Water quality and ecological integrity of Andean rivers facing hydropower development

Abstract:

In search of the least-cost pathway toward energy independence and de-carbonization, tropical developing countries are pursuing hydropower en masse. The resulting global dam construction boom will drastically alter the character of tropical rivers. The tropical Andes of northern South America is an important hotspot for dam construction and for biodiversity, but the region lacks a synthetic understanding of the potential threats dams pose to river water quality and aquatic ecosystems. Limited understanding stems from the relative scarcity of available data, a reality commonly cited as a barrier to geographical knowledge generation throughout the global tropics. In Colombia, however, government agencies are investing in database management infrastructure making systemic assessments possible for the first time. We analyzed water quality and aquatic biota datasets maintained by the National Environmental Licensing Authority (ANLA) for all of Colombia’s major existing hydropower projects in order to systematically test for effects of dams on water quality and aquatic biota. We observe widespread evidence for sediment trapping, stratification within reservoirs and assess the associated changes in thermal regimes, dissolved oxygen content and sediment/nutrient availability in downstream waters compared to reference streams. We also assess the extent to which such physico-chemical changes manifest into observable differences in fish community composition. We argue that tracing the physical changes imposed by dams, to changes in river water quality, to impacts on fish, is essential for understanding and estimating potential losses of ecosystem services associated with dams. As dam construction continues in Colombia and throughout tropical South America, an improved understanding of the nature of potential environmental and ecological costs will be critical for informing design and best practices in the hydropower industry.