When, where and how to intervene? Trade-offs between time and costs in coastal nutrient management

Policies and regulations designed to address nutrient pollution in coastal waters are often complicated by delays in environmental and social systems. For example, social and political inertia may delay implementation of cleanup projects, and even after the best nutrient pollution management practices are developed and implemented, long groundwater travel times may delay the impact of inland or upstream interventions. These delays and the varying costs of nutrient removal alternatives used to meet water quality goals combine to create a complex dynamic decision problem with trade-offs about when, where, and how to intervene in the system. We use multi-objective optimization to quantify the trade-offs between costs and minimizing the time to meet in-bay nutrient reduction goals, represented as a Total Maximum Daily Load (TMDL). We calculate the impact of using in-bay (in-situ) nutrient removal through shellfish aquaculture. We apply these methods to the Three Bays Watershed in Cape Cod, Massachusetts. The avoided costs equate to an average value of 37¢ (2035 target date) and 11¢ (2060 target date) per animal harvested over the plan implementation period, depending on the year target for TMDL achievement. Our results encourage the consideration of alternative and in-situ approaches to tackle coastal pollution while traditional source control is implemented and its effects realized over time.