Quantifying Transport of Aquaculture Particulate Wastes

Abstract

Scientific understanding of aquaculture interactions with the environment is limited, especially with regard to the far-field transport and possible impacts of particulate wastes. Both modelling and field studies have focused on near-field effects from organic enrichment, while the far field has received far less attention. In chapter 2, a pilot study was carried out to determine the size, settling velocity, and density of suspended particles at an active salmon aquaculture cage site. Flocs had a larger fractal dimension and smaller component-particle density than in other studies, suggesting that particles from the aquaculture operation may be incorporated into suspended flocs with average settling velocities of 1 mm s-1. In chapter 3, a laboratory study was carried out to examine the effect of bed sediment texture on the erodibility of salmon aquaculture waste fecal material and salmon feed pellets. Results show that cumulative mass eroded (CME) can vary by up to an order of magnitude depending on substrate composition, with a mud substrate having higher values than that of substrates composed of sand, gravel and cobble. In chapter 4, cores collected with an intact sediment-water interface were coupled to a Gust erosion chamber to examine the effect of increasing shear stress on bottom sediments in areas of salmon aquaculture. Cores were collected along transects of stations at a cohesive and a non-cohesive seabed site. Results show that as the amount of organics in bottom sediments increased the erodibility of the bed sediments decreased. In chapter 5, dispersal from a fin-fish aquaculture facility