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.