Nitrogen Modeling to Support Watershed Management: Comparison of Approaches and Sensitivity Analysis

Overview: Coastal embayments throughout the State of Massachusetts (and along the U.S. eastern seaboard) are becoming nutrient enriched. The nutrients are primarily related to changes in watershed land-use associated with increasing population within the coastal zone over the past half century. Many of Massachusetts' embayments have nutrient levels that are approaching or are currently over their assimilative capacity, which begins to cause declines in their ecological health. The result is the loss of fisheries habitat, eelgrass beds, and a general disruption of benthic communities. At its higher levels, enhanced loading from surrounding watersheds causes aesthetic degradation and inhibits even recreational use of coastal waters. In addition to nutrient related ecological declines, an increasing number of embayments are being closed to swimming, shellfishing, and other activities as a result of bacterial contamination. While bacterial contamination does not generally degrade the habitat, it restricts human uses. However, like nutrients, bacterial contamination is related to changes in land-use as watershed become more developed. The regional effects of both nutrient loading and bacterial contamination span the spectrum from environmental to socioeconomic impacts and have direct consequences to the culture, economy, and tax base of Massachusetts's coastal communities. DEP, SMAST, and others have partnered under the Massachusetts Estuary Project to address these embayment management and planning issues. A central component of the Massachusetts Estuary Project is the task of providing a quantitative tool for watershed-embayment management throughout Southeastern Massachusetts. This Massachusetts Estuary Project is founded upon science-based management. The Project will use a consistent, state-of-the-art approach throughout the region's coastal waters and provide technical expertise and guidance to the municipalities and regulatory agencies tasked with their management, protection, and restoration. The overall goal of the project is to provide technical guidance to DEP in support of policies regarding nitrogen loading to embayments and to conduct nitrogen TMDL's. In appropriate estuaries, TMDL's for bacterial contamination will also be conducted in concert with the nutrient effort (particularly if there is a 303d listing). However, the goal of the bacterial program is to provide information to guide targeted sampling for specific source identification and remediation. As part of the overall effort, the evaluation approach will be used to assess available options for meeting selected nitrogen goals protective of embayment health. The major Project goals are to: • develop a coastal TMDL working group for coordination and rapid transfer of results, • determine the nutrient sensitivity of each of …