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thresholds. In addition, TN levels in the pond have been relatively stable so that detecting even small improvements as nitrogen management alternatives are implemented, e.g. oysters, in these tributary salt ponds appears achievable. Popponesset Bay has a completed system-wide Massachusetts Estuaries Project analysis and MassDEP/USEPA TMDL. Popponesset Bay and its component basins have lost their historical eelgrass habitat(prior to 1995)and the upper tributaries presently support impaired or degraded habitat for benthic animal communities. The 2010-2016 sampling results are consistent with the prior years in showing that nitrogen levels of the tributary basins are still well above their TMDL designated thresholds,which vary from 0.5 mg U1 for Shoestring and Ockway Bays (0.55 nig L-1 in upper Mashpee River) and 0.38 mg 1-1 for Popponesset Bay main basins (sentinel station near tip of Mashpee Neck) to re-establish eelgrass habitat(Figure 11). Equally important, it appears that recent TN levels have significantly increased over historic(pre-2010) conditions, which is generally associated with habitat decline. In contrast, the main basin has remained relatively constant due to its volume, flushing rate and continuation of maintenance of the tidal inlet. The consequences of these elevated total nitrogen levels can be seen in the high amounts of phytoplankton biomass(measured as chlorophyll-a pigments),which saw.bloom conditions in 2016, and associated depletion of bottom water oxygen. Since estuarine phytoplankton, including those in Waquoit and Popponesset Bays,are stimulated by nitrogen additions, the effect of the nitrogen enrichment is to cause phytoplankton blooms and turbid waters within both estuaries. Generally,the reaches with the highest nitrogen (Figures 7, 11) support the highest chlorophyll-a pigment levels (Figures 8, 12), although local factors can interfere with this response. Analysis of the total chlorophyll-a and particulate organic nitrogen(PON) data indicate that the PON is directly related to the chlorophyll-a concentration(R2=0.96). This underscores the contention that the particulate matter in the water column of these estuaries in not "imported"but comprised of phytoplankton growing within the water column,providing a direct link between nitrogen additions and poor water clarity. These measurements support the Town's management plan,which focuses on lowering the nitrogen levels to reduce phytoplankton biomass and improve water and habitat quality and likely restore eelgrass beds. In the Waquoit Bay system, the 2010-2015 chlorophyll-a levels are generally consistent with the long-term historical data,however,results from 2016 are significantly higher, supporting the contention that these estuaries are presently nitrogen enriched, resulting in high levels of phytoplankton production. In addition to the amount of phytoplankton, it is important to note the large and prolonged bloom in summer 2016, to levels not previously observed. The effects of continuing nitrogen enrichment is to increase average pigment levels and also to increase the frequency and duration of periodic blooms (Figure 8). Average levels of—3 ug F are typical of high quality coastal waters,with average levels of<5 ug 1;1 in summer in shallow estuaries still indicative of moderately healthy waters. Average chlorophyll-a levels>I 0 ug U 1 indicates some impahment. Chlorophyll-a levels within the tidal rivers of both systems and in particular Childs River, Quashnet River and upper Eel Pond in the Waquoit Bay System and Shoestring Bay and the Mashpee River in the Popponesset Bay System are all showing significantly impaired conditions(Figures 8 and 12). Okway Bay and the main basin of Popponesset show lower chlorophyll levels than elsewhere,however, total pigment levels from 2016 seem uniformly high compared to the average levels from 2010-2012 and 2013- 2015. While the western basins of Waquoit Bay tend to have relatively high chlorophyll-a levels, the eastern basins (Hamblin Pond,7ehu Pond) continue to support only moderate levels 17