Flooding of ecosystems for hydro electricity generation had been known to result in elevated concentrations of toxic methyl mercury in fish since the 1970s. In 1993, researchers suggested that reservoirs might be an important source of greenhouse gases to the atmosphere. Studies investigating both pre- and post-flooding conditions, and factors promoting elevated mercury and greenhouse gases, were lacking. Both the Experimental Lakes Area Reservoir Project (ELARP) and the FLooded Uplands Dynamics EXperiment (FLUDEX) were devised to understand the full effect of flooding wetlands and uplands, respectively. Results from these studies showed, for the first time, that flooding wetlands produced higher amounts of greenhouse gases and mercury than flooding upland areas. Another whole-lake study also examined the ecosystem effects of winter water drawdown, a common feature of many northern reservoirs.
Key findings included: 1) that reservoirs produce GHGs through the decomposition of flooded soils and vegetation; and 2) that flooded wetlands produced higher amounts of GHGs and mercury than upland areas. Power companies such as Manitoba Hydro and Hydro Quebec have used study findings to build reservoirs with lower environmental impacts.
The research and its findings are summarized in this blog post.