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

The hyporheic corridor (HC) is a critical component of riverine ecosystems that encompasses the river-11 groundwater continuum. The mixing of groundwater (GW) with river water (RW) in the HC can 12 stimulate biogeochemical activity, and here we (i) propose a novel thermodynamic mechanism 13 underlying this phenomenon, and (ii) reveal broader impacts on dissolved organic carbon (DOC) 14 biogeochemistry and microbial ecology. We show that thermodynamically-favorable DOC 15 accumulates in GW despite decreases in DOC concentration along subsurface flow paths, and that RW 16 contains less thermodynamically-favorable DOC, but at higher concentrations. This indicates that DOC 17 in GW is protected from microbial oxidation by low total energy contained within the DOC pool, while 18 RW DOC is protected by lower thermodynamic favorability of carbon species. We propose that GW-19 RW mixing overcomes these protection mechanisms and stimulates respiration. Mixing models 20 coupled with time-lapse electrical resistance tomography revealed that stimulated respiration leads 21 to tipping points in spatiotemporal dynamics of DOC across the HC. Further, shifts in DOC speciation 22 and biochemical pathways were associated with shifts in microbiome composition, highlighting 23 feedbacks among hydrology, DOC biochemistry, and microbial ecology. These results reveal that 24 previously unrecognized thermodynamic-based mechanismsmore » regulated by GW-RW mixing can strongly 25 influence biogeochemical and microbial dynamics in riverine ecosystems.« less
Authors:
ORCiD logo [1] ;  [1] ;  [1] ; ORCiD logo [2] ;  [1] ; ORCiD logo [1] ;  [1] ;  [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ;  [1] ; ORCiD logo [1] ;  [1]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  2. The Ohio State Univ., Columbus, OH (United States)
Publication Date:
Report Number(s):
PNNL-SA-129526
Journal ID: ISSN 2041-1723; 47533; KP1702030
Grant/Contract Number:
AC05-76RL01830
Type:
Accepted Manuscript
Journal Name:
Nature Communications
Additional Journal Information:
Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 2041-1723
Publisher:
Nature Publishing Group
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; Environmental Molecular Sciences Laboratory
OSTI Identifier:
1423411