Managing anthropogenic nitrogen inputs to coastal embayments: Technical basis and evaluation of a management strategy adopted for Buzzards Bay.

In 1990, the Buzzards Bay Project, a participant in the U.S. Environmental Protection Agency's National Estuary Program, developed a Total Maximum Annual Loads (TMAL) strategy to manage anthropogenic nitrogen inputs to coastal waters. This strategy, contained in a Comprehensive Conservation and `Management Plan for Buzzards Bay, was designed to protect and restore water quality and living resources in more than 30 coastal embayments in Buzzards Bay. The recommended TMAL approach to manage point and non-point sources, was empirically based on a comparison of embayment conditions to estimated nitrogen loads together with a synthesis of previous studies of loading and ecosystem response. Existing nitrogen loads to the Buzzards Bay embayments were based on land use data contained in a Geographic Information System, and a well defined set of nitrogen loading assumptions for different kinds of land uses and sewage disposal. Drainage basins for each embayment were delineated by either land surface topography or groundwater elevations as appropriate. Recommended embayment TMAL limits were established with a tiered system that incorporated existing regulatory water quality classifications, together with embayment area or volume and hydraulic turnover time and depth, so that embayment specific TMALs were established. The appropriateness of these recommended nitrogen loading limits was evaluated using seven years of data collected through a citizens-based water quality monitoring program. Average summertime total nitrogen concentrations and a Eutrophication Index developed by the Buzzards Bay Project show a good correlation with estimates of nitrogen loading derived from land use data. Of the various methods used to characterize nitrogen loadings, a Vollenweider type model incorporating flushing and volume showed the best correlation to water quality parameters. The results of the citizens' water quality monitoring program has led the Buzzards Bay Project to revise its methodology, including reducing recommended TMAL N limits by as much as 50%.