Map showing locations of 9 large subbasins used in CENR hypoxia assessment.

Map showing locations of 42 interior subbasins used in CENR hypoxia assessment.

Long-term pattern in nitrate-N concentrations in the Mississippi River at St. Francisville, LA, 1955-2003.

Long-term pattern in nitrate flux from Mississippi River Basin to the Gulf of Mexico (1955-2003).

Long-term pattern in silica (Si) concentration in the Mississippi River at St. Francisville, LA, 1955-97.

Long term pattern in silica (Si) flux from the Mississippi River Basin to the Gulf of Mexico (1955-96).

Average annual yields (1980-96) of nitrogen, phosphorus, and silica from nine large subbasins in the Mississippi River basin.

Average annual yields (1980-96) of nitrate-N from 42 interior subbasins in the Mississippi River Basin.

Boxplots showing the distribution of annual nitrate-N yields from 42 interior basins (1980-96).

Average annual nitrate-N yields and standard errors for the Scioto River near Higby, OH (1980-94).

Average annual nitrate-N yields and standard errors for the Minnesota River near Jorden, MN (1980-96).

Average annual nitrate-N yields and standard errors for the Iowa River near Wapello, IA (1980-96).

Percentage of the average annual total nitrogen flux to the Gulf of Mexico contributed by selected States in the Mississippi River Basin.

Nitrogen fertilizer use in the Mississippi River Basin shown by hydrologic accounting unit for 1992.

Ammonium nitrogen in wet atmospheric deposition in the Mississippi River Basin shown by hydrologic accounting unit (annual average for 1990-96).

Nitrate nitrogen in wet atmospheric deposition in the Mississippi River Basin shown by hydrologic accounting unit (annual average for 1990-96).

Point source discharges of total nitrogen in the Mississippi River Basin shown by hydrologic accounting unit for 1996.

Estimated nitrogen inputs and outputs for the Mississippi River Basin, 1955-96.

Average annual nitrogen yields from point and nonpoint sources for 42 interior basins in the Mississippi River Basin.

Sources of nitrogen inputs to Mississippi River Basin and 42 interior subbasins, (average for 1980-96).

Nitrogen mass balance for the Mississippi River Basin.