Eutrophication remains a challenge to ecosystem health in coastal waters worldwide. Reductions of nutrient discharge from land-based sources have not been sufficient in many places to achieve desired water quality improvements. The use of oysters and other bivalve shellfish has shown promise as an in-water nutrient management tool to complement land-based strategies. Harvested oyster tissue was approved as a Best Management Practice (BMP) in the Chesapeake Bay region, and oyster and clam harvest is being used in other locations to fulfill mandated nutrient reduction requirements. Discussion continues of potential compensation to oyster growers, within a nutrient credit-trading program, for their nutrient removal ecosystem services. Active oyster leases and ongoing restoration within the Choptank Habitat Focus Area, parts of which are nutrient impaired, provides an opportunity to estimate the combined impact of cultivated oysters and restored reefs. Nitrogen (N) removal and the value of the ecosystem service were estimated using the local-scale Farm Aquaculture Resource Management (FARM) production model and an avoided-costs analysis of wastewater treatment, agricultural and urban BMPs as alternative management measures. A previous local estimate of reef denitrification was included to estimate the full nutrient removal capacity of reefs. Aquaculture related denitrification estimates are currently being determined.
Results/Conclusions
Results of the local-scale FARM model application show filtration related removal estimates of 199 kg N acre-1 yr-1 by restored reefs and 332 kg N acre-1 yr-1 by oyster aquaculture. A previous study reported reef related denitrification rates of 225 kg N acre-1 yr-1. The total acres of aquaculture lease (528) remove an estimated 175 x 103 kg N yr-1 via filtration and sequestration into tissue and shell, while 937 acres of restored reef remove an estimated 186 x 103 kg N yr-1. Estimated denitrification losses from restored reef acres are 211 x 103 kg yr-1. The value of this ecosystem service based on costs to remove a kilogram of N by 3 levels of wastewater treatment ($32 - $100), agricultural ($13) and urban ($350) BMPs is an estimated $7.44 - $200 million yr-1 for reef and aquaculture sequestration and reef denitrification combined. Results indicate that the potential value of these ecosystem services to a coastal municipality is considerable. This approach can be applied broadly to other jurisdictions seeking to raise awareness of potential ecosystem service value provided by their shellfish resources. This work lends further support for including shellfish ecosystem services as a tool in comprehensive nutrient management programs.