NUTRIENT LOAD CHARACTERIZATION FROM INTEGRATED SOURCE DATA FOR THE LOWER MISSISSIPPI RWER¹

Abstract

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

Statistical analysis of trends in organic pollution and pollution by nutrients at selected Danube river stations

“…Similar studies on pollutants concentrations in Seine, 2 Odra, 3 Elbe, 4 Nemunas, 5 Mississippi, 6 Mekong, 7 Yangtze, 8 etc. can be found in the literature.…”

“…[11][12][13] They address three types of problems: (i) to decide whether the series exhibit a trend, 7,14,15 (ii) to estimate a trend 16 (either non-parametrically, e.g. by a locally weighted scatterplot smoothing, 6 or parametrically, e.g. by a linear regression 17 ) and (iii) to predict the future behaviour of the studied time series using its past data.…”

Declining Threshold for Hypoxia in the Gulf of Mexico

“…Large nitrogen fluxes to the Gulf ( − ) and the concurrent eutrophication problems are only the more obvious symptoms of a suite of changes that have occurred in the Mississippi River watershed (). The recently reported increase in exported alkalinity from the Mississippi River () suggests that additional more subtle, long-term changes in water quality may be occurring.…”

The impact of cropland cover on river nutrient levels in the Mississippi River Basin

“…This simple relationship between cropland cover and nutrient levels suggests a potential explanation for the observed change in nutrient chemistry in the Mississippi river during the last century. The N:Si in the Lower Mississippi changed from 1 : 4.5 in the 1960s to nearly 1 : 1 in the 1980s, due to a doubling of the N levels and a 50% decrease in silica levels (Rabalais et al ., 1996; Bollinger et al ., 2000). The N:Si:P ratio in the lower Mississippi River is now much closer to the Redfield ratio (16 : 16 : 1) commonly observed in ocean waters worldwide, and may change the nutrient limitation in the northern Gulf of Mexico (Redfield, 1958; Rabalais et al ., 1996).…”