KINETIC CONTROLS ON SULFATE REDUCTION DESCRIBED USING IN SITU TECHNIQUES IN A WETLAND-AQUIFER SYSTEM

Describing the kinetic controls on important biogeochemical processes such as sulfate reduction is critical for understanding microbial respiration, carbon cycling and contaminant degradation. Current rate estimates have a wide range in the literature making it difficult to determine representative rates for a given system. This variability in rate data may be explained by varying kinetic controls on reactions. In situ field experiments conducted at a landfill-leachate contaminated aquifer-wetland system at the Norman Landfill research site, Norman, OK were designed to explore the complexities controlling the kinetics of microbial sulfate reduction including physical, microbiological, and chemical controls. Push-pull tests were designed to evaluate sulfate reduction rates at the wetland-aquifer interface. Anaerobic aquifer water containing abundant sulfate was injected into sulfate-depleted wetland porewater. Injected ground water subsequently was withdrawn and analyzed for geochemical indicators of sulfate reduction. Complexities in rate data such as the presence of a lag phase, changing rate order and spatial variability were observed and are hypothesized to be linked to changes in microbial community structure. Subsequent experiments explored the response of native microorganisms to introductions of fluids containing sulfate and electron donor. In situ experiments involved colonization of a substrate by microorganisms native to the wetland sediments. Additional in situ tests were performed to evaluate spatial variability in sulfate reduction rates. Geochemical data collected in a radial array around a push-pull well after injection of a sulfate-rich test solution showed that rates of sulfate reduction were spatially variable and related to the mixing interface between injected and native waters.