SREL Reprint #3792

Microbial community dynamics and cycling of plutonium and iron in a seasonally stratified and radiologically contaminated pond

Nancy Merino1, Naomi L. Wasserman1, Fanny Coutelot2,3, Daniel I. Kaplan4, Brian A. Powell2,3,5,
Yongqin Jiao1, Annie B. Kersting1, and Mavrik Zavarin1

1Glenn T. Seaborg Institute, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA 94550, USA
2Department of Environmental Engineering and Earth Sciences, Clemson University,
Anderson, SC 29625, USA
3Center for Nuclear Environmental Engineering Sciences and Radioactive Waste Management,
Clemson University, Anderson, SC 29625, USA
4Savannah River Ecology Lab, University of Georgia, Aiken, SC 29802, USA
5Savannah River National Laboratory, Aiken, SC 29625, USA

Abstract: Plutonium (Pu) cycling and mobility in the environment can be impacted by the iron cycle and microbial community dynamics. We investigated the spatial and temporal changes of the microbiome in an iron (Fe)-rich, plutonium-contaminated, monomictic reservoir (Pond B, Savannah River Site, South Carolina, USA). The microbial community composition varied with depth during seasonal thermal stratification and was strongly correlated with redox. During stratification, Fe(II) oxidizers (e.g., Ferrovum, Rhodoferax, Chlorobium) were most abundant in the hypoxic/anoxic zones, while Fe(III) reducers (e.g., Geothrix, Geobacter) dominated the deep, anoxic zone. Sulfate reducers and methanogens were present in the anoxic layer, likely contributing to iron and plutonium cycling. Multinomial regression of predicted functions/pathways identified metabolisms highly associated with stratification (within the top 5%), including iron reduction, methanogenesis, C1 compound utilization, fermentation, and aromatic compound degradation. Two sediment cores collected at the Inlet and Outlet of the pond were dominated by putative fermenters and organic matter (OM) degraders. Overall, microbiome analyses revealed the potential for three microbial impacts on the plutonium and iron biogeochemical cycles: (1) plutonium bioaccumulation throughout the water column, (2) Pu–Fe-OM-aggregate formation by Fe(II) oxidizers under microaerophilic/aerobic conditions, and (3) Pu–Fe-OM-aggregate or sediment reductive dissolution and organic matter degradation in the deep, anoxic waters.

SREL Reprint #3792

Merino, N., N. L. Wasserman, F. Coutelot, D. I. Kaplan, B. A. Powell, Y. Jiao, A. B. Kersting, and M. Zavarin. 2023. Microbial community dynamics and cycling of plutonium and iron in a seasonally stratified and radiologically contaminated pond. Scientific Reports 13(19697).

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).