BIOGEOCHEMICAL PROCESSES TO ASSESS THE WATER QUALITY IMPROVEMENT FUNCTION OF MITIGATED AND REFERENCE WETLANDS

A key function of wetlands is the capacity to protect down gradient surface water bodies from excess nutrient and sediment loading. Biogeochemical carbon, nitrogen, and phosphorus cycling processes in soils largely determine the water quality improvement function of wetlands. Historically, most of the wetlands in Kentucky have been lost due to agriculture and mining activities, which has resulted in a corresponding decrease in the aerial extent of nutrient transforming potential. More recently, there has been interest in restoring and recreating wetlands with the goal of regaining this potential. Presently, it is unknown how well these systems function compared to their natural counterparts. The objectives of this research were to (i) develop a series of measurements to assess biogeochemical nutrient and carbon cycling processes in wetlands and (ii) compare cycling rates in bottomland hardwood forest reference wetlands and mitigated wetlands of various ages in western Kentucky. Seventeen wetland sites of various mitigation ages (0 to > 30 years) and reference standard wetland sites of the bottomland hardwood class in western Kentucky were selected with the cooperation of the Army Corps of Engineers. Litter and soil samples (0-5 cm depth, 5-20 cm depth) were collected in the summer and fall of 2001 and incubated in laboratory microcosms for the determination of biogeochemical processes including carbon storage and cycling (total and dissolved carbon, aerobic and anaerobic carbon mineralization, methanogenesis), nitrogen storage and cycling (total N, ammonium, nitrate, N mineralization, nitrification, denitrification), and phosphorus storage and cycling (total, labile and non-labile P, P mineralization). In situ gas fluxes of CO₂, CH₄ and N₂O were also determined. Results show major differences in nutrient storage and transformation rates between soil layers and wetland sites, which were also a function of soil type and water content. Results suggest that soil biogeochemical properties can be a useful diagnostic tool to assess the water quality improvement function of restored wetland ecosystems.