Bioextractive Removal of Nitrogen by Oysters in Great Bay Piscataqua River Estuary, New Hampshire, USA

Abstract

Eutrophication is a challenge to coastal waters around the globe. In many places, nutrient reductions from land-based sources have not been sufficient to achieve desired water quality improvements. Bivalve shellfish have shown promise as an in-water strategy to complement land-based nutrient management. A local-scale production model was used to estimate oyster (Crassostrea virginica) harvest and bioextraction of nitrogen (N) in Great Bay Piscataqua River Estuary (GBP), New Hampshire, USA, because a system-scale ecological model was not available. Farm-scale N removal results (0.072 metric tons acre −1 year −1) were up-scaled to provide a system-wide removal estimate for current (0.61 metric tons year −1), and potential removal (2.35 metric tons year −1) at maximum possible expansion of licensed aquaculture areas. Restored reef N removal was included to provide a more complete picture. Nitrogen removal through reef sequestration was~3 times that of aquaculture. Estimated reef-associated denitrification, based on previously reported rates, removed 0.19 metric tons N year −1. When all oyster processes (aquaculture and reefs) were included, N removal was 0.33% and 0.54% of incoming N for current and expanded acres, respectively. An avoided cost approach, with wastewater treatment as the alternative management measure, was used to estimate the value of the N removed. The maximum economic value for aquaculture-based removal was $105,000 and $405,000 for current and expanded oyster areas, respectively. Combined aquaculture and reef restoration is suggested to maximize N reduction capacity while limiting use conflicts. Comparison of removal based on per oyster N content suggests much lower removal rates than model results, but model harvest estimates are similar to reported harvest. Though results are specific to GBP, the approach is transferable to estuaries that support bivalve aquaculture but do not have complex system-scale hydrodynamic or ecological models.

Sustainable Oyster Aquaculture, Water Quality Improvement, and Ecosystem Service Value Potential in Maryland Chesapeake Bay

“…The multiple simulations with differing mortalities at Site 1 also afforded us an opportunity to evaluate the accuracy of the FARM model at predicting harvest. Although previous studies have shown that the FARM model estimates harvest of cultivated oyster and other bivalves reasonably well (Ferreira et al 2009, Bricker et al 2020, it would be useful to have reported harvest at all Maryland farm study sites for confirmation of that for the Chesapeake Bay calibrated FARM model. The Maryland industry is young and growing, and there was only one site for which harvest numbers were made available for comparison with model results.…”

“…Maryland Chesapeake Bay (this study) 1.78-25 28-457 Great Bay Piscataqua River Estuary (Bricker et al 2020) 0.57-5.27 37-101 Long Island Sound (Bricker et al 2018) 5.96 125 Multinational study* (Rose et al 2015) 1.18-8.70 51-345…”

“…The grower reviewed records of seed and harvest to confirm that the actual mortality was 70%. Model simulations using eight mortalities representing the range observed by all growers (20%-90%) were performed to estimate the potential range of harvest and N removal at this site, as an example of the range that Comparative FARM model estimates of oyster harvest and oyster-related N removal via sequestration into tissue and shell for Chesapeake Bay (this study), Great Bay Piscataqua River Estuary (Bricker et al 2020), and Long Island Sound (Bricker et al 2018).…”

“…An avoided or replacement cost economic analysis was performed to assign an economic value to the estimated N removal. A similar approach was used previously in Potomac River (Bricker et al 2014), in Long Island Sound (Bricker et al 2018), and in Great Bay Piscataqua River Estuary (Bricker et al 2020).…”

“…In addition to provision of seafood, oysters are well known for their ability to effectively remove nutrients from the water column through filtration and assimilation of phytoplankton and detritus into tissue and shell (Bricker et al 2014(Bricker et al , 2018(Bricker et al , 2020. Denitrification from sediments associated with cultivation is an additional oyster-related nitrogen (N) removal method (Kellogg et al 2013), but was not considered in this study.…”