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ISU researchers get drenched studying wetland health in Upper Midwest

By Staff | Nov 5, 2010

AMES – Slogging through ponds and marshes to collect fish, test for chemicals and monitor plant and invertebrate populations makes for long, tiring days.

When you’re trying to discover what criteria can distinguish a healthy wetland from an ailing one, you need to get wet yourself.

Timothy Stewart, assistant professor of natural resource ecology and management at Iowa State University, and Kristine Maurer, an ISU graduate student, are collecting physical, chemical and biological data from 37 wetlands in northern Iowa which are part of the Prairie Pothole Region.

They hope to identify the most reliable indicators of a healthy wetland ecosystem.

The Prairie Pothole Region is an area stretching from Iowa, northwest across western Minnesota and much of North and South Dakota, and into Manitoba, Saskatchewan and Alberta, Canada. It was created when the glaciers receded, leaving millions of shallow depressions.

“We are measuring more than 100 variables in the wetlands. And our goal is to identify a subset of those, maybe 12 indicators, that we can measure in a wetland and, based on values obtained, will tell us whether or not the wetland is in good condition,” said Stewart. “A healthy wetland, for example, generally has good water quality, supports high biological diversity, and has greater capacity to support waterfowl than one in poor condition. If a wetland is found to be in poor condition, indicators will help identify specific problems and guide remediation strategies.”

These 12 measurable wetland condition indicators will be transferable to other wetlands in the Prairie Pothole Region.

Maintenance of healthy wetlands is important because of the wide variety of services these ecosystems perform, said Stewart.

The value of wetlands is exemplified by recent flooding problems in Iowa, he added.

“For example, wetlands are important for flood prevention because they absorb water flowing off the landscape, thereby reducing the rate at which water falling on the earth reaches streams,” said Stewart. “Similarly, wetlands help retain sediment and soil on the landscape, preventing this material from being washed into streams where it contributes to water-quality problems.”

Healthy wetlands can also provide critical habitat for several of Iowa’s endangered species, such as certain types of turtles.

Stewart also stresses that wetlands have huge economic impact for Iowa and other states.

Healthy wetlands provide breeding, resting and foraging sites for wildlife that, in turn, attract hunters and birdwatchers, affecting sales of hunting licenses, tourism and hospitality-based businesses, he said.

Stewart suspects that a few of the wetland condition indicator variables he identifies through his research will include invertebrate species richness, water clarity and presence of large-bodied fish.

Large-bodied fish appear to be critical determinants of wetland condition. Common carp, bullhead and other large fish were not historically abundant in Iowa prairie pothole wetlands, but now occur in many of these ecosystems and are causing significant problems, according to Stewart.

“Large fish stir up wetland sediment while foraging, and that reduces water clarity,” he said. “Fish foraging activities also increase nitrogen and phosphorus in the water, which stimulates noxious algae blooms. Fish can also physically uproot plants and reduce the number invertebrates by eliminating their habitat and predation [consuming them].”

Large fish may be introduced to wetlands when nearby streams and rivers flood. When the flood water recedes, many fish are ‘stranded’ in the ponds where they often thrive. Fish can also invade wetlands from streams and rivers via constructed drainage ditches, said Stewart.

Once wetland condition index criteria are established, Stewart and Maurer’s research will provide guidance to the Iowa Department of Natural Resources and other agencies and individuals that monitor or restore wetlands in the Prairie Pothole Region.

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