The legacy of decades of industrial pollution affecting our Great Lakes now appears to have taken the form of slimy crustaceans choking the life out of these precious aquatic ecosystems.
A new study released this past week in Proceedings of the Royal Society B has shown that the years of acidification of the lake waters has caused a dramatic decline in calcium levels in Canadian lakes, and that in turn has severely impacted the population of tiny shrimp-like creatures called Daphnia.
Known more commonly as water-fleas because of their swimming style, these tiny creatures that are less than 0.3 mm in size but represent the foundation of all natural, healthy aquatic ecosystems. They can clear waters of toxic algae and are the staple food supply of many fish species.
And this new change in lake water chemistry has led to a boom in the number of another tiny organism that is literally leaving parts of the Great Lakes oozing with slimy jelly. Holopedium is a jelly-clad plankton species that turns out is a direct competitor to the Daphnia and only need one-tenth the amount of calcium to flourish.
Scientists say this jellification will not only affect stocks of critical fish species but also may very well damage vital filtration systems that are used to provide drinking water to urban centres.
“As calcium declines, the increasing concentrations of jelly in the middle of these lakes will reduce energy and nutrient transport right across the food chain, and will likely impede the withdrawal of lake water for residential, municipal and industrial uses,” said study co-author Andrew Tanentzap, an aquatic scientist from the University of Cambridge, in.
“In Ontario, 20 per cent of government-monitored drinking water systems now come from landscapes containing lakes with depleted calcium concentrations that favour Holopedium, and this is only set to increase.”
The Great Lakes are the largest freshwater bodies in the world and have been a primary source of drinking water and fisheries for generations. However, with industrial development and population growth in the region, human-caused acid pollution has skyrocketed in the lakes over the past hundred years.
Increased acidification leads to less calcium carbonate minerals present in the lakes, which are the building blocks of shells and skeletons of tiny crustaceans and mussels, too. And the disappearance of all this calcium from the lakes is not the only foe the hapless Daphnia have to face. Climate change has also led to the loss of oxygen in the waters, which has led to ideal conditions to one of the main insect predators of Daphnia - and has just hastened their decline even more.
According to core samples of lake sediments, calcium loss began precisely at the same time as the start of the industrial revolution in the 1850s, but really began to pick up steam in the 1980s. And the changes will stay for a long time to come, Tanentzap says.
“It may take thousands of years to return to historic lake water calcium concentrations solely from natural weathering of surrounding watersheds,” said Tanentzap.
“In the meanwhile, while we’ve stopped acid rain and improved the pH of many of these lakes, we cannot claim complete recovery from acidification. Instead, we many have pushed these lakes into an entirely new ecological state.”