In northwestern Ontario, Canada, a decades-old experiment on a small lake has reportedly helped scientists understand the lasting effects of acid rain on freshwater ecosystems.
Why did scientists add sulfuric acid to a Canadian lake?
Researchers at the International Institute for Sustainable Development Experimental Lakes Area (IISD-ELA) started adding sulfuric acid to Lake 223 every week to simulate acid rain. The experiment began in 1976 and, over the next 17 years, researchers witnessed its pH level drop from 6.8 (close to neutral) to 5.2 (slightly acidic), triggering major changes to its ecosystem that continued even after the experiment ended.
According to media reports, Lake 223 is one of 58 lakes and their watersheds that the IISD-ELA set aside to carry out whole-ecosystem research, rather than isolated laboratory studies. As gradual acidification led to the disappearance of several fish and invertebrate species, researchers closely monitored the experiment, which demonstrated how changes in water chemistry can disrupt entire food chains. Fathead minnows nearly disappeared, while lake trout populations also declined as their food sources and the wider ecosystem were affected.
What did the experiment reveal?
The experiment concluded in 1993, and the gradual addition of acid was halted, with the water chemistry beginning to recover over time. However, IISD-ELA scientists observed that Lake 223's biology did not recover quickly. Roughly 30 years later, the lake's trout population is less than half of what it was before the experiment began, and growth rates are still significantly depressed. The lasting damage from acidification is believed to be associated with changes lower in the food web, especially the disappearance of Mysis diluviana, a small shrimp-like invertebrate that vanished during the period of acidification.
At the time, the findings from the IISD-ELA experiment had far-reaching implications. The experiment showed that acid rain, which is caused by sulfur dioxide and nitrogen oxides emitted from burning fossil fuels, was a major environmental concern during the 1970s and 1980s. Research from Lake 223 provided important evidence linking industrial emissions to declining fish populations, supporting efforts to strengthen air-emission regulations in Canada and the United States.
What happened to Lake 223 after the experiment?
Today, Lake 223 stands as a real-world example of ecological recovery. In an attempt to restore the food web, researchers began introducing Mysis diluviana to the lake in 2019. By 2021, they detected that a new population had become established. According to ongoing research, scientists are studying the effects of the lake's recovery on lake trout, including their population growth, recovery, and mercury levels.
The experiment in Lake 223 underscores a lesson for environmental policy and conservation efforts: While water chemistry can return to normal after pollution ends, restoring an ecosystem is far more difficult and slow-moving. Decades after acid rain altered this Canadian lake, the continued decline in its trout population highlights how environmental damage can persist long after the pollution that caused it has subsided.