Dr. B. McKee - LUMCON
Objective:
The retrospective analysis portion of the NECOP program set out
to document the linkage(s) between anthropogenic activities within the
continental United States, since the turn of the century, and concomitant
increases in nutrient loading within the Mississippi River with seasonal
hypoxia on the Louisiana inner-continental shelf.
Rationale:
Increases in anthropogenically-derived river-borne nutrients
(e.g. nitrates) over the last several decades have resulted in changes in
river water quality, and have been associated with documented seasonal
bottom-water hypoxia and hypothesized modifications in coastal food
webs. An apparent linkage
between these observations led to the Nutrient Enhanced Coastal Ocean
Productivity (NECOP) Program's central hypothesis that "anthropogenic
nutrient inputs have enhanced coastal ocean productivity with subsequent
impact on coastal ocean water quality and living resource yields."
Method:
To test our hypotheses a multi-disciplinary approach was utilized.
Stratigraphy, radioisotope-based geochronology, organic and inorganic
chemical analyses, detailed characterization of the sediment's
coarse-grained fraction, and foraminifera and ostracode biostratigraphy
were examined.
Accomplishment:
We concluded that anthropogenic influences have enhanced coastal primary
productivity in our study area over the last century and that these changes are
recorded in the sediment record.
We demonstrated that hypoxia-related upcore benthic
foraminifera species shifts, expressed as a decrease in diversity, and authigenesis
of a hypoxia-related solid-phase component (glauconite) were related to
anthropogenic activities such as fertilizer usage in the United States
(figure).
More specifically, our results suggest that
anthropgenically-induced hypoxic conditions on the Louisiana shelf, at
least at our primary coring site, had an inception date of the early-1940s.
THIS PROJECT WAS RECENTLY COMPLETED
Key reference:
Nelsen, T., P. Blackwelder, T. Hood, B. McKee, N. Romer, C.
Alvarez-Zarikian, and S. Metz, 1995, Time-Based Correlation of Biogenic,
Lithogenic and Authigenic Sediment Components with Anthropogenic Inputs in
the Gulf of Mexico, NECOP Study Area. Estuaries , V. 17, #4, pp 872-85.
Blackwelder, P., T. Hood, C. Alvarez-Zarikian, T. Nelsen and B. McKee, (1996),
Benthic Foraminifera from the NECOP Study Area Impacted by the
Mississippi River Plume and Seasonal Hypoxia. Quaternary International,
V. 31, pp 19-36.
Nelsen, T. A., (1996), Coastal Ocean Water Resources: Linkages with Terrestrial
Freshwater Resources, Anthropogenic Influences and Climatic Change,
NATO ASI Series,
Diachronic Climatic Impacts on Water Resources, (eds. A. Angelakis and A. Issar),
Chapter 14, pp. 319-347, Springer-Verlag, Berlin Heidelberg.
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