UNDERSTANDING AND PREDICTING THE IMPACT OF AGRICULTURE ON THE ENVIRONMENTAL INTEGRITY OF MANAGED WATERSHEDS
Location: Water Quality and Ecology Research
Title: Nutrient levels in the Yazoo River Basin
Submitted to: National Sedimentaton Laboratory (NSL)- 50 Years of Soil & Water Research in a Changing Agricultural Environment
Publication Type: Proceedings
Publication Acceptance Date: October 1, 2008
Publication Date: April 5, 2011
Citation: Shields Jr, F.D., Testa III, S., Cooper, C.M. 2011. Nutrient levels in the Yazoo River Basin. In: Proceedings of the conference "Fifty Years of Soil & Water Research in a Changing Agricultural Environment". National Sedimentation Laboratory, September 2-5, 2008. Oxford, Mississippi. CD-ROM.
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. This process revealed several key facts. Although processes that govern transport of nitrogen and phosphorus are very different, levels of both nutrients tend to be much 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.
High nitrogen (N) and phosphorus (P) loadings to aquatic ecosystems are linked to environmental problems including harmful algal blooms and hypoxia. Presented is an assessment of accessible data on nutrient sources, sinks and inputs to streams within the Yazoo River Basin of northern Mississippi. Accessible data included published research and data reposing either in our laboratory, or in online data sets maintained by the U.S. government agencies. Nutrient transport differs widely for the two major physiographic regions of the basin (Delta and Hills). Our search produced total N values for 72 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, about two to four times higher than US EPA criteria. Total P data were found for 121 sites with periods of record ranging from 3.2 to 28.6 years. Delta mean 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 for these ecoregions. Delta concentrations peak strongly in spring when agricultural fertilizers are applied. Concentrations of N and P in Hill streams do not exhibit seasonal trends, but tend to be one half to one fourth as great as the Delta levels.