Dynamic Hydrology Shapes Microbial Activity and Biogeochemistry in a Great Lakes Coastal Estuary
Authors
Lauren E. Kinsman-Costello1* (lkinsman@kent.edu), Chelsea Monty-Bromer2, Sai Prasanna Chinthala2, Bukola Adesanmi2, John M. Senko3, Joshua Davis3, Thomas Quick3, Timothy H. Morin4, Ethan Kubatko5, Gil Bohrer5, Elizabeth M. Herndon6, Erin Eberhard1, Terry Heard3, Chelsea Smith1, Michael Back1, Erin Hassett4, Talia Pope1
Institutions
1Kent State University, Kent, OH; 2Cleveland State University, Cleveland OH; 3University of Akron, Akron, OH; 4The State University of New York, College of Environmental Science and Forestry, Syracuse, NY; 5The Ohio State University, Columbus, OH; 6Oak Ridge National Laboratory, Oak Ridge, TN
Abstract
The propensity for redox processes to occur is sometimes predicted by measured or assumed redox potential (Eh), but process measurements often deviate from predictions based on the thermodynamic “redox tower” paradigm. Researchers hypothesize that poorly measured, granular scale soil heterogeneity causes apparent departures from thermodynamic exclusion principles at bulk scales with consequences for biogeochemical cycling, which are not currently resolved in ecosystem, regional, or global scale models. Researchers will combine empirically measured traditional biogeochemical indicators with newly developed electrochemical approaches to determine how fluctuating hydrology shapes redox regimes and processes. Specifically, the objectives are to: (1) relate dynamic hydrology in a freshwater terrestrial-aquatic interface wetland (Old Woman Creek, OH) to redox regimes; (2) determine how redox heterogeneity drives elemental cycling at multiple scales, and; (3) assess the sensitivity of process-based models to the inclusion of fine-scale variability in redox conditions. Researchers will use zero resistance ammetry (ZRA) to exploit redox disequilibria among discrete zones to detect the distributions, extents, and kinetics of biogeochemical processes. ZRA can measure electrical current that arises from microbially induced redox disequilibrium. In 2021 to 2022, researchers worked to refine a ZRA sensor system that detects electrochemical signals across the sediment-water interface and into sediments at nested scales (sub-millimeter to decimeter) at a shallow location (< 10 cm surface water) in the Old Woman Creek wetland. The team deployed the manufactured sensor system from late June through November in 2022. During that time, the sensors experienced fluctuating hydrologic conditions with depths ranging from zero (no standing water) to at least 50 cm. ZRA sensors detected redox disequilibria, and thus heterogeneous redox conditions, over spatial scales as small as 2 mm.
Concurrent measurements of greenhouse gas fluxes measured in vegetated and unvegetated plots using static chambers in the vicinity indicated that ecosystem functions also responded to fluctuating hydrology. In 2023, the ZRA sensors will be re-deployed in multiple locations simultaneously with traditional redox potential (Eh) electrode sensors. The team will monitor concentrations of redox process substrates and products in surface water, pore water, and sediment samples to relate electrochemical signals to biogeochemical processes. To assess the importance of fine-scale heterogeneity in ecosystem-scale processes, researchers are incorporating microsite heterogeneity into the ecosys ecosystem model.