13 Jun 2022
13 Jun 2022
Status: this preprint is open for discussion.

Patterns and drivers of water quality changes associated with dams in the Tropical Andes

R. Scott Winton1,2,a, Silvia López-Casas3,4, Daniel Valencia-Rodríguez4,5, Camilo Bernal-Forero6, Juliana Delgado7, Bernhard Wehrli1,2, and Luz Jiménez-Segura4 R. Scott Winton et al.
  • 1Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, 8092 Zurich, Switzerland
  • 2Department of Surface Waters, Eawag, Swiss Federal Institution of Aquatic Science and Technology, 6047 Kastanienbaum, Switzerland
  • 3Wildlife Conservation Society Colombia, Bogotá
  • 4Grupo de Ictiología, Instituto de Biología, Universidad de Antioquia, Medellín, Colombia
  • 5Fundacion Horizonte Verde, Cumaral, Colombia
  • 6Autoridad Nacional de Licencias Ambientales, Bogotá, Colombia
  • 7The Nature Conservancy Colombia, Bogotá
  • acurrent address: Department of Earth System Science, Stanford University, Stanford, CA, USA

Abstract. The Tropical Andes is a biodiversity hotspot facing pressure from planned and ongoing hydropower development. However, the effects of dams on river ecosystems of the region as mediated by physico-chemical changes to water quality are poorly known. Colombia is unique among its peers in South America for managing central public environmental databases, including surface water quality data sets associated with environmental monitoring of dams. To assess the relationship between hydropower and Colombian river conditions, we analyze monitoring data, focusing on oxygen availability, thermal regimes and sediment losses because these properties are influenced directly by river damming and impose fundamental constraints on the structure of downstream aquatic ecosystems. We find that most Colombian dams seasonally reduce concentrations of total suspended solids by large percentages (50–99 %) through sediment trapping and, via discharge of warm reservoir surface waters, seasonally increase river temperatures by 2 to 4 °C with respect to upstream conditions. A subset of dams generates downstream hypoxia (<4 mg L-1) and water 2 to 5 °C colder than inflows—both processes driven by the turbination and discharge of cold and anoxic hypolimnetic waters during periods of reservoir stratification. Reliance on monitoring data likely leads us to under-detect impacts because many rivers are only sampled once or twice per year and cannot capture temporal shifts across seasons and days (i.e. in response to hydropeaking). Despite these blind spots, the monitoring data point to some opportunities for planners and hydropower companies to mitigate downstream ecological impacts. These findings affirm the scientific utility and importance of environmental monitoring schemes associated with hydrologic infrastructure in developing countries.

R. Scott Winton et al.

Status: open (until 08 Aug 2022)

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R. Scott Winton et al.

R. Scott Winton et al.


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Short summary
Dams are an important and rapidly growing means for energy generation in the Tropical Andes of South America. To assess the impacts of dams in the region, we assessed differences in upstream and downstream water quality of all hydropower dams in Colombia. We found evidence for substantial dam-induced changes to water temperatures, concentrations of dissolved oxygen and suspended sediments. Dam-induced changes to Colombian waters violate regulations and are likely impacting aquatic life.