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Calculation of Oyster Benefits with a Bioenergetics Model of the Virginia Oyster - April Draft

Published on April 1, 2014

A bioenergetics model is formulated and validated for the Virginia oyster (Crassostrea virginica). The model considers two basic properties of a bivalve population: number of individuals and individual size. Individuals are represented as three energy stores: soft tissue, shell, and reproductive material. The bioenergetics model is coupled to an oyster benefits module. Calculated benefits include various aspects of carbon removal, nitrogen removal, phosphorus removal, solids removal, and shell production. Benefits are calculated for natural mortality and for fisheries harvest. The calculation of benefits is based on mass-balance principles and upon user-supplied values for parameters including resuspension, sediment diagenesis, and dentrification rate. The bioenergetics model is coupled with a representation of the physical environment based on the tidal prism approach and with eutrophication kinetics from the CE-QUAL-ICM model.

The bioenergetics model was demonstrated through application to the Great Wicomico River, Virginia, 2000 - 2009. The model provided excellent representation of individual oyster size, of population number, and of average individual age. An overarching conclusion from the application was that representation of the detailed data set collected in this system required corresponding detailed information on recruitment, mortality, and other factors. We concluded that 164 metric tons of carbon per annum was filtered from the water column by oysters and 15.2 tons was buried to deep inactive sediments. An additional 13 metric tons of carbon was buried in the form of shell. Oysters filtered 28 metric tons nitrogen per annum from the Great Wicomico water column. Most was recycled but, ultimately, 6.2 metric tons nitrogen per annum was removed through denitrification and burial of oyster deposits. This nitrogen rate compared favorably with the 18.6 metric tons per annum calculated watershed load of total Kjeldahl nitrogen.

The report concludes with recommended next steps. The two foremost recommendations are for additional validation through application to additional systems and for operation with the eutrophication kinetics activated.

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