Expansion of the shrimp aquaculture sector has resulted in the destruction and degradation of mangrove ecosystems across much of Asia and South America. Although the rate of mangrove deforestation has largely decreased over the last several decades, the deficit of ecosystem services from lost and fragmented forests remains, leaving communities vulnerable to coastal climate risks. While habitat conversion was the primary environmental concern for the mostly extensive shrimp aquaculture sector in previous decades, the shift to more intensive production creates new environmental risks (Figure 1). Intensification increases the nutrient loads in effluent from aquaculture production, which amplifies the potential for untreated effluent to degrade surrounding water bodies and ecosystem. Conventional gray infrastructure, such as settling ponds and mechanical filtration, are most commonly used to treat effluent before discharging into the environment, but these systems provide few ecosystem services beyond their water quality benefits. Here, we compare the spatial requirements, farm-level economics, and ecosystem services of conventional and nature-based effluent treatment options to understand their viability, costs, and co-benefits.
Constructed mangrove wetlands emerged as the green-gray engineering approach with the most potential to reduce negative impacts from aquaculture, while also realizing environmental co-benefits at competitive capital and operational expenditure costs. By combining both engineered design of conventional treatments, with the environmental benefits and further removal of nutrients of NbS options, a green-gray engineering combination provides ecosystem services in addition to water purification attributes. We propose that effluent treatment can be designed in a way that improves water quality, while conferring increased coastal climatic resilience that benefits both the farmer and the environment.