Geotimes - September 2003 - A muddy picture for the Great Lakes

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A muddy picture for the Great Lakes

Ridges of sand wrap around the offshore edges of Lake Michigan, delineating old shorelines. For the past decade, Todd Thompson, a geologist with the Indiana Geological Survey, has used these ridges to reconstruct the lake’s water level over the past 5,000 years. He has found that the lake swings between highs and lows over roughly 30- and 160-year intervals. Those fluctuations have continually varied the habitat near the lake’s edge — submerging it at times and letting it go dry at others. This has widened the swath of wetlands rimming the lakes, and maintained a diverse assembly of plants and animals at Lake Michigan and the other Great Lakes.

Beach ridges near Manistique, Mich., mark where Lake Michigan once lapped against the shore — and provide clues for reconstructing the history of the lake’s ups and downs over several millennia. Photo courtesy Todd Thompson.

Similar water fluctuations on Lake Ontario have all but stopped, however, according to the State of the Great Lakes 2003 report released in August by the U.S. Environmental Protection Agency (EPA) and Environment Canada. Locks and channels built along the St. Lawrence River in the early 1950s to make room for cargo ships evened out the amount of water flowing into the lake each year. Consequently, the wetland margins have shrunk, and cattails have taken over what remains, says Doug Wilcox, a wetland ecologist with the U.S. Geological Survey (USGS). “Cattail invasion has resulted in the loss of much of the short emergent plant community, and especially the sedge and grass wetlands that once occupied much of the shoreline,” Wilcox says.

Lake level is just one of 43 indicators of lake health described in the EPA report that together paint a mixed picture of the lakes — noting some environmental gains but also persistent problems. The report, which comes out once every two years, tracks progress in restoration efforts since Canada and the United States passed the Great Lakes Water Quality Agreement in 1972. Geologists, hydrologists and environmental scientists typically contribute to the report on a volunteer basis, supplying data that they have collected through independently funded projects.

This year’s report is only the second to use the suite of indicators to quantitatively assess the condition of the lakes. In April, the General Accounting Office criticized the indicator process for lacking sufficient funding, coordination and data to quantify progress or regress in the lakes. Largely in response to that report, bipartisan bills in the U.S. House and Senate are working their way through committee, each proposing several billion dollars for restoration efforts, much of which would be used to develop and monitor new indicators. Still, the Great Lakes report provides useful snapshots of the overall condition of the lakes.

While the concentrations of certain chemicals and microorganisms frequently exceed health limits in untreated water, treatment plants remove the majority of those contaminants. The groundwater and surface water in the Great Lakes region, therefore, is safe to drink, the report says. PCBs and mercury levels in fish, however, remain high. Also, E. coli concentrations in coastal waters, mainly from sewage overflow during heavy rains, can make swimming dangerous. In 2001, there were 98 days when at least one of the U.S. beaches along the Great Lakes closed because of dangerously high levels of E. coli. That number is up from 73 in 1998; however, an analysis in the report could not determine if that increase came from a true rise in incidences or just in the rate of reporting.

The report also shows that phosphorous levels have declined significantly since efforts to reduce phosphorous loading began in the 1970s. Excess phosphorous, often from human sources, can stimulate the growth of algae and drive oxygen out of the bottom waters in lakes, making them inhospitable to fish and other wildlife. The report says that total phosphorous in the water for all lakes met or went below target levels, except for in Lake Erie.

The reasons why Lake Erie’s phosphorous levels exceed the target remain unclear, in part because of a lack of data, but are certainly a concern, says Donna Myers, a USGS hydrologist in Columbus, Ohio. During the summer of 2001, the bottom waters in the center of Lake Erie lost all of their oxygen, leading EPA to declare the area a “dead zone.” The following year, EPA funded a $2 million project to determine the cause of the hike in phosphorous levels. The invasion of non-native zebra mussels may have released phosphorous that was bound to sediments or locked into other components of the ecosystem, Myers says. But, she adds, it may also be that phosphorous loading to the lake via streams has increased but gone undetected. In the early 1990s, the USGS measured phosphorous discharge through streams at nearly 40 sites throughout the Great Lakes basin, but funding cuts have winnowed down the number to about a dozen today, Myers says. “It may be invasive species, or it could be increases in phosphorous loading. Our network is simply not in place to measure that,” she says.

Passage of either the House or Senate bill aimed at restoring the Great Lakes could funnel millions of dollars into monitoring indicators, such as phosphorous discharge. These additional resources would allow geologists, hydrologists and environmental scientists, who now contribute to indicators on a voluntary basis, to delve more systematically into the process.

Greg Peterson

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