Comparative analysis of nutrient data in the lower Mississippi River

As the second phase of a large-scale Tulane University Mississippi River wa ter-qualify database project, nutrient data on the lower Mississippi River have been examined for potential differences among sampling agencies, geogr aphic locations and chemically similar nitrogen parameters. These data repr esent the most comprehensive source of information on nutrients in the Miss issippi River available as a single database. Monthly means, grouped by par ameter, sampling location and agency, were calculated and compared as paire d sets, excluding months where data were not available for both sets. Evalu ations using ANOVA indicated few differences among agencies providing nitro gen-compound data, although differences were observed in phosphorus-compoun d data from different sources. Unfiltered and filtered fractions of nitrate -nitrite were found to be comparable throughout the study area. Spatial exa mination of the nutrient data indicated few differences in inorganic nitrog en concentrations throughout the study area, but significant variability in total Kjeldahl nitrogen (TKN). Orthophosphate and total phosphorus concent rations increased through the study area from Arkansas [river miles (RM) 50 0-810] downstream to St. Francisville (RM 231-315), bur with little or no c hange from Baton Rouge (RM 111-230) to the Gulf of Mexico. Results provide a combined data set From which preliminary calculations of daily nutrient l oads in the Mississippi River between 1960 and 1997 were conducted. (C) 199 9 Published by Elsevier Science Ltd. All rights reserved.