Spatial and temporal variation in cumulative mass eroded and organic matter percentage in surface sediments near areas of active salmon aquaculture

Abstract

Cores collected with an intact sediment-water interface were coupled to a Gust erosion chamber to measure cumulative mass eroded at increasing shear stress steps in areas of salmon aquaculture. Cores were collected along transects of stations at a cohesive and a non-cohesive seabed site. Organic matter percentage in bottom sediments near aquaculture sites (<200 m from operations) correlated with the cumulative mass eroded. As the percentage of organics increased, the mass eroded decreased over the sampling periods. Two-way ANOVA indicated that a significant increase (p < 0.05) in organic matter percentage in bottom sediments occurred at both sites over the times of the sampling, which were coincident with the periods from when the aquaculture sites were first stocked with salmon smolt until just before fish were removed for market. Along the sampled transect at the cohesive site, the percentage of organic matter in bottom sediment increased significantly out to 200 m from the site. At the non-cohesive site, organic matter percentage in the sediment only increased at locations that were immediately adjacent to the cage site. Organic matter flux in kg m-2 d-1 doubled over the time of the study at both sites and values suggest that material would have been available for resuspension and transport from both sites. The ability to parameterize the movement of this material in transport models will increase predictive capacity regarding dispersal of farm wastes, which may help to increase the environmental sustainability of salmon aquaculture in the marine environment.