The Great Lakes Stress Test New Tool Helps Monitor Environmental Threats

The Great Lakes, consisting of Lakes Superior, Michigan, Huron, Erie and Ontario, are under threat. Now, a new mapping tool allows researchers to see just how deep the problem runs.

Great Lakes' width=These freshwater lakes contain 21% of the world’s surface fresh water. They are a major source of trade and commerce and, as a result of the ships and manufacturing plants that use them, have some of the highest concentrations of pollutants in the country, including mercury, PCBs and agricultural runoff.

Researchers led by the University of Michigan have created a comprehensive map of the Great Lakes’ stressors, and the first map to date that details all major stressors on the lakes in a quantitative way. “Despite clear societal dependence on the Great Lakes, their condition continues to be degraded by numerous environmental stressors,” said David Allan, the project’s lead researcher and a professor of aquatic sciences at the University of Michigan’s School of Natural Resources and Environment, in a related release

The map was created by a team of researchers known as the Great Lakes Environmental Assessment and Mapping (GLEAM) project. In addition to a cumulative stress index map, the research team generated separate digital maps for 34 individual lake stressors. The stressors are broken down into seven categories which include changes to aquatic habitat, climate change, coastal development, fisheries management, invasive species, nonpoint source pollution and toxic chemical pollution. The researchers will continue to add stressors as more data becomes available

The comprehensive map illustrates both high- and low-stress regions, showing that stress is highest closer to shorelines, but also extends offshore in some areas. “Current efforts to conserve, manage and restore the Great Lakes often take a piecemeal approach, targeting threats one by one,” Allan said. “We need to recognize that the Great Lakes are affected by multiple environmental stressors and devise strategies [accordingly].” Large areas of cumulative stress were found in Lakes Erie and Ontario and along Michigan’s shorelines. In contrast, offshore areas of Lakes Superior and Huron, where the coasts are less populated and developed, showed relatively little stress.

A key goal of the mapping effort is to help lawmakers and natural resource managers better plan Great Lakes-area investments, such as those under the Great Lakes Restoration Initiative. The initiative is a federal effort launched in 2009 that funds projects at sites where ecosystem stress is very high. The researchers caution against using the finer scales of the online mapping tool, since there is a risk of over-interpreting the data as you zoom in. The most meaningful scale, they say, is at 30,000 feet, which provides for regional comparisons among the lakes and drawing conclusions at large spatial scales.

The Great Lakes region serves a number of important functions including drinking water, food, water purification and recreational and aesthetic benefits. Researchers mapped the ecosystem services provided by the region by including locations of beaches, marinas and bird-watching sites. To quantify provisioning services, the researchers accounted for the distribution and magnitude of commercial harvests and home ports for charter fishing vessels. The map also includes spawning locations of two important species of fish, lake trout and yellow perch. Comparing maps of ecosystem services to maps of stress, the researchers found that locations providing human benefits were often disproportionately stressed.

The climate change maps showed evidence of changing water levels, decreased winter ice cover and warming water temperatures, too. As with other mapped stressors, the maps display this climate change data in a way that hasn’t previously been available. The water temperature map illustrates that summer surface water temperatures are increasing across all five lakes. Warming temperatures in the lakes are expected to alter the range and abundance of many species and promote the spread of algae and other invasive aquatic organisms. Lake Superior is one of the most rapidly warming lakes in the world. The ice cover map shows the greatest loss in ice cover along the shorelines of the upper Great Lakes, especially in large bays like Grand Traverse Bay, Georgian Bay and on Lake Superior. Over the last few months, there have been record low water levels reported in Lakes Michigan and Huron

In addition to helping identify high stress areas for restoration, the maps may also help broaden the types of restoration projects in the Great Lakes region. With detailed information on the types of stressors, more strategic restoration projects can be used to target areas of high stress. The maps make it clear just how crucial it is that Great Lakes remediation efforts are a success.