Most of the nitrogen pollution that is killing marine life in the Gulf of Mexico, creating the infamous “dead zone,” originates in Midwestern states such as Ohio and Minnesota, according to a new study by the U.S. Geological Survey, published in the journal Nature. Areas near rivers in the Midwest deliver more deadly nitrogen to the Gulf, and at a faster rate, than areas near streams that are only a few hundred miles away from the Gulf. Sources such as fertilizer, animal waste, runoff from developed land, and soil erosion account from some 90 percent of the nitrogen pollution in waterways. In addition to threatening aquatic life, increased use of nitrogen fertilizer in farming also decreases the number of plant species that can survive on land. University of Minnesota ecologist David Tilman estimates that by 2050 the use of nitrogen will quadruple, causing serious declines in biodiversity.