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towns to test specific management scenarios and weigh the resulting water quality impact <br /> against the cost of that approach. In addition to the management scenarios modeled for this <br /> report, the Linked Model can be used to evaluate additional management scenarios and may be <br /> updated to reflect future changes in land-use within an embayment watershed or changing <br /> embayment characteristics. In addition, since the Model uses a holistic approach (the entire <br /> watershed, embayment and tidal source waters), it can be used to evaluate all projects as they <br /> relate directly or indirectly to water quality conditions within its geographic boundaries. Unlike <br /> many approaches, the Linked Model accounts for nutrient sources, attenuation, and recycling <br /> and variations in tidal hydrodynamics and accommodates the spatial distribution of these <br /> processes. For an overview of several management scenarios that may be employed to restore <br /> embayment water quality, see Massachusetts Estuaries Project Embayment Restoration <br /> Guidance for Implementation Strategies, available for download at <br /> http://www.state.ma.us/dep/smerp/smerp.htm. <br /> Application of MEP Approach: The Linked Model was applied to the Waquoit Bay <br /> embayment system by using site-specific data collected by the MEP and water quality data. <br /> collected by both the Waquoit Bay National Estuarine Research Reserve and a joint effort <br /> comprised of water sampling undertaken by the Town of Mashpee with the Coastal Systems <br /> Program at.SMAST-UMD (see Section II for full explanation). Evaluation of upland nitrogen <br /> loading was conducted by the MEP, data was provided by the Town of Falmouth Planning <br /> Department, and watershed boundaries delineated by USGS. This land-use data was used to <br /> determine watershed nitrogen loads within the Waquoit Bay embayment system and the <br /> systems sub-embayments as appropriate (current and build-out loads are summarized in Table <br /> IV-3). Water quality within a sub-embayment is the integration of nitrogen loads with the site- <br /> specific estuarine circulation. Therefore, water quality modeling of this tidally influenced estuary <br /> included a thorough evaluation of the hydrodynamics of the estuarine system. Estuarine <br /> hydrodynamics control a variety of coastal processes including tidal flushing, pollutant <br /> dispersion, tidal currents, sedimentation, erosion, and water levels. Once the hydrodynamic <br /> characteristics of the system were quantified, transport of nitrogen was evaluated from tidal <br /> current information developed by the numerical models. <br /> A two-dimensional depth-averaged hydrodynamic model based upon the tidal currents <br /> and water elevations was employed for the Waquoit Bay embayment system. Once the <br /> hydrodynamic properties of the estuarine system were computed, two-dimensional water quality <br /> model simulations were used to predict the dispersion of the nitrogen at current loading rates. <br /> Using standard dispersion relationships for estuarine systems of this type, the water quality <br /> model and the hydrodynamic model was then integrated in order to generate estimates <br /> regarding the spread of total nitrogen from the site-specific hydrodynamic properties. The <br /> distributions of nitrogen loads from watershed sources were determined from land-use analysis. <br /> Boundary nutrient concentrations in Vineyard Sound source waters were taken from water <br /> quality monitoring data. Measurements of current salinity distributions throughout the estuarine <br /> waters of the Waquoit Bay embayment system was used to calibrate the water quality model, <br /> with validation using measured nitrogen concentrations (under existing loading conditions). The <br /> underlying hydrodynamic model was calibrated and validated independently using water <br /> elevations measured in time series throughout the embayment. <br /> MEP Nitrogen Thresholds Analysis: The threshold nitrogen level for an embayment <br /> represents the average water column concentration of nitrogen that will support the habitat <br /> quality being sought. The water column nitrogen level is ultimately controlled by the watershed <br /> nitrogen load and the nitrogen concentration in the inflowing tidal waters (boundary condition). <br /> The water column nitrogen concentration is modified by the extent of sediment regeneration. <br /> Executive Summary 4 <br />