Developing a cost-effective methodology to manage Fecal Coliform loading in shellfish harvesting areas of upper Chesapeake Bay, Maryland

There are more than 75 shellfish harvesting areas in the upper Chesapeake Bay of Maryland that are impaired due to elevated bacterial levels. A comprehensive plan must be established to support the management of bacterial sources in the drainage areas of these waterbodies 1) to protect water quality for public health, 2) to identify potential pollutant sources in the watershed, and 3) to establish the assimilative capacity of the waterbody. Traditionally, a linked watershed and receiving waters modeling approach has been used for estimating assimilative capacity of the waterbodies and developing pollutant load reductions. However, the horizontal scales of these impaired areas vary from a few kilometers to more than 100 kilometers, while the required assessment period to demonstrate the attainment of the water quality standard is 3 to 5 years, requiring long-term observation data and model simulations. Therefore, application of this traditional approach is not feasible for these many areas due to the requirements of large modeling efforts to simulate both the watershed processes and instream fecal coliform concentrations for long-term simulation. To address this challenge, the Virginia Institute of Marine Science and the Maryland Department of the Environment have worked together to develop a cost-effective methodology to achieve these goals. The key element of our approach is to use inverse modeling to estimate fecal coliform loads from the watershed and to establish the assimilative capacity for the waterbody. The inverse modeling approach can be invoked by either the tidal prism model or 3D transport models; it is thus applicable to the large range of spatial scales encountered. By integrating, modeling results with GIS-based source analysis and bacteria source tracking results, potential fecal coliform sources can be identified. With the use of an inverse modeling approach, accurate loads estimation can be achieved while watershed modeling is not available. A case study of the inverse modeling approach for Maryland's Choptank River is presented here to demonstrate the feasibility of simulating the fecal coliform distribution in the tidal river and the capability of using the system to support management needs.