Watershed study solidifies science behind ecosystem restoration projects
Working with The Nature Conservancy in Wisconsin and the state Department of Natural Resources (DNR), a pair of University of Wisconsin–Madison hydroecologists is evaluating the efficacy of an ecosystem restoration project along a stretch of the Pecatonica River near the small town of Barneveld in southwest Wisconsin.
Results of their research could apply to similar watershed restoration initiatives around the country.
In southwest Wisconsin — the undulating, unglaciated terrain known as the Driftless Area — 170 years of farming and grazing has wiped out former prairies and oak savannahs and eroded hill slopes, resulting in sediment runoff into neighboring streams.
“When you have this different surface — the agriculture on the upland, contributing more water to the valleys — you have more floods, and with those floods, you have a lot more sediment in them,” says limnology Ph.D. student Eric Booth, who, with assistant professor Steven Loheide, is studying the area.
Over time, floods carried sediment over the Pecatonica floodplain, depositing it on the land. The sediment buried former wet prairies and sedge meadows, building up the watershed and triggering ecosystem changes driven by the rising land surface.
“What you’re left with now is a floodplain surface that’s much further from the water table, and it’s drier, without the sedge meadow and wet prairie,” says Booth. “You also have cropland and grazing on the floodplains.”
For the restoration project (funded through state wildlife action grants), crews “scraped” sediment more than 2 feet deep — the equivalent of 12,000 cubic yards of topsoil — from about 20 acres of floodplain. “If you reduce that land surface elevation, you have more room for floods to spread out during a major flood event,” says Booth. “That is helpful for not only reducing the flood peaks downstream — you’re reducing the energy of the flood by letting it spread out — but you’re also improving the connection between the channel and the flood plain. That can have effects on water-quality improvement.”
Plants and soil on the flood plain, says Booth, act as a filter, removing excess nutrients from floodwaters.
During the project, The Nature Conservancy, which owns the restored land, gave the scraped topsoil away as a means to generate community awareness of and interest in the restoration. “The soil is also a possible funding mechanism for this type of restoration,” says Loheide. “It’s really good topsoil.”
For projects like this one, and others, it’s not enough to simply restore a site and trust that nature will take care of itself. Both The Nature Conservancy and DNR view the Pecatonica site as a restoration observation laboratory, says Loheide, and the groups are interested in learning how to improve the science behind restoration. “Right now, restoration is really a qualitative science,” he says. “A lot of restoration is being done — about $1 billion a year in the country — but only about 10 percent of those projects are monitored or evaluated.”
Steve Richter, director of conservation for the southwest Wisconsin chapter of The Nature Conservancy, says Booth’s analysis will tell the group whether the restoration project has affected water quality, water flow, temperature and many other variables. “To me, it’s answering these very simple, but critical, questions,” he says. “Too many times we don’t do that.”
Since summer 2007, Booth has monitored the site to quantify the hydrologic and vegetative effects of the restoration project. He hopes to learn more about how water moves through the site and the relationship between the water table and vegetation communities.
In late summer 2007, Booth got an unexpected experimental opportunity in the form of torrential rain — 9 inches fell in less than 12 hours — and flooding in the area. When he arrived at the restoration site, he found that it had effectively reduced the velocity of floodwaters through the river and gently spread the excess over the floodplain, lessening erosion and encouraging sediment deposition.
“We’re very pleased,” says Richter. “Last year’s August rain and this spring’s rain has done minimal damage to the site. To me, it’s doing what it’s supposed to be doing.”
In contrast, an adjacent unrestored site showed powerful water flow down the river, causing more bank erosion.
Like other restoration initiatives, the Pecatonica project provides increased natural habitat for wildlife and amphibians. That’s an area of interest for groups such as Trout Unlimited, Ducks Unlimited or the Wisconsin Waterfowl Association, whose missions include restoring and managing habitats for fish, wildlife and waterfowl.
Already, says Richter, a large number of frogs have taken up residence at the restored site. “I likewise hope that there’ll be some indication that turtles, birds and snakes will find that this instant habitat — the reconnection of land to the stream, which is so, so rare in southwest Wisconsin — will provide a great habitat,” he says.
Ultimately, Booth plans to translate his field data into a computer model that will enable watershed managers to predict the ecological effects of the changes they make.
For Loheide and Booth, it’s rewarding that citizens and environmental groups are passionate not only about ecosystem restoration, but also how to apply scientific analyses to improve the outcome. “They’re probably not going to read your journal articles, but they care about your results,” says Loheide. “They want to know what this research is finding and how it can help the system.”