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the basin configuration and circulation in the middle to upper portions of the Quashnet River support lower salinities than the larger lower basin, nearest the tidal inlet. Brackish salinities within this upper basin have been observed in past years,but in recent years,a freshening appeared to be occurring that did not continue into the drought year of 2016. Upon return to average annual rainfall conditions, if this basin further freshens, phosphorus management may need to be evaluated(Figure 18). The Mashpee River upper basin also supports brackish salinities (3-5 ppt) similar to the upper Quashnet River Basin. However, the Mashpee River has supported a stable salinity structure for many years and no tidal restrictions are found within the tidal river itself. In contrast to these riverine habitats,the larger more open basins within both Waquoit and Popponesset Bay Systems generally show only small salinity gradients and little variation in average salinities from year to year. This pattern results from their larger volumes, proportionally lower freshwater inflow rates and closer proximity to the lower nitrogen,higher salinity waters of Nantucket Sound, especially the lower main basins of Popponesset Bay, Waquoit Bay and Eel Pond. The generally high salinities(-25-30 ppt) of these major basins is typical of the shallow enclosed estuaries of southeastern Massachusetts where major rivers are generally absent and tidal volumes are large relative to freshwater discharges. Monitoring results from summers 2010-2016, show that total nitrogen levels throughout the Waquoit Bay and Popponesset Bay Systems are significantly enriched over the high quality waters of Nantucket Sound(0.28 mg/1-TN) entering during flooding tides and are generally consistent with prior historical data (Figure 7 and 11). The pattern of nitrogen gradients in both systems roughly follows the salinity gradients, as the major source of the "excess"nitrogen is from groundwater and surface freshwater inflows. Within each sub-embayment, nitrogen levels were highest within the headwaters and declined with decreasing distance from the tidal inlets, with the lowest nitrogen levels being recorded at the stations proximate to each inlet. In both systems there are inter-annual differences,probably the result of inter-annual variation in weather related factors (wind,rain,temperature, etc.) or small differences in the sampling. For example, based on the 2010-2012 and 2016 TN averages, there is a very high average TN value at the head of the Quashnet River, much higher than in the long-terra historical data or the 2013- 2015 average results (Figure 7). The higher TN years are caused by elevated PON levels associated with major phytoplarikton blooms. The observed inter-annual variability results from the higher average PON (total chlorophyll a)and TN values for the 2010-12 and 2016 seasons. These"peaks"in TN were not repeated in 2013, 2014, 2015 or 2016. The cause of the blooms is a combination of temperature, sunlight and circulation which allows a bloom to develop, possibly related to elevated inorganic nitrogen inputs in strearnflows. The variation itself indicates the need to establish a long-term baseline to be able to demonstrate changes in water and habitat quality related to changes in nitrogen loading versus inter-annual variations related to circulation and weather. In general, the 2010-2016 sampling results are consistent with the prior years in showing that these tributary basins are still well above their assimilative capacity with total nitrogen levels well above their TMDL designated threshold. The threshold total nitrogen level for these basins varies from 0.5 mg L' for Quashnet to restore bottom animal habitat to 0.38 mg L' for Hamblin and Jehu Ponds to re-establish eelgrass habitat (Figure 7). It should be noted that Hamblin and Jehu Pond only recently lost their eelgrass habitat and therefore may be able to be restored more quickly than other larger basins that are much farther beyond their acceptable nitrogen 16