Scientist finds vast areas of prairie being drained, warns of consequences
By Kevin Woster
For the Daily Republic
The prairie pothole region of the eastern Dakotas is losing wetlands at a rate up to 15,000 acres a year, according to research that raises questions about the impacts of expanded row-crop production on wildlife and water quality.
Carol Johnston, a wetlands and soil science specialist at South Dakota State University in Brookings, took a birds-eye view of the wetland losses by comparing crop maps and wetland maps and verifying changes through available aerial photography. The data indicated an average loss of 13,000 acres a year over the last three decades and more than 15,000 acres a year in the decade leading up to the 2011 comparison. That's about 20-25 square miles of wetlands losses per year.
Expanded row-crop production driven by higher market prices and the loss of wetland acres enrolled in the federal Conservation Reserve Program are key factors in the conversion of wetlands to croplands, Johnson said.
"We are changing the Dakota landscape and those changes may have real ecosystem consequences," Johnston said.
Those consequences could include degraded water quality, reduced wildlife habitat and less natural flood control in watersheds. Natural wetlands are complicated and valuable features of a prairie landscape shaped by glaciers thousands of years ago, she said.
"They provide fantastic benefits to people," Johnston said of prairie wetlands. "There's just a lot going on there. And once it's gone, it's very difficult to reproduce."
A corn-industry spokeswoman cautioned against reading too much into the study results, noting that some wetlands in parts of northeastern South Dakota have grown during recent periods of heavy moisture.
Lisa Richardson, executive director of the corn-industry association South Dakota Corn in Sioux Falls, said Johnston's study doesn't really account for the expansion of lakes and wetlands in prairie pothole country. Previously small or even dry wetlands have grown and in some cases became lakes, she said.
"You have to give both pieces of it, to be fair," she said.
Richardson also noted that duck production has been strong during the time of the study.
Former state wildlife biologist George Vandel said both of Richardson's assertions are true. But that doesn't diminish the importance of Johnston's study or the need to understand the problems caused by small-wetlands conversion.
Vandel, a retired Game, Fish and Parks Department staffer, said flooding and expanded wet areas in some places do not compensate for the loss of small wetlands that offer particular benefits that a larger flooded area cannot.
The smaller wetlands typically melt and warm up sooner in the spring, for example, providing crucial resting and feeding areas for waterfowl migrating north to breeding areas, Vandel said.
"It's a rural myth to say you can take away a bunch of little wetlands and then create some big wetlands and everybody is happy," he said. "The smaller wetlands of generally less than an acre are incredibly valuable to all kinds of wildlife, not just ducks."
Some SDSU scientists are trying to replicate natural wetland functions that are lost through drainage and tiling. The East Dakota Water Development District in Brookings is helping fund that research, which is aimed at mitigating the impacts of wetland destruction.
District Manager Jay Gilbertson said the project includes the use of "bioreactors" created by digging trenches and filling them with wood chips to strip nitrogen from runoff and release it as harmless gas.
"What we are building there is essentially a tiny underground wetland that acts as a natural nitrogen-removal system," he said.
Nitrogen from unfiltered runoff can cause increased eutrophication -- the presence of excessive nutrients -- in water bodies and safety issues in domestic wells. Nitrate-nitrogen in drinking water can be a particular health threat to children and pregnant women.
Controlling nitrogen levels is essential to maintaining good water quality, particularly in East River areas where aquifers are close to the surface, Gilbertson said.
"Nitrates are big. They're the biggest real concern in drinking water in eastern South Dakota," he said. "The high nitrate levels we see are typically tied to what is going on at the land surface."
Other SDSU research examines the benefits of collecting runoff and diverting it through grass strips that also provide the filtering benefits, to one degree or another, lost when wetlands are destroyed.
The intent of the research is to prevent more serious water-quality issues and the need to clean them up, which is a difficult, expensive chore.
"You can treat it, but it's ferociously expensive," Gilbertson said. "There really isn't a good excuse to let it happen. If we are going to change the landscape, we need to do things to minimize the adverse impacts."
'People need to be aware'
Bill Antonides, a former state conservation officer and past president of the South Dakota Wildlife Federation, said the impacts of wetland drainages are vast and difficult to mitigate. Along with water-quality issues, reducing the wetland acreage lowers the land's ability to slow floodwaters and hurts a variety of wildlife species, including the popular ring-necked pheasant as well as deer and songbirds.
"High corn prices mean more acres converted to cropland. And since they aren't making any more land, it has to come from grasslands, wetlands and even shelterbelts," Antonides said. "When we lose the grasslands, wetlands and shelterbelts, we lose our pheasants."
Richardson said there are misconceptions about how much of the corn expansion in recent years is involving wetlands and other natural lands. The more stable potholes that most people think of when they hear "wetlands" are typically not being farmed because involvement in federal farm programs don't allow it, Richardson said.
"You really can't drain the true wetlands," she said.
Richardson said much of the expansion of corn acreage has been in existing fields previously planted to small grain. That trend has been driven by increased row-crop prices mixed with improved seed genetics and farm equipment that allows farmers to expand corn acreage, she said.
"You have farmers out there who are entrepreneurs, and that's going to guide their decisions," Richardson said. "They're still working to feed the world."
Johnston believes her research gave a fair and accurate accounting of previously mapped wetlands that have been lost to agricultural practices. It did not study wetlands that have grown in size or even turned into lakes because of heavy moisture.
With the coming expiration of several hundred thousand Conservation Reserve Program acres, some of it wetlands, in the pothole region of the Dakotas, there is no indication that the wetland loss will end soon, she said.
The wetlands research is not intended to pass judgment on farm practices but rather make sure the public understands trends out on the land, she said.
"I think people need to be aware of this."