1996 Citizens Report: Megansett and Squeteague Harbor, Bourne and Falmouth
Embayment: Megansett and Squeteague Harbor
Embayment and Watershed Characteristic
Megansett and Squeteague Harbors are really the outer and inner portions of a larger embayment complex. These Harbors are situated much like the Buttermilk Bay and Phinneys Harbor complexes, with a larger well flushed outer basin and a much smaller shallower more circulation restricted inner basin. In these systems the inner basin tend to receive much of the watershed nitrogen input which is then passed to the outer system in tidal flows. Fortunately for the water quality of Squeteague Harbor the source water from Megansett Harbor which has excellent water quality comparable to offshore Buzzards Bay conditions, and these waters therefore aids in diluting nitrogen inputs from the adjacent uplands and moderate conditions in Squeteague.
The Megansett Harbor drainage basin is one of the larger sub-basins on Buzzards Bay's eastern
shore and contains 2 public water supply wells and a large parcel of open space. These land-uses
should help to preserve water quality by reducing nitrogen sources within those portions of the
watershed. The embayment also has extensive eelgrass coverage. Turnover times of seawater in
the embayment have not been assessed, but the Project selected a water turnover time of 3.5 days
for the purpose of calculations, a value that is somewhat higher than comparable open systems of
similar depth like Clarks Cove, Mattapoisett Harbor and Aucoot Cove. In contrast to the outer
basin of Megansett Harbor, the inner basin, Squeteague Harbor, is one of the smallest
embayments studied in Buzzards Bay. Based on the Buzzards Bay NEP's 1994 subwatershed
evaluation, the Megansett Its drainage basin is over 68% forested and has extensive potential for
additional development. The drainage basin has been redefined, however, by the Cape Cod
Commission, based on more detailed groundwater elevation data, consequently the land use
evaluation needs to be revised.
Water Quality monitoring
Water quality in Megansett and Squeteague Harbors was among the best of all of the embayments monitored in Buzzards Bay. Oxygen was only monitored at these sites in 1992 and 1993. Oxygen was not monitored in outer Megansett Harbor, but for the calculation of outer embayment Eutrophication Index scores inner Megansett Harbor oxygen data was used as a conservative estimate of oxygen conditions (oxygen represents 25% of the Eutrophication Score).In those years, oxygen levels were excellent in Megansett Harbor, showing only small variations and almost always remaining above 80% of saturation. These conditions support a high quality habitat for fish, benthic animals and eelgrass beds. Squeteague Harbor oxygen concentrations were slightly lower than within the outer harbor, but were high compared to comparable enclosed embayments.
Nitrogen and chlorophyll and chlorophyll levels were monitored in all 4 years at the sites and present a more interesting story. Outer Megansett had some of the lowest total nitrogen concentration observed, with summertime averages ranging from 0.23 to 0.38 ppm, with a four year mean of 0.3 ppm. Inner Megansett Harbor and Squeteague were somewhat higher and more variable with 4 year means of 0.42 and 0.41 ppm respectively, but still low for inner embayments. Total nitrogen concentrations continuously elevated in Squeteague during the study period and were highest in 1995 at 0.59 ppm. Similarly, chlorophyll levels were very lower in outer Megansett, with concentrations rising in the inner harbor and Squeteague.
Eutrophication Index scores
Squeteague
Both in 1992 and 1993, water quality in Megansett Harbor was better than most other embayments. These findings suggest that loadings are small to the Harbor compared to the volume and flushing of the embayment and that tidal and wind-driven mixing of the water column is sufficient to prevent stratification.
Megansett
Nitrogen Management needs
The Buzzards Bay NEP estimated that existing nitrogen loadings to the outer system of Megansett Harbor is well below Project recommended limits. The principal source of nitrogen is residential development. The watershed has considerable growth potential, but at buildout the embayment will only be at 21% of the recommended Project limits. Consequently management action was ranked a low priority for Megansett harbor.Similarly, the Buzzards Bay NEP estimated that existing nitrogen loadings to Squeteague
Harbor are only a quarter of Project recommended "SA" water quality standard limits (the second
most stringent water quality standard). The watershed also has considerable growth potential, but
will still only be 56% of the recommended limit at buildout. Should the Town of Bourne adopt
the more protective Outstanding Resource Water standard, some nitrogen management controls
will be required, since future loading could exceed the Projects recommended limits by 17%.
This evaluation needs to be revised since the Cape Cod Commission has revised the watershed
delineation originally prepared by the BBP based on new well data. However, this harbor
complex represents a significant resource and nitrogen management should focus on maintenance
of one of the highest quality ecological sub-systems to Buzzards Bay.
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