Use and abuse of the Mississippi river basin

A musty smell repels swimmers from some Iowa lakes in summer, when the bodies of water too often turn brown, green, or blue-green. Researcher John Downing says his state is 92 percent cultivated, so fertilizers seep off croplands into waterways during rains, prompting algae blooms that can harm drinking water and make it tough to boat or catch sport fish. Less than half a pinhead of phosphorus per gallon of water-"a phenomenally tiny quantity," said Downing-is enough to turn a lake bright green. A fleck of phosphorus fertilizer costs a farmer almost nothing. "But that half pinhead per gallon can cost society millions in lost recreational value and cleanup costs," said Downing, an Iowa State University professor whose water-monitoring group tests 137 Iowa lakes.  "We don't have lakes that we could point to and say: 'Here is a pristine lake that has been unimpacted by people.' " (See an interactive map of the world's most important river basins.) You wake up to cereal made from midwestern corn. You slip on cotton clothes, get into a vehicle fueled partly by ethanol and dine later on chicken and rice—all made possible by crops from the Mississippi River Basin, a vast area that stretches from Montana to New York and drains all or parts of 31 states. The part of the basin east of the Mississippi River largely relies on rain to grow crops; farmers on the west side irrigate much, much more. All told, it's among the most productive farming regions in the world. Trouble is, fertilizer that flows from fields (and cities) takes a toll on local waters and eventually reaches the Mississippi River and the economically important fisheries of the Gulf of Mexico, where nitrogen and phosphorus pollution suffocates marine life and has led to a dead zone larger than the state of Connecticut. What's Grown Nearly four out of 10 ears of corn grown in the world come from the Mississippi River watershed. So much corn, soy, and wheat grow here that some communities claim superlatives—Decatur, Illinois, "Soybean Capital of the World;" Sumner County, Kansas, "Wheat Capital of the World;" and Iowa, "Food Capital of the World." The lion's share of the country's corn, grain, livestock, poultry, cotton, sorghum, and soy is grown in the Mississippi basin. A whopping 60 percent of Americans' "water footprint"—their impact on water resources—is in the Mississippi basin, according to new data from the Water Footprint Network and its partner, The Nature Conservancy. And because of American exports of farm products, the Mississippi watershed also supports part of the water footprint of people around the world. It turns out that the United States is the world's biggest net exporter of "virtual water" because of agricultural sales. With corn and other imports, Mexico receives a Nile River's worth of virtual water annually from the U.S.