Cost-effectiveness of mussel farming as a water quality improvement measure: Agricultural, environmental and market drivers

This study aims to understand the economic and bio-physical conditions under which mussel farming is a cost-effective mitigation measure for improving water quality related to excess nitrogen in fjords and coastal areas. To that end, we set-up a mixed-integer optimization model including every farm in the catchments surrounding Limfjorden, the largest fjord in Denmark. We consider 14 possible mitigation measures, including mussel farming, to find the cost minimizing combination of mitigation measures to improve water quality. We run three scenarios for the catchment to explore the role of variations in the environmental conditions for mussel productivity and market opportunities for mussel-based products as organic animal feed. We analyze the resulting marginal abatement curves and draw insights about the potential scale of mussel farming that would be desirable under different market and environmental conditions for mussel production. We show that mussel farming is a cost-effective option for 2 of the 3 catchments, but that decreasing mussel productivity over time may remove it from the optimum solution for one of them. The possibility of a market for mussel-based organic feed significantly increases the share of nitrogen reduction done by mussels and decreases social cost up to 56%. Ultimately, the results indicate that, for catchments where environmental conditions are adequate, mussel farming can be a cost-effective nutrient reduction measure. Therefore, mussel farming can potentially increase the cost-effectiveness of incentive schemes aimed at reducing eutrophication in fjords and coastal waters.