Protesters, led by representatives of Indigenous groups, have seized control of the site of the Muskrat Falls hydroelectric project in Labrador. They have also come to Ottawa. On Sunday, Inuk artist Billy Gauthier, who was on the 10th day of a hunger strike, joined other hunger strikers, Inuit elders and supporters at a demonstration at the Human Rights Monument.

The protesters are demanding that Nalcor Energy, the Crown utility of the Government of Newfoundland and Labrador, clear away vegetation and the surface soil layer from the area to be flooded by the project in order to reduce poisoning of water, fish and humans by methyl mercury. Their demands have considerable scientific support.

Authors of a 2016 study of the large, shallow Tobin Lake reservoir created on the Saskatchewan River in 1963 point out that methyl mercury “is a potent and environmentally relevant neurotoxin, teratogen and potential chronic cardiovascular toxin.” After flooding of the reservoir, mercury levels in species such as pike and walleye exceeded Health Canada consumption guidelines for several decades. Previous studies had suggested that mercury concentrations in fish might return to baseline levels in less than 30 years, but this new study suggests a “less optimistic timeline upwards of 40 years.”

There is also scientific evidence that clearing vegetation and surface soils can reduce mercury contamination. A 2013 study by researchers at the Université du Québec à Montréal examined the Churchill Falls hydroelectric project in Labrador. Similar to the Saskatchewan study, “flooded soils continued to be major sources of mercury and organic matter to sediments of these lakes more than 40 years after impoundment.” Researchers concluded that surface and upper soil layers, which have high levels of readily decomposable organic carbon, were the major source of mercury.

Elemental mercury vapour is volatile and readily transported as an atmospheric pollutant. Mercury is strongly absorbed and retained in the organic surface layers of forest soils. After flooding, it is these mercury-enriched surface soils that contribute most strongly to mercury contamination of reservoir sediments. According to the Quebec researchers, mercury-contaminated sediments can continue to release this toxic element for many years. More mercury can enter the water and the food chain when sediments are stirred up and redeposited by wave action, or when erosion during cycles of reservoir draw-down and re-flooding creates new sediments.

In addition to mercury contamination, hydroelectric projects can cause large increases in greenhouse gas emissions. A study published in 1997, done at the world-famous Experimental Lakes Area, found that experimental flooding of a boreal forest wetland changed it from a small, natural carbon sink to a large source of carbon. Flooding killed vegetation, which eliminated photosynthetic carbon uptake and stimulated microbial release of carbon dioxide and methane from decaying plant tissues and peat. Furthermore, flooding increased the release of methyl mercury from the wetland 40-fold, and methyl mercury also increased in rotting vegetation and peat, in lower food-chain organisms, and in fish.

The Muskrat Falls project itself has been dogged by controversy. A joint federal-provincial environmental assessment panel concluded in August 2011 that Nalcor had not proven the need for the project and that it would likely have significant adverse effects on fish, wetlands and terrestrial habitats. But in March 2012 the federal and provincial governments rejected the panel’s recommendation to conduct further analysis to determine the project’s viability and gave it a green light.

Nalcor’s own website admits that the project will increase mercury levels in fish. It says that after the reservoir is created, increases in methyl mercury will occur in the reservoir and downstream in the Churchill River, “peaking in fish approximately 5-15 years later and then returning to current levels over time.” Nalcor has committed to measuring current levels of mercury in hair for about 300 residents from communities along the Churchill River, and to surveying “dietary habits, such as which locally harvested foods residents regularly consume.” If mercury reaches unacceptable levels, this monitoring will help “determine if consumption advisories for certain foods are needed.”

A cynic might conclude that the message is: “We’ll let you know when to stop eating fish.”

With huge amounts of money already spent on the Muskrat Falls project there is no chance that it will be abandoned. Clearing vegetation and surface soil before flooding the reservoir is clearly the right thing to do, to protect the environment and the livelihoods and health of local residents. The project was approved by federal and provincial governments despite its adverse impacts. Now it is time for them to act to mitigate those impacts to the greatest degree possible.

Ole Hendrickson is a retired forest ecologist and a founding member of the Ottawa River Institute, a non-profit charitable organization based in the Ottawa Valley.

Photo by Ossie Michelin

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Ole Hendrickson

Ole Hendrickson

Ole Hendrickson is an ecologist, a former federal research scientist, and chair of the Sierra Club Canada Foundation's national conservation committee.