Long-term Changes in Concentrations and Flux of Nitrogen in the Mississippi River Basin

Current and historical data show that nitrogen concentrations and flux in the Mississippi River Basin have increased significantly during the past 100 years. Most of the increase observed in the lower Mississippi River has occurred since the early 1970s and is due almost entirely to an increase in nitrate. The current (1980-99) average annual nitrogen flux from the Mississippi Basin to the Gulf of Mexico is about 1,555,500 t per year, of which about 62% is nitrate-N. The remaining 38% is organic nitrogen and a small amount of ammonium. The current (1980-99) average nitrate flux to the gulf is almost three times larger than it was during 1955-70.