Effect of Hydrological Forcing on the Biogeochemical Transformation of Carbon and Greenhouse Gas Emissions in Riparian and Streambed Sediments
Authors
Martial Taillefert1* (mtaillef@eas.gatech.edu), Anthony Boever1, Chloe Arson2, Chengwu Jiang2, Thomas J. DiChristina1, Tianze Song1, Daniel I. Kaplan3, Kenneth M. Kemner4, Christa Pennacchio5, Stephen J. Callister6
Institutions
1Georgia Institute of Technology, Atlanta, GA; 2Cornell University, Ithaca, NY; 3Savannah River National Laboratory, Aiken, SC; 4Argonne National Laboratory, Argonne, IL; 5Joint Genome Institute, Berkeley, CA; 6Environmental Molecular Sciences Laboratory, Richland, WA
Abstract
Hydrological processes in riparian and hyporheic sediments create strong biogeochemical gradients and redox microniches that are metabolically influenced by temporal changes in precipitation, temperature, and stream discharge. The complex temporal and spatial variability of these processes and their effect on the transformation and exchange of carbon (C), nutrients, and greenhouse gases (GHGs) with surface waters are difficult to account for in reactive transport models. Reactive transport in these systems is traditionally simulated on the continuum scale using upscaled empirical parameters that are not able to reproduce the effect of biogeochemical reactions on pore scale heterogeneities and their feedback on biogeochemical rates. In this project, state-of-the-art in situ physical and geochemical measurements are combined with metaomic signals of the active microbial populations in riparian and hyporheic sediments of Steed Pond at the Savannah River National Laboratory to predict the role of hydrological forcing on the spatiotemporal transformation of C, nutrients, redox processes, and GHG emissions along this gaining and losing wetland stream. During Year 3, the data from two in situ electrochemical systems that monitored the temporal variations in pore water redox biogeochemistry at both a gaining and losing reach were correlated with monitoring well water levels and rainfall to determine how redox processes in the hyporheic zone are affected by hydrological forcing. In addition, the production of methane (CH4) in streambed sediments was compared to CH4 benthic fluxes measured simultaneously to investigate the role of vegetation in net GHG emissions under both gaining and losing conditions. In parallel, metagenomic signals from sediment slurry incubations designed to investigate the competition between anaerobic microbial processes in hyporheic sediments were analyzed using Pacific Northwest National Laboratory’s supercomputer COMPASS to identify the main microbial metabolic processes under various geochemical conditions. Finally, the main redox geochemical processes involved in the transformation of carbon were incorporated in the reactive transport model PFLOTRAN in both 2D and 1D to investigate how gaining and losing conditions affect redox processes. Along with the high spatial and temporal resolution of biogeochemical processes, the developed numerical models will predict how variations in hydrological forcing, competition between microbial metabolic processes, and porosity changes associated with biogeochemical feedback affect C and nutrient cycling as well as GHG emissions.