Dynamics of hydric soil formation across the edge of a created deep marsh

Abstract

Hydric soils are identified on-site using visible features called “field indicators.” It is not known how long it takes for these indicators to form nor whether they occur in created wetlands less than 5-years old. This study evaluated chemical and morphological changes in a created wetland to monitor the development of hydric soil field indicators over time. A deep marsh, created in 1989, was studied from 1992 through 1994 at the Des Plaines River Wetlands Demonstration Project near Chicago, Illinois, USA. Soil and water samples were collected twice a year from two transects having plots in the following landscape positions: in the marsh, along the marsh edge, in a transition zone to the upland, and in the upland. Detailed profile descriptions were also completed twice per year. In 1994, the soils were classified from the marsh to upland as Typic Endoaquoll, Mollic Endoaquept, Aquic Hapludalf, and Ochreptic Hapludalf. Soil pH values ranged from 7.3 to 7.8 in the upper 15 cm. Carbonates were closest to the surface in the marsh and edge positions. Organic C levels were similar among soils throughout the study at approximately 20 g C/kg soil. Redox potentials and water-table measurements indicated that soil in the marsh and edge positions met the definition of hydric soils throughout the study, while upland positions did not, and soil in the transition positions met the definition in some years. Hydric soil field indicators formed by Fe reduction developed over time in the marsh and edge plots and in some plots of the transition to the upland. The depleted matrix indicator, which formed by the reduction and removal of Fe from the soil matrix, gave the most consistent results for identifying hydric soils. Full development of the indicator in all edge plots was complete 5 years after the marsh was constructed. Indicators formed by organic matter accumulation (organic bodies) also developed in the marsh within this period.