Are elevated levels of mercury in the river birds due to run-of-river dams?

Date:  November 1, 2017

Source:  Society of Environmental Toxicology and Chemistry

Summary:

A new study used American dippers to determine if run-of-river dams altered food webs and mercury levels at 13 stream sites in British Columbia.

Run-of-river dams are deemed "green energy" because they produce lower greenhouse gas emissions, have lower water storage, barrier size, extent of flooding and water level fluctuations than conventional hydropower facilities. They divert part of a stream through turbines before returning it to the stream downriver. The impact this process has on the ecosystem is unknown, particularly with regards to the production of methylmercury as a result of the dam and the disruption of natural flows. RoR dams can cause a spike in methylmercury in two ways -- they can form small reservoirs, called headponds, which flood soil and create slow-flowing, low-oxygen environments; or they can create higher temperatures in the stream as a result of the reduced flow conditions when portions of the stream are diverted to the turbines.

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