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Title: Snowmelt controls on concentration-discharge relationships and the balance of oxidative and acid-base weathering fluxes in an alpine catchment, East River, Colorado: ACID-BASE VERSUS OXIDATIVE WEATHERING FLUXES

Although important for riverine solute and nutrient fluxes, the connections between biogeochemical processes and subsurface hydrology remain poorly characterized. We investigate these couplings in the East River, CO, a high-elevation shale-dominated catchment in the Rocky Mountains, using concentration-discharge (C-Q) relationships for major cations, anions, and organic carbon. Dissolved organic carbon (DOC) displays a positive C-Q relationship with clockwise hysteresis, indicating mobilization and depletion of DOC in the upper soil horizons and emphasizing the importance of shallow flowpaths during snowmelt. Cation and anion concentrations demonstrate that carbonate weathering, which dominates solute fluxes, is promoted by both sulfuric acid derived from pyrite oxidation in the shale bedrock and carbonic acid derived from subsurface respiration. Sulfuric acid weathering dominates during baseflow conditions when waters infiltrate below the inferred pyrite oxidation front, whereas carbonic acid weathering plays a dominant role during snowmelt as a result of shallow flowpaths. Differential C-Q relationships between solutes suggest that infiltrating waters approach calcite saturation before reaching the pyrite oxidation front, after which sulfuric acid reduces carbonate alkalinity. This reduction in alkalinity results in CO 2 outgassing when waters equilibrate to surface conditions, and reduces the riverine export of carbon and alkalinity by roughly 33% annually. In conclusion, futuremore » changes in snowmelt dynamics that control the balance of carbonic and sulfuric acid weathering may substantially alter carbon cycling in the East River. Ultimately, we demonstrate that differential C-Q relationships between major solutes can provide unique insights into the complex subsurface flow and biogeochemical dynamics that operate at catchment scales.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ; ORCiD logo [5] ;  [1]
  1. Department of Geological Sciences, Stanford University, Stanford California USA
  2. Division of Hydrologic Sciences, Desert Research Institute, Reno Nevada USA
  3. Lawrence Berkeley National Laboratory, Berkeley California USA; Rocky Mountain Biological Laboratory, Crested Butte Colorado USA
  4. Hydrologic Science and Engineering Program, Colorado School of Mines, Golden Colorado USA
  5. Lawrence Berkeley National Laboratory, Berkeley California USA
Publication Date:
Grant/Contract Number:
SC0014556; EAR-1254156; AC02- 05CH11231; (DOE-DE-SC0014556)
Type:
Accepted Manuscript
Journal Name:
Water Resources Research
Additional Journal Information:
Journal Volume: 53; Journal Issue: 3; Journal ID: ISSN 0043-1397
Publisher:
American Geophysical Union (AGU)
Research Org:
Stanford Univ., CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); National Science Foundation (NSF)
Contributing Orgs:
Desert Research Institute; Colorado School of Mines; Rocky Mountain Biological Laboratory
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; water quality; watersheds; catchments; carbon cycle; concentration-discharge; critical zone; pyrite oxidation
OSTI Identifier:
1348990
Alternate Identifier(s):
OSTI ID: 1402333