Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 12, issue 14
Biogeosciences, 12, 4345-4359, 2015
https://doi.org/10.5194/bg-12-4345-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 12, 4345-4359, 2015
https://doi.org/10.5194/bg-12-4345-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 28 Jul 2015

Research article | 28 Jul 2015

Dam tailwaters compound the effects of reservoirs on the longitudinal transport of organic carbon in an arid river

A. J. Ulseth1,2,a and R. O. Hall Jr.2 A. J. Ulseth and R. O. Hall Jr.
  • 1Program in Ecology, University of Wyoming, Laramie, Wyoming, USA
  • 2Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming, USA
  • anow at: École Polytechniqe Fédérale de Lausanne, Lausanne, Switzerland

Abstract. Reservoirs on rivers can disrupt organic carbon (OC) transport and transformation, but less is known how river reaches directly below dams contribute to OC processing. We compared how reservoirs and their associated tailwaters affected OC quantity and quality by calculating particulate OC (POC) and dissolved OC (DOC) fluxes, and measuring composition and bioavailability of DOC. We sampled the Yampa River near Maybell, Colorado, USA, and the Green River above and below Fontenelle and Flaming Gorge reservoirs as well as their respective tailwaters from early snowmelt to base flow hydrological conditions. In unregulated reaches (Yampa River, Green River above Fontenelle reservoir), DOC and POC concentrations increased with snowmelt discharge. POC and DOC concentrations also increased with stream discharge below Fontenelle reservoir, but there was no relationship between DOC and stream flow below Flaming Gorge reservoir. The annual load of POC was 3-fold lower below Fontenelle Reservoir and nearly 7-fold lower below Flaming Gorge reservoir, compared to their respective upstream sampling sites. DOC exported to downstream reaches from both reservoirs was less bioavailable, as measured with bioassays, than DOC upriver of the reservoirs. Lastly, tailwater reaches below the reservoirs generated OC, exporting potentially 1.6–2.2 g C m−2 d−1 of OC to downstream ecosystems. Therefore, the effect of impounding rivers on C fluxes is greater than the impact of the reservoirs alone given the additive effect of tailwater reaches below dams, which may produce and export comparable amounts of likely autochthonous carbon to downstream reaches.

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Dams impact river reaches. Upstream of dams, reservoirs transform terrestrial organic carbon and produce autochthonously derived organic carbon. In addition, tailwater reaches below dams may produce and export similar amounts of organic carbon to that stored behind dams. Our work demonstrates that not only do reservoirs need to be considered for their capacity to store and transform organic carbon but also the combined impact of their tailwater ecosystems should to be considered as well.
Dams impact river reaches. Upstream of dams, reservoirs transform terrestrial organic carbon and...
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