Terms of Reference

Sulphide Concentrations Around Select Aquaculture Sites in Southwest New Brunswick: Review of DEPOMOD Predictions Versus Observations

Maritimes Region Peer Review Process

Dartmouth, Nova Scotia
February 15-16, 2012

Chairperson: Peter Cranford

Context

The risk of organic enrichment impacts to the seafloor associated with marine finfish aquaculture production have been studied extensively, and the relationship between carbon enrichment, sulfide levels and the biodiversity of benthic infauna organisms is well known.  Measurements of surface sediment sulfide serve as an indicator of changes in benthic biodiversity.  Processes leading to sediment accumulations are highly site specific and are dependant on currents, topography, resuspension, redeposition, and flocculation processes that affect the residence time of material in the water column and on the sediment surface as well as individual farm operating practices (Milligan and Law 2005). 

The flux of organic material at lower levels can have both positive and negative impacts to the biodiversity of fish habitat, depending on the habitat type and the species affected.  However, at higher rates, it is generally accepted that the flux of organic material to the seafloor is likely to pose a risk to fish habitat.  Hargave et al. (2008) gives a basis for the classification of the oxic status of marine sediments providing a quantification of organic enrichment.  Increases in organic enrichment result in a decrease in the oxic status and changes to the macrobenthic infauna community structure.  Classification by oxic status can be used to describe the risk to the biodiversity of fish habitat.

Models that predict potential benthic impacts can be used by regulators during the assessment stage of an aquaculture development.  To be effective, the model must incorporate all the variables that can affect the degree of carbon loading, including particle size, current speed, feeding rate, biomass in the cages, depth of the cage and the bottom.  The most commonly used model of the processes leading to the deposition of particulate wastes from marine finfish aquaculture is the DEPOMOD model (Cromey et al. 2000; Chamberlain et al. 2005).  Using the sinking characteristics and quantity of wastes along with hydrographic and bathymetric conditions, the model predicts the spatial deposition of waste. 

This meeting will review the effectiveness of DEPOMOD in the Maritimes Region through the investigation of predictions versus monitoring results from select aquaculture sites in Southwest New Brunswick (SWNB). Alternative models will also be reviewed.

Objectives

The objectives of the meeting are:

• To determine effectiveness of DEPOMOD (i.e. how precise is the model when compared to post impact monitoring) in predicting:
  1. the intensity of organic enrichment from marine finfish aquaculture sites in the Maritimes Region,
  2. the geographic location of impact from marine finfish aquaculture sites in the Maritimes Region, and
  3. the magnitude of area (in m²) of impact from marine finfish aquaculture sites in the Maritimes Region
     
• To identify any alternate model(s) that would more accurately predict organic enrichment intensity, magnitude and area of impact from marine finfish aquaculture sites in the Maritimes Region.

Expected Publications

• CSAS Science Advisory Report
• CSAS Proceedings
• CSAS Research Document

Participation

• DFO Science
• DFO Habitat Management
• DFO Aquaculture Management Office
• NS and NB Provincial Government
• Industry

References

Chamberlain, J., D. Stucchi, L. Lu, and C. Levings. 2005. The suitability of DEPOMOD for use in the management of finfish aquaculture sites, with particular reference to Pacific Region. DFO. Can. Sci. Advis. Sec. Res. Doc. 2005/35.
http://www.dfo-mpo.gc.ca/csas-sccs/publications/resdocs-docrech/2005/2005_035-eng.htm

Cromey, C.J., T.D. Nickell, and K.D. Black. 2002. DEPOMOD – modelling the deposition and biological effects of waste solids from marine cage farms. Aquaculture 214: 211-239.

Hargrave, B.T., M. Holmer, and C.P. Newcombe. 2008. Towards a classification of organic enrichment in marine sediments based on biogeochemical indicators. Mar. Pollut. Bull. 56: 810–824.

Milligan T.G., and B.A. Law. 2005. The effect of marine aquaculture on fine sediment dynamics in coastal inlets, Chapter 12; In: B.T. Hargrave (Ed.), Environmental Effects of Marine Finfish Aquaculture, Handbook of Environmental Chemistry, Springer, Berlin Heidelberg New York (in press).