Nutrient Concentrations in the Scioto River and the Relative Importance to the Problem of Hypoxia in the Gulf of Mexico

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The Ohio State University

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Nutrients from the Mississippi-Atchafalaya River Basin have been found to be a principal cause of the hypoxic zone that forms every spring and summer on the Louisiana-Texas continental shelf in the northern Gulf of Mexico. Water that has less than 2 mg/l of dissolved oxygen content is referred to as hypoxic. The low levels of oxygen cause stress and can prove to be lethal to immobile bottom-dwelling species, thus altering the food chain and energy relationships. The hypoxic zone has been growing since it first mapped. Fertilizers applied in agricultural lands are the primary source of nutrients that contribute to hypoxia. The Mississippi River Basin drains some of the most productive, and most fertilized, agricultural land in the world. The goals of this study are to 1) gain a better understanding about the problem of hypoxia in general 2) investigate the relative importance of the different sources of nutrients and the contributions of sub basins in the Mississippi River Basin and to 3) examine available data in the Upper Scioto River Basin to assess it's contribution of nutrients and identify trends of nutrient concentrations. This thesis is divided into five chapters. Section 2 presents an overview of nutrient chemistry, sources, and different factors that govern nutrient loading in streams, with an emphasis on agricultural settings. Section 3 describes the problem of hypoxia in the northern Gulf of Mexico and the factors that control its year-to-year extent. Section 4 examines the Scioto River Basin and nutrient data from Griggs and O'Shaughnessy Reservoirs, which are feed by the Scioto River near Columbus Ohio. These data sets were taken monthly over a 15-year period and provides the basis to understand the local contribution to the hypoxic zone, suggest factors that control nutrient concentrations in the Scioto River, and to understand the trends in nutrient levels near Columbus, Ohio. Section 5 summarizes the major conclusions of the study.