of wetland hydrology and hydric soil conditions, (ii) examine associations between observed soil hydrology and soil morphologic properties, and (iii) evaluate current field indicators of hydric soils for their applicability to presumed hydric Mollisols. We used wells, piezometers, and tensiometers to measure saturated conditions, and Pt electrodes to measure anaerobic and reducing conditions for five soils along a hillslope transect from summit to drainageway in southeastern Minnesota. Saturated conditions were observed within 25 cm of the soil surface for all five soils for at least a few days each year between 1992 and 1995, mainly in the early spring and the late fall when soil temperatures at 50 cm were not always >5 °C. Only the soil in the drainageway was saturated and anaerobic during the microbial activity season in more than one year. Soil morphology reflects the presence of saturated and anaerobic conditions in the form of thick, black surface horizons. Absence of Fe concentrations and depletions in the upper 30 cm of presumed hydric soils may reflect the absence of Fe-reducing conditions as a result of saturated conditions when soil temperatures do not facilitate abundant microbial activity.