Reservoir Stratification Affects Methylmercury Levels in River Water, Plankton, and Fish Downstream from Balbina Hydroelectric Dam, Amazonas, Brazil

• Published in: Environmental science & technology Vol. 48; no. 2; pp. 1032 - 1040
• Main Authors: Kasper, Daniele, Forsberg, Bruce R, Amaral, João H. F, Leitão, Rafael P, Py-Daniel, Sarah S, Bastos, Wanderley R, Malm, Olaf
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 21.01.2014
• Subjects: Animal, plant and microbial ecology; Animals; Applied ecology; Applied sciences; Biological and medical sciences; Brazil; Contamination; Continental surface waters; Correlation analysis; Dams; Earth sciences; Earth, ocean, space; Ecosystem; Ecotoxicology, biological effects of pollution; Engineering and environment geology. Geothermics; Environmental Monitoring; Exact sciences and technology; Fishes - metabolism; Floods; Fresh water environment; Fundamental and applied biological sciences. Psychology; Geography; Mercury; Mercury - analysis; Methylmercury Compounds - analysis; Muscles - metabolism; Natural water pollution; Plankton; Plankton - metabolism; Pollution; Pollution, environment geology; Reservoirs; Rivers; Rivers - chemistry; Seasons; Water Pollutants, Chemical - analysis; Water Quality; Water treatment and pollution; Wetlands; South America; Brazil; America; Amazonas Brazil; Brazil, Amazonas; Brazil, Amazonas, Balbina Reservoir; Organic mercury compounds; Pollutant behavior; Thermal stratification; Neurotoxic; Freshwater environment; Vertebrata; Plankton; Seasonal variation; Environment impact; Artificial lake; Pisces; Surface water; Methylmercury; Poison; Stream; Water pollution; Organic compounds
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es4042644

The river downstream from a dam can be more contaminated by mercury than the reservoir itself. However, it is not clear how far the contamination occurs downstream. We investigated the seasonal variation of methylmercury levels in the Balbina reservoir and how they correlated with the levels encountered downstream from the dam. Water, plankton, and fishes were collected upstream and at sites between 0.5 and 250 km downstream from the dam during four expeditions in 2011 and 2012. Variations in thermal stratification of the reservoir influenced the methylmercury levels in the reservoir and in the river downstream. Uniform depth distributions of methylmercury and oxygen encountered in the poorly stratified reservoir during the rainy season collections coincided with uniformly low methylmercury levels along the river downstream from the dam. During dry season collections, the reservoir was strongly stratified, and anoxic hypolimnion water with high methylmercury levels was exported downstream. Methylmercury levels declined gradually to 200 km downstream. In general, the methylmercury levels in plankton and fishes downstream from the dam were higher than those upstream. Higher methylmercury levels observed 200–250 km downstream from the dam during flooding season campaigns may reflect the greater inflow from tributaries and flooding of natural wetlands that occurred at this time.