Abstract
Increased energy demand has led to plans for building many new dams in the western Amazon, mostly in the Andean region. Historical data and mechanistic scenarios are used to examine potential impacts above and below six of the largest dams planned for the region, including reductions in downstream sediment and nutrient supplies, changes in downstream flood pulse, changes in upstream and downstream fish yields, reservoir siltation, greenhouse gas emissions and mercury contamination. Together, these six dams are predicted to reduce the supply of sediments, phosphorus and nitrogen from the Andean region by 69, 67 and 57% and to the entire Amazon basin by 64, 51 and 23%, respectively. These large reductions in sediment and nutrient supplies will have major impacts on channel geomorphology, floodplain fertility and aquatic productivity. These effects will be greatest near the dams and extend to the lowland floodplains. Attenuation of the downstream flood pulse is expected to alter the survival, phenology and growth of floodplain vegetation and reduce fish yields below the dams. Reservoir filling times due to siltation are predicted to vary from 106-6240 years, affecting the storage performance of some dams. Total CO2 equivalent carbon emission from 4 Andean dams was expected to average 10 Tg y-1 during the first 30 years of operation, resulting in a MegaWatt weighted Carbon Emission Factor of 0.139 tons C MWhr-1. Mercury contamination in fish and local human populations is expected to increase both above and below the dams creating significant health risks. Reservoir fish yields will compensate some downstream losses, but increased mercury contamination could offset these benefits.
Grants and funding
The synthetic work for this paper was supported by the Science for Nature and People (SNAP) sponsored by the National Center for Ecological Analysis and Synthesis (NCEAS), the Wildlife Conservation Society (WCS) and the Nature Conservancy (TNC). At WCS we thank Cristián Samper, John Robinson, Julie Kunen, Mariana Varese, Mariana Montoya, Carlos Durigan, Guillermo Estupiñán, Micaela Varese, Natalia Piland and Sofia Baca; for SNAP workshop support we thank Charo Lanao; at TNC Craig Groves and Peter Kareiva; at NCEAS Frank Davis and Lee Ann French. We thank D. Kasper, J.R.P. Peleja, E.M. Nakazono, A.P. Souza, J.B. Rocha and D.R. Dietrich for help during the collection and analysis of fish and hair for mercury at Balbina Reservoir and orientation. We also thank the Museu Paraense Emilio Goeldi (MPEG) and the Instituto Nacional de Pesquisas da Amazônia (INPA) for their support. For fisheries data we are indebted to the Dirección Regional de la Producción (DIREPRO), Peru. SNAP funding was provided by the David and Lucile Packard Foundation (Grant # 2013-38757 & #2014-39828), Ward Woods (Grant # 309519), the Wildlife Conservation Society (WCS) and The Nature Conservancy (TNC). Field data reported for the first time was supported by the Gordon and Betty Moore Foundation (Grant 500) and the John D. and Catherine T. MacArthur Foundation (Grant 84377). The Brazilian National Research Council (CNPq) provided a productivity grant to B.R. Forsberg (Grant 309636/2011-6). J.M. Melack received support from the US Department of Energy (Contract No. DE-0010620), NASA and a Fulbright fellowship. From the above institutions, past or present, we thank Avecita Chicchón, Adrian Forsyth, Rosa Lemos da Sá and Enrique Ortiz.