The shadow of the Balbina dam: A synthesis of over 35 years of downstream impacts on floodplain forests in Central Amazonia

Made available in DSpace on 2021-06-25T10:22:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-05-01 Fundação de Amparo à Pesquisa do Estado do Amazonas Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) The Balbina hydropower dam in the Central Amazon basin, established in the Uatumã River in the 1980s, is emblematic for its socio-environmental disaster. Its environmental impacts go far beyond the reservoir and dam, however, affecting the floodplain forests (igapó) in the downstream area (dam shadow), which have been assessed using a transdisciplinary research approach, synthesized in this review. Floodplain tree species are adapted to a regular and predictable flood pulse, with high- and low-water periods occurring during the year. This was severely affected by the operation of the Balbina dam, which caused the suppression of both the aquatic phase at higher floodplain elevations and the terrestrial phase at lower floodplain elevations (termed the ‘sandwich effect’). During the period of construction and reservoir fill, large-scale mortality already occurred in the floodplains of the dam shadow as a result of reduced stream flow, in synergy with severe drought conditions induced by El Niño events, causing hydraulic failure and making floodplains vulnerable to wildfires. During the operational period of the dam, permanent flooding conditions at low topographical elevations resulted in massive tree mortality. So far, 12% of the igapó forests have died along a downstream river stretch of more than 125 km. As a result of flood suppression at the highest elevations, an encroachment of secondary tree species from upland (terra firme) forests occurred. More than 35 years after the implementation of the Balbina dam, the downstream impacts caused massive losses of macrohabitats, ecosystem services, and diversity of flood-adapted tree species, probably cascading down to the entire food web, which must be considered in conservation management. These findings are discussed critically, emphasizing the urgent need for the Brazilian environmental regulatory agencies to incorporate downstream impacts in the environmental assessments of several dam projects planned for the Amazon region. Grupo de Pesquisa Ecologia Monitoramento e uso Sustentável de Áreas Úmidas (MAUA) Instituto Nacional de Pesquisas da Amazônia (INPA) Institute of Geography and Geoecology Department of Wetland Ecology Karlsruhe Institute for Technology (KIT) Programa de Pós-graduação em Botânica Instituto Nacional de Pesquisas da Amazônia (INPA) Programa de Pós-graduação em Ecologia Instituto Nacional de Pesquisas da Amazônia (INPA) Programa de Pós-graduação em Clima e Ambiente Instituto Nacional de Pesquisas da Amazônia (INPA)/Universidade do Estado do Amazonas (UEA) Programa de Pós-graduação em Biologia de Água Doce e Pesca Interior Instituto Nacional de Pesquisas da Amazônia (INPA) Instituto de Ciências Biológicas Departamento de Ecologia Universidade de Brasília (UnB) Department of Biogeochemical Processes Max-Planck-Institute for Biogeochemistry Universidade Estadual Paulista (UNESP) Instituto de Geociências e Ciências Exatas Naturalis Biodiversity Center Systems Ecology Vrije Universiteit Amsterdam Instituto Nacional de Pesquisas da Amazônia (INPA) Laboratório de Ecofisiologia e Evolução Molecular (LEEM) Instituto Nacional de Ciência e Tecnologia em Adaptações da Biota Aquática da Amazônia (ADAPTA) Instituto Nacional de Ciência e Tecnologia em Áreas Úmidas (INAU) Universidade Federal de Mato Grosso (UFMT) Programa de Pós-graduação em Ciência Ambiental (PROCAM) Universidade de São Paulo (USP) Centro de Formação em Ciências Agroflorestais Universidade Federal do Sul da Bahia (UFSB) Faculty of Natural Sciences University of Stirling Núcleo de Estudos e Pesquisas Ambientais (NEPAM) Universidade Estadual de Campinas (UNICAMP) Universidade Estadual Paulista (UNESP) Instituto de Geociências e Ciências Exatas Fundação de Amparo à Pesquisa do Estado do Amazonas: 062.1187/2017 CNPq: 403792/2012-6 CNPq: 441462/2017-0 CNPq: 441498/2017-5 CNPq: 441590/2016-0 CNPq: 457893/2013-3 CNPq: 465540/2014-7 CAPES: Finance Code 001 Fundação de Amparo à Pesquisa do Estado do Amazonas: FIXAM 017/2914