A plague of "aquatic osteoporosis" is spreading throughout many North American soft-water lakes due to declining calcium levels in the water and hindering the survival of some organisms, says new research from Queen's University.

Researchers from Queen's, working with colleagues from York University and the University of Cambridge, as well as other collaborators, have identified a biological shift in many temperate, soft-water lakes in response to declining calcium levels after prolonged periods of acid rain and timber harvesting.

The reduced calcium availability is hindering the survival of aquatic organisms with high calcium requirements and promoting the growth of nutrient-poor, jelly-clad animals.

In the study, researchers looked at the microscopic organisms (~1 mm) Daphnia and Holopedium - the latter whose size is greatly increased by its jelly capsule.

"Calcium is an essential nutrient for many lake-dwelling organisms, but concentrations have fallen so low in many lakes that keystone species can no longer survive," says Adam Jeziorski, one of the lead authors of the study and a postdoctoral fellow in the Department of Biology at Queen's.

The research team found that when calcium levels are low, the water flea Daphnia, which has high calcium requirements, becomes less abundant. Importantly, this keystone species is being replaced by its jelly-clad competitor, Holopedium.

"Conditions now favour animals better adapted to lower calcium levels, and these changes can have significant ecological and environmental repercussions," says Dr. Jeziorski. Tiny fossils from lake sediments were studied to determine the pre-impact conditions of the lakes as the calcium decline began before monitoring programs were in place. Using this technique, the team was able to examine the environmental trends from the past approximately 150 years.

"Lake sediments act like a history book of past changes in a lake, recording what happened before the problem was identified," says John Smol (Biology), Canada Research Chair in Environmental Change.

"Jelly-clad invertebrates have been increasing in an alarming number of lakes. This is likely a long-term effect of acid rain on forest soils, logging and forest regrowth."

The increase in jelly-clad invertebrates can have important implications for lake biology, altering food webs, but can also clog water intakes.

"Many lakes we investigated have passed critical thresholds," says Dr. Smol. "We have been reduced to the role of spectator as these changes continue to unfold. Once again we see there are many unexpected consequences of our actions, most of which are negative."