What are the implications of bioaccumulation of mercury in reservoirs created by hydroelectric dams?

Bioaccumulation of mercury in reservoirs created by hydroelectric dams has significant implications for human health and aquatic ecosystems. When a reservoir is created, previously terrestrial areas are flooded, leading to the decomposition of organic matter. This decomposition process creates anoxic (oxygen-deprived) conditions in the sediment, which promotes the conversion of inorganic mercury into methylmercury, a highly toxic and bioavailable form of mercury. Bioaccumulation is the process by which organisms accumulate contaminants in their tissues at levels higher than those found in their environment. Methylmercury bioaccumulates as it moves up the food chain. Small organisms, like plankton, absorb methylmercury from the water and sediment. These organisms are then eaten by small fish, which in turn are eaten by larger fish, and so on. At each step in the food chain, the concentration of methylmercury increases, leading to very high levels in top predatory fish, such as bass, walleye, and pike. Human consumption of fish from these reservoirs can lead to mercury exposure, which can have serious health effects, particularly for pregnant women and young children. Methylmercury is a neurotoxin that can damage the developing brain and nervous system. Mercury contamination can also impact wildlife, such as birds and mammals that consume fish from the reservoir. Monitoring mercury levels in fish and implementing strategies to reduce mercury contamination are essential for mitigating the risks associated with hydroelectric dams. Strategies to reduce mercury levels include careful removal of organic material prior to flooding new reservoirs or using best management practices to reduce mercury release from watershed soils. The Grassy Narrows First Nation in Canada, for instance, has suffered significant health and economic impacts due to mercury contamination from a paper mill that contaminated the English-Wabigoon River system prior to the dam construction, leading to bioaccumulation in the reservoir's fish.