The mystery of restored wetlandsBy Laura Miller It is surprising that the water quality in the Iowa Great Lakes region has not improved in recent years. More than 300 restored wetlands and large amounts of land in agricultural set-aside programs haven't stemmed the flow of nitrates, phosphorus and other nutrients into the region's lakes. Why not is a mystery. Arnold van der Valk, Iowa State University botany professor and director of Iowa Lakeside Laboratory at West Okoboji Lake, is searching for the clues needed to solve the wetlands mystery. He is director of a three-year research project jointly funded by the Leopold Center and the Iowa State Water Resources Research Institute. Working with van der Valk are Bill Crumpton, also in botany at ISU, and Steve Fisher who runs the Bovbjerg Water Chemistry Laboratory at Lakeside. The Leopold Center work further expands an update of a water quality study done in the 1970s by Roger Bachmann and John Jones from ISU. Bachmann and Jones identified 50 subwatersheds in the Iowa Great Lakes Watershed (IGLW), a 64,000-acre area in northwest Iowa that drains into the Okoboji lakes, Spirit Lake and the Gar lakes. They took weekly samples from the lakes and water leaving the subwatersheds between March and August of 1971, 1972 and 1973. Starting in spring 1998, van der Valk's team began monitoring some of the same watersheds on a weekly basis during the ice-free season for concentrations of nitrate, total nitrogen and total phosphorous. "We found out that the overall water quality has not changed in 30 years and in some cases, it has gotten worse, despite a lot of water quality improvement projects in the watershed," van der Valk said. "Phosphorus levels remain about the same and if anything, nitrate levels seem to be considerably higher." The Leopold Center project, now in its second year, builds on ISU's updated study in two ways:
First, subwatersheds in the Bachmann and Jones study were matched to 10 subwatersheds sampled in the updated study. The watersheds represented a variety of areas in which row-crop production had changed since the 1970s. "There is no evidence that nitrate loads to the Iowa Great Lakes have decreased significantly since the 1970s," van der Valk reported. "Nevertheless, efforts to reduce nitrate loadings to the lakes have been effective in those subwatersheds in which cropland acres have been reduced and in which wetlands have been restored." During the second year, researchers identified six restored wetlands on private property surrounded by crop fields. Since March, they have been taking weekly samples from inflow and outflow at each wetland to determine the levels of nitrogen and phosphorus. The goal is to determine the effectiveness of each restored wetland in removing nutrients. "This has been more time consuming than we anticipated," van der Valk said. "We are finding drainage tiles that were not broken when the wetlands were constructed because there weren't any records when the tiling was done. There might not be records when the tiles were fixed or changed, and it can be very difficult to find tiles underground." van der Valk explained that in the construction of wetlands, existing tiles must either be broken to interrupt the water flow, or made impermeable to local water if they are part of a larger drainage network. Location and size of the tile break, pipes to channel water to the surface, small dams, and other construction designs are all part of the wetland restoration. The team is analyzing data, but van der Valk said they are finding that many of the restored wetlands are improperly designed or sited. He explained that restored wetlands, in general, might not work because they are not located at critical points in a watershed, or they are not large enough to handle nutrient loads. Restored wetlands also may need as many as 8 to 10 years to reach optimum nutrient-removal capacity. "The bad news is that many of these restored wetlands were not well designed and in some cases are short-circuiting the problems they were intended to solve," he said. "The good news is that if wetlands are restored in a proper way, they can remove up to 90 percent of the nitrates and a large amount of the phosphorus that normally would be washed into a lake or waterway." The team has identified 304 restored wetlands in the IGLW. During the next year, team members hope to develop a model that can be used to evaluate other wetlands in the watershed and pinpoint areas where improvements may be needed. van der Valk said water quality improvement is a long-term process. Research on buffers and wetlands, including major efforts funded by the Leopold Center, have been important but need time to be put to use on the landscape. "The political and social realities don't always match the biological and hydrological boundaries, " he said. "Farmers have been very, very supportive of wetland restoration and land conservation programs but as of yet, these are nontargeted programs available on a voluntary basis. It's going to take a lot of time and more fine-tuning to see results." "We do know one thing," he added. "Nutrient loads will go up if we don't do anything at all." Total Phosphoras concentrations for West Lake Okoboj from 1972 through 1999.
Iowa wetlands: An overview • The Iowa Department of Natural Resources estimates that 97.5 percent of Iowa's pre-settlement wetlands has been lost and only 36,500 acres of prairie pothole marshes remain. • Private landowners control 78 million acres of wetlands in the United States. "We have no buffers anymore between farm fields and lakes and rivers," explains ISU botany professor Arnold van der Valk. "Historically, wetlands provided such a buffer. "The preservation of existing wetlands and the restoration of wetlands, which are both needed, is going to require a partnership between farmers and environmentalists. And it will need to be done on private land if it is to be effective." |
