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The Massachusetts Water Resources Authority (MWRA) conducts a comprehensive multidisciplinary monitoring program in Massachusetts Bay, Cape Cod Bay, and Boston Harbor to assess the environmental effects of a relocated secondary-treated effluent outfall. Through 2007, 8.7 years of baseline data and 7.3 years of postdiversion data (16 total years), including species level estimates of phytoplankton and zooplankton abundance, have been collected. MWRA's monitoring program and other studies make this region one of the most thoroughly studied and well-described marine systems in the world. The data show that the diversion of MWRA effluent from the harbor to the bay has decreased nutrients concentrations and improved water quality in the harbor (e.g., higher dissolved oxygen, lower chlorophyll). The diversion also resulted in an increase in dissolved inorganic nutrients (especially ammonium) in the vicinity of the bay outfall, but no obvious impacts such as increased biomass or decreased bottom water dissolved oxygen have been observed. Regional changes in phytoplankton and zooplankton unrelated to the diversion have been seen, and it is clear that the bays are closely connected both physically and ecologically with the greater Gulf of Maine. Direct responses to modifications of the nutrient field within a 10×10-km area centered near the midpoint of the 2-km long outfall diffuser in Massachusetts Bay (a.k.a. the nearfield) have not been seen in the plankton community. However, plankton variability in the bays has been linked to large regional to hemispheric scale (NAO) processes.

The transition metals Cu, Pb, Fe, Mn, and Cd were examined to estimate short- and long-term release rates from highly contaminated sediments and to compare this release with present metal flux into an ecosystem. The concentration of Cu and Pb increased in the water column over contaminated marine sediments when these sediments were isolated from metal and organic carbon sources and held in large (13 m3) marine microcosms. During the summer and early fall, Cu concentrations increased by a factor of 3 relative to the concentration in microcosms containing slightly polluted and uncontaminated sediments. Mass balance calculations indicate that 840 and 21 μmol∙m−2∙yr−1 Cu and Pb, respectively, were mobilized and exported from the microcosms with highly contaminated sediments, while less-contaminated sediments lost 120 μmol Cu∙m−2∙yr−1. Iron and Mn were not exported from the microcosms. In the absence of high sedimentation rates and high bioturbation rates, the diffusive loss of Cu and Pb may be sufficient to return the upper 1 cm of sediment to background levels in 44 and 400 yr, respectively. This remobilization is a small percentage of current inputs to Narragansett Bay.

The flux of Mn2+ from estuarine sediments contained in large cylinders was studied over a 14-month period by periodically capping the entire 2.5-m2 sediment surface with a benthic chamber. The seasonal magnitude in the Mn 2+ flux could be described by an exponential function of the temperature.IIowcver, the flux at a given temperature varied by a factor of 6-10. During summer (June-September), Mn flux was strongly correlated not to temperature but to the average primary productivity during the month preceding the flux determination. Significant correlations between Mn flux and primary productivity were also obtained for discrete 15-day intervals up to 68 days before the flux measurement.Postflux correlations were not significant except for a 2-week interval immediately following the measurement when annual data were considered. The results suggest that the input of new organic matter to the sediments exerts a major control over the production of Mn"+ in anoxic sediments and that temperature relationships alone do not predict the magnitude nor variability in benthic Mn flux.

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