It may take thousands of years to return to historic lake water calcium concentrations solely from natural weathering of surrounding watersheds
- Andrew Tanentzap
New research on a number of Canadian lakes shows that historical acid deposits as a result of industry have greatly reduced calcium levels in the water - dramatically impacting populations of calcium-rich plankton such as Daphnia water fleas that dominate these ecosystems.
Falling calcium levels mean Daphnia cannot get the nutrients they need to survive and reproduce, and are consequently consuming less food and becoming more susceptible to predators, leaving more algae for other organisms to feed on.
This has left a small jelly-clad organism called Holopedium to take advantage. Holopedium are plankton competitors of the Daphnia that use less calcium, as well as having a jelly coat that affords them greater protection from predators.
Lakes across eastern Canada have seen Holopedium populations explode in the last 30 years; particularly in lakes in the province of Ontario that have seen a recent Eurasian invasion of the spiny water flea - which also favours hunting Daphnia, affording Holopedium even more room in these ecosystems to expand.
Researchers say the average population of these small invertebrate jellies in many Ontario lakes doubled between the mid-1980s and the mid-2000s. They warn that the increasing ‘jellification’ of Canada’s lakes will prevent vital nutrients being passed up the food chain to fish stocks, as well as clogging filtration systems that help the lakes contribute drinking water to many residents in these areas.
The team used data from monthly surveys of lakes that recorded water chemistry and plankton populations for over 30 years, and used the latest statistical techniques to map all the cause-and-effect relationships in these ecosystems to determine that falling water calcium was causing the jelly boom. The results are published in the journal Proceedings of the Royal Society B.
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Image Left: a handful of Holopedium from a lake in the Muskoka-Haliburton region of Ontario. Right: a Holopedium up close
Credit: Left: Ron Ingram, Ontario Ministry of the Environment. Right: Michael Arts, Canada Centre for Inland Waters
Reproduced courtesy of the University of Cambridge
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