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Restoring order: UW Arboretum runoff solutions combine ecology and engineering

Aerial photographs of the progressive invasion of plants and trees
                        into Wingra Marsh

Under the guidance of Civil and Environmental Engineering Assistant Professor Steven Loheide II, 10 students studied hydroecological changes in an area of the UW Arboretum that receives nearly a half-billion gallons of stormwater each year. The students compared several aerial photos; in 1937 (top), wetland vegetation dominated the area, while a photo 70 years later shows a variety of invasive plants and trees—evidence of ecosystem change triggered by sedimentation buildup on the former marsh. (large image)

If the city of Madison were a sink, the UW Arboretum would be the drain.

“It’s right in the middle of Madison, and it’s in a geographic low point—so it gets stormwater from all sides,” says Steven Loheide, an assistant professor of civil and environmental engineering at the University of Wisconsin-Madison.

In theory, an area known as Wingra Marsh filters 470 million gallons of pollutant-laden stormwater that annually flows into the Arboretum from the Madison area. “It runs through a drainage ditch into this area where Secret Pond used to exist, and then through the wetland, into Lake Wingra,” says Loheide. “And the purpose of the pond was to capture the sediment, improve the water quality going into Wingra, reduce the nutrient load, and try to prevent eutrophication problems within the lake.

Now filled completely with sediment, Secret Pond is choked with reed canary grass—Wisconsin’s worst wetland plant, says Arboretum research director Joy Zedler, the UW-Madison Aldo Leopold Professor of Restoration Ecology.

Sediment deposits up to three feet thick also cover the former Wingra Marsh, which has become primarily a forest dominated by invasive species. “Aldo Leopold’s vision was that the Arboretum would provide examples of habitats as they existed prior to European settlement,” says Zedler. “Sedge meadows are good examples. What we have in the Secret Pond area is now mostly invasive vegetation—both exotic and native species. The existing weedy trees, forbs and grasses do little to sustain biodiversity.

In spring 2008, Loheide and 10 undergraduate and graduate students studied a section of Wingra Marsh to learn more about the hydroecologic effects of the massive stormwater inflow. “Stormwater management infrastructure throughout the Arboretum is failing due to age and increased flows of runoff from the surrounding watershed,” says David Liebl, a UW-Madison engineering professional development faculty associate who chairs the Arboretum stormwater committee.

The study was the focus of Loheide’s hydroecology course, which drew on the academic backgrounds of students in civil engineering, geology, geography, environmental science, and water resources management. He developed the course because of a growing need for expertise in hydroecology, a sub-discipline that seeks to study the interaction between the hydrologic cycle and ecosystems. “This research is what people who go out and work for departments of natural resources, for state and federal agencies, or restoration consulting firms—this is what they have to work on, but they don’t have the background,” says Loheide. “Very few people have the background, within one person, to work on it. This class at least gives the students the ability to talk with people from the other disciplines, as well as to handle some of that integration on their own.

With help from Arboretum staff, the students studied vegetation changes evident in historical aerial photos of Wingra Marsh. Seventy years ago, the area was a wetland flanked by a small drainage ditch to the southwest that drains springs from the Nakoma golf course. Twenty years later, an additional 10-foot-wide stormwater drainage ditch appeared in the photos; over time, large cottonwood, box elder, buckthorn, garlic mustard, dame’s rocket, reed canary grass and other invasive plants transformed the wetland to woodland. “A good part of the study area is now covered with trees, whereas almost none was in 1937,” says Loheide.

The students also mapped existing vegetation communities, including the invasive species. “We can start to correlate what vegetation exists there with the soil moisture measurements that are taken and with the water table depth that’s recorded,” says Loheide.

For those measurements, the students installed instruments (some purchased with funds from the Wal-Mart Storm Water Compliance Team) in 21 locations around the study area. The instruments enabled them to observe and monitor groundwater fluctuations, changes in soil moisture, and storm- and groundwater flow along the drainage ditch, as well as to log air temperature and relative humidity. In addition, they used thermal imaging techniques to learn how and where groundwater flows through the study area. “Student projects like these provide valuable data that improves our understanding of site conditions and the options for restoration,” says Liebl.

The Manitou Way/Secret Pond rehabilitation project is scheduled to begin in 2009. In place of the upland and sedge meadow that originally existed, crews will engineer a pond to detain stormwater and capture sediment. In addition, a new drainage channel will include experimental plantings of native species.

Eventually, those plantings will enable researchers to study native plants’ ability to reduce erosion, infiltrate water and resist reed canary grass invasions. “Restoration of native vegetation is needed to sustain biodiversity and compensate for the many losses of habitat elsewhere in the region,” says Zedler. “Our children and grandchildren deserve opportunities to learn from examples of historical ecosystems as intended by the founders of the Arboretum.

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10/9/2008