Effects of Water Quality on Hypoxia in the Gulf of Mexico

Zimba, Paul
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In many aquatic systems, incidences of low oxygen (hypoxia) waters have been causally linked to increased nutrient concentrations. The Mississippi River accounts for approximately 80-90% of the freshwater inflow to the Gulf of Mexico; water quality in the Mississippi River should serve as a indicator of conditions in the Gulf. Near its mouth, the Mississippi River splits, with approximately one-third of its discharge diverted into the Atchafalaya River. A review of the literature (primarily peer reviewed journals and technical publications) suggests that the Mississippi River waters enriches the Gulf of Mexico and this enrichment has increased in recent years. However, 21 years of data collected and published by the United States Geological Survey indicates no change in total phosphorus. Nitrogen values for the Mississippi River have increased (concomitantly with a decline in nitrogen values in the Atchafalaya River). There is good evidence that hypoxic areas in the Gulf of Mexico have increased following the 1993 flooding of the central midwestern United States. The timing and intensity of river discharge into the Mississippi River apparently controls the duration and extent of hypoxia within the Gulf of Mexico.