1996 Citizens Report: New Bedford Harbor
Embayment: New Bedford Harbor (Acushnet River)
Embayment and Watershed Characteristic
New Bedford Harbor, also referred to as the Acushnet River, is an urban harbor surrounded by 35% of the entire Buzzards Bay watershed population. The hurricane barrier, connecting New Bedford and Fairhaven with a gate entrance, greatly reduces flushing to the estuary. When the barrier was constructed in the early 1960s, water quality became degraded and eelgrass disappeared. In 1994, the Buzzards Bay NEP estimated that two point sources--the New Bedford combined sewer overflows (CSOs) and the Fairhaven wastewater treatment plant--account for 86% of the nitrogen load to the embayment entering the Acushnet River estuary, making it Buzzards Bay's most heavily nitrogen loaded embayment in terms of total pounds per year. However, it ranks number three in loading when bay volume and flushing time is considered because the Harbor is so deep compared to other Buzzards Bay embayments. Since the Buzzards Bay NEP conducted its nitrogen loading evaluation, reductions of dry weather discharges by the City of New Bedford are resulting in lower N-loadings to the estuary and probably now leave the Fairhaven sewage treatment plant as the largest single source of nitrogen in the watershed.The area outside the hurricane barrier, which we refer to as the outer harbor, is expansive and well flushed, and has conditions more similar to Clarks Cove. Prevailing summertime southwesterly winds probably direct more of the New Bedford wastewater treatment to New Bedford outer harbor than Clarks Cove, influencing water quality to a greater degree here.
It is worth noting that New Bedford Harbor has sever toxic contamination of sediments with
PCBs and metals, and the PCB superfund sites are now under remediation. After remediation of
the superfund sites, nitrogen management should become a higher management priority.
Water Quality monitoring
Eutrophication Index scores for the Acushnet River exist only for 1993 and 1995, but these data show the Acushnet River is among the most eutrophic embayments monitored. Total nitrogen was monitored in three years (93-95), with concentrations being highest recorded in two of the three years (1993 and 1995). The concentrations recorded for those years--1.31 and 1.26 ppm respectively--were remarkably high for sites with high salinity (>31 ppt). Such levels of nitrogen are generally only seen around Buzzards Bay in rivers and streams before uptake of nitrogen by marine algae. Not surprisingly, chlorophyll concentrations in the water (10-18 ppb) were also very high and similar to other eutrophic systems like the East Branch of the Westport River and Apponagansett Bay. In calculating the eutrophication Index, these phytoplankton pigment levels earned scores of zero for the three years monitored.Only the oxygen data portrayed better conditions and buoyed up Eutrophication Index scores for
the Harbor, with average summertime oxygen saturation values of 82% and 84% in 1992 and
1993, but only 44% saturation in 1995, somewhat more consistent with all the other water quality
indicators monitored. We acknowledge some weaknesses in the oxygen data in that only in 1992
and 1993 was oxygen monitored within the hurricane barrier. In 1995 oxygen was monitored
only in the outer harbor (actually very low that year), and this was used in the Eutrophication
Index score for that year. Generally outer harbor oxygen saturation were higher than inner harbor
measurements as might be expected for a better flushed area, but in 1993, the outer harbor
actually showed slightly lower oxygen concentrations (84% vs 72%) for the average lowest third
of the observations used in the Eutrophication Index scoring.
Eutrophication Index scores
Nitrogen Management needs
The Acushnet River is one of two Buzzards Bay embayments with a "SB" water quality designation from the Massachusetts DEP, and the only Buzzards Bay embayment that the Buzzards Bay NEP recommended with the SB classification. The Buzzards Bay NEP estimated that existing nitrogen loadings are 100% over Project recommended limits. Clearly the Fairhaven Treatment Plant and CSOs should be the primary focus of nitrogen management for this estuary. With the reduction of dry weather discharges from the New Bedford CSO, new nitrogen estimates need to be developed for this source. Because the Fairhaven Treatment plant now appears to be the largest nitrogen source to the estuary, improvements in the nitrogen removal efficiency of the plant should be a priority.Back