1996 Citizens Report: West Falmouth Harbor
Embayment: West Falmouth Harbor
Embayment and Watershed Characteristic
West Falmouth Harbor is a shallow, mid-size embayment that had eelgrass beds covering more than 80% of the bottom during the 1980s. Fringing salt marshes are common along shore, but there are only two larger marsh systems, one in the northeast (Snug Harbor), and one in south (Harbor Head). Recreational boaters extensively utilize the Harbor. Two creeks discharge to this embayment (to Snug Harbor and brackish water from Oyster Pond), but because of the glacial soils at the site it is likely that most freshwater discharge (and nitrogen inputs as well) enter the embayment via groundwater. A flushing study partially funded by the Buzzards Bay NEP and completed early in 1995 showed most of West Falmouth Harbor very well flushed, with a turnover time of less than a day. The inner most areas like Snug Harbor and Harbor Head had longer flushing times of 4.5 and 0.6 days respectively, and Oyster pond, connected to the bay by a culvert, had a flushing time of more than 100 days. Based on this data, the Buzzards Bay project adopted a 2.4 day turnover time calculated from a volume weighted mean of all the inner embayment components and is using this rate to calculate acceptable loading rates to the Harbor.Most development is clustered along shore, and the upper estuary is largely undeveloped. Thus,
the watershed contains several major point sources including the Falmouth wastewater treatment
facility, the Falmouth landfill, and plumes from previous discharges such as Falmouth's now
closed septage lagoons. The most recent Buzzards Bay NEP loading estimates are sewage
treatment facility (62%), septage lagoon plume (13%), and residential development (23%).
Water Quality monitoring
In 1992 and 1993, West Falmouth Harbor was monitored through the Buzzards Bay citizen monitoring program. To avoid overlap with the Falmouth PondWatchers program, this embayment was monitored exclusively by the PondWatchers in 1994 and 1995, at the Buzzards Bay Monitoring Program sites. Unfortunately however, chlorophyll concentrations are not monitored in the PondWatchers program so we were unable to calculate a Eutrophication Index for those years. To overcome this problem, we calculated Eutrophication Index scores for West Harbor using only the remaining four Index parameters (see centerfold map) for all four years. We believe this approach is valid because in 1992, the five parameter index resulted in a score of 66, whereas the four parameter score was 65. In 1993, the five parameter score showed a slight decline in water quality with 63 points, whereas the four parameter score showed an improvement at 70 points. Nonetheless, we feel a 4 year, four parameter score useful for evaluating trends in the estuary.As shown in the centerfold map, like several other Cape Cod embayments, water quality was moderately worse in 1994 and 1995 as compared to the first two years of the study. Total nitrogen concentrations, while showing considerable year to year variability were clearly higher in the last two years of the study than the first two years. The increase in total nitrogen appeared largely caused by increases in organic nitrogen. Dissolved inorganic nitrogen concentrations did not show any clear trend, but occasional high concentrations were observed at station WF2 (Snug Harbor). Oxygen concentration was relatively good, but showed very wide summertime fluctuations. In 1995 inner stations WF4 and WF1 dropped to 60% and 40% saturation. Station WF2 (Snug Harbor) has consistently lower oxygen saturations than either of these sites, but unfortunately was no monitored that year because of a shortage of volunteers.
Eutrophication Index scores
Nitrogen Management needs
In 1994 the Buzzards Bay NEP partially funded a town flushing study of the harbor (ACI report), and in 1995 the town, with assistance from the Project completed a watershed buildout analysis. This summer, the Project will provide the town with an updated analysis of nitrogen loadings in the watershed and identify management options for the town. Based on the ACI report, the Buzzards Bay NEP calculated a weighted average flushing time for the whole Harbor of 1.x days. (An alternative management strategy would be to establish specific nitrogen loading limits for each major segment of the estuary). Using the single flushing standard approach, with an "SA" water quality standard loading limit (the second most stringent standard for coastal waters), this embayment is now 20% below recommended loading limits, but would exceed these limits at full buildout conditions. If the less stringent SA designation were applied to this embayment (somewhat analogous to the towns' "Stabilization Area" designation under its nutrient loading bylaw), a critical loading limit of 37,000 kilograms per year would be established. Nitrogen management to this level of protection would be less challenging to the town because existing loadings are now 40% of this limit and would only be slightly over limit if future nitrogen inputs were not managed. The "Outstanding Resource Water" designation (ORW-the most stringent standard for coastal water quality) limit would be more difficult to achieve since the Harbor is already above the 17,000 kg per year limit under that designation, but the valuable resources and habitat of the harbor may warrant such action. Clearly this decision will be one for the town's officials and residents to decide.Back