Brazil’s Tucuruı´ Dam provides valuable lessons for; ; improving decision-making on major public works in Amazonia; ; and elsewhere. Together with social impacts, which were reviewed in a companion paper, the project’s environmental costs; ; are substantial. Monetary costs include costs of construction and; ; maintenance and opportunity costs of natural resources (such as; ; timber) and of the money invested by the Brazilian government.; ; Environmental costs include forest loss, leading to both loss of; ; natural ecosystems and to greenhouse gas emissions. Aquatic; ; ecosystems are heavily affected by the blockage of fish migration; ; and by creation of anoxic environments. Decay of vegetation left; ; in the reservoir creates anoxic water that can corrode turbines,; ; as well as producing methane and providing conditions for methylation of mercury. Defoliants were considered for removing forest in the submergence area but plans were aborted amid a; ; public controversy. Another controversy surrounded impacts of; ; defoliants used to prevent regrowth along the transmission; ; line. Mitigation measures included archaeological and faunal; ; salvage and creation of a “gene bank” on an island in the reservoir. Decision-making in the case of Tucuruı´ was virtually; ; uninfluenced by environmental studies, which were done concurrently with construction. The dam predates Brazil’s 1986; ; requirement of an Environmental Impact Assessment. Despite; ; limitations, research results provide valuable information for; ; future dams. Extensive public-relations use of the research; ; effort and of mitigation measures such as faunal salvage were; ; evident. Decision-making was closely linked to the influence of; ; construction firms, the military, and foreign financial interests; ; in both the construction project and the use of the resulting; ; electrical power (most of which is used for aluminum smelting). Social and environmental costs received virtually no consideration when decisions were made, an outcome facilitated; ; by a curtain of secrecy surrounding many aspects of the; ; project. Despite improvements in Brazil’s system of environmental impact assessment since the Tucuruı´ reservoir was; ; filled in 1984, many essential features of the decision-making; ; system remain unchanged.
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