Reversal of eutrophication following sewage treatment upgrades in the New River Estuary, North Carolina |
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| Authors: | Michael A Mallin Matthew R McIver Heather A Wells Douglas C Parsons Virginia L Johnson |
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| Institution: | 1. Center for Marine Science, University of North Carolina Wilmington, 28409, Wilmington, North Carolina
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| Abstract: | The New River Estuary consists of a series of broad shallow lagoons draining a catchment area of 1,436 km2, located in Onslow County, North Carolina. During the 1980s and 1990s it was considered one of the most eutrophic estuaries
in the southeastern United States and sustained dense phytoplankton blooms, bottom water anoxia and hypoxia, toxic outbreaks
of the dinoflagellatePfiesteria, and fish kills. High nutrient loading, especially of phosphorus (P), from municipal and military sewage treatment plants
was the principal cause leading to the eutrophic conditions. Nutrient addition bioassay experiments showed that additions
of nitrogen (N) but not P consistently yielded significant increases in phytoplankton production relative to controls. During
1998 the City of Jacksonville and the U.S. Marine Corps Base at Camp Lejeune completely upgraded their sewage treatment systems
and achieved large improvements in nutrient removal, reducing point source inputs of N and P to the estuary by approximately
57% and 71%, respectively. The sewage treatment plant upgrades led to significant estuarine decreases in ammonium, orthophosphate,
chlorophylla, and turbidity concentrations, and subsequent increases in bottom water dissolved oxygen (DO) and light penetration. The
large reduction in phytoplankton biomass led to a large reduction in labile phytoplankton carbon, likely an important source
of biochemical oxygen demand in this estuary. The upper estuary stations experienced increases in average bottom water DO
of 0.9 to 1.4 mg l−1, representing an improvement in benthic habitat for shellfish and other organisms. The reductions in light attenuation and
turbidity should also improve the habitat conditions for growth of submersed aquatic vegetation, an important habitat for
fish and shellfish. |
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