Integration of Omics into a New Comprehensive Rate Law for Competitive Terminal Electron-Accepting Processes in Reactive Transport Models

Surface waters represent important sources of alternate energy and drinking water in the United States, and characterizing the biogeochemical processes that affect the quality of surface waters is relevant to the BER mission. Biogeochemical processes in the underlying sediments regulate the release of carbon, nutrients, and contaminants to the overlying waters and thus influence water quality. Biogeochemical processes in sediments are dynamic and depend on a variety of factors, including the deposition and remobilization of solid material and changes in redox conditions in response to variations in water discharge. In turn, wetlands are important natural filters of surface waters which may either trap, metabolize, or mobilize nutrients and contaminants depending on the intensity of biogeochemical processes. Despite their importance, the dynamic of biogeochemical processes regulating the release of nutrients and contaminants in the sediments of streams and wetlands and their role in the transformation of carbon cannot be predicted accurately by the current reactive transport models. These models largely rely on detectable changes in geochemical conditions to activate metabolic processes, do not accurately account for the competition between microbial processes, and poorly constrain the effect of hydrological perturbations on biogeochemical processes. In this project, new rate laws will be developed for reactive transport models that rely on a combination of transcriptomics and geochemical signatures to identify the underlying anaerobic microbial processes in stream and wetland sediments, describe the competition between the dominant metabolic processes involved in the release of nutrients and the mobilization of contaminants such as U and Hg, and more accurately quantify carbon transformation processes and the response of microbial processes to changes in redox conditions associated with hydrological forcing. These rate laws will be optimized in sediment slurry incubations of Steeds Pond at the Savannah River Site, where iron and sulfate reduction alternate seasonally and uranium is mainly found in the solid phase, and from East Fork Poplar Creek at the Oak Ridge National Laboratory facility, where nitrate reduction, iron reduction and mercury transformations are significant. State-of-the-art analytical (i.e. voltammetric microelectrodes, X-ray absorption spectroscopy) and molecular (metatranscriptomic and real-time qPCR) techniques will be used to characterize the biogeochemical processes in the sediments of both sites and follow the evolution of the geochemistry, microbial community structure, and functional gene expression in the slurry incubations. These measurements will be used in successive inverse modeling approaches that fix processes and optimize parameters in incubations of increasing complexity. The optimized reaction network will then be used in a forward reactive transport model to test our ability to reproduce the transition of metabolic processes over the time course of flow-through incubations. Rate laws that account for competitive biogeochemical reactions in complex microbial communities are critical for predicting the fate of uranium and mercury contaminations in surface waters and accurately quantifying carbon transformation processes in the underlying sediments. These topics are relevant to both the SBR and TES programs, as anaerobic respiration reactions play significant roles in a variety of sedimentary environments, including permafrost and tropical soils. To realize these objectives, we have assembled an interdisciplinary geochemistry and microbiology research team with expertise in metal reduction, electrochemistry, modeling, molecular genetics, and 'omic' technologies, that will complement the synchrotron, uranium, and mercury analytical capabilities of the Argonne and Oak Ridge SFAs.