Long-Term Evaluations of Seasonally Saturated “Wetlands” in Western Kentucky

A research program was initiated in 1993 to monitor water-table depth, redox potential, and soil matric potential at four sites. The selected sites were woodlands with water tables present at or near the soil surface during late winter and spring. Soil morphology was described and permanent monitoring instruments were installed on eight soils. Hydrosequences of three soils, which represented an Endoaquept-Fragiaqualf-Fraglossudalf and a Fraguaqualf-Fraglossudalf-Fraglossudalf sequences, were studied at two sites. An Epiaqualf and a Fragiaqualf were monitored at each of the remaining sites. Six of the eight soils experienced wetland hydrology in most years, while the other two exhibited sporadic saturation events above 25 cm. Saturated conditions occurred mainly in late winter and spring, with longest duration in the lowest landscape positions. On the wettest soils, redox levels <200 mV developed during late winter and continued into the growing season. Of the six soils meeting the hydrology criterion only three experienced both, functional hydric soil conditions (<200 mV redox potential) and exhibited definitive hydric soil indicators. However, hydric soil indicators were also present in two of the three other soils that developed only moderately reduced conditions (<350 mV). In contrast, only one of the six soils with wetland hydrology did not meet the hydrophytic vegetation criterion, while one nonhydric soil met the criterion. The presence, depth, and quality of fragipans appeared to influence the expression of hydric conditions through episaturation, endosaturation, and amphisaturation processes, creating a range of aquic and oxyaquic conditions. These findings emphasize the complexity of seasonally saturated wetland ecosystems and the difficulties in assessing and implementing wetland identification and delineation criteria.