Little Wind
Slate Head Water
Riverton Fall

Floodplain Hydro-Biogeochemistry Science Focus Area

The SLAC SFA scientific program addresses the grand challenge: How do biogeochemical and transport processes in shallow alluvial groundwater systems (bedrock to soil) couple to one-another and control water quality under hydrologically variable conditions? We are identifying hydro-biogeochemical mobilization and retention processes for C, nutrients (P, S, and Fe) and contaminants (U, Mo, Pb, Zn) at molecular to meter scales. Emphasis is placed on understanding the spatio-temporal coupling of biogeochemical and hydrological processes in soil, the capillary fringe, and the upper portion of the saturated zone. Field studies at the mining impacted Coal Creek and Slate River head-watersheds (Gunnison county, CO) and the former ore processing site in semi-arid Riverton, WY are combined with laboratory experiments to understand the impact of timing, duration, and intensity of wet-dry cycling, transport direction, organic carbon content and sediment texture on redox and nutrient and contaminant mobilization. Quantitative process representations that are developed within the SLAC SFA program will be shared with collaborating SFAs and the wider community for incorporation into larger-scale models. Results from this work will advance short- and long-term prediction of water quality by DOE and multi-agency collaborations.

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SLAC SFA 2020 flyer

Meet the SLAC SFA scientists videos:

Bradley Tolar's video: Current work being done at Slate River, CO

Zach Perzan's video: Short-term water quality forecasting with continuous-time recurrent neural networks

Tristan Babey's video: Simulation of biogeochemical cycling in an alluvial aquifer

John Bargar's video: How an x-ray microprobe can solve groundwater quality problems

John Bargar at Slate River, CO

Recent Research Highlights

Exported organic carbon promotes reducing conditions and redox cycling in oxic aquifers

N. Kumar, et al. “Redox heterogeneities promote thioarsenate formation and release into groundwater from low arsenic sediments.” Environ. Sci. Te

chnol. 54, 6, 3237–3244 (2020). [DOI:10.1021/acs.est.9b06502] thioarsenate-formation-release-groundwater-from-low-arsenic-sediments

Highlight Slide

The Science: Aquifers contain abundant organic-enriched, fine-grained, and sulfidic lenses. While it is widely understood that these heterogeneities are important sources of organic carbon, Fe(II), and S, the reactive transport mechanisms.... Read more >

Soil organic matter controls Pb release during redox cycles in floodplain soils

Dewey, C. et al. “Porewater Lead Concentrations Limited by Particulate Organic Matter Coupled with Ephemeral Iron(III) and Sulfide Phases during Redox Cycles within Contaminated Floodplain Sediments.” Environ. Sci. Technol. 9, 5878-5886 (2021).

Highlight Slide

The Science: Lead contamination in soils is a major threat to water quality. Although Pb tends to occur in sparingly soluble minerals, changes in dissolved oxygen concentrations can promote dissolution of these minerals, potentially causing... Read more >

Spatial and Compositional Heterogeneities Control Zn Retention Mechanisms in a Simulated Aquifer

Engel, M., Boye, K., Noël, V., Babey, T., Bargar, J.R., Fendorf, S. (2021) Simulated Aquifer Heterogeneity Leads to Enhanced Attenuation and Multiple Retention Processes of Zinc. Environmental Science & Technology.

Highlight Slide

The Science: Alluvial aquifers are an essential source of groundwater worldwide, particularly for water storage purposes.  Fine-grained lenses of clay and organic matter, enriched in iron and sulfur, are abundant within aquifers and support cycling of... Read more >

For more research highlights read more>

Contacts and Websites

Principal Investigator

John Bargar,, (650) 926-4949


This program is funded by the Subsurface Biogeochemistry program within the U.S. Department of Energy, Office of Biological and Environmental Research, Climate and Environmental Sciences Division. Funding for SSRL is provided by the Department of Energy, Office of Basic Energy Sciences.

BER Program Managers

David Lesmes,, (301) 903-2977

Paul Bayer,, (301) 903-5324