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Effect of Organic Enrichment and Hypoxia on the Biodiversity of Benthic Communities in Narragansett Bay
Citation:
Hale, S. Effect of Organic Enrichment and Hypoxia on the Biodiversity of Benthic Communities in Narragansett Bay. Presented at New England Estuarine Research Society (NEERS), Avery Point, CT, October 16 - 18, 2014.
Impact/Purpose:
Excessive input of nitrogen to coastal waters leads to eutrophication and hypoxia that reduce biodiversity and impair key ecosystem services provided by benthic communities; for example, fish and shellfish production, bioturbation, nutrient cycling, and water filtration. Constraints on the upper limit of biodiversity imposed by organic over-enrichment (total organic carbon in sediments) and hypoxia in the coastal waters of the northeastern US result in a loss of potential biodiversity, shown by a 95th quantile regression of species richness versus dissolved oxygen. The mean species richness of benthic community at stations in seasonally-hypoxic areas of Narragansett Bay, Rhode Island was significantly lower than those in normoxic areas, as was a multidimensional scaling of species abundances. Many rare species found in normoxic areas were not present in hypoxic areas. Eutrophication-related reductions in biodiversity and benthic community ecosystem production functions lead to a loss of things valued by the human population surrounding and using the Bay. These stressor-response ecosystem production functions will be used by the Narragansett Bay SSWR project in a model projecting future scenarios, including one where the reduction in nitrogen load from improvements to the major wastewater treatment plants may result in fewer summer hypoxic events and therefore, a restoration of ecosystem services from the benthic community. The product will give guidance that the Office of Water could use to help development of nutrient criteria and TMDLs. The product will be useful to the Rhode Island Department of Environmental Management in developing a nitrogen TMDL for upper Narragansett Bay, developing nutrient criteria, and structuring a proposed regional stormwater management plan.
Description:
Excessive input of nitrogen to coastal waters leads to eutrophication and hypoxia that reduce biodiversity and impair key ecosystem services provided by benthic communities; for example, fish and shellfish production, bioturbation, nutrient cycling, and water filtration. Hypoxia is commonly defined in the literature as dissolved oxygen <2.0 mg/l, but this fails to take into account sub-lethal effects on benthic organisms (such as lowered growth rate) that occur at levels up to 4 or 5 mg/l. Constraints on the upper limit of biodiversity imposed by organic over-enrichment (total organic carbon in sediments) and hypoxia in the coastal waters of the northeastern US result in a loss of potential biodiversity, shown by a 95th quantile regression of species richness versus dissolved oxygen. The mean species richness of benthic community at stations in seasonally-hypoxic areas of Narragansett Bay, Rhode Island was significantly lower than those in normoxic areas, as was a multidimensional scaling of species abundances. Many rare species found in normoxic areas were not present in hypoxic areas. Eutrophication-related reductions in biodiversity and benthic community ecosystem production functions lead to a loss of things valued by the human population surrounding and using the Bay.