Anthropogenic inputs of nitrogen and phosphorus and riverine export for Illinois, USA

Agricultural nonpoint sources are important contributors of N and P to surf ace waters. We determined N and P net anthropogenic inputs for Illinois, ex amining changes during the last 50 yr and linkages to surface water:export of N and P. Inputs (fertilizer, atmospheric deposition, and IV, fixation) w ere compared to exports (grain export, after accounting:for animal and huma n consumption, plus animal product export) from 1945 through 1998 using sta te-reported data on fertilizer sales,crop production, and human and animal populations. Large inputs of N were found beginning about 1965, coinciding with increased N fertilizer applications (about 800 000 Mg N yr(-1)). The N input (about 400 000 Mg N yr(-1)) was 8.6 million Mg N for the 1979 to 199 6 crop Sears, with a corresponding riverine flux of 4.4 million Mg N:(51% o f et anthropogenic inputs discharged by rivers). Using literature estimates of field and in-stream denitrification, we could account for nearly all of the missing N in a mass balance. For P, a different pattern was found for state net anthropogenic inputs with a large input from 1965 to 1990, and on average no net inputs since 1990. For rivers, we estimated that 16% of the total N load and 47% of the total P load was from sewage effluent. We esti mate that Illinois contributed 15 and 10% of the annual total N and P loads of the Mississippi River, respectively, and that any reduction strategy in Illinois must address agricultural sources.