Linking Landscape and Water Quality in the Mississippi River Basin for 200 years


Prof. Eugene Turner
LSU
The world's second largest zone of coastal hypoxia (oxygen depleted waters usually without marine organisms) is on the northern Gulf of Mexico continental shelf, adjacent to the outflows of the Mississippi and Atchafalaya Rivers. Decades of research, monitoring and retrospective analyses support the conclusion that land use in the watershed is reflected in the ecology of the continental shelf. Nitrogen loading in the Mississippi River at New Orleans is moving towards a situation encouraging N and Si limitation. This result will likely alter phytoplankton community composition, and may compromise diatom—zooplankton—fish food webs. It is clear that nitrogen reductions in the sub-basins of the upper Midwest will be a key to the success of government polices to reduce hypoxia, and scientists are playing a unique and important role in informing this policy process. The Action Plan developed by State, Federal and Tribal entitles identifies a quantitative goal for a reduced hypoxic zone—a 30% reduction in the nitrogen load. The Plan recognizes that all nitrogen sources should be included in the strategy and includes other nutrients. However, because 74% of the nitrate load is from agricultural non-point sources, and because 56% of the total nitrate load comes from north of the Ohio River, it is clear that nitrogen reductions in the sub-basins of the upper Midwest will be a key to its implementation.