Magazine article Natural History

Acid Reign

Magazine article Natural History

Acid Reign

Article excerpt

Calcium levels in many lakes across North America and Western Europe are dropping, and the main culprit is acid rain, a legacy of industrial air pollution. Acid in soils displaces calcium from those soils, as well as from drainage areas that feed lakes. In Canada, the resulting declines in calcium in softwater lakes-those with low levels of dissolved minerals-have been linked to decreases in Daphnia, a tiny but important algae-eating water flea. A key part of many lake food webs, Daphnia needs lots of calcium to maintain its armor-like carapace for predator defense.

Holopedium glacialis, also a water flea and a direct competitor of Daphnia's, doesn't need to beef up its carapace, since it also has a jelly coat that protects it from its predators; hence it has much lower calcium requirements. Paleolimnologist John P. Smol of Queen's University in Ontario, Canada, and eleven colleagues wanted to find out whether Holopedium was receiving a boost over Daphnia as calcium levels dwindled in lakes. First, they examined sediment cores from eighty-four lakes in Ontario and Nova Scotia to compare Holopedium numbers from recent years with those before 1850, prior to the onset of acid deposition. Next, they analyzed two sets of modern-day lake survey data. …

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