Long-term Acid-Rain Experiment Leaves Lake Trout Numbers at Half Pre-Study Levels
After a 17-year acid-rain simulation that lowered Lake 223’s pH from 6.8 to 5.2, the lake’s chemistry has rebounded but its trout population remains under half of its original size.
Lake 223 in northwestern Ontario served as a whole-lake laboratory for a 17-year acid-rain study, during which scientists added sulfuric acid each week, driving the pH down from 6.8 to 5.2. The experiment, conducted from 1976 to 1993, demonstrated the vulnerability of freshwater food webs, with several fish and invertebrate species disappearing. After the acid additions stopped, the lake’s water chemistry gradually returned to its original state, yet biological recovery lagged.
The International Institute for Sustainable Development's Experimental Lakes Area notes that lake trout now number less than half of their pre-experiment population and exhibit slower growth rates, likely due to lasting disruptions lower in the food chain. Since 2019, researchers have been restocking Mysis diluviana, a key invertebrate that vanished during acidification, and have observed a nascent population by 2021. Monitoring continues to assess impacts on trout health, survival, and mercury levels, making the lake a long-term test of ecosystem restoration beyond chemical remediation.
Why it matters
The study shows that fixing water chemistry alone may not restore fish populations after acid-rain damage.
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