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(consistent with moderate TN levels), But again, total chlorophyll a levels in 2016 are still slightly higher than the long term average at most stations, including in the eastern basins and did approach the 10 ug/L threshold cut point that indicates decreasing habitat health. The levels of nitrogen and total chlorophyll a pigment in the eastern.basins is also consistent with these basins only losing eelgrass recently and having only moderate nitrogen.enrichment: However, most waters of both estuarine systems have total chlorophyll a averages greater than 5 ug I; These levels of phytoplankton biomass result in enhanced deposition of organic matter to the bottom sediments which results in higher arnounts of oxygen uptake,negative impacts of organic matter loading on the bottom dwelling organisms and at highest levels, bottom habitats comprised of sulfidic-organic rich soft sediments after many years of nitrogen enrichment. Also, the higher amounts of phytoplankton in the water column increases the amount of oxygen being consumed during periods of low light or darkness adding to oxygen depletion and loss of fish, shellfish and bottom dwelling animals and the other organisms that feed upon them. Equally significant, the higher amounts of phytoplankton increase turbidity in the water column and reduce the amount of light that can penetrate to support eelgrass plants that are rooted to the bay bottom. This shading effect is one of the primary proximate causes of eelgrass loss world-wide, and in Popponesset Bay and Waquoit Bay in specific. Eelgrass has not been observed for over a decade in Popponesset Bay and has been reduced in Waquoit Bay to a few remaining patches in Hamblin Pond and Jehu Pond(Short and Burdick, 1996). Concomitantly, observed macroalgal growth and accumulations stimulated by high nitrogen inputs have been significant across Waquoit Bay and large areas within the Popponesset Bay Estuary. Macroalgal accumulations are a key metric indicating nitrogen enrichment and impaired habitat quality due to the associated negative effects of smothering the benthic habitat and overwhelming eelgrass habitat. Eelgrass has not been observed in the Quashnet River sub-embayment for many decades; instead high levels of macroalgae have been documented(Curley et al., 1971, Valicla et al., 1992). Oxygen depletion of bottom waters was variable but still evident within both systems in 2010- 2016 and were generally consistent with historical data, however, DO was generally lower in 2016 across the Waquoit Bay and Popponesset Bay stations with the exception of Shoestring Bay and Okway Bay which showed less summer DO depletion in 2016 compared to the 2013- 2015. Interestingly, the generally lower DO in the Waquoit and Popponesset Bay systems follows the distribution of higher total chlorophyll-a and TN levels (Figures 9, 13)with the exception of stations in Okway Bay and Shoestring Bay. The linkage of oxygen depletion to nitrogen enrichment is seen in each year's results with higher oxygen levels at lower levels of nitrogen enrichment and greater depletion in basins with higher nitrogen enrichment. In 2016 oxygen depletion tended to be greater than in previous years with the exception of the more well flushed tidal basins of the Popponesset Estuary,particularly Okway Bay and Shoestring Bay. More specifically, 8 of the 13 stations sampled in Popponesset Bay in 2016 recorded lower D.O. than the 2013-2015 average and only 1 station showed higher DO levels. Similarly,DO conditions in Waquoit Bay were generally worse in 2016 compared to the average levels for 2013-2015. In 2016, 10 stations showed lower DO concentrations compared to the 2013-2015 average and only 3 stations were higher. The depressed DO levels likely result from the large, prolonged phytoplankton bloom in 2016,which results in higher organic loading to the sediments and elevated water column night-time respiration. However, it is likely that the basins of these estuaries remain generally nutrient and organic matter enriched to the point where oxygen depletion will begin to occur when vertical mixing of the water column decreases or a period of low light occurs(Sawabini �t al. 2014). Both factors are inter-related and both likely 18