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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/hess-2019-310
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2019-310
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 18 Jul 2019

Submitted as: research article | 18 Jul 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

Temperature controls production but hydrology controls export of dissolved organic carbon at the catchment scale

Hang Wen1, Julia Perdrial2, Susana Bernal3, Benjamin W. Abbott4, Rémi Dupas5, Sarah E. Godsey6, Adrian Harpold7, Donna Rizzo8, Kristen Underwood8, Thomas Adler2, Rebecca Hale9, Gary Sterle7, and Li Li1 Hang Wen et al.
  • 1Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA 16802, USA
  • 2Department of Geology, University of Vermont, Burlington, VT 05405, USA
  • 3Center of Advanced Studies of Blanes (CEAB-CSIC), Accés Cala St. Francesc 14, 17300, Blanes, Girona, Spain
  • 4Department of Plant and Wildlife Science, Brigham Young University, Provo, UT 84602, USA
  • 5INRA, UMR1069 SAS, Rennes, France
  • 6Department of Geosciences, Idaho State University, Pocatello, ID83201, USA
  • 7Department of Natural Resources and Environmental Science, University of Nevada, Reno, NV 89557, USA
  • 8Department of Civil and Environmental Engineering, University of Vermont, Burlington, VT 05405, USA
  • 9Department of Biological Sciences, Idaho State University, Pocatello, ID 83201, USA

Abstract. Lateral carbon flux through river networks is an important and poorly-understood component of the global carbon budget. This work investigates how temperature and hydrology control the production and export of dissolved organic carbon (DOC) in the Susquehanna Shale Hills Critical Zone Observatory in Pennsylvania, USA. We applied the catchment-scale hydro-biogeochemical reactive transport model BioRT-Flux-PIHM to simulate the DOC dynamics. We estimated the daily DOC production rate (Rp; the sum of local DOC production rates in individual modeling grid cell) and the daily DOC export rate (Re; the product of concentration and discharge at the stream outlet) to downstream ecosystems. Simulations showed that Rp varied by less than an order of magnitude and primarily hinged on seasonal temperature change. In contrast, Re varied by more than three orders of magnitude with a strong dependence on discharge and hydrological connectivity. During summer, high temperatures led to high atmospheric water demand (and evapotranspiration) that dried and disconnected hillslope to stream. Rp reached its maximum but Re was at its minimum. The stream only exported DOC from the organic-poor groundwater and from soil water in the narrow organic-rich swales with enriched DOC such that DOC accumulated in the catchment. During the wet period (winter and spring), Rp reached its minimum but Re peaked because the stream was re-connected to a greater uphill area, flushing out the stored DOC. The model reproduced the observed concentration discharge (C–Q) relationship characterized by a flushing-dilution pattern with a rise in concentrations to a maximum (flushing) at a threshold discharge and then followed a general dilution with concentrations decreasing with discharge. This pattern was explained by the comparable contribution of organic-poor deeper groundwater and soil water from organic-rich swales at the minimum flow, maximized percentage contribution of soil water from organic-rich swales at the low flow regime, and increased contribution of uphill soil water interflow from uphill with less DOC at the high flow regime. This pattern persisted regardless of DOC production rate as long as the contribution of deeper groundwater flow remained low (< 18 % of the streamflow). When the groundwater flow increased to > 18 %, the flushing-dilution C–Q pattern shifted towards a flushing-only pattern with DOC concentrations increasing with discharge. This study illustrates the temporal asynchrony of DOC production, mostly controlled by temperature, and DOC export, primarily governed by hydrological flow paths at the catchment scale. The occurrence of warmer and more extreme hydrological events in the future could accentuate this asynchrony, with major lateral export of DOC dominated by a few major storm events whereas DOC is produced and stored in the catchment in the prolonged drought periods.

Hang Wen et al.
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Short summary
Lateral carbon fluxes from terrestrial to aquatic systems remain central uncertainties in determining ecosystem carbon balance. This work explores how temperature and hydrology control production and export of dissolved organic carbon (DOC) at the catchment scale. Results illustrate that asynchrony of DOC production, controlled by temperature, and export, governed by flow paths; Concentration–discharge relationships are controlled by the relative contribution of shallow versus groundwater flow.
Lateral carbon fluxes from terrestrial to aquatic systems remain central uncertainties in...
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