Laserfiche WebLink
portion of Eel Pond and the Childs River have regions with accumulations of macroalgae which <br /> further contribute to the organic enrichment and enhance bottom water oxygen depletion and <br /> further impair benthic animal habitat. <br /> The dissolved oxygen records for the tidally influenced lower Quashnet River and the <br /> upper region of Hamblin Pond indicate that these sub-embayments currently maintain a high <br /> and moderate level of oxygen stress, respectively. Jehu Pond showed a high level of oxygen <br /> depletion, at a level which will impair habitat quality, with dissolved oxygen levels periodically <br /> approaching anoxia. Based upon measured total chlorophyll-a pigments (sum of chlorophyll-a <br /> and its immediate breakdown product, pheophythin a, as a better indicator of bloom conditions) <br /> it is clear that the Quashnet River is highly eutrophic with total chlorophyll-a levels in the upper <br /> and mid regions averaging >20 ug L"'. Jehu and Hamblin Ponds support moderate to high total <br /> chlorophyll levels, averaging 11.9 and 7.4 ug L"', respectively. Jehu Pond appears to be <br /> showing more nutrient enrichment than Hamblin Pond, both on average and relative to the size <br /> of the blooms. The high phytoplankton biomass in Jehu Pond is consistent with the observation <br /> of oxygen stress in this system. The moderate total chlorophyll levels in Hamblin Pond are <br /> consistent with its moderately good oxygen status. Similarly, Little River and Great River had <br /> average total chlorophyll levels of 5-6 ug L"', as might be expected from the outflow <br /> concentrations from their upper basins. The agreement between the chlorophyll land oxygen <br /> levels in these Pond basins is likely the result of their physical structure. <br /> Eelgrass surveys and analysis of historical data for the Waquoit Bay Embayment System <br /> indicated that eelgrass beds, when the watershed was relatively undeveloped (1951), were <br /> generally found within each sub-embayment, with the exception of Quashnet River and the <br /> uppermost portion of the western branch of Eel Pond. Multiple lines of evidence clearly <br /> indicated that the main basin of Waquoit Bay historically supported significant eelgrass <br /> coverage, primarily in the northern basin (large fringing beds) and in the region of the tidal inlet, <br /> although there is no evidence of coverage in central region of the lower main basin over the <br /> past 60 years. Similarly, within the western sub-embayments significant eelgrass coverage has <br /> been documented for the lower Childs River and the east branch and lower basin of Eel Pond, <br /> with no historic documented beds in the west branch. It should be noted that given the <br /> configuration of the Childs River, it is likely that the historic beds were primarily confined to the <br /> shallower margins rather than filling the basin. In contrast, presently virtually all eelgrass has <br /> been lost from the Waquoit Bay Embayment System, with the exception of Sage Lot Pond and a <br /> possible remnant patch associated with the main tidal inlet to Waquoit Bay. All of the basins <br /> with well documented historic eelgrass coverage within this system, which no longer support <br /> eelgrass coverage, are classified as significantly impaired relative to eelgrass habitat by the <br /> protocols of the MEP. The present levels of nitrogen, chlorophyll, periodic oxygen depletion <br /> and accumulations of macroalgae support that nitrogen enrichment is the primary mechanism of <br /> eelgrass decline in these basins. <br /> The near complete loss of the extensive eelgrass beds within the Waquoit Bay <br /> Embayment System has paralleled the increase in watershed development and the associated <br /> nitrogen enrichment to the System's estuarine waters. It appears that as the component sub- <br /> embayments became nutrient enriched, they could no longer support eelgrass beds. The <br /> proximate cause of loss is most likely related to nutrient related shifts in habitat quality, most <br /> significantly increased phytoplankton biomass as seen by high chlorophyll-a (turbidity/shading), <br /> resulting in decreased light penetration through the water column. However, it is likely that if <br /> nitrogen loading were to decrease, eelgrass could be restored in these basins to the 1951 <br /> pattern. This is supported by the fact that small areas still remain and that the decline from "full" <br /> coverage has been relatively recent. <br /> Executive Summary 7 <br />