Citation:

Piscopo, A., N. Merrill, S. Balogh, AND K. Mulvaney. Multi-objective optimization of nitrogen abatement plans for a coastal estuary of Cape Cod, Massachusetts. International Conference on Evolutionary Multi-Criterion Optimization, East Lansing, Michigan, March 10 - 13, 2019.

Impact/Purpose:

Nitrogen from septic systems and other sources is transported in groundwater to receiving water bodies such as bays. Excess nitrogen can degrade water quality in bays, and in turn, have negative consequences for areas dependent on clean water for fish habitat and tourism. One such area is the Three Bays watershed of Cape Cod, Massachusetts. Three Bays and other areas across the Cape are considering the use of nitrogen abatement technologies to manage water quality issues. However, to reduce nitrogen loads to acceptable levels, decision-makers in Three Bays must develop abatement plans that specify when, where, and how many technology upgrades to implement. Optimization algorithms can be used to efficiently solve this problem, resulting in plan options that reflect tradeoffs between minimizing cumulative plan cost (economic goal) while minimizing the amount of time to reduce nitrogen to acceptable levels (environmental goal).

Description:

Eutrophication of coastal estuaries is an issue of growing concern, especially in areas with economies dependent on clean water for fish habitat and tourism. One such example is the Three Bays estuary of Cape Cod, Massachusetts, USA, which is impaired by excess nitrogen primarily from septic systems. Nitrogen abatement technologies, such as advanced septic systems and sewers, have the potential to reduce nitrogen loads in this watershed to acceptable levels; however, because nitrogen from existing septic systems is transported to the estuary via groundwater, many years to decades may pass before upgrades reduce nitrogen levels in the bay. The lag in environmental impact is also economically undesirable, since present-day spending on upgrades does not result in near-term improvements in water quality (i.e., delayed gratification). Our research addresses this dynamic management problem by using a multi-objective evolutionary algorithm to generate abatement plans that minimize both cumulative cost and the amount of time to reduce nitrogen loads down to acceptable levels. The result of this dual-objective optimization is a set of nondominated plans that specify when, where, and how many residential properties should be treated with technology upgrades to achieve acceptable nitrogen loads in the estuary. We analyze these plans by examining tradeoffs between time and cost and investigating how the addition of in-estuary nitrogen abatement, such as increased shellfish aquaculture, could improve performance in either of these objectives.

Record Details: