Washington, Nov 28 : A team of biologists from Queen's and York University in Canada has detected a new and dangerous environmental threat in North American lakes, in the form of declining levels of calcium.
Along with scientists from several Canadian government laboratories, the team has documented biological damage caused by declining levels of calcium in many temperate, soft-water lakes.
Calling the phenomenon "aquatic osteoporosis," Queen's PhD candidate Adam Jeziorski, lead author of the study, notes that calcium is an essential nutrient for many lake-dwelling organisms.
"Once calcium declines below a certain threshold, some keystone species can no longer reproduce," he said. "These species and other organisms that feed on them are endangered," he added.
For the research, the team examined a water flea, Daphnia, known to be a key component of many aquatic foodwebs.
Having identified the calcium levels that would damage Daphnia in a laboratory setting, they worked with government scientists to assemble hundreds of "water quality time series" from across the province, explained Biology professor Norman Yan from York University, the Canadian research lead on the threat to aquatic life of calcium decline.
"Our hope was to determine if damage was already occurring at key sites, and then see how common these conditions were across the province," he said.
By studying tiny fossils and other indicators in sediment accumulated at the bottom of each lake, Queen's paleoecologist professor John Smol, Canada Research Chair in Environmental Change, and his colleagues found that key invertebrate species were disappearing in the lakes with declining calcium levels, often starting in the 1970s.
Linking the problem to the long-term effects of acid rain on forest soils, as well as to logging and forest re-growth, the researchers note that, despite signs of chemical recovery from recent reductions in sulphur dioxide emissions, lower calcium levels may delay the biological recovery of lakes from acidification.
According to the research team, the phenomenon of calcium decline is causing widespread transformation of aquatic food webs in boreal lakes in North America, and in other acid-sensitive regions of the globe.
While their work focuses on the water flea Daphnia, they note that all life in lakes requires calcium, and many creatures including crayfish, mollusks and fish have quite high calcium demands.
"They are all at risk, but we don't yet know if calcium levels have fallen to the point of damage," according to the researchers.
"The good news is that we have found the 'miner's canary' in the form of these water fleas that track the decline in calcium levels," said Dr. Smol. "The bad news is that many lakes have already passed these critical thresholds," he added.