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When and where to intervene? Coastal nutrient loading, groundwater travel times, and watershed dynamics
Citation:
Merrill, N., S. Balogh, A. Piscopo, AND K. Mulvaney. When and where to intervene? Coastal nutrient loading, groundwater travel times, and watershed dynamics. 30th Annual Nonpoint Source Pollution Conference, Portsmouth, NH, April 18 - 19, 2019.
Impact/Purpose:
This work uses simulation and optimization to find efficient plans to address coastal pollution problems for a watershed and bay on Cape Cod, MA. The effects of cleaning up sources of pollution are delayed because of the varying travel times of groundwater from the sources to the bay. We show how modeling these groundwater lag times affect the efficient plans through time.
Description:
This paper presents the dynamic planning problem of addressing coastal eutrophication, with an example and parameterization for an estuary system on Cape Cod (Barnstable County, MA). Due to varying groundwater travel times across the aquifer, there is a relationship between the spatial location of nitrogen abatement efforts and the eventual effect on pollution loading at the estuary along this travel time gradient. Interventions under consideration vary from source control--upgrading septic systems and sewering--to in-estuary approaches such as increasing aquaculture. For a community, finding the right balance of these technologies is more complicated than simply implementing the option with the fastest impact first, or prioritizing the least expensive option. This is because travel time, marginal costs, scalability, and watershed dynamics combine to make efficient choices more nuanced in space and time. We present a model of groundwater transport and estuary nutrient loading combined with an economic model of pollution abatement costs over time. This model is parameterized for the Three Bays estuary system, on Cape Cod, MA and the associated watershed. Our results inform the timing, spatial allocation and combination of treatment options by simulating the optimal control paths. The results show dynamically efficient approaches that balance source control and in-estuary efforts across a range of target pollution limit attainment dates. We discuss the tradeoffs between the economic objectives and the spatial and temporal pollution abatement plans.