|Shields Jr, Fletcher|
|Cooper, Charles - ARS, RETIRED|
Submitted to: Journal of Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 18, 2009
Publication Date: October 1, 2009
Citation: Shields Jr., F.D., Testa III, S., Cooper, C.M. 2009. Nitrogen and Phosphorus Levels in the Yazoo River Basin, Mississippi. Journal of Ecohydrology. 2(3): 270-278. DOI: 10.1002/eco.49 [online]. Interpretive Summary: Plant nutrients such as nitrogen and phosphorus are entering coastal marine systems from rivers at greatly elevated rates, causing excessive growth of algae, triggering episodes of oxygen depletion when the algae die and decay. Sources of nutrients include fertilizers, manure, and atmospheric deposition. Available data regarding the concentrations of nitrogen and phosphorus in streams draining the Yazoo River basin of Mississippi were compiled and summarized. Although processes that govern transport of nitrogen and phosphorus are very different, levels of both nutrients tend to be three to four times higher in the Delta portion of the Yazoo River basin than in the Hills. Nutrient levels in Delta streams are much higher in the Spring than in other seasons. The Yazoo River basin retains most of the nutrients that are input to it, and water leaving the basin generally carries lower concentrations of nutrients than the receiving stream, the Mississippi River. However, nutrient concentrations are several times higher than water quality criteria set by the US Environmental Protection Agency for this region. This information is useful to land managers seeking to develop strategies for controlling nutrient pollution at the landscape scale.
Technical 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 but only 1.2 mg/L for the Hills, both about two to four times higher than 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 Hill sites were not. The Hill mean P concentration was 0.15 mg/L while the mean for Delta sites was more than four times greater, 0.66 mg/L. These values are about 4-5 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.