Nitrogen and phosphorus levels in the Yazoo River Basin, Mississippi

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  • This article is a U.S Government work and is in the public domain in the U.S.A.

Abstract

Nitrogen (N) and phosphorus (P) loadings to aquatic ecosystems are linked to environmental problems such as hypoxia. Presented is an assessment of accessible data on nutrient sources, sinks and inputs to streams within the Yazoo River Basin of northern Mississippi. Spatial trends were examined by plotting the temporal mean and median concentration for each site versus contributing drainage area, and seasonal patterns were examined by comparing monthly mean and median concentrations computed across a range of sites. Mean total N values were computed for 75 sites with periods of record ranging from 3·3 to 28·6 years. The global mean (mean of site means) total N concentration for the Delta was 3·3 mg l−1 but only 1·2 mg l−1 for the Hills, and both were about two to four times higher than US Environmental Protection Agency (US EPA) criteria for each of these ecoregions. Total P data were found for 122 sites with periods of record ranging from 3·2 to 28·6 years. Delta mean N and P concentrations were inversely proportional to contributing drainage area, while those of Hill sites were not. The Hill mean P concentration was 0·15 mg l−1, while the mean for Delta sites was more than four times greater, 0·66 mg l−1. These values are about four to five times the levels set as criteria by the US EPA. Delta N and P concentrations peak strongly in spring when agricultural fertilizers are applied and stream flows are highest. Concentrations of N in Hill streams do not exhibit seasonal patterns, but mean monthly P levels are correlated with mean monthly discharge. Copyright © 2009 John Wiley & Sons, Ltd.

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