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Home  >   Technical Data > Citizens Monitoring Program  >   1996 Water Quality Report

1996 Citizens Report: Eel Pond, Mattapoisett

Please also see our Eel Pond Flushing Study Page.

Embayment: Eel Pond, Mattapoisett

Embayment and Watershed Characteristic

Eel Pond receives nitrogen inputs from some of the most heavily developed portions of the Mattapoisett River drainage basin. However, most of the residences are sewered and dominant nitrogen sources include a golf course, lawn fertilizer, runoff. These loadings, couple with poor circulation because of tidal restriction from a railway bed, create adverse conditions here. The Buzzards Bay NEP has not conducted a separate nitrogen loading assessment for this subwatershed, but in light of the results discussed on the section on Mattapoisett Harbor and below, a separate nitrogen management strategy is needed for the estuary. Eel Pond has important shellfish resources, including a sizable Oyster population. The Pond remains closed to shellfishing however, due to high fecal coliform levels as well. Hence this subwatershed also needs a management strategy to reduce fecal coliforms as well.

Water Quality monitoring

Oxygen was monitored in Eel Pond in all four years, but other parameters of water quality were monitored only after 1992. Those three years of monitoring show that Eel Pond was among the most eutrophic sites monitored, with Eutrophication Index scores ranging from 14 to 23 points, some of the worst scores observed in Buzzards Bay. Total nitrogen was also consistently high, ranging from 0.64 to 0.87 ppm during the study period, and chlorophyll concentrations were also very high, ranging from 13 to 24 ppb, earning scores of zero in all three years. Only dissolved inorganic nitrogen had occasional good scores, perhaps a sign that any inorganic nitrogen entering this estuary is rapidly removed by phytoplankton and algae growing on the bottom. Inorganic nitrogen concentrations in 1994 were the exception, with concentrations nearly triple previous and subsequent years. Overall there was an excellent correlation between total nitrogen and phytoplankton pigments in the water with best conditions existing for both parameters in 1995, and worst conditions for both in 1994. Water transparency (Secchi disk depth) was a consistently low 80 centimeters during the entire study period, consistent with the very high phytoplankton pigments observed.

Oxygen concentration in Eel Pond (EL1) were highly variable, similar to other shallow and poorly flushed eutrophic systems. Oxygen saturation values were quite low, especially in 1993, 1994, and 1995, with oxygen often dipping below 50% saturation and dropping to 30% saturation on several dates in both 1993 and 1995. In those years, mean oxygen saturations of the lowest third of all observations were low enough to warrant scores of zero for the calculation of the Eutrophication Index in those years. Like several other bays, the higher oxygen concentrations in 1992 may have been a function of cooler water temperatures or other weather related factors. The time of sampling was consistent in each year, and does not appear to be a factor in the higher oxygen saturations in 1992.

Eutrophication Index scores

Nitrogen Management needs

Eel Pond probably receives less of a nitrogen load than the area at the mouth of the Mattapoisett River, but it is impacted because this cove receives little flushing, and the nitrogen load is quite high for the estuary's volume. The first order of business in this estuary should be the delineation of the subwatershed and the completion of build out and loading assessments. This summer, the Buzzards Bay NEP will fund a flushing study of Eel Pond as part of a grant to the Town of Mattapoisett. The results of these initiatives should identify the management goals and options for this small estuary. An important management option here will be the restoration of tidal flushing to the embayment.

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