1996 Citizens Report: West Branch Westport River
Embayment: West Branch Westport River, Westport, MA
Embayment and Watershed Characteristic
The West Branch of the Westport River is a broad, shallow embayment with extensive salt marsh and eelgrass beds. More acres of eelgrass have been mapped in the West Branch and salt marsh acreage is fourth greatest among Buzzards Bay embayments. The estuary, together with the East Branch, has some of the best shellfish resources in Buzzards Bay and historically has lead Buzzards Bay in scallop catch.Agricultural land is the dominant land use in this watershed, and is nearly three times more extensive in area than commercial and residential lands. It is not surprising then that most inputs of nitrogen to the West Branch are estimated to be derived from cropland (40%). Residential and commercial land use is the second largest source (34%) followed by farm animals (13%), then other development. It is worth noting that farm animals (primarily dairy cows) play a more important role in fecal coliform loading and shellfish bed closures than coastal eutrophication.
Water Quality monitoring
During the past 4 years, water quality in the lower West Branch has generally been good, with Eutrophication Index scores ranging between 50 and 78. Water quality was best in 1993, the year with the most severe drought conditions, a response also seen in the East Branch. Most dramatically, total nitrogen in the water was exceptionally low that year (0.28 ppm) compared to other years (0.51-0.86 ppm). In 1992, with a summer of exceptionally heavy rains, dissolved inorganic nitrogen was highest, as might be expected from runoff of fertilizer in agricultural areas. The large increases in dissolved inorganic nitrogen in 1994 and 1995, however, are more enigmatic. Phytoplankton pigment concentrations are quite low in the West Branch, and only in 1995 did they increase, in this case by nearly 30%. This increase in phytoplankton is seen also in particulate nitrogen levels in 1994 and 1995. While increases in phytoplankton often also results in increased dissolved organic nitrogen, at levels of 5 ppb, it seems unlikely that increased phytoplankton are elevating dissolved organic nitrogen in the water to the degree observed. Other possible explanations for the big increase in dissolved organic nitrogen include increase use of urea, manure, or other organic fertilizers in this watershed, or analytical error. Analytical error seems unlikely because both inner and outer West Branch showed elevated dissolved organic nitrogen in 1995, whereas the East Branch did not have the same increase in dissolved organic nitrogen.As might be expected from the foregoing results, Eutrophication Index scores were worst in 1994 and 1995. These score reductions were driven not only by increases in dissolved organic nitrogen but by drops in dissolved oxygen as well. The drop in dissolved oxygen is illustrated by station 112W, Carey's Boat Yard. During 1992, oxygen never dropped below 70% saturation. In 1993, oxygen concentrations never were observed below 85%. In contrast, in 1994 and 1995, dissolved oxygen dropped below 70% saturation on 4 dates and 3 dates respectively with a low value below 30% in 1995. Monitoring in 1994 and 1995 also showed big jumps in organic nitrogen in the water, also helping lower the eutrophication scores for those years. The lowering of oxygen could also affect the regeneration of nutrients from bottom sediments and could be a factor in the elevated organic nitrogen concentrations.
Station 12W, the northernmost regularly monitored station, exhibited worse water quality in 1992--a year of exceptionally heavy rainfall-- than the more southerly stations 9 and 6. During dry years, this distinction was less apparent. These findings suggest that the runoff of nutrients may be an important factor affecting water quality in the upper West Branch.
One difficulty in evaluating the West Branch is that because of unavailable land access, the upper reaches of the estuary were not monitored in the Citizen Program. The stations more southerly of 12W reflect "dilution" with cleaner offshore waters, hence, stations 12W, 9 and 6 were classified as "outer embayment", and we have no summer data for "inner" West Branch. Thus, water quality of the estuary as a whole appears better than would be predicted by the theoretical loading assessment conducted by the Buzzards Bay NEP which was meant to predict inner embayment characteristics.
Eutrophication Index scores
Nitrogen Management needs
The Buzzards Bay NEP estimated that existing nitrogen loadings are 22% over Project recommended limits. This analysis was based on an Outstanding Resource Water designation, the highest of four possible classifications for coastal waters. The Massachusetts Department of Environmental Protection, however, has ranked the West Branch as having only "SA" waters, the second highest water quality standard. If this lower standard were used, the embayment would not now exceed recommended limits, but would do so in the future when the watershed reaches full development buildout. The Project recommends the more stringent standard because of the value of the resources in this estuary.Generally water quality in the West Branch is fair to good, and is greatly better than conditions in the East Branch. Some loss of eelgrass beds in the upper estuary have been documented, a finding consistent with the overloading to the estuary. The watershed also has considerable growth potential, especially from conversion of agricultural land to residential land. Consequently, future growth in the watershed should be planned for and managed. The West Branch watershed is large and includes two municipalities in the state of Rhode Island. The Westport Planning Board in partnership with the Buzzards Bay NEP has already begun a buildout analysis for Westport. For this effort to be completed, Rhode Island parcel data must be obtained and analyzed. Nitrogen management for this estuary will require implementation of agricultural "best management practices" and controls on the number or performance of future septic systems. Upgrade of cesspools to septic systems with advanced nitrogen removal is another management option. Purchase of open space, agricultural protection restrictions, and conservation easements are important strategies to help manage future growth and nitrogen inputs. Given that conditions in the West Branch are not severely degraded, strategies to manage future inputs will prove worthwhile.
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