Citation:

Ouyang, Y., G. Feng, P. Parajuli, T. Leininger, Y. Wan, AND J. Jenkins. Assessment of Surface Water Quality in the Big Sunflower River Watershed of Mississippi Delta Using Nonparametric Analysis. WATER, AIR, & SOIL POLLUTION. Springer, New York, NY, 229(11):11, (2018). https://doi.org/10.1007/s11270-018-4022-8

Impact/Purpose:

Understanding water quality conditions in Lower Mississippi River Basin (LMRB) continues to rely on water quality monitoring in smaller watersheds. In this study, we estimated the characteristics and variations of surface water quality in the Big Sunflower River Watershed (BSRW) within the Mississippi Delta using our field measurements in conjunction with the US Geological Survey data from three surface water monitoring stations at Leland, Merigold, and Sunflower in the BSRW from 1997 to 2017. Our assessment revealed complex spatial and temporal patterns at annual, seasonal, and daily scales. The concentrations of some nutrient species such as and TP varied with sites each year, whereas some physical variables such as pH and DO had very small variations. The highest median concentrations were observed in spring for and TN, in summer for Cl, Na and SC, and in winter for DO at all of the three study sites. There was a slightly increasing annual trend for concentrations at Leland, a slightly decreasing annual trend for concentrations at Merigold, and no trend for concentrations at Sunflower. The overall water quality patterns emphasize the important roles that land use plays and the needs to reduce nutrient loading to alleviate eutrophication in the Gulf of Mexico.

Description:

Assessment of surface water quality in the Mississippi Delta is essential to quantify the eutrophication of the Gulf of Mexico. This study estimated the characteristics and variations of surface water quality at three study sites in the Big Sunflower River Watershed (BSRW) within the Mississippi Delta using Kruskal-Wallis, Dunn, Mann-Kendall, and Pettitt tests. In general, contents of some water quality constituents such as nitrate-nitrogen (NO3 − N) and total phosphorus (TP) in the BSRW varied from site to site each year, whereas variations of other constituents such as pH and dissolved oxygen (DO) each year were basically not significant. The highest median concentrations were found in spring for NO3 − N and total nitrogen (TN); in summer for specific conductance (SC), Na, and Cl; and in winter for DO. Mann-Kendall trend analysis revealed that there was an increasing annual trend at Leland but a decreasing annual trend at Merigold for NO3 − N concentrations even though such changes were very small, whereas there was no annual trend for TP at any of the three study sites. Pettitt’s test further identified that the NO3 − N concentrations had an abrupt increase in February 2009 at the median value of 0.44 mg L−1 in Leland and an abrupt decrease in June 2012 at the median value of 3.65 mg L−1 in Merigold. A very good linear correlation existed between total dissolved solid (TDS) and magnesium (Mg) in the BSRW, which could be used to estimate TDS from Mg concentrations for this watershed when the data for TDS are absent.

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