Deciphering the Role of Anaerobic Microsites for Hot Spot and Hot Moment Dynamics of Metal Redox Chemistry and Methane Emissions Within Riverine Floodplains
Authors
Amrita Bhattacharyya1* (abhattacharyya@usfca.edu), Elizabeth L. Paulus2, Hermes Ruiz1, Kathryn Farber1, Eldridge Walker3, Amalia Kokkinaki1, Ruth M. Tinnacher3, Kristin Boye2, Vincent Noël2
Institutions
1University of San Francisco, San Francisco, CA; 2SLAC National Accelerator Laboratory, Menlo Park, CA; 3California State University East Bay, Hayward, CA
Abstract
Rates and reactions of biogeochemical (BGC) processes vary in space and time to produce hot spots and hot moments of elemental cycling. These dynamics are particularly enhanced at terrestrial-aquatic interfaces (TAIs), such as floodplains with strong redox fluctuations. Anaerobic microsites are zones of oxygen depletion in otherwise oxic soil environments, which can serve as redox hot spots, generating and exporting anaerobic BGC products, such as methane (CH4). Despite the importance of anaerobic microsites in TAIs, significant knowledge gaps still exist regarding their abundance, spatial distribution, and specific contributions to BGC processes, especially CH4 production. Hence, there is limited data to support model parameterizations and predictions of the impacts of anaerobic microsites on BGC functions at the field scale.
The main objectives of this study are: (1) to quantify the abundance and the impact of anaerobic microsites on methanogenesis and link this to elemental speciation and abundance of trace metals of importance for methane-cycling; (2) to compare microscale anaerobic microsite characteristics with macroscale observations on the field scale for methane emissions; and (3) to quantify reaction kinetics of relevant BGC processes within anaerobic microsites.
The Laboratory for Observing Anaerobic Microsites in Soils (LOAMS) is a novel approach that utilizes the fact that X-ray fluorescence 2D mapping can reliably detect, quantify, and characterize anaerobic microsites in natural soil core slices (up to 100 cm long) at µm-scale resolutions. To date, LOAMS investigations have revealed direct evidence of iron (Fe) and sulfur (S) reducing microsites in predominantly oxic toeslope soils (Pumphouse Lower Montane site by East River, CO), where anaerobicity would typically not be expected. In parallel, the microbial data suggest the presence of methanogens and methanotrophs in similar Fe and S reducing environments at both East and Slate River, CO sites. Researchers anticipate that the results will provide much needed quantification of hot spot and hot moment contributions to coupled BGC of redox-active and enzymatically important metals in relation to CH4 emissions in TAIs.