While many Canadians are aware that Lake Superior is the largest of the Great Lakes, few people know that it also holds the title of the clearest Great Lake — or, that is, it used to. A new study has come out in the Journal of Great Lakes Research stating that in rankings of clarity, Lake Superior has dropped not just to second but to third place, behind Lakes Michigan and Huron.
But while beachgoers may appreciate a clear lake, does the clarity of a lake actually matter? Well, yes, according to scientists. It turns out changes in a lake’s clarity can mean many things, including an increase or decrease in pollutants, or a change in the food supply.
“This is a change of significant historical and economic importance,” the multi-authored study states. “More important may be the ecological implications of the large increases in water clarity in lakes Huron and Michigan.”
While the decreased clarity of Lake Superior may indicate increases in things like farm runoff, the higher clarity of Lakes Huron and Michigan may also be an indication of problems. For starters, one of the reasons for the clearer water is the presence of invasive zebra and quagga mussels, which eat huge quantities of plankton, clearing the water but also decreasing a vital food supply. As the National Wildlife Federation writes on its website, “Clear water may look nice to us, but the lack of plankton floating in the water means less food for native fish.”
Increased clarity also allows sunlight to penetrate deeper into the water, which can contribute to troublesome algae blooms. “Algae foul beaches and cause botulism outbreaks that have killed countless fish and more than 70,000 aquatic birds in the last 10 years,” says the National Wildlife Federation.
As scientists are well aware, ecosystems are complex, and changes tend to ripple outward throughout the whole system. As Robert Shuchman of the Michigan Tech Research Institute and a co-author of the study put it, “It is disruptive to the food web. You go from one-cell algae all the way up to the game fish people like to catch.”
Scientists have yet to figure out a way to eliminate invasive mussels without harming other wildlife, so for now, they are monitoring the situation. People who boat on lakes containing mussels can prevent further spread of the species by thoroughly cleaning their boats’ exteriors before placing them in new bodies of water.