Microbial metabolic activity and biogeochemical reaction networks in redox cycled alluvial systems
EMSL Project ID
50365
Abstract
Redox conditions and related switches in microbial metabolic activities exert primary control over the stability of carbon, nutrient, and contaminant stocks in alluvial systems, such as floodplains. This project focuses on a uranium-contaminated floodplain near Riverton, WY, where significant seasonal fluctuations in redox conditions are indicated by temporary and spatially heterogeneous presence of sulfides, dissolved Fe and Mn (reducing conditions), and Fe oxides (oxidizing conditions). These fluctuations appear tied to water saturation and organic matter availability, and they drive the export of organic carbon, nutrients, and contaminants (U, Mo) to groundwater and surface water. What remains unresolved, are the detailed underlying reaction networks that connect microbial metabolism, redox reactions, organic matter transformations, and contaminant export in response to hydrological changes. Thus, our overall goal is to identify the principle reactions, the extent and timing of shifts from oxidizing to reducing (and vice versa) conditions, their impact on microbial communities, and the thresholds that trigger these redox transitions. To accomplish these objectives, we require a suite of methods available from JGI and EMSL to complement our existing spectroscopic, geochemical, and microbiological workflows. We propose analysis of the stability and function of active microbial communities at Riverton, paired with high-resolution fingerprinting of dissolved and colloidal/complexed chemical species (including organic matter and metals) from samples collected throughout a full runoff-drainage hydrologic cycle. These analyses will inform a reactive transport model capable of testing and projecting the sensitivity of such alluvial sediments to hydrologic perturbations, sediment texture, and organic matter content in order to broaden our understanding of important alluvial element cycles. Within soils and sediments, the capillary fringe constitutes a hotspot for microbial metabolic activity and biogeochemical processes. In alluvial systems the capillary fringe is particularly dynamic due to extensive water table fluctuations, resulting in strong redox oscillations and related switches in microbial metabolic activities. We know that redox-driven reaction switches are tied to water saturation and organic matter availability, and that they regulate the retention, transformation, and release of organic carbon, nutrients, and contaminants with impact on groundwater quality. However, our ability to accurately model redox transitions in the capillary fringe and variably saturated sediments and predict their impact on water quality is nascent. What is critically needed is (i) an identification of key microbial functional guilds and understanding of their metabolic activity in relation to hydrologically impacted geochemical conditions, (ii) detailed knowledge of key thresholds and environmental triggers of biotic and abiotic reactions, and (iii) conceptual and numerical reaction networks that accurately connect organic matter to microbial metabolism and resulting geochemical transformations in response to hydrological changes. Further, linking biogeochemical reactions in variably saturated sediments to the transport of carbon, nutrients, and contaminants requires improved knowledge of which phases are mobile under various redox conditions. We aim to address these knowledge gaps by: (i) capturing key redox transition periods and co-occurring changes in microbial presence and metabolic activity; (ii) performing concomitant molecular-level identification of C, N, Fe, S, and metal contaminant (U, Mo) transformations; and (iii) correlating these with the mobility of these elements. Our primary model site is a uranium-contaminated floodplain near Riverton, WY, where seasonal and episodic inversions in redox conditions are indicated by the transient and spatially heterogeneous presence of sulfides, dissolved Fe and Mn (reducing conditions), and Fe oxides (oxidizing conditions), and are associated with mobilization of contaminants (U, Mo). To address gaps in knowledge and accomplish our objectives, we require a suite of methods available from JGI and EMSL that complement our existing spectroscopic, geochemical, microbiological, and modeling workflows. We propose to analyze the stability and function of active microbial communities at Riverton, paired with high-resolution fingerprinting of dissolved and colloidal/complexed chemical species (including organic matter and metals) from samples collected throughout a full runoff-drainage hydrologic cycle. Further, we propose controlled laboratory experiments targeted at elucidating the key thresholds and triggers that promote switches in microbial metabolic activity and redox reactions, as well as the mechanisms and phases responsible for contaminant mobilization to groundwater. These analyses will inform a reactive transport model capable of testing the sensitivity of alluvial systems to hydrologic perturbations, sediment texture, and organic matter content. Such model advancements are urgently needed to broaden and improve our predictive understanding of important elemental cycles in the capillary fringe and variably saturated zones, which have large-scale impacts on watershed function and groundwater quality.
Project Details
Project type
FICUS Research
Start Date
2018-10-01
End Date
2021-03-31
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members
Related Publications
1. Boye, K.; Kumar, N.; Noel, V.; Spielman, L. E.; Barragan, L.; Planer-Friedrich, B.; Besold, J.; Bargar, J. R.; Fendorf, S. (2019). Influence of redox interfaces on metal(loid) contaminant mobility in shallow alluvial groundwater aquifers. Presented at ACS National Fall Meeting, San Diego, CA, Aug 25-29
Bargar, J.R., Boye, K., Fendorf, S., Francis, C., Maher, K. 2019. SLAC Groundwater Quality Scientific Focus Area 2019 Annual Report
Engel, M.; Boye, K.; Fendorf, S. (2019) Heavy metal mobility in a model aquifer exhibiting redox heterogeneities. Presented at AGU Fall Meeting, San Francisco, CA, Dec 9-13. [Invited talk].
John R. Bargar, Callum Bobb, Kristin Boye, Christopher A. Francis, Kate Maher, Bradley B. Tolar. 2020. "Stability of Floodplain Subsurface Microbial Communities Through Seasonal Hydrological and Geochemical Cycles." Frontiers in Earth Science 8 doi.org/10.3389/feart.2020.00338
Noël V., Kumar, N., Barragan, L., Boye, K., Bargar, J.R. (2019) Colloid formation driven by redox processes: impact on groundwater quality in shallow alluvial aquifers. American Chemical Society. San diego, CA, USA [Talk]
Noël, V., Kumar, N., Boye, K., Kukkadapu, R., Bargar, J.R., Brown, G.E. Jr., Williams, K.H. (2019) SLAC Groundwater Quality SFA: Mechanisms controlling colloid formation and impact on water quality in alluvial sediments. Environmental System Science (ESS) PI Meeting, Potomac, Maryland, USA [Poster]
Tolar, B. B.; Boye, K.; Bobb, C.; Francis, C. A.; Bargar, J. R. (2019) Stability of microbial communities through seasonal hydrological transitions and the resulting biogeochemical redox response. Presented at AGU annual meeting, San Francisco, CA, Dec 9-13. [Talk].
Tolar, B. B., Boye, K., Bobb, C., Spielman, L. E., Cardarelli, E., Bargar, J. R. and Francis, C. A. (2019). SLAC Groundwater Quality SFA: Biogeochemical redox responses of soil microbial communities to seasonal hydrological transitions at Riverton, WY. Presented at the 2019 Environmental System Science (ESS) PI Meeting, Potomac, MD. Apr 30-May 1. [Poster]
Tolar, B. B., Boye, K., Bobb, C., Spielman, L. E., Francis, C. A. and Bargar, J. R. (2019). Microbial Signatures of Seasonal Redox Transitions in a Uranium-Contaminated Floodplain. Presented at the Association for the Sciences of Limnology and Oceanography 2019 Aquatic Sciences Meeting, San Juan, Puerto Rico. Mar 1. [Talk]