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GLERL What's New 1998
Great Lakes Environmental Research
Laboratory
Distinguished Scientist Seminar Series
"Gulf of Mexico Ecosystem Responses to Changing Mississippi River Nutrient
Loads"
Dr. Nancy N. Rabalais
Location: Great Lakes Environmental Research Laboratory 2205 Commonwealth Blvd. Ann Arbor, MI 48105-2945 Date: Tuesday, August 25, 1998 Time: 9:00 am Room: 105 Main Conference Room
Dr. Nancy N. Rabalais, Associate Professor with the Louisiana Universities Marine Consortium, will be presenting a talk entitled "Gulf of Mexico Ecosystem Responses to Changing Mississippi River Nutrient Loads" on Tuesday, August 25th at 9:00 am in the main conference room of the NOAA Great Lakes Environmental Research Laboratory, Ann Arbor, Michigan. Dr. Rabalais earned her Ph.D. from the University of Texas in 1983 and her research interests include continental shelf ecosystems, benthic ecology, and biological oceanography.
The Mississippi River system ranks among the world's top ten rivers in freshwater and sediment inputs to the coastal ocean. The river contributes 90% of the freshwater loading to the Gulf of Mexico, and terminates amidst one of the U.S.'s most productive fisheries regions and location of the largest zone of hypoxia in the western Atlantic Ocean. Significant increases in riverine nutrient concentrations and loadings of nitrate and phosphorus and decreases in silicate have occurred this century, and accelerated since 1950. Consequently, major alterations have occurred in the probable nutrient limitation and overall stoichiometric nutrient balance in the adjacent continental shelf system. Changes in the nutrient balances and reduction in riverine silica loading to the continental shelf appear to have led to phytoplankton species shifts offshore and to an increase in primary production. The phytoplankton community response, as indicated by long-term changes in biological uptake of silicate and accumulation of biologically bound silica in sediments, has shown how the system has responded to changes in riverine nutrient loadings. Indeed, the accumulation of biologically bound silica in sediments beneath the Mississippi River plume increased during the past two decades, presumably in response to increased nitrogen loading. The duration, size and severity of hypoxia has probably increased as a consequence of the increased primary production.
Last updated: September 19, 2002 mbl