Citation:

Bricker, S., R. Grizzle, P. Trowbridge, J. Rose, J. Ferriera, K. Wellman, C. Zhu, E. Galimany, G. Wikfors, C. Saurel, R. Landeck Miller, J. Wands, R. Rheault, J. Steinberg, A. Jacob, E. Davenport, S. Ayvazian, M. Chintala, AND M. Tedesco. Bioextractive Removal of Nitrogen by Oysters in Great Bay Piscataqua River Estuary, New Hampshire, USA. Estuaries and Coasts. Estuarine Research Federation, Port Republic, MD, 43:23-38, (2020). https://doi.org/10.1007/s12237-019-00661-8

Impact/Purpose:

Nutrient load reductions have been mandated (e.g. US Clean Water Act, EU Water Framework Directive) around the world to alleviate eutrophication impacts to estuaries and coastal waters, including excessive algal blooms, hypoxic bottom waters, and loss of seagrasses. Management of excessive nitrogen has primarily targeted land-based sources of nutrients including maximizing efficiency of nutrient removal from wastewater treatment plants, reducing nutrient runoff from fertilizer application and roadways. In some U.S. locations these measures have been successful; however in other locations nutrient source reductions have not resulted in achievement of water quality goals. With increasing coastal populations other innovative solutions are being sought. Recently removal of nutrients directly from the water by cultivation of bivalve shellfish has shown promise as a complement to land-based measures. The focus of this study was the quantification and valuation of the ecosystem service of N removal provided by cultivated Eastern oyster (Crassostrea virginica) at present production and the potential increase in services in expanded production to maximum allowable cultivation areas in Great Bay-Piscataqua River Estuary, N.H.

Description:

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.

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