P> 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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Contact: Deane Morrison
morri029@umn.edu
612-624-2346
University of Minnesota
8-Aug-2001

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