The general public and policymakers at all levels of government use Dr. Rennie's stellar research work for the sustainable resource management of aquatic ecosystems.

Acid rain fell unrelentingly on Canada's lakes from the Industrial Revolution until the 1980s when modern environmental regulations came into effect.

The effects of this rain, generated by manufacturing and coal-burning industries belching pollutants into the atmosphere, were catastrophic. Many pristine northern Ontario lakes were acidified and the plants, fish, and other aquatic life native to them died off. But for several years, Lakehead University's Dr. Michael Rennie and his team of students have been researching how to reverse this environmental devastation.

"The lakes were greatly helped by bi-lateral agreements between Canada and the United States that dramatically reduced the levels of sulfur dioxide and nitrogen oxides that cause acid rain," explains Dr. Rennie—a Lakehead University biology professor and the head of the Community Ecology and Energetics Lab.

"By the 2000s, the pH levels of many lakes had returned to normal, but the diversity of fish, zooplankton, and invertebrate communities were very low, indicating that these lakes had not recovered biologically."

To restore these fragile ecosystems, Dr. Rennie focused on Lake 223 in northwestern Ontario, one of 58 lakes that are part of the International Institute for Sustainable Development's Experimental Lakes Area (IISD-ELA)—the world's largest freshwater laboratory.

An Unassuming Crustacean Becomes a Mighty Hero

"The IISD-ELA purposely acidified Lake 223 in the 1970s to study acid rain," Dr. Rennie says. "They discovered that lake trout populations declined during the experiment, starving as the animals they ate were decimated by acidification."

It's not only humans who love shrimp. Mysis diluviana is a high-protein food that's a favourite of lake trout.

This included Mysis diluviana—a googly-eyed crustacean about the size of your thumbnail commonly known as opossum shrimp—which turned out to be a keystone animal species that many aquatic creatures rely upon for food. "Although the pH of the lake recovered, the remaining lake trout population was smaller in size, fewer in number, and had higher mercury concentrations after the shrimp were extirpated."

Dr. Rennie's team developed a new scientific method to extract Mysis DNA from sediment cores in Lake 223. The lake itself was important in developing the method because the extirpation date of Mysis was known. "The disappearance of the DNA from the dated core corresponded exactly to the date we knew they were no longer found in the lake—1979."

The implications go far beyond this single lake. "Lake 223 is proof of concept that analyzing DNA in sediment cores enables us to identify the aquatic organisms that previously lived in disturbed lakes, allowing managers to use this information to guide biological restoration."

His team has also shown that reintroduction can work. From 2018 to 2021, they reintroduced small numbers of opossum shrimp into the lake and there's now an abundance of them. "It's the first time ever that these shrimp have been successfully re-established in a lake where they were extirpated."

Dr. Rennie and his team continue to track the lake's recovery. "It'll be a few years for us to tell if the lake trout population will recover, but things are looking good so far." Dr. Rennie is currently collaborating with government, industry, and researchers to apply the same technology to reveal historical biological communities in lake sediments in the Sudbury area to guide the restoration of lakes damaged by former nickel smelting operations.

His hope is that future Earth Days will be times for celebrating healthy lakes that sustain all of us.

Dr. Rennie received an NSERC Discovery Grant and a Government of Ontario Early Career Researcher Award for his ecosystem restoration work. He currently has an NSERC Alliance Grant for his work to restore lakes in the Sudbury area.