new global study evaluated how calcium concentrations are changing in freshwater lakes around the world.

The study revealed that in widespread areas in Europe and eastern North America, calcium levels are declining towards levels that can be critically low for the reproduction and survival of many aquatic organisms, such as freshwater mussels and zooplankton.

Researchers found that the global median calcium concentration was 4.0 mg L-1, with 20.7 per cent of the water samples showing calcium concentrations ≤ 1.5 mg L-1.

≤ 1.5 mg L-1 is a threshold considered critical for the survival of many organisms that require calcium for their survival. Therefore, some lakes are approaching levels of calcium that endanger organisms that rely on that calcium for structure and growth.

The study also attributes some of its results to freshwater lakes’ ongoing recovery from the impacts of acid rain.

“Given governmental and industry action in the last few decades to reduce sulphate deposition associated with acid rain, lakes are now subject to less calcium leaching from surrounding terrestrial areas,” said Gesa Weyhenmeyer, professor in the Department of Ecology and Genetics/Limnology at Uppsala University in Sweden. Weyhenmeyer is also the lead researcher of the study.

“Paradoxically, therefore, successful actions taken to address the harmful impacts of acid rain may have led a decline towards critically low levels of calcium for many aquatic organisms,” Weyhenmeyer said.

The study drew on 440,599 water samples from 43,184 inland water sites from 57 countries and analyzed decadal trends in over 200 water bodies since the 1980s. It was a global study conducted by multiple researchers across Europe and North America.

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The IISD Experimental Lakes Area contributed a significant amount of expertise and data from its long-term monitoring dataset of over 50 years.

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