Science Advisory Report  2012/042

Review of DEPOMOD Predictions Versus Observations of Sulfide Concentrations Around Five Salmon Aquaculture Sites in Southwest New Brunswick

Summary

• Science advice is presented on the effectiveness of a commercial model (DEPOMOD) for predicting the magnitude and area of seabed organic enrichment impacts from marine finfish aquaculture sites in the Maritimes Region. Model accuracy was assessed based on comparisons of predicted carbon deposition rates at five active marine finfish aquaculture sites in southwest New Brunswick with measurements of total ‘free’ sulfide concentrations collected at these sites. Sulfide levels are used as an indicator of seabed community impacts for aquaculture monitoring in the Maritimes Region.
• DEPOMOD predictions of the total area impacted by particulate waste deposition at the five sites in southwest New Brunswick did not show a strong relationship to the measured impact area.
• Comparisons of the maximum organic carbon deposition rate at each site predicted by DEPOMOD (resuspension turned off) did not show a strong relationship with the maximum measured sulfide concentrations.
• Comparisons of measured sulfide concentrations showed a positive correlation with DEPOMOD predicted carbon deposition rates (with resuspension off) at the same locations, but with much variation, and the variation in observed sulfide concentrations increased with the level of predicted carbon deposition.   
• For aquaculture sites where feeding had been relatively consistent over the previous few months, observed sulfide concentrations were in the same categories (<3,000 µM) at 85% of the sampling locations where DEPOMOD predicted a low degree of impact (<5 g C m^-1 d^-1; equivalent to Oxic A to Hypoxic A).
• At sampling locations where DEPOMOD predicted a high degree of impact (>5 g C m^-2 d^-1; equivalent to Hypoxic B to Anoxic), observed sulfide concentrations were in the same categories (>3,000 µM) at only 63% of the sampling locations. Model accuracy for predicting impact magnitude varied among the sites.
• A simple model for predicting waste deposition was tested at the five sites. This model required much less input data compared with DEPOMOD. The simple model did not provide an estimate of the intensity of impacts but focused on predicting the spatial extent of impacts, based on median current speeds and average water depths at sites. Comparisons among sites of the spatial extent of elevated seafloor impacts predicted by DEPOMOD and the simple model showed relatively good agreement.

This Science Advisory Report is from the 15-16 February 2012 review of Sulfide Concentrations Around Select Aquaculture Sites in Southwest New Brunswick: Review of DEPOMOD Predictions Versus Observations.  Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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