이투스 리딩마스터 실전독해 7회 5번 분석노트

05 TEXT

Hydropower’s air pollution emissions are negligible because no fuels are burned in the production of electricity. However, if a large amount of vegetation is growing along the riverbed when a dam is built, it can decay in the lake that is created, causing the buildup and release of methane. Hydropower often requires the use of dams, which can greatly affect the flow of rivers, thereby altering ecosystems and affecting the wildlife and people who depend on those waters. Often, water at the bottom of the lake created by a dam is inhospitable to fish because it is much colder and oxygen-poor compared with water at the top. When this colder, oxygen-poor water is released into the river, it can kill fish living downstream that are accustomed to warmer, oxygen-rich water. Eroded material from upstream sources also collects in dams, and over time, they become filled with huge deposits of silt that must be dredged. Nutrients and stream load (sediments) necessary for the health and balance of the waterway, which would have naturally been carried down river, become trapped in the reservoir behind the dam. This can have negative effects.