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1996 Citizens Report: Clarks Cove, New Bedford

Embayment:Clarks Cove

Embayment and Watershed Characteristic

Clarks Cove is a deep well flushed embayment surrounded by a highly urbanized watershed. The Cove receives many sizable pollution discharges, including seven combined sewer overflows (CSOs). It also contains one of the most significant quahog fisheries in Buzzards Bay and contains two extensively used public beaches (Dartmouth's Jones Beach and New Bedford's West Beach). Because Clarks Cove is somewhat exposed, and part of the embayment waterfront is obstructed by the hurricane barrier, it does not contain as many moorings and slips as other embayments its size.
The City of New Bedford has made remarkable progress during the past 6 years in eliminating dry weather discharges from its CSOs. This effort has resulted in Clarks Cove being reopened to shellfishing in 1992 for the first time in nearly eighty years. The elimination of the CSO dry weather discharges has likely resulted in a reduction of nitrogen loadings as well. The Town of Dartmouth is implementing a project to reduce pollution discharges on the western side of the Cove, and this effort is expected to expand shellfish bed openings in Clarks Cove. Today the major nitrogen sources that affect water quality in this cove are the wet weather CSO discharges and the daily discharge from the City's wastewater treatment plant 2000 feet from the tip of Clarks Point.

Water Quality monitoring

The inner portions of Clarks Cove showed very good water quality during the two years when all parameters were measured (1994 and 1995). The Eutrophication Scores (76 and 90 respectively) were among the best of the embayments monitored. Oxygen concentrations, measured in 1993, 1994, and 1995 were generally between 80% and 100% saturation, but in 1993 and 1994, oxygen concentrations dropped to between 50% and 60% saturation in the latter part of the summer when water temperatures were highest. The respiration of benthic bacteria, especially during warm water periods, has been documented as playing an important role in controlling oxygen concentrations in the vicinity of the outfall, and this phenomenon could affecting oxygen concentrations somewhat in the cove. Interestingly on a couple of dates, dissolved inorganic nitrogen concentrations are somewhat higher in the outer embayment than in the inner embayment, and this too represents a "signature" from the outfall. Nonetheless, the lowest summertime oxygen values seemed to make a gradual improvement during the three year study period.
Total nitrogen concentrations were low--0.33 ppm in 1994 and 0.38 in 1995--values more like "offshore" Buzzards Bay water. Similarly phytoplankton pigments were remarkably low in both years--less than 0.38 ppm. Overall the scores for each individual parameter measured were fairly consistent with each other although phytoplankton pigments scores were especially good. Water transparency was a very good 2.2 and 2.3 meters in 1994 and 1995 respectively. These findings are consistent with the fact that loadings to Clarks Cove are low with respect to the Cove's volume and flushing time. That is to say, because Clarks Cove has one of the largest volumes of those studied, and among those with the best flushing time, the existing loading is low relative to what the embayment can handle. Whether there is a definite trend in improving water quality as evidenced by the oxygen and Eutrophication Index scores will require additional years of monitoring.

Eutrophication Index scores

Nitrogen Management needs

Formerly CSOs were the primary nitrogen source to the Cove, however CSO discharges may now be only 10% of their 1980 flows. In 1992, the Buzzards Bay NEP estimated that total nitrogen loadings to Clarks Cove had been 125,000 kg/yr during the 1980s, then reduced to 20,720 kg/yr. This loading is a small fraction of the Project's recommended limits for an embayment of this size and flushing. Even these loadings may be overestimated because large portions of the watershed are isolated from Clarks Cove by the hurricane barrier and the City's network of combined stormdrains, so some non-point sources of nitrogen in the watershed do not reach the Cove. On the other hand, a major "offshore" source of nitrogen was not included in this assessment--the 24 million gallon per day New Bedford wastewater plant outfall--which is located several thousand feet to the south of the Cove. The observed good water quality in the Cove, however, suggest that the effect of the outfall is not focussed in the Cove.
Long term fecal coliform data and anecdotal information suggests that the reduction in CSO discharges has resulted in remarkable improvements in water quality. Besides the reduced fecal coliforms levels, eelgrass beds, formerly restricted to the clearer waters at the tip of Clarks Point on the New Bedford side and south of Ricketsons Point on the Dartmouth side are now spreading throughout the Cove (and Acushnet River) apparently because of greatly improved water clarity. Unfortunately, this Buzzards Bay monitoring program was not in place prior to most of the reduction in CSO discharges.
The New Bedford Sewage Treatment plant will soon upgrade to secondary treatment which will greatly reduce loadings of organic materials and solids to Buzzards Bay and modestly reduce nitrogen discharges. It appears that Clarks Cove does not require a comprehensive nitrogen management strategy. Remediation efforts should focus on further reducing CSO and stormwater pipe rainfall discharges, especially to achieve further fecal coliform reductions.

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