1996 Citizens Report: Westport River East Branch
Embayment:East Branch Westport River, Westport, MA
Embayment and Watershed Characteristic
The East Branch of the Westport River probably has greater shellfish resources than any other Buzzards Bay embayment, and together with the West Branch lead the Buzzards Bay area in scallop catch. This estuary also has more salt marsh acreage than any other embayment, and probably has among the highest eelgrass bed acreage. The watershed is the second largest in Buzzards Bay and principally lies in three municipalities (Westport, Dartmouth, and Fall River. Most anthropogenic nitrogen loading to the East Branch of the Westport River is derived from residential land use, closely followed by cropland, then other development and farm animals. Like the West Branch, it is likely that farm animals like dairy cows play a far more important role in fecal coliform loading and shellfish bed closures than in coastal eutrophication.
Water Quality monitoring
During the past four years, the East Branch had the worst or was among the worst in overall water quality of the Buzzards Bay embayments monitored. Generally the lowest scores of individual parameters were water transparency, chlorophyll, and organic forms of nitrogen. These findings are consistent with overland runoff noted from other agricultural areas like the West Branch. The role of overland runoff is also suggested by the fact that testing of fecal coliforms by the Westport Board of Health and Westport River Watershed Alliance have been exceptionally high in the central River throughout the 1990s, often exceeding 1000 fecal coliform per 100 ml, levels unparalleled in any embayment in Buzzards Bay except perhaps New Bedford inner harbor.The East Branch is clearly dominated by the flow of the River. In 1992, rainfall was well above average during the summer (18.9"), and included a single rainfall of 8". This event resulted in elevated nutrients, turbidity, and chlorophyll for several weeks. In contrast, in 1993, a summer of severe drought (only 5.7"), water quality showed a dramatic improvement. The rainfall during the summers of 1994 and 1995 were also somewhat below average (10.0" and 8.4" respectively), but not as severe as the 1993 conditions. The Eutrophication Index scores appeared to mirror the degree of rainfall in the estuary. The relationship between rainfall and water quality conditions suggests that overland runoff may be an important conveyor of pollutants to this estuary.
The lowest 33% of oxygen concentrations in the outer East Branch are quite similar to values observed in the outer West Branch, however there is a steep gradient in water quality as one moves up the river. For example, in 1994, mean oxygen percent saturation in the outer East Branch was 74%, whereas in the upper East Branch, oxygen averaged only 60% saturation. The oxygen data for that year at Cadmans Neck is interesting. Oxygen ranged widely from close to 100% at the start of the season and declined to a low of 40% by September. This pattern was repeated at Cadmans Neck, but somewhat less dramatically in 1992.
Like oxygen, other parameters of water quality also decline dramatically in the upper East
Branch. Phytoplankton concentrations in the outer (lower) portions of the East Branch were quite
similar to the West Branch, as might be expected from the co-mingling of waters in the
confluence of the Rivers. At the Head of the East Branch, phytoplankton concentrations are two
to three times higher. In both inner and outer East Branch, phytoplankton concentrations were
highest in 1994.
Eutrophication Index scores
East Branch Outer
Total Nitrogen in the water was also particularly high in 1994 and 1995. These elevations were
largely due to increased organic nitrogen, especially in 1994. It is possible that this increase may
have been due to changes in analytical procedures adopted by our laboratory in 1994, but because
other independent measures of water quality such as particulate nitrogen and dissolved oxygen
and chlorophyll also showed marked increases (chlorophyll concentrations tripled from 1993 to
1994), we believe that the decline in water quality was genuine in 1994 and 1995 and may reflect
increased nitrogen inputs to the estuary. It is also possible that these changes could have resulted
from a bloom of plankton in the estuary or because rainstorms more closely coincided with
sampling days. Whatever the case, both transport of nutrients and water quality in the East
Branch are affected considerably by weather conditions.
Eutrophication Index scores
East Branch, Inner
Nitrogen Management needs
All indicators suggest water quality in the East Branch is impaired, and the estuary has had some of the worst Eutrophication Index Scores and total nitrogen levels around Buzzards Bay. Historical aerial photographs suggest eelgrass beds have disappeared in the upper estuary a pattern consistent with the effects of eutrophication. Management action is required to remediate existing sources as well as to control new inputs. Like the West Branch, the watershed also has considerable growth potential, especially from conversion of agricultural land to residential land and in development of the Upper watershed lying in the City of Fall River and Town of Dartmouth. Because this upper watershed region has considerable wetland, and land in forest use, a concerted effort to preserve open space can have long term benefits for protecting water quality and drinking supplies. The Buzzards Bay NEP is now working with the City of Fall River and town of Westport in preparing Open Space Plans to meet this need.Under so-called "outstanding resource water" designation loading limits--the strictest water
quality standards--the bay is now overloaded by 200%, and future buildout loadings could further
double the loading. This ORW classification may be too difficult to achieve in this estuary. In
fact, currently, the Massachusetts Department of Environmental Protection has ranked the East
Branch as having SB waters. The only other Buzzards Bay embayment with this low a ranking is
New Bedford Harbor. For practical reasons the intermediate SA classification loading limits may
be most achievable for this estuary. Using this standard, the East Branch would be classified as
only being slightly over limits today.
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