Simulating Greenhouse Gas Fluxes Across the Terrestrial–Aquatic Interface: A Spatially Explicit Approach

Authors

Debjani Sihi¹* (debjani.sihi@emory.edu), Alexandra Cory¹, Jianqiu Zheng², Taylor Cyle¹, Eric Davidson³, Patrick Megonigal⁴, Michael Weintraub⁵, Zoe Cardon⁶, Suzanne Thomas⁶

Institutions

¹Emory University, Atlanta, GA; ²Pacific Northwest National Laboratory, Richland, WA; ³Center for Environmental Science Appalachian Laboratory, University of Maryland–Frostburg, MD; ⁴Smithsonian Environmental Research Center, Edgewater, MD; ⁵University of Toledo, Toledo, OH; ⁶Marine Biological Laboratory, Woods Hole, MA

URLs

• https://ess.science.energy.gov/summary-of-environmental-system-science-projects-awarded-in-summer-2021/

Abstract

Terrestrial–aquatic interfaces (TAIs) undergo frequent variations in soil saturation that result in heterogeneous distribution of greenhouse gas (GHG)–regulating components—such as dissolved organic carbon content, terminal electron acceptor (TEA) availability, pH, and nutrient abundance. The formation of soil microsites (i.e., microscale regions with unique biogeochemical characteristics compared to the surrounding area) enable seemingly disparate processes—such as oxic respiration and methanogenesis—to occur simultaneously within one soil column. Most GHG flux models fail to predict such co-occurrences as they assume a homogeneous distribution of GHG-regulating components across a given soil column. Here, the project addresses this discrepancy by developing a spatially explicit model of GHG fluxes in TAIs. To mimic in situ conditions, researchers conduct incubations of intact soil cores collected from a hydrology gradient in Old Woman Creek, OH, near Lake Eerie, which the team subjects to hydrological fluctuation. High-resolution two-dimensional maps of dioxygen concentration are obtained using colorimetric planar oxygen optode imaging. Spatially specific measurements of pH and redox state are obtained using microelectrodes, and dissolved nutrient/TEA abundances are obtained from extracted porewater samples. GHG fluxes are measured continuously using a Cavity Ring-Down Spectrophotometer (Picarro G2508). These measurements are used to generate probability distribution (or density) functions of GHG-regulating components. By employing a model-experiment framework and constraining a spatially explicit GHG flux model (DAMM-GHG) coupled with a redox-reactive network module (AquaMEND), the project assesses whether capturing redox heterogeneity in soil microsites aids with improved predictions of GHG fluxes from TAIs.