Date of Award
Master of Science in Oceanography
Candace A. Oviatt
This study fulfilled a portion of an ongoing program at the Environmental Protection Agency (Narragansett, RI) to examine cumulative human impacts in New Bedford Harbor, Massachusetts. One of the many changes New Bedford Harbor has experienced since the 1600s has been an increasing urban population along with an increased volume of poorly treated wastewater and combined sewer overflows. In addition to the threat of increased production and anoxia of harbor waters, industrial toxic wastes deposited in the harbor over the last three to four decades have raised concern for the health of estuarine inhabitants. These toxic wastes include the industrial discharge of polychlorinated biphenyls from electrical component manufacturing plants, and the discharge of heavy metals into the Acushnet River, the primary tributary into the harbor.
The Environmental Protection Agency has approached the problem by examining anthropogenic impacts on various ecosystem components. A relatively pristine estuary, the Slocums River, Massachusetts, was selected to compare parameters which may indicate differences in the state of estuarine health between the two sites. The objects of this portion of the study was to examine differences in rates of phytoplankton primary production between the two sites to detect eutrophication in New Bedford Harbor. This was measured by performing in situ incubations for production and respiration of oxygen over the summer of 1994. The top trophic consumers, estuarine fish, were also studied at both sites to examine differences in fish biomass, abundance and diversity. Beach seining was performed at stations in both sites bimonthly in the summer of 1994 and monthly from October 1994 to May 1995. Two indices, which reflect water quality, were applied to water column parameters measured at both sites. The Estuarine Biotic Integrit}r index (EBO which evaluates the quality of habitat to support estuarine fish was employed at both sites.
Average phytoplankton primary production over the summer of 1994 was higher in New Bedford Harbor, 0.61 +/- 0.16 (standard deviation) gO2 m-2 hr-1, when compared to the average production rate in the Slocums River, gO2 (standard deviation) m-2 hr-1. Phytoplankton biomass, measured as chlorophyll a, was significantly higher in New Bedford Harbor. The higher phytoplankton production rates in New Bedford Harbor suggest that the harbor was eutrophied, in comparison to the Slocums River. However, production from macrophytes needs to be accounted for in future studies. The eutrophication index indicated that neither estuary was eutrophied, and that a strong difference in water quality did not exist. The second index indicated that habitat was suitable for growth of submersed aquatic vegetation (SAV) in the Slocums River, but not all New Bedford stations met criteria for growth of SAV.
Higher fish biomass and abundance was evident in New Bedford Harbor where 32,027 individuals with a dry-weight biomass of 13,863 g were collected. In the Slocums River, 20,864 individuals with a dry-weight biomass of 7,710 g were collected over the study period. However, diversity was higher in the Slocums River where the Shannon-Wiener index was 0.541 compared to 0.329 in New Bedford Harbor during the summer months. Summertime growth rates of Menidia species and Fundulus majalis were higher in New Bedford Harbor. Higher phytoplankton production resulting from urbanization of the New Bedford area may be the cause of higher fish biomass and higher growth rates of Menidia, the dominant species. Production rates do not appear to be too high to cause fish mortality from . anoxia. The higher diversity in the Slocums River is likely due to a higher distribution of Spartina marsh sites. The decreased extent of marsh areas in New Bedford Harbor may be due to human impact due to extensive fining of marsh areas since the late 1700s. The Estuarine Biotic Integrity index (EBI) was applied to the marsh and beach habitats of both systems. The index showed that all stations in both systems have poor quality of habitat when compared to the eelgrass habitats of Waquoit Bay and Buttermilk Bay, Massachusetts.
Absher-Mitchell, Erica Louise, "Phytoplankton Primary Production and Fish Community Structure in New Bedford Harbor: A Comparison Study to Evaluate Human Impacts" (1995). Open Access Master's Theses. Paper 812.