Role of flocculation in the spatial and temporal variation in organic matter flux at an active salmon aquaculture site in a deep fjord

Sediment traps with programmable bottles collected settling material in a deepwater fjord on the southwest coast of Newfoundland at active salmon aquaculture sites and at sites 1000 m away from operations. Both the total and organic fluxes were up to an order of magnitude larger at the 2 aquaculture sites compared to the 2 sites 1000 m away. Stable isotopes, organic matter %, % carbon, and grain size were used to characterize the transport of aquaculture-derived waste material away from active sites. Floc fraction, a process-based parameterization of the disaggregated inorganic grain size of collected sediment, was used to show that flocculation was the dominant process in controlling the deposition of suspended particulate matter. Up to 79% of the material deposited was flocculated. Stable isotope and organic carbon analysis of the deposited material indicated that aquaculture waste products could be elucidated 1000 m from operations, consistent with other studies. In this fjord setting, the simplistic model AutoDEPOMOD was unable to predict the amount of organic matter deposition that was observed in our sediment traps. Better model parameterization is required in order to confidently simulate and manage the effects of finfish aquaculture discharges.