Abstract
Impacts of aquaculture on the local current field and the erosion of the bottom sedi- ment in the Bay of Fundy, Canada, have been investigated with a 3-dimensional hydrodynamic model. The model is evaluated against independent observations of the current. Model results show that the presence of fish cages restricts water flow and reduces the velocity in the surface layer occupied by the cages, but enhances the water velocity in the bottom layer beneath the cages. Sensitivity studies show that the change in the flow velocity beneath the cages is sensitive to variations in the drag coefficient and the height of the fish cages. As the drag coefficient increases, the bottom velocity also increases until a steady state value is reached. For the cage height, however, the tidal speed beneath the cages first increases with cage height and then sig- nificantly decreases with further increasing height. The maximum increase in velocity occurs when the cage height is about half the local water depth (H/H0 = 0.5, where H is the cage height and H0 is the water depth). The increase in bottom velocity significantly speeds up the erosion of the bottom sediment. The model results also indicate that there is an optimal drag coefficient and an optimal cage height for a specific farm site. By utilizing the optimal drag coefficient and height, it is possible to speed up sediment erosion beneath the cages and, thus, decrease the environ - mental problems caused by accumulated fish farm waste.
Highlights
Aquaculture in marine coastal waters is a rapidly growing area of sea food production in Canada (Environment Canada 2009)
In southwest New Brunswick (SWNB), for example, the number of salmon aquaculture sites increased from a single site in 1978 to 92 sites in 2011 (New Brunswick Department of Agriculture, aquaculture sector in review 2011)
The model used in this study is the Finite-Volume Coastal Ocean Model (FVCOM), which is a 3-D, finite-volume, unstructured grid ocean model developed at the University of Massachusetts-Dartmouth (Chen et al 2003, 2007, Cowles et al 2008)
Summary
Aquaculture in marine coastal waters is a rapidly growing area of sea food production in Canada (Environment Canada 2009). The bottom sediment can be eroded and transported due to currents and waves, and the aquaculture site can thereby affect the water quality in the far-field (Gyllenhammar & Hakanson 2005). The transport of sediment from the local area of fish farms to far-field areas can be quantitatively described by hydrodynamic models coupled to sediment models. Several research groups have demonstrated that these models can be successfully applied to predict the footprints of the waste from fish farms in the near- or far-field waters (Panchang et al 1997, Dudley et al 2000, Grant & Bacher 2001, Henderson et al 2001, Cromey et al 2002b, Doglioli et al 2004, Ali et al 2011, Moreno Navas et al 2011). Detailed reviews of the implementations and applications of such models can be found in Cromey et al (2002a) and Andréfouët et al (2006)
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