SPATIAL VARIABILITY AND KINETIC CONTROLS ON BIOGEOCHEMICAL PROCESSES: INSIGHTS INTO THE ROLE OF HYDROLOGIC VARIABILITY AND DONOR AVAILABILITY

Aqueous natural systems are inherently complex due to small-scale heterogeneities in nearly every conceivable environmental variable. Yet, the vast majority of environmental research today focuses on specific elements or compounds that pose human or ecosystem threats. While there is great need to tease out controls on the fate and transport of harmful chemicals in the environment there is still much to be learned about natural biogeochemical processes in relatively pristine environments, especially at dynamic boundaries such as the sediment-water interface. Our ability to successfully implement strategies for natural attenuation and bioremediation of specific contaminants is rooted in our understanding of complex processes occurring in the natural environment. This study presents results from research aimed at identifying and teasing out controls on biogeochemical processes under a range of environmental conditions. High resolution samplers, “peepers”, were used to evaluate the spatial variability of geochemical processes (ex. iron and sulfate reduction) under different hydrologic conditions in a relatively pristine, but hydrologically dynamic, reservoir system. Peepers were used to collect water samples at 1 cm intervals for profiles spanning the interface between surface water and underlying sediments. Laboratory microcosms were also constructed to evaluate the role of 1) electron donor availability, 2) electron acceptor availability and 3) abundances of microbial species. Results from peepers showed steep biogeochemical gradients in pore-water at the cm-scale. Results from laboratory microcosms found that addition of electron donor (lactate and acetate) stimulated faster reduction rates, though results varied for different electron acceptor and substrate conditions. Results from both in-situ peepers and laboratory microcosms revealed the importance of conducting research in a wide variety of environments under a range of environmental conditions. Natural system complexities are the biggest factor controlling biogeochemical processes and thus our ability to successfully implement remediation strategies in a given environment. More emphasis should be given to teasing out the controls on key biogeochemically-mediated redox reactions in both pristine and contaminated systems.