nitrate and herbicides were transported (Goolsby et al., 1993). The Mississippi River basin
contains 65 percent of the cropland in the United States. An estimated 100,000 metric tons of
pesticides and 6,300,000 metric tons of nitrogen fertilizer are used annually in the basin. In
comparing 1992 and 1993 loads at the mouth of the Mississippi, Goolsby et al. (1993) found a
112 percent increase in the 1993 total load of nitrate. Similarly, the load of atrazine, a common
herbicide used in corn production, increased by 235 percent.