Aug. 8, 2001 MINNEAPOLIS / ST. PAUL -- Wetlands lost to agricultural development can be reflooded with relative ease, but they won't regain their former flora and fauna without a huge effort, according to research at the University of Minnesota. In what may be the largest study of wetlands restored in agricultural landscapes, Susan Galatowitsch, an associate professor of horticulture, and John Mulhouse, an assistant scientist in applied ecology, found that restored prairie potholes in southwest Minnesota, southeast South Dakota and northern Iowa were quickly colonized by waterfowl-dispersed plants but were slow to acquire a diverse plant community resembling the original wetlands. Their work is being presented Tuesday, Aug. 7, at the Ecological Society of America annual meeting in Madison, Wis.
"To achieve no net loss of both quality and quantity of wetlands will require a bigger commitment to seeing these things through than was previously assumed," said Galatowitsch. "It's a lot more work than people thought. But I think restorations are worth doing, and interest in high-quality wetland habitats is high."
The Farm Bill of 1985 first linked agricultural policy and ecological policy, said Galatowitsch. Farmers were encouraged to restore wetlands historically used as waterfowl breeding grounds. Restorations in the three states studied were funded by the U.S. Fish and Wildlife Service and, in Minnesota, the Minnesota Board of Water and Soil Resources through its Reinvest in Minnesota program. All restorations were done voluntarily by farmers. Galatowitsch and Mulhouse found that while newly refilled wetland basins readily acquired aquatic plants, bulrushes and cattails, the normally diverse edges of marshes tended to become populated with a few weedy species.
"About half [the species] we saw came in fast," said Galatowitsch. "Unfortunately, much of what's spreading is perennial weeds, such as reed canary grass. Weeds can keep other plants from thriving."
Also, she said, although nitrates transported to wetlands are soon converted to nitrogen gas by soil bacteria, the early nitrate load may tip the balance in favor of weeds. Compounding the problem, the fragmented landscape prevents all but common weedy species from making the leap to the next wetland. Swales (intermittently flooded drainage areas) and rivers, however, can connect wetlands.
Much remains to be discovered about how species disperse into wetlands and become abundant and what factors determine species dispersal and survival. One thing is clear, however: Restoring wetlands doesn't come cheaply. For wetlands of up to 10 hectares, restoring water alone costs perhaps $2,000, Galatowitsch said. But a wetland planted with native species could run to $20,000 or even as high as $200,000. The researchers are working to make restoration more efficient and predictable.
"Even though restoration is difficult, we have to do it. We understand more as we go along," said Mulhouse.
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