Massachusetts Estuaries Project
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Massachusetts Estuaries Project Linked Watershed-Embayment Model to Determine Critical Nitrogen Loading Thresholds for the New Bedford Inner Harbor Embayment System, New Bedford, MA University of Massachusetts Dartmouth Massachusetts Department of School of Marine Science and Technology Environmental Protection UPDATED FINAL REPORT – November 2015 Massachusetts Estuaries Project Linked Watershed-Embayment Model to Determine Critical Nitrogen Loading Thresholds for the New Bedford Inner Harbor Embayment System, New Bedford, MA UPDATED FINAL REPORT – NOVEMBER 2015 Brian Howes Roland Samimy David Schlezinger Ed Eichner John Ramsey Trey Ruthven Contributors: US Geological Survey Don Walters and John Masterson Applied Coastal Research and Engineering, Inc. Elizabeth Hunt and Sean W. Kelley Massachusetts Department of Environmental Protection Charles Costello and Brian Dudley (DEP project manager) SMAST Coastal Systems Program Jennifer Benson, Michael Bartlett, Sara Sampieri and Elizabeth White M A E, Inc. Maisy McDarby-Stanovich Massachusetts Department of Environmental Protection Massachusetts Estuaries Project Linked Watershed-Embayment Model to Determine Critical Nitrogen Loading Thresholds for the New Bedford Inner Harbor Embayment System New Bedford, Massachusetts Executive Summary 1. Project Overview This updated report (revised to Final based on two rounds of comments from the MassDEP {Dec. 2013 and Aug. 2014} and comments from the Town of Fairhaven consultant {Feb. 2014}) builds on the Massachusetts Estuaries Project’s Linked Watershed-Embayment Approach which was applied to the Acushnet River – New Bedford Inner Harbor embayment system and first completed in December 2008. This updated report presents the results generated from the implementation of the Massachusetts Estuaries Project’s Linked Watershed- Embayment Approach to the Acushnet River – New Bedford Inner Harbor embayment system, a coastal embayment within the City of New Bedford and the Town of Fairhaven, Massachusetts. Analyses of the New Bedford Harbor embayment system was originally performed to assist the City and the Town with nitrogen management decisions associated with current and future wastewater planning efforts, as well as wetland restoration, anadromous fish runs, shell fishery, open-space, and harbor maintenance programs. The present update incorporates information obtained subsequent to the completion of the original analysis (2008) and addresses clarifications requested by the Buzzards Bay Project. Minor editorial comments provided to the MEP Technical Team by the Coalition for Buzzards Bay were also integrated into this updated report. The key underlying refinement in the present report involves an update to the land-use database used by the Towns and provided to the MEP. The updating of the parcel database included reformatting GIS files and cross-checks as well as a re-evaluation of water use and sewershed linkages, updates related to developed versus undeveloped and developable parcels, in addition to new wetland survey information and the treatment of cranberry bogs, all of which has been conducted over the past several years by the Buzzards Executive Summary 1 Bay Project, MassDEP and MEP/SMAST staff. The refinements to the land-use database have been used by the MEP to reconstruct the watershed nitrogen loading model, which then required a recalibration of the water quality model and associated assessments. In support of the revision of the loading models, additional data on nitrogen sources/strength were integrated into the update of the MEP threshold analysis. As a result of the refinements to the land-use database, the MEP/SMAST Technical Team completed a new build-out nitrogen loading projection for the present report update which will greatly enhance on-going nutrient management planning associated with these estuaries. In addition to the updates made to the watershed nitrogen loading module, water quality was re-evaluated to include monitoring that has taken place throughout the harbor since completion of the original MEP threshold analysis. Benthic regeneration (nutrient cycling from sediments) was re-evaluated as well in the summer of 2012 in order to capture potential changes in sediment nutrient flux rates which may have resulted from nutrient load reductions to the harbor between 2002 and 2012. In the fall of 2012, additional sediment cores were collected for the purpose of reassessing the benthic infaunal populations and how they may have changed over the ten years since the original infaunal assessment was completed. As part of the MEP approach, habitat assessment was conducted on the embayment based upon available water quality monitoring data, historical changes in