Hypoxia in the Northern Gulf of Mexico: An update by the EPA Science Advisory Board

Authors: DALE, VIRGINIA - OAK RIDGE NAT'L LAB; BIANCHI, THOMAS - TEXAS A & M; BLUMBERG, ALAN - STEVENS INST. OF TECH.; BOYNTON, WALTER - UNIV. OF MARLAND; CONLEY, DANIEL - LUND UNIV, LUND SWEDEN; CRUMPTON, WILLIAM - IOWA STATE UNIV; DAVID, MARK - UNIV OF ILLINOIS; GILBERT, DENIS - MAURICE-LAMONTAGNE INST.; HOWARTH, ROBERT - CORNELL UNIV; KLING, CATHERINE - IOWA STATE UNIV; Lowrance, Robert; MANKIN, KYLE - KANSAS STATE UNIV; MEYER, JUDITH - UGA; OPALUCH, JAMES - UNIV OF RHODE ISLAND; PAERL, HAND - UNIV OF N. CAROLINA; RECKHOW, KENNETH - DUKE UNIV.; SANDERS, JAMES - SKIDAWAY INST. OF OCEAN.; SHARPLEY, ANDREW - UNIV OF ARKANSAS; SIMPSON, THOMAS - UNIV OF MARYLAND; SNYDER, CLIFFORD - INT.PLANT NUTRITION INST; WRIGHT, DONELSON - SCHOOL OF MARINE SCIENCE; STALLWORTH, HOLLY - EPA SCIENCE ADV. BOARD; ARMITAGE, THOMAS - EPA SCIENCE ADV.BOARD; WANGSNESS, DAVID - US GEOLOGICAL SURVEY

Submitted to: Environmental Protection Agency
Publication Type: Government Publication
Publication Acceptance Date: 7/28/2008
Publication Date: 7/30/2008
Citation: Dale, V., Bianchi, T., Blumberg, A., Boynton, W., Conley, D.J., Crumpton, W., David, M., Gilbert, D., Howarth, R.W., Kling, C., Lowrance, R.R., Mankin, K., Meyer, J.L., Opaluch, J., Paerl, H., Reckhow, K., Sanders, J., Sharpley, A.N., Simpson, T.W., Snyder, C., Wright, D., Stallworth, H., Armitage, T., Wangsness, D. 2008. Hypoxia in the Northern Gulf of Mexico: An update by the EPA Science Advisory Board. Environmental Protection Agency. 333p. 2008. (Technical Report)

Interpretive Summary: The USDA-Natural Resources Conservation Service is evaluating the environmental benefits of wetland conservation practices as part of the national Conservation Effects Assessment Project. As part of this assessment, a review of the state of knowledge concerning wetland functions is being done for the entire U.S. on a region by region basis. The most common wetland practices used in the southeastern U.S. are Riparian Forest Buffers and Wetland Wildlife Habitat Management. The water quality and wildlife habitat functions of riparian forest buffers are well established although riparian buffer widths and connectivity (lack of gaps in the riparian forest) are more important for wildlife. Very few direct studies of Wetland Wildlife Habitat Management exist but because these practices are generally based on those applied successfully in state and federal wildlife refuge systems, they are likely to be successful. In some parts of the southeast it is possible to maintain wetland functions in grazing lands and it is possible to restore some seasonal wetland functions through drainage management. There is limited information on the typos of wetlands restored and managed in the southeast and a move to a more functional assessment of ecological benefits could make evaluation of effects more quantitative. More information on the wetland types used as targets for wetland practices and how the functions of restored and managed wetlands compare to reference conditions would be useful.

Technical Abstract: This report was prepared by the authors serving as part of an EPA Science Advisory Board (SAB) panel. The report reaffirms the major finding of theIntegrated Assessment, namely that contemporary changes in the hypoxic area in the northern Gulf of Mexico are primarily related to nutrient loads from the Mississippi Atchafalaya River basin. If the size of the hypoxic zone is to be reduced, the SAB finds that a dual nutrient strategy is needed that achieves at least a 45% reduction in both riverine total nitrogen flux and riverine total phosphorus flux. Climate change will likely contribute to changing conditions. A number of studies have suggested that climate change will create conditions where larger nutrient reductions, e.g., 50 – 60% for nitrogen, would be required to reduce the size of the hypoxic zone. An adaptive management approach, coupling nutrient reductions with continuous monitoring and evaluation, can provide valuable lessons to improve future decisions. The SAB was asked to comment on the Task Force’s goal of reducing the size of the hypoxic zone to 5,000 km2 by 2015. With respect to the time frame, the SAB finds that such a significant reduction is not likely to be achievable over the next eight years. We conclude this for two reasons. First, there is limited current movement to implement policies, programs and strategies that reduce nutrients. Second, there are time lags between reductions in nutrient inputs and the response of the ecological system. Hence, while the 5,000 km2 target remains a reasonable objective in an adaptive management context; it may no longer be possible to achieve this goal by 2015. This makes it even more important to proceed in a directionally correct fashion to manage factors affecting hypoxia than to wait for greater precision in setting the goal for the size of the zone. The SAB underscores that in considering management strategies to reduce Gulf hypoxia, EPA should consider the many benefits of nutrient reduction in the Mississippi Atchafalaya River basin. Such “co-benefits” include improved groundwater and surface water quality, wildlife and biodiversity, recreation, soil quality, greenhouse gas reduction and carbon sequestration. In many cases, co-benefits may exceed the benefits of hypoxia reduction. Finally, to reduce hypoxia in the Gulf, a systems view, looking at all sources and effects, is needed. The SAB urges the Agency to consider its options with respect to both non-point and point sources. Non-point sources have long been acknowledged as the primary source of nutrient loadings, however the SAB finds point sources are a more significant contributor than previously thought. Atmospheric deposition of nitrogen is also playing a role in hypoxia. In addition, it may be necessary to confront the conflicts between hypoxia reduction as a goal on the one hand and incentives provided by current agricultural and energy policy on the other. Some aspects of current agricultural and energy policies are providing incentives that contribute to greater nutrient loads now and in the future. The SAB recognizes that if agricultural, environmental, and energy policies are to be aligned to support hypoxia reduction, cooperation across a broad spectrum of interests, including the highest levels of government, would be required. We note that regulatory options under the Clean Water Act, an area within EPA’s purview, are addressed by the National Academy of Sciences (NAS) in its recent study, the “Mississippi River and the Clean Water Act.” As pointed out by the NAS, EPA has regulatory authority under the Clean Water Act to address watershed wide issues. The Executive Summary in the attached Advisory highlights the SAB’s findings.