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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2018-510
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2018-510
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Reviews and syntheses 02 Jan 2019

Reviews and syntheses | 02 Jan 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Reviews and syntheses: Dams, water quality and tropical reservoir stratification

R. Scott Winton1,2, Elisa Calamita1,2, and Bernhard Wehrli1,2 R. Scott Winton et al.
  • 1Department of Environmental Systems Science, ETH Zürich, Zürich, 8092, Switzerland
  • 2Department of Surface Waters Eawag, Kastanienbaum, 6047, Switzerland

Abstract. The impact of large dams is a popular topic in environmental science, but the importance of altered water quality as a driver of ecological impacts is often missing from such discussions. This is partly because information on the relationship between dams and water quality is relatively sparse and fragmentary, especially for low latitude developing countries where dam building is now concentrated. In this paper, we review and synthesize information on the effects of damming on water quality with a special focus on low latitude contexts. We find that most water quality changes are driven by a two ultimate physical processes: the trapping of sediments and nutrients, and thermal stratification and oxygen depletion in reservoirs. Since stratification emerges as an important driver and there is ambiguity in the literature regarding the stratification behavior of low latitude water bodies, we synthesize data and literature on the 54 largest low latitude reservoirs to assess their mixing behavior using three classification schemes. Direct observations from literature as well as classifications based on climate and/or morphometry suggest that most, if not all, low latitude reservoirs will stratify on at least a seasonal basis. This finding suggests that low latitude dams have the potential to discharge cooler, anoxic deep water, which can degrade downstream ecosystems by altering thermal regimes or causing hypoxic stress. Many of these reservoirs are also capable of efficiently trapping sediment and bed load, which alters downstream habitats and causes losses of floodplain and delta ecosystems. Water quality impacts imposed by stratification and sediment trapping can be mitigated through a variety of approaches, but implementation often meets physical or financial constraints. The impending construction of thousands of planned low latitude dams will alter water quality throughout the worlds tropical and subtropical river systems. The water quality changes and their associated environmental impacts could be better understood by better baseline data and more sophisticated predictors of reservoir stratification behavior.

R. Scott Winton et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
R. Scott Winton et al.
Data sets

Physical data for the 54 most voluminous low latitude reservoirs R. S. Winton, E. Calamita, and B. Wehrli https://doi.org/10.3929/ethz-b-000310656

R. Scott Winton et al.
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Short summary
A global boom in dam construction throughout the world’s tropics motivated us to review and synthesize information on the water quality impacts of dams with a focus on low latitude contexts and scope for mitigation. Sediment trapping and reservoir stratification are key process driving chemical and ecological impacts to tropical rivers. We analyze the 54 most-voluminous low latitude reservoirs and find that stratification seems to be a ubiquitous phenomenon.
A global boom in dam construction throughout the world’s tropics motivated us to review and...
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