Loss of wetlands linked to Great Lakes algal blooms

The loss of smaller wetlands is linked to increases in algal blooms in the Great Lakes, a study in Water Resources Research has found.

Wetlands act as natural filters of water runoff from agricultural and urban areas, preventing waste from fertilizer from moving downstream. But as they are lost to development, concentrations of nitrogen and phosphorous in the Great Lakes are rising, resulting in higher levels of algal blooms. The algae have a number of deleterious effects on the Lakes, including making beaches unsafe for swimming, degrading drinking water quality, and depleting oxygen relied on by aquatic fauna.

Lake Erie algal blooms, August 2011
Photo: Tom Archer, Michigan Sea Grant, University of Michigan

The study found that smaller wetlands are more effective nutrient sinks than larger ones because more of their water is in contact with soil, either at the bottom or shoreline, where excess nutrients are removed and prevented from moving downstream. However, wetland conservation efforts have largely concentrated on preserving total wetland area rather than maintaining a distribution of wetlands of various sizes within the landscape.

“Wetland loss has multiple impacts, including flooding, loss of the nutrient filter and loss of flora and fauna and biodiversity in general,” said study co-author Nandita Basu, assistant professor of water sustainability and ecohydrology at the University of Waterloo, Ontario, Canada. “Different wetlands have different functions, and thus our goal should be to understand these differences and preserve a portfolio of functions.”

Aqua Earth-observing satellite image of algae in the Great Lakes. NASA Earth Observatory.

In their study, Basu and Fred Cheng, a PhD candidate at Waterloo, looked not just at wetlands, but at a variety of still-water systems, including lakes and reservoirs as well. “This was motivated partially by the fact that similar research has demonstrated small streams to be more effective nutrient processors, and we believed that the same would hold true for wetlands,” said Basu.

Her research group’s earlier work had shown that smaller wetlands are often disproportionately lost compared to their larger, downstream counterparts, said Basu. A recent study by the US Geological Survey Powell Center Group explored the loss and need for protection of geographically isolated wetlands globally.

The Great Lakes Basin has already lost more than 50 percent of its wetlands, with coastal wetlands in some areas having declined by as much as 95 percent. I asked Dr. Basu if she thinks we’ve passed we can still recover from or at least mitigate the effects of this loss.

“That’s a tough one,” she said. “There are people who argue that Lake Erie has passed a tipping point. I am an optimist. I believe that we can mitigate at least some of the issues, but it would take time and resources.”



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