eelgrass distribution, time-series water column oxygen measurements, and benthic community structure. Nitrogen loading thresholds for use as goals for watershed nitrogen management are the major product of the MEP effort. In this way, the MEP offers a science-based management approach to support the City of New Bedford and the Town of Fairhaven resource planning and decision- making process. The primary products of this effort are: (1) a current quantitative assessment of the nutrient related health of the New Bedford Harbor embayment, (2) identification of all nitrogen sources (and their respective N loads) to embayment waters, (3) nitrogen threshold levels for maintaining Massachusetts Water Quality Standards within embayment waters, (4) analysis of watershed nitrogen loading reduction to achieve the N threshold concentrations in embayment waters, and (5) a functional calibrated and validated Linked Watershed-Embayment modeling tool that can be readily used for evaluation of nitrogen management alternatives (to be developed by the City and the Town) for the restoration of the New Bedford Harbor embayment system. As increasing numbers of people occupy coastal watersheds, the associated coastal waters receive increasing pollutant loads. Coastal embayments throughout the Commonwealth of Massachusetts (and along the U.S. eastern seaboard) are becoming nutrient enriched. The elevated nutrients levels are primarily related to the land use impacts associated with the increasing population within the coastal zone over the past half-century. The regional effects of both nutrient loading and bacterial contamination span the spectrum from environmental to socio-economic impacts and have direct consequences to the culture, economy, and tax base of Massachusetts’s coastal communities. The primary nutrient causing the increasing impairment of our coastal embayments is nitrogen, with its primary sources being wastewater disposal, and nonpoint source runoff that carries nitrogen (e.g. fertilizers) from a range of other sources. Nitrogen related water quality decline represents one of the most serious threats to the ecological health of the nearshore coastal waters. Coastal embayments, because of their shallow nature and large shoreline area, are generally the first coastal systems to show the effect of nutrient pollution from terrestrial sources. In particular, the New Bedford Harbor embayment system within the City of New Bedford and the Town of Fairhaven is at risk of eutrophication (over enrichment) from enhanced nitrogen Executive Summary 2 loads entering through groundwater and surface water from the increasingly developed watershed to this coastal system as well as the single point discharge of treated effluent directly to the inner harbor from the Town of Fairhaven Wastewater Treatment Facility. Eutrophication is a process that occurs naturally and gradually over a period of tens or hundreds of years. However, human-related (anthropogenic) sources of nitrogen may be introduced into ecosystems at an accelerated rate that cannot be easily absorbed, resulting in a phenomenon known as cultural eutrophication. In both marine and freshwater systems, cultural eutrophication results in degraded water quality, adverse impacts to ecosystems, and limits on the use of water resources. The City of New Bedford and the Town of Fairhaven, as the primary stakeholders to the New Bedford Inner Harbor embayment system, have been concerned over the quality of this local coastal resource. The community has worked to implement controls on direct stormwater discharges, PCB clean-up, and institute an aggressive program for controlling nutrient inputs to the Harbor from combined sewer overflows (CSOs) as well as upgrading the New Bedford Wastewater Treatment Facility to secondary treatment (85 - 90 percent reduction of the influent biochemical oxygen demand and suspended solids). The Town of Fairhaven has also completed and implemented wastewater planning and sewering in other regions of the Town not associated with the Acushnet River – New Bedford Inner Harbor embayment system. The Town has nutrient management activities related to their tidal embayments, which have been associated with the MEP effort in the Little Bay and Nasketucket Bay embayment system. In addition, the Town of Acushnet has been expanding its sewer system thereby capturing nutrient load that would otherwise discharge directly into the Acushnet River. This wastewater flow is being sent to the New Bedford Wastewater Treatment Facility for treatment and eventual discharge to Buzzards Bay via ocean outfall. In addition, the City of New Bedford and the Town of Fairhaven have supported the Coalition for Buzzards Bay’s Water Quality Monitoring Program which has been collecting data on nitrogen related water quality within the