Robert Burdis, a fisheries expert at the Minnesota Department of Natural Resources, pulls a water sample from Lake Pepin. The birthplace of water skiing, Pepin is rapidly filling in with sediment.
Lake Pepin is filling in fast, and U resesarchers are going to the rescue
By Deane Morrison
Standing in a boat on a hot July day, Deborah Swackhamer surveys the shimmering expanse of Lake Pepin. "It looks so pretty, with all the egrets and pelicans and blue water," she says. "You'd never guess anything was wrong. But you wouldn't want to drink this water." Indeed not. Pepin, a 40-mile bulge in the Mississippi River, is a shallow lake in deep trouble. It is filling in fast and getting more than its share of farm and lawn chemical runoff. The Minnesota Pollution Control Agency (MPCA) wants to know where the sediment and chemicals come from, and Swackhamer, a professor of environmental chemistry and a director of the University's Water Resources Center, is one of many University researchers helping find out. She and fellow director Jim Anderson serve on a scientific advisory panel that will pass University research findings to the MPCA, whose job it is to set limits on sediment and chemical inputs to the lake's waterways and recommend ways to achieve them. If the process works for Lake Pepin, says Swackhamer, it will work for anywhere in the state because Pepin presents a tough challenge. Situated downstream from where the Minnesota and St. Croix rivers feed into the Mississippi and receives inputs from all three--especially the muddy Minnesota. "The Minnesota carries about 25 percent of the flow into the lake but 85 to 90 percent of the sediment load," explains Swackhamer, who is also the interim director of the University's new Institute on the Environment.
"Farmers are losing land to [erosion of streambanks and topsoil]," says Gran. "This is the most valuable farmland in the state."Sediment carried into the lake sinks, choking weeds that provide fish habitat. Fertilizer chemicals like nitrogen and, particularly, phosphorus cause noxious blooms of bluegreen algae. Some chemicals may flow all the way to the Gulf of Mexico, where they are thought to help maintain a huge "dead zone" bereft of fish. By trapping sediment and chemicals, Lake Pepin spares the lower Mississippi some of the burden, but at the price of filling in quickly. Legacy of lobal warming The sediment carried by the Minnesota River was left behind by a lobe of a large glacier during the last ice age. The river runs in a valley gouged out by the ice, through thick layers of rich glacial deposits. It drains a wide area once covered by lush vegetation and extensive wetlands that held and filtered rain and kept the river relatively clear. But early 19th century farmers turned the Minnesota watershed into fields of row crops, and erosion accelerated when they installed drainage tile in fields and wetlands. These underground networks of pipes channel water from the low points in fields to the nearest ditch or stream. "Most rain falls in spring, when fields are empty," says Carrie Jennings, a researcher at the Minnesota Geological Survey. "Drainage tiles concentrate the [runoff]." "Tile is still going in at millions of feet per year," adds geology and geophysics professor Calvin Alexander. " University researchers are taking the first steps to ameliorate the situation in the Minnesota River and Lake Pepin, focusing on the river watershed south of Mankato. Karen Gran, of the University-based National Center for Earth-surface Dynamics (NCED), is one of the leaders of a team conducting a thorough study of sediment movements in the watershed of the Le Sueur River, one of the Minnesota River's most sediment-laden tributaries. The first project of its kind in the country, it will include studies of how tiles and manmade ditches contribute to sediment pollution. A particularly vexing problem is the spread of gullies. During a rain, a gully often splits open like a wound, sometimes ripping a big gash in a farm field overnight. This process exposes huge amounts of soil to erosion. "Farmers are losing land to [erosion of streambanks and topsoil]," says Gran. "This is the most valuable farmland in the state." Among several related projects, an NCED-affiliated researcher from the University of Colorado will survey farmers to see under what conditions and for what ends-such as soil or waterfowl preservation-they would keep water from draining out of their fields. And an NCED affiliate from Johns Hopkins University will study how people make decisions about managing rivers. Many county organizations and landowners are also involved. "The project integrates science and social sciences, whch is good because it's not enough just to identify the main sediment sources," says Gran. "You also need to provide information about the social aspects of solving the problem." The MPCA aims to draw up limits on water turbidity (muddiness) next spring, and the University's work will inform the action plan to achieve those standards. "This is exactly the kind of thing a land-grant institution is supposed to do for the state," says Jennings. FURTHER READING Environment experts join forces
The University's budding Institute on the Environment will put the best talent to work solving pressing problems.