1996 Citizens Report: Sippican Harbor, Marion
Embayment: Sippican Inner Harbor
Embayment and Watershed Characteristic
Sippican Harbor has one of the smaller embayment drainage basins in Buzzards Bay and the watershed is the fifth most developed in Buzzards Bay. Housing unit density in the embayment is close to the Bay-wide medium, but total population is low. Residential and commercial land use accounts for approximately 79% of the nitrogen inputs to Sippican inner harbor. The inner harbor is close to the median size and depth of Buzzards Bay embayments but the estuaries flushing time is considerably longer than most. Sippican Harbor has one of the greatest populations of boats and has three public beaches and eight private beaches. Sippican Harbor has three major sub-embayment areas whose water quality is somewhat different from the main stem of the estuary. These are Hammett Cove at the head of the estuary and Planting Island Cove and Blankenship Cove paired in the northeastern central harbor. In 1990, the shellfish warden reported in the Town annual report that there was a widespread die-off of Oysters in Hammets Cove.
Water Quality monitoring
Water Quality in inner and outer Sippican Harbor, including Planting Island Cove and Blankenship Cove were consistently fair to average. Total nitrogen concentrations were lowest in Blankenship Cove and outer Sippican Harbor, averaging about 0.4 ppm for the four years of study, followed by Planting Island Cove, averaging around 0.44 ppm (not statistically significantly higher), followed by Inner (upper) Sippican Harbor averaging around 0.52 ppm. Condition in Hammett Cove were far worse than the other sites with total nitrogen concentrations averaging around 0.72 ppm for the 4 years of study.Paralleling these patterns of Total Nitrogen were phytoplankton pigments. As before, Blankenship Cove had the lowest study period average of 5.0 ppb, followed by Sippican Outer Harbor at 5.8 ppb, then Planting Island at 5.9 ppb, then inner Sippican at 7.3 ppb. Again Hammett Cove was worse off with concentrations averaging a high 15.3 ppb.
The oxygen data was more variable, and little data was collected for Sippican Outer Harbor and Planting Island Cove. Blankenship Cove showed the best values for low summertime average concentrations, and Hammett Cove showed the worse, although there was considerable year to year variation. Inner Sippican showed intermediate oxygen concentrations, but in 1992, mean low saturation values were lower with a number of saturation values between 50% and 60% at station SH1, whereas oxygen values in other years were generally between 70 and 100%.
In the Inner Harbor, the variability in the individual parameters offset each other and the
Eutrophication Index scores during the four years of study fell in remarkably narrow range of 52
to 56 points, with no apparent trends in water quality. Blankenship and Planting Island
Eutrophication scores were incomplete, but the little available data showed clearly better water
quality typical of outer Sippican Harbor. In 1993, Planting Island had a Eutrophication Index
Score of 63. In the same year Blankenship had a score of 71 points, followed by 65 points the
following year. Again these values starkly contrasted with Hammett Cove Eutrophication Index
scores which ranged from 20 to 45 points, with a four year average of 35 points. Two out of 4 of
these scores fell in the "poor" water quality category.
Eutrophication Index scores
Nitrogen Management needs
The Buzzards Bay NEP estimated that existing nitrogen loadings are 16% over Project recommended outstanding resource waters limits and is expected to be 69% over limits in the future. Any nitrogen management strategy must include remediation of existing sources, particularly septic system inputs, since residential lands account for an estimated 79 % of nitrogen inputs. Considerable opportunity exists to protect this watershed. The first order of business is to conduct a parcel level nitrogen loading analysis since large portions of the watershed are sewered, and these areas were only approximated in the Project's 1994 subwatershed nitrogen loading report. The Hammett Cove subwatershed should be the focus of nitrogen management action since that area appears most degraded.Back