The Role of the Mississippi River in Gulf of Mexico Hypoxia Oversimplifications and Confusion

A report produced for The Fertilizer Institute by the University of Alabama entitled The Role of the Mississippi River in the Gulf of Mexico Hypoxia raises several questions about whether the large-scale oxygen depletion (hypoxia) in bottom waters of the Louisiana continental shelf is the result of anthropogenic nutrient loading from the Mississippi River, as has been reported in the scientific literature and concluded by the Gulf of Mexico Hypoxia Assessment carried out under the Committee on Environment and Natural Resources. The University of Alabama (UA) report calculates that “terrigenous (land-derived) organic carbon is likely to be an important component of the total organic matter flux” driving oxygen depletion in hypoxic zones. It also suggests that discharges of biologically available actually decreased since the 1950s. In addition, it draws inferences that hydrological changes in the river basin coupled with increased river flow may be responsible for increased hypoxia rather than just increased loadings of nutrients from fertilizers and other human sources.