Map: Chris Brackley/Canadian Geographic

It’s no secret that the Great Lakes are suffering tremendous ecological strain — Lake Erie was even pronounced “dead” for a time during the 1960s because of an overload of phosphorus from municipal waste. Back in 1615, though, when the entire region was pristine and explorers Samuel de Champlain and Étienne Brûlé gazed out together from Lake Huron’s shores, they dubbed it la mer douce, “the sweet sea.” Today roughly one-quarter of Canada’s population and a 10th of America’s population drink from the Great Lakes basin; the beleaguered lakes alone hold more than a fifth of Earth’s freshwater.

The Great Lakes Environmental Assessment and Mapping Project — a group of about 20 American and Canadian researchers and environmentalists — produced the data for this map, which illustrates the cumulative impacts of human activity across the Great Lakes. It speaks volumes at a glance. David Allan, team lead for GLEAM’s project and a professor at the University of Michigan’s School of Natural Resources and Environment, hopes the map will help improve how we manage the Great Lakes.

For three years, GLEAM’s scientists analyzed, weighted, plotted and merged 34 environmental stressors, including various effects of residential, commercial and industrial development, crisscrossing shipping lanes, thriving invasive species (in many areas, zebra and quagga mussels are a more serious problem than pollution) and climate change.

“The red spots on this map are not all red for the same reasons,” says Allan. “Our goal is to help people understand that there are many complex combinations of stressors at play here and that they have a spatial pattern. We have to resist the temptation to say, ‘What’s the most important thing? Let’s fix that.’ ”

Five of the most significant stressors:

Tributary dams
The damming of tributaries impedes the flow of water, nutrients and sediment to and between the Great Lakes, and threatens the diversity of native fish species by blocking routes between spawning, nursery and overwintering habitats. (Map: GLEAM)

Reduced ice cover
Ice cover on the Great Lakes has decreased by more than 71 per cent during the last 40 years. When ice cover melts earlier in the spring, water temperatures are likely to be higher throughout the year. (Map: GLEAM, see data credit #1)

Zebra and quagga mussels
These highly invasive species have colonized all five of the Great Lakes. Zebra mussels first appeared in Lake St. Clair (north of Lake Erie) in 1986, having come from the Black and Caspian seas, while Quagga mussels came to Lake Erie in 1989 from the Dneiper River drainage of Ukraine. (Map: GLEAM, see data credit #2)

Phosphorous loading
High phosphorus levels in the Great Lakes, the result of agricultural and municipal runoff, propels eutrophication and the growth of nuisance algae. This can lead to hypoxia (oxygen depletion) and threatens numerous lake species. (Map: GLEAM)

PCBs in Great Lakes Sediments
PCBs haven't been manufactured and imported to North America since around 1980, but the effects of these highly toxic compounds — once used as coolants and insulating fluids in transformers, capacitors and electric motors — are still felt in the complex food web of the Great Lakes. (Map: GLEAM, see data credit #3)

Go to greatlakesmapping.org for information on all 34 lake stressors.

Credits

  1. Reduced ice cover
    Ice cover on the Great Lakes has decreased by more than 71 per cent during the last 40 years. When ice cover melts earlier in the spring, water temperatures are likely to be higher throughout the year.

    Map credit:
    a. Wang, J., X. ai, H. Hu, A. Clites, M.Colton, and B. Lofgren. 2012: Temporal and Spatial Variability of Great Lakes Ice Cover, 1973–2010. J. Climate, 25, 1318–1329.

    b. Assel, R., K. Cronk, and D. Norton. 2003. Recent trends in Laurentian Great Lakes ice cover. Climatic Change, 57(1-2):185-204.

  2. Zebra and quagga mussels
    These highly invasive species have colonized all five of the Great Lakes. Zebra mussels first appeared in Lake St. Clair (north of Lake Erie) in 1986, having come from the Black and Caspian seas, while Quagga mussels came to Lake Erie in 1989 from the Dneiper River drainage of Ukraine.

    Map credit:
    Lake Superior: Data collected by US Environmental Protection Agency, provided by J. Scharold. Lake Huron: Nalepa, T.F., D.L. Fanslow, S.A. Pothoven, A.J. Foley III, G.A. Lang, S.C. Mozley, and M.W. Winnell. 2007. Abundance and distribution of benthic macroinvertebrate populations in Lake Huron in 1972 and 2000-2003. NOAA Technical Memorandum GLERL-140. Ann Arbor, Michigan. Lake Michigan: Nalepa, T.F., D.L. Fanslow, G.A. Lang, D.B. Lamarand, L.G. Cummins, and G.S. Carter. 2008. Abundance of the amphipod Diporeia and the mussels Dreissena polymorpha and Dreissena rostriformis bugensis in Lake Michigan in 1994-1995, 2000, and 2005. NOAA Technical Memorandum GLERL-144. Ann Arbor, Michigan. Lake Erie: Data collected through Lake Erie Collaborative Comprehensive Survey, provided by J. Ciborowski Lake Ontario: Watkins J.M., R. Dermott, S.J. Lozano, E.L. Mills, L.G. Rudstam, and J. Scharold. 2007. Evidence for remote effects of dreissenid mussels on the amphipod Diporeia: analysis of Lake Ontario benthic surveys, 1972-2003. Journal of Great Lakes Research 33(3):642-657.

  3. PCBs in Great Lakes Sediments
    PCBs haven't been manufactured and imported to North America since around 1980, but the effects of these highly toxic compounds — once used as coolants and insulating fluids in transformers, capacitors and electric motors — are still felt in the complex food web of the Great Lakes.

    Map credit:
    a. Henny C..J, R.A. Grove, J.L. Kaiser, and B.L. Johnson. 2010. North American Osprey Populations and Contaminants: Historic and Contemporary Perspectives. Journal of Toxicology and Environmental Health. Part B 13(7-8):579-603.

    b. Canadian Environmental Law Association and University of Illinois-Chicago. 2001. Human health effects associated with PCB exposure. Report: Environmental Profile of PCBs in the Great Lakes. Online: http://www.uic.edu/sph/glakes/pcb/health_effects.htm. Accessed 09 February 2012.

    c. Marvin, C., S. Painter, D. Williams, V. Richardson, R. Rossmann, and P. Van Hoof. 2004. Spatial and temporal trends in surface water and sediment contamination in the Laurentian Great Lakes. Environmental Pollution. 129:131-144.