Nutrient load characterization from integrated source data for the lower Mississippi River

Nutrient data from all available sources for the lower Mississippi River we re examined for potential differences among sampling agencies and geographi c locations for the period between 1960 and 1998. Monthly means grouped by parameter, sampling location and agency, were calculated and compared as pa ired sets, excluding those months where data were not available for both se ts. Some significant differences were found between various agencies collec ting nutrient data on the river, as well as between various stretches of ri ver, especially in the case of phosphorus nutrient data. Results were used to synthesize data sets from which a history of nutrient loading in the Mis sissippi River was determined. General trends in nitrate+nitrite, total Kje ldahl nitrogen, orthophosphate, total phosphorus and silica loads, as well as changes in nutrient proportions and the specific limiting nutrient (by m onth) are reported. This study provides a useful summary of contemporary an d historical nutrient data that may assist in the evaluation of Mississippi River water quality and its potential effect on the Gulf of Mexico.