OTTAWA - Acid rain, one of the biggest environmental scourges of recent decades, has sapped the calcium from lakes across the Canadian Shield, slowly wiping out tiny creatures that need high doses of the nutrient to survive, new research shows.
A study published Thursday in the journal Science warns declining numbers of water fleas called daphnia, which are prey for small fish and insects, could spell trouble for other lake life.
"We're thinking of them as almost a miner's canary or an alarm bell," said the lead author of the study, Adam Jeziorski of Queen's University in Kingston, Ont.
It has been known for some time that some boreal lakes are low on calcium, partly because acid rain has leached the nutrient from the soil.
However, the authors say their study sheds new light on the consequences of declining calcium on aquatic life.
"I think we're the first to show the biological damage," said John Smol of Queen's University, who holds the Canada research chair in environmental change.
Many lake creatures, including crayfish, mollusks and fish, have high calcium demands. The study says some species can no longer reproduce once calcium levels dip below a certain threshold. That results in food shortages for other creatures that feed on the disappearing species.
"The ecological impacts of environmental calcium loss are likely to be both widespread and pronounced," the study says.
Researchers from Queen's and York University in Toronto gathered samples of sediment from 770 lakes across the Canadian Shield, a massive horseshoe-shaped slab of bedrock stretching across Eastern Canada up to the Arctic Ocean. These regions were most affected by acid rain during the 1980s.
Water flea fossils in the sediment gave scientists a good idea of how many creatures have lived in the lake at different times over the past 200 years.
Next, the researchers studied changes in the calcium and pH levels of the lakes from the 1980s to the 2000s. They found that as calcium levels fell, so too did the number of water fleas in the lakes.
"There was a clear decline in the animals that require a lot of calcium versus the ones that don't so much," Jeziorski said.
Acid rain was one of the most prolific environmental issues of the 1980s after forests and fish began dying in Canada and the U.S.
Acid rain occurs when sulphur and nitrogen released by the burning of fossil fuels combines with water vapour, sunlight and oxygen. The toxic brew then falls as rain, sometimes hundreds of kilometres from where the pollutants were emitted.
Former prime minister Brian Mulroney and former U.S. president George Bush signed an acid rain accord in 1991, which pledged to lower sulphur dioxide emissions by 40 per cent by 2010. Provincial governments also set limits on industrial air pollutants that cause acid rain.
However, as this new study shows, many lakes across Eastern Canada still suffer the ill-effects of acid rain.
The western provinces were once seen as relatively safe from acid rain because of their low levels of industrialization, east-moving weather patterns and resistant soils.
However, a boom in industrial production, including in Alberta's oilsands, threatens another acid rain problem in that part of the country.
