Influences of organic carbon speciation on hyporheic corridor biogeochemistry and microbial ecology

James C. Stegen (), Tim Johnson, James K. Fredrickson, Michael J. Wilkins, Allan E. Konopka, William C. Nelson, Evan V. Arntzen, William B. Chrisler, Rosalie K. Chu, Sarah J. Fansler, Emily B. Graham, David W. Kennedy, Charles T. Resch, Malak Tfaily and John Zachara
Additional contact information
James C. Stegen: Pacific Northwest National Laboratory
Tim Johnson: Pacific Northwest National Laboratory
James K. Fredrickson: Pacific Northwest National Laboratory
Michael J. Wilkins: Department of Microbiology The Ohio State University
Allan E. Konopka: Pacific Northwest National Laboratory
William C. Nelson: Pacific Northwest National Laboratory
Evan V. Arntzen: Pacific Northwest National Laboratory
William B. Chrisler: Pacific Northwest National Laboratory
Rosalie K. Chu: Pacific Northwest National Laboratory
Sarah J. Fansler: Pacific Northwest National Laboratory
Emily B. Graham: Pacific Northwest National Laboratory
David W. Kennedy: Pacific Northwest National Laboratory
Charles T. Resch: Pacific Northwest National Laboratory
Malak Tfaily: Pacific Northwest National Laboratory
John Zachara: Pacific Northwest National Laboratory

Nature Communications, 2018, vol. 9, issue 1, 1-11

Abstract: Abstract The hyporheic corridor (HC) encompasses the river–groundwater continuum, where the mixing of groundwater (GW) with river water (RW) in the HC can stimulate biogeochemical activity. Here we propose a novel thermodynamic mechanism underlying this phenomenon and reveal broader impacts on dissolved organic carbon (DOC) and microbial ecology. We show that thermodynamically favorable DOC accumulates in GW despite lower DOC concentration, and that RW contains thermodynamically less-favorable DOC, but at higher concentrations. This indicates that GW DOC is protected from microbial oxidation by low total energy within the DOC pool, whereas RW DOC is protected by lower thermodynamic favorability of carbon species. We propose that GW–RW mixing overcomes these protections and stimulates respiration. Mixing models coupled with geophysical and molecular analyses further reveal tipping points in spatiotemporal dynamics of DOC and indicate important hydrology–biochemistry–microbial feedbacks. Previously unrecognized thermodynamic mechanisms regulated by GW–RW mixing may therefore strongly influence biogeochemical and microbial dynamics in riverine ecosystems.

Date: 2018
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DOI: 10.1038/s41467-018-02922-9

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