University researchers have teamed up with international colleagues in a recently released study to analyze the most pressing issues that endanger the Great Lakes.

The University-centered Great Lakes Environmental Assessment and Mapping project identified mercury contamination, changing water levels, four invasive species and 28 other environmental stressors disruptive to the Great Lakes.

GLEAM presented these findings on a website launched in December that features interactive maps of the Great Lakes. The findings are also published in the Jan. 2 Proceedings of the National Academy of Sciences journal.

The maps exhibit how each individual stressor affects an area in the Great Lakes, and a general map shows the total impact of the stressors. The stress index of the latter map indicates that Lake Ontario is the most affected, followed by Lakes Erie, Michigan, Huron and Superior. Other maps illustrate the benefits that the lakes provide humans, such as beaches and commercial fishing.

J. David Allan, a professor in the School of Natural Resources and Environment and one of four leaders of GLEAM, said the ongoing project is intended to “develop the right kinds of information to assist restoration.”

The project — now tied to the three-month-old University of Michigan Water Center — was funded by the Fred A. and Barbara M. Erb Family Foundation, a group that supports initiatives to better the Great Lakes community.

Adrienne Marino, a research specialist at the Water Center, said she assisted in the collection of data provided by researchers and resource management agencies hailing from the Great Lakes region. The team compiled data by analyzing, processing and mapping published research and weighing the importance of each stressor.

“Applying stressor weightings and completing other transformations and calculations were necessary to put the individual maps on a consistent scale and to develop the cumulative map,” Marino said.

Gregory Boyer, chair of chemistry at the State University of New York’s College of Environmental Science and Forestry, was one of the 15 working group members.

Boyer noted that the most destruction has occurred in shallow waters. In deeper offshore waters, Boyer said, water separates into warmer top waters and cooler deep waters. Between these two layers is a thermocline, an area where dramatic temperature change occurs.

Boyer said this stratification is necessary to prevent pollutants from affecting humans and to ensure that harmful algal blooms cannot reach sunlight that would support its growth, a process that would lead to other environmental complications.

“When you’re talking about a chemical pollutant … offshore, it absorbs through a particle, goes through the thermocline and is effectively removed from human contact,” Boyer said.

Boyer said he worries that shallow waters were most affected.

“This is especially troublesome because these are the waters that humans use more, like in beaches,” Boyer said. “Nearshore often sees more stress than the offshore waters.”

Allan said the GLEAM project has already provided data to the Nature Conservancy, the U.S. Fish and Wildlife Service and other environmental groups. But, he said, additional work is still necessary. For example, the cumulative stress index used by the maps, which totals up each stressor and its weighted importance, doesn’t fully convey environmental problems.

“Increasingly in the field of understanding environmental stressors affecting ecosystems, we realized that stressors are interactive,” Allan said. “Invasive species one and invasive species two might be a double whammy that’s bigger than their sum.”

In the meantime, Sigrid Smith, a research associate of the School of Natural Resources and Environment who also led GLEAM, said the Great Lakes might never reach hypothetical “normal” environmental conditions. For that reason, targeted goals may need rethinking.

“I think of the target of restoration as promoting ecosystem health, so that the native populations of plants, animals and other organisms are as healthy as possible and produce as much human benefit as possible,” Smith said.

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