Modeling the impact of floating oyster (Crassostrea virginica) aquaculture on sediment-water nutrient and oxygen fluxes

Abstract

Bivalve aquaculture relies on naturally occurring phytoplankton, zooplankton, and detritus as food sources, thereby avoiding external nutrient inputs that are commonly associated with finfish aquaculture. High filtration rates and concentrated bivalve biomass within aquaculture operations, however, result in intense biodeposition of particulate organic matter (POM) on surrounding sediments, with potential adverse environmental impacts. Estimating the net depositional flux is difficult in shallow waters due to methodological constraints and dynamic processes such as resuspension and advection. In this study, we combined sediment trap deployments with simulations from a mechanistic sediment flux model to estimate seasonal POM deposition, resuspension, and processing within sediments in the vicinity of an eastern oyster Crassostrea virginica farm in the Choptank River, Maryland, USA. The model is the stand-alone version of a 2-layer sediment flux model currently implemented within larger models for understanding ecosystem responses to nutrient management. Modeled sediment−water fluxes were compared to observed denitrification rates and nitrite + nitrate (NO 2 − +NO 3 − ), phosphate (PO 4 3− ) and dissolved O 2 fluxes. Model-derived estimates of POM deposition, which represent POM incorporated and processed within the sediment, comprised a small fraction of the material collected in sediment traps. These results highlight the roles of biodeposit resuspension and transport in effectively removing oyster biodeposits away from this particular farm, resulting in a highly diminished local environmental impact. This study highlights the value of sediment models as a practical tool for computing integrated measures of nitrogen cycling as a function of seasonal dynamics in the vicinity of aquaculture operations.

The Benthic Exchange of O₂, N₂ and Dissolved Nutrients Using Small Core Incubations

“…Results from sediment flux measurements near an aquaculture facility on the Choptank River (Chesapeake Bay, MD) are shown in Figure 1 and the interpretation of these results in an ecosystem context are presented elsewhere 26 . The incubations were carried out over 7 hours, with dark incubations followed by illuminated incubations data.…”

Nutrient Extraction Through Bivalves

“…Cranford et al 2007;Guyondet et al 2015). By using a model where sediment trap deployments were combined with a sediment flux model in an area with oysters (Crassostrea virginica), Testa et al (2015) demonstrated that resuspension and transport effectively removed oyster biodeposits from the studied farms, resulting in limited local environmental impact as there was no long-term sediment accumulation near the oysters, creating hot spots for nutrient recycling. Guyondet et al (2015) applied a coupled hydrodynamic-biogeochemical model in an area with mussel aquaculture and found that mussel harvest extracts nitrogen resources equivalent to 42% of river inputs and 46.5% of phytoplankton primary production.…”

Farm-Scale Production Models

“…The release of nutrients from biodeposits on shellfish farms may balance consumption indirectly (Asmus and Asmus 1991;Testa et al 2015) by stimulating phytoplankton growth. In this case, the farms themselves may influence bay scale productivity.…”

“…Organism growth models can also predict individual rates of water filtration and particle consumption, oxygen consumption, ammonium excretion, and biodeposit production, Fig. 24.7 Erosional area from tides (light green) and waves (dark green) with the sedimentation rates indicated on an oyster farm, channel and control areas in Maryland, U.S.A. (Testa et al 2015) or be used in combination with hydrodynamics to predict deposition, resuspension and benthic impacts (Grant et al 2005).…”