Nutrient Concentrations in the Scioto River and the Relative Importance to the Problem of Hypoxia in the Gulf of Mexico
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Date
2003-03
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The Ohio State University
Abstract
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.