Iowa- how much is nature and how much is man?

""I sense that the flooding is not the result of a 500-year event," said Jerry DeWitt, director of the Leopold Center for Sustainable Agriculture at Iowa State University. "We're farming closer to creeks, farming closer to rivers. Without adequate buffer strips, the water moves rapidly from the field directly to the surface water."
Corn alone will cover more than a third of the state's land surface this year. The ethanol boom that began two years ago encouraged still more cultivation.
Between 2007 and 2008, farmers took 106,000 acres of Iowa land out of the Conservation Reserve Program, which pays farmers to keep farmland uncultivated, according to Lyle Asell, a special assistant for agriculture and environment with the state's Department of Natural Resources (DNR). That land, if left untouched, probably would have been covered with perennial grasses with deep roots that help absorb water.
The basic hydrology of Iowa has been changed since the coming of the plow. By the early 20th century, farmers had installed drainage pipes under the surface to lower the water table and keep water from pooling in what otherwise could be valuable farmland. More of this drainage "tiling" has been added in recent years. The direct effect is that water moves quickly from the farmland to the streams and rivers.
"We've lost 90 percent of our wetlands," said Mary Skopec, who monitors water quality for the Iowa DNR. " LINK