U.S. Environmental Protection Agency
EPA Science Advisory Board
Background Information

Document NameForecasting Hypoxia in the Gulf of Mexico: Responses to Nutrient Loadings from the Mississippi River Basin.
Document AuthorBierman, V.J., Jr.
Hinz, S.C.
Wiseman, Jr., W.J.
Rabalais, N.N.
Turner, R.E.
Short DescriptionIn: N.J. Valette-Silver and D. Scavia (eds.), Ecological Forecasting: New Tools for Coastal and Ecosystem Management. NOAA Technical Memorandum NOS NCCOS. pp. 111-115.
CategorySubgroup 1: Characterization of the Cause(s) of Hypoxia
Publication Year2003

Abstract: A zone of hypoxia (<2 mg O2/l) forms each spring and summer on the Louisiana-Texas continental shelf and stresses aquatic life. The principal causes are increased nitrogen loads from the Mississippi River Basin (MRB) combining with the physical stratification of Gulf waters. A mass balance model was developed to address broad, macro-scale questions related to the impacts of nutrient loadings from the MRB on water quality in the northern Gulf of Mexico. Simulations were conducted for a range of nutrient load reductions to determine how much the bottom water dissolved oxygen concentrations improved. Reducing the nutrient load 20-30 percent led to forecasts of a 15-50 percent increase of bottom water dissolved oxygen concentrations. These results were used to develop a 30 percent nitrogen loading reduction target to meet the long-term Coastal Goal for reducing the areal extent of hypoxia in the northern Gulf of Mexico. A major accomplishment in this study established watershed-scale links between nutrient loads from the MRB and water quality responses in the northern Gulf of Mexico. The study also called attention to some challenging questions facing policy-makers when implementing forecast results developed from research. In view of the complexities of the system, uncertainties in the level of knowledge, and the potentially long time period required to observe changes resulting from management action, an adaptive management approach was recommended. This approach includes a comprehensive program of monitoring, modeling, and research to facilitate continual improvement in scientific knowledge and gradual adaptation of management approaches. Specific recommendations are made for reducing uncertainties and improving forecasting ability for water quality responses. Modeling needs cannot be met independently of monitoring and research needs because models are only tools for synthesizing environmental data, not substitutes for these data. In the end, there must be compatibility among management questions, model capabilities and available data.