Total Nitrogen and Phosphorus Flux Delivered to the Gulf of Mexico

Total Nitrogen flux and total phosphorus flux (in metric tons as nitrogen and phosphorus) delivered to the Gulf of Mexico by the Mississippi River Basin during the period 1981 to 2005. The average annual streamflow to the Gulf of Mexico, for the period 1981-2005 was 21,700 cubic meters per second. The average annual flux of total nitrogen and total phosphorus was 1,470,000 and 140,000 metric tons as nitrogen (N) and phosphorus (P), respectively. For the period, annual average streamflow ranged from 13,000 (2000) to 29,500 (1993) cubic meters per second. Annual average flux of total nitrogen ranged from 810,000 (2000) to 2,210,000 (1983) metric tons as N. Annual average flux of total phosphorus ranged from 80,700 (1985) to 180,000 (1987) metric tons as P. Among other factors, nutrient flux was dependent upon streamflow, the major mechanism for downstream transport and delivery to the Gulf of Mexico. For the period 1981-2005, the Upper Mississippi and Ohio/Tennessee subbasins contributed 39 and 34 percent of total nitrogen and 27 and 31 percent of total phosphorus, while comprising only 15.7 and 16.7 percent of the land area, respectively.