Canadian lakes are suffering serious damage from a takeover by a jelly-like organism. The cause is a shortage of an element that is often a blight in the water supply: Calcium.
Too much calcium and other dissolved minerals produces hard water, which is a curse for many cities. Calcium and magnesium ions give water an unpleasant taste,
damage boilers and prevent soap suds forming. However, some Canadian Lakes are now experiencing the opposite problem: Water that is too low in calcium, rather than too high.
Many eastern Canadian lakes have been plagued in recent years by outbreaks of Holopedium, particularly H. glacialis, a type of plankton that in large concentrations turns water to jelly. While the effects have been obvious, the cause is not. However, a paper in The Proceedings of the Royal Society B has pointed to a cascade of effects set off by acid rain and factory waste.
The burning of sulfur-rich coal, among many other industrial processes, releases substances that make rain acidic when they combine with water. The release of these chemicals have fallen 75% in North America since 1980 when the Acid Deposition Act was passed, but with huge quantities already in the environment, many lakes are so damaged they need hard rain to fall.
Acid lakes stop fish eggs from hatching and kill insects but the connection to Holopedium was not clear. However, in what freshwater biologists call “aquatic osteoporosis”, the acids combine with calcium and remove it from the water column.
The loss of calcium is exacerbated by rapid forest regrowth after logging, and many Canadian lakes now have calcium concentrations 40% below their levels in the 1980s. In “hardwater lakes”-- where calcium levels are naturally high -- the effect is small, but where surrounding soils lack calcium to begin with, there is now often not enough for crustaceans to form their shells.
Daphnia is a genus of crustacean that have been seriously affected as a result, and they are disappearing from many lakes. In the process other species are losing their major food source.
“Now we’re asking question: if they’re losing, who’s winning?” Queen's University, Canada's John Smol told The Star, “I wish we had some good news here.”
Michael Arts, Canada Centre for Inland Waters. Under a microscope Holpedium looks beautiful, but it is proving disasterous
Smol and colleagues sampled sediments from 84 lakes to demonstrate that the increase in Holopedium is a result of the decline in Daphnia. This trend apparently started in 1850 and accelerated recently. Like all living things, Holopedium need calcium, but not nearly as much as Daphnia, and they compete for other resources.
Native and introduced species that feed on Daphnia but not Holopedium are exacerbating the problem, since low calcium reduces Daphnia's defences.
The authors conclude, “Greater representation by Holopedium within cladoceran zooplankton communities will reduce nutrient transfer through food webs, given their lower phosphorus content relative to daphniids, and greater absolute abundances may pose long-term problems to water users. The dominance of jelly-clad zooplankton will likely persist while lakewater calcium levels remain low.”
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