11/13/2017 BOARD OF SELECTMEN Minutes

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MONITORING RESULTS In regard to the Popponesset Bay and Waquoit Bay Systems,nutrient related water quality decline continues to represent the primary enviromnental problem facing the citizens of Mashpee, Falmouth, Barnstable and Sandwich. Nitrogen management planning and implementation are underway and the Mashpee Water Quality Monitoring Partnership is tracking short and long term changes resulting from continued watershed nitrogen loading increases, variation in tidal flushing, and implementation of nitrogen management alternatives (including propagation of oysters). As implementation is still in its initial stages, it is not surprising that the results of the 2010-2016 Mashpee Water Quality Monitoring Program indicate that both Popponesset Bay and Waquoit Bay continue to show poor nutrient related water quality throughout most of their tidal reaches. However,with the collection of multi-year high quality data, it appears that the more impaired areas of Popponesset Bay and Waquoit Bay were showing some improved water quality through 2014,while the higher quality areas appear to be stable (see below). Unfortunately both bays experienced large blooms and an associated decline in water quality in summer 2016 and both estuaries still support impaired habitats and remain below the water quality Ievels set by the MassDEP/EPA TMDL. Summer 2016 was dominated by a very large bloom of Cochlodin um (Rust Tide),which was found in many other southeastern Massachusetts estuaries,including adjacent Three Bays, and bad negative effects on water clarity and bottom water dissolved oxygen as the bloom declined. Although Cochlodinium has sometimes been thought to impact shellfish,there was no evidence that it did so in the recent blooms in Mashpee estuaries. The salinity gradients within each estuary in 2010-201.6 are generally consistent with historical levels (Figures 6 and 10). The gradients show the concentration of freshwater discharges at the headwaters of the upper tributary basins. For example, the Childs River and Quashnet River estuarine reaches in Waquoit Bay and the Mashpee River in Popponesset Bay are functionally tidal rivers with drowned river valley morphology and significant stream discharge to the headwaters. As a result the saline waters entering on the flooding tide from the adjacent main basin become significantly diluted. The upper reaches of the Quashnet River and the Mashpee River showed salinities generally—5 ppt (Figures 6 and 10) and the long term salinity at the head of the Childs River was generally around 10 ppt, however, in recent years, 2010-2016, the salinity levels in the headwaters have risen to—16-18 ppt,which appears to be a real shift. This likely results from lower freshwater inflows allowing more saline water to push higher up into the Childs River estuary. These freshwater inflows are rich in nitrogen from terrestrial sources and support much of the eutrophication in the more estuarine areas downstream. Interestingly, the corresponding average TN levels at the Childs River head station have remained relatively constant from historic levels through 2015, with only 2016 showing a major increase in TN, apparently associated with the very large phytoplankton bloom. It should be noted that the Quashnet River above the Meadow Neck Road bridge continued to be very brackish with low salinities (upper, <5 ppt, and mid, <8 ppt, stations) as has been observed in the long term record and samplings from 2010 through 2016. The abrupt increase in salinity from the mid station to the lower basin (-22 ppt), an increase of more than 12 ppt, was thought to result from a restriction in tidal flow in this region. However, no significant tidal restriction was found in a follow-up study completed by the Coastal Systems Program (SMAST) in collaboration with the Town of Mashpee. This study also confirmed,using tidal stage data, that there is very little tidal damping due to the Meadow Neck Road bridge. It may rather be that 15