Simulating the effects of parameter uncertainty on waste model predictions of marine finfish aquaculture

Models that simulate the input and fate of waste material from marine cage finfish farms are considered valuable tools within management strategies for predicting environmental impacts. However, the overall utility of these models may be limited because of uncertainty regarding values used to parameterize and configure simulations, and variability in coupling predicted flux and benthic impacts. This study applies the aquaculture waste model DEPOMOD (Cromey, C.J., Nickell, T.D., Black, K.D. 2002a. DEPOMOD-modelling the deposition and biological effects of waste solids from marine cage farms. Aquaculture 214, 211-239.) at a marine finfish farm in British Columbia and examines i) the effect of uncertainty in three model parameters (percent waste feed, carbon concentration of feed and fecal material) and one process (resuspension) on model outputs; ii) the relative contribution of waste feed and fecal material to the predicted carbon flux distribution; and iii) the relationships between model outputs and high resolution field survey data collected at the site. Simulation of resuspension processes resulted in predictions that were considered unrealistic as 98% of the applied material was transported outwith the model domain. When resuspension processes were not simulated, the applied waste feed value was the most significant contributing factor to the predicted range in model outputs up to ∼ 100 m from the farm site. The waste feed component accounted for between 50 and 75% of the overall carbon deposition, dependant upon the applied carbon concentration of the particles, and potentially in excess of 80% of the predicted carbon flux at the cage edge. The effect of uncertainty in the applied carbon concentrations of fecal material to the overall range in predicted flux was minimal. Coupling of model outputs with field measurements indicated that, within the predicted envelope of uncertainty, significant alterations to the benthic community structure (H`, ITI) and sediment geochemistry (S=) indicative of the transition between oxic and anoxic benthic zonation status occurred at predicted flux values of between ∼ 1 and 5 gC m− 2 d− 1.