1996 Citizens Report: Apponagansett Bay, Dartmouth
Embayment: Apponagansett Bay
Embayment and Watershed Characteristic
Apponagansett Bay is a busy harbor with more than 3000 boat moorings. The bay also has one public beach and four private beaches. Fewer moorings are sited in the upper estuary because of areas set aside for water skiing. The upper estuary is degraded from nutrients and other inputs, is closed to shellfishing, and important shellfish habitat and other resources have been lost. Buttonwood Brook, which drains the bulk of the watershed, is also one of the principal conveyors of fecal bacteria and nitrogen, but dense development on the eastern shore contribute substantially. Despite the fact that the watershed is mostly sewered, most remaining anthropogenic nitrogen loading to Apponagansett Bay remains residential land use (septic systems and lawns), followed by other commercial and industrial development, then farmland and other sources. Portions of the watershed, which encompasses parts of the West End of the City of New Bedford are sewered and heavily urbanized. The sources of nutrients and coliforms along Buttonwood Brook include residential land, cropland, farm animals, and a zoo. The Buttonwood Brook watershed has also been beset with flooding problems due to poor stormwater management from the urbanized areas and new construction.Eelgrass populations began disappearing in Apponagansett Bay during the 1960s and is largely
absent in the upper estuary. Drift algae, including large sheets of Ulva are present. The bottom
sediments are characterized by organically rich muds with a consistency of mayonnaise, and
these observations are also consistent with severe eutrophication.
Water Quality monitoring
The monitoring program has shown that Apponagansett Bay has had consistently poor water quality, with eutrophication index scores consistently below 35, and on average the fourth worst embayment of 27 core embayments monitored. Total Nitrogen concentrations in the Bay are consistently among the highest of those embayments. For example, in 1995, mean summertime total nitrogen concentration was 0.99 ppm, a value exceeded only in two other upper embayments. The best values of water quality were found in the oxygen concentrations observed, which may be a result of oxygen production by the considerable amounts of benthic algae that occur in this embayment. The role of benthic algae in elevating oxygen concentrations is also borne out by the fact that at station AB2, the New Bedford Yacht Club station, samples taken close to the bottom were often higher than concentrations at the surface. Station AB2 also illustrates the importance of taking early morning oxygen measurements. The highest 20% of oxygen concentration measured were from samples taken after 8:30 AM, and the lowest 20% of the oxygen concentrations were observed before 8:30 AM.Station AB1, down gradient of Buttonwood Brook typically showed the highest inorganic
nitrogen with concentrations typically above 5 (and up to 57 micromolar on one date) compared
to less than 5 micromolar typically at other stations. Many of the concentrations above 10
micromolar were observed where salinities were above 25 ppt (compared to 32-33 ppt for
Buzzards Bay water) suggesting that the Brook is an important conveyor of inorganic nitrogen
from the watershed. Total water column nitrogen showed a big jump in 1995. This was partly
due to big increases in total nitrogen (especially organic nitrogen) observed at Station 1A, and
to a lesser degree at other stations. There may be a bias in the elevated values because station
1A (a more eutrophic site) was more intensively sampled in 1995, but phytoplankton
concentrations, and independent measurement, were also considerably higher in 1995 than early
years. The outer embayment data, shows increases in phytoplankton pigments during the study
period, but certain other parameters improved slightly. When these findings were combined into
the Eutrophication Index, scores remained consistently low during the four year study period
(between 27 and 35 points) without any apparent trend.
Eutrophication Index scores
Nitrogen Management needs
In 1994, the Buzzards Bay NEP estimated that existing nitrogen loadings are only 8% over recommended nitrogen limits. Since then, the project revised its estimates to 22% over recommended limits. Still, this overload does not seem as bad as the degraded conditions documented by the citizen's water quality monitoring program suggesting existing nitrogen loadings were underestimated or sources omitted from the Project's analysis. Of course the 22% over limit was based on the so called "SA water quality" standard (second most stringent) and that the bay would be more overloaded (by more than 150%) if the more stringent "outstanding resource waters" designation limits were adopted.Apponagansett Bay is very shallow and resuspension of sediments because of boat traffic prop wash may also be contributing to poor water transparency and nutrient release to the water. Better controls on boat speeds in the upper estuary could be included as part of any management strategy.
Because most of the embayment basin is already developed, it has less build-out potential
compared to other embayments its size. Remediation of existing septic systems is a high priority.
Long term strategies include upgrading cesspools to nitrogen removal systems, or through
connections to the town's sewage treatment facility. Setting aside open space and establishing
per acre nitrogen loading limits on new development are important options for managing inputs
from new development.
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