Preprints
https://doi.org/10.5194/bg-2022-19
https://doi.org/10.5194/bg-2022-19
 
22 Feb 2022
22 Feb 2022
Status: a revised version of this preprint was accepted for the journal BG.

Organic Matter Transformations are Disconnected Between Surface Water and the Hyporheic Zone

James Stegen1, Sarah Fansler1, Malak Tfaily4, Vanessa Garayburu-Caruso1, Amy Goldman3, Robert Danczak1, Rosalie Chu2, Lupita Renteria1, Jerry Tagestad3, and Jason Toyoda2 James Stegen et al.
  • 1Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, U.S.A.
  • 2Environmental Molecular Sciences Laboratory, Richland, WA 99352, USA
  • 3Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, WA, U.S.A.
  • 4Department of Environmental Science, University of Arizona, Tucson, AZ, 85719, USA

Abstract. Biochemical transformations of organic matter (OM) are a primary driver of river corridor biogeochemistry, thereby modulating ecosystem processes at local to global scales. OM transformations are driven by diverse biotic and abiotic processes, but we lack knowledge of how the diversity of those processes varies across river corridors and across surface and subsurface components of river corridors. To fill this gap we quantified the number of putative biotic and abiotic transformations of organic molecules across diverse river corridors using ultra-high resolution mass spectrometry. The number of unique transformations is used here as a proxy for the diversity of biochemical processes underlying observed profiles of organic molecules. For this, we use public data spanning the contiguous United States (ConUS) from the Worldwide Hydrobiogeochemical Observation Network for Dynamic River Systems (WHONDRS) consortium. Our results show that surface water OM had more biotic and abiotic transformations than OM from shallow hyporheic zone sediments (1–3 cm depth). We observed substantially more biotic than abiotic transformations, and the number of biotic and abiotic transformations were highly correlated with each other. We found no relationship between the number of transformations in surface water and sediments, and no meaningful relationships with latitude, longitude, or climate. We also found that the composition of transformations in sediments was not linked with transformation composition in adjacent surface waters. We infer that OM transformations represented in surface water are an integrated signal of diverse processes occurring throughout the upstream catchment. In contrast, OM transformations in sediments likely reflect a narrower range of processes within the sampled volume. This indicates decoupling between surface water and sediment OM, which is surprising given the potential for hydrologic exchange to homogenize OM. We infer that the processes influencing OM transformations and the scales at which they operate diverge between surface water and sediments.

James Stegen et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-19', Peter Herzsprung, 02 Mar 2022
    • AC1: 'Reply on RC1', James Stegen, 09 Apr 2022
  • RC2: 'Comment on bg-2022-19', Anonymous Referee #2, 16 Mar 2022
    • AC2: 'Reply on RC2', James Stegen, 09 Apr 2022

James Stegen et al.

James Stegen et al.

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Short summary
Rivers are vital to Earth and in rivers, organic matter (OM) is an energy source for microbes that make greenhouse gas and remove contaminants. To predict Earth’s future requires understanding how and why river OM is transformed. Our results help meet this need. We found that the processes influencing OM transformations diverge between river water and riverbed sediments. This can be used to build new models for predicting the future of rivers and, in turn, the Earth system.
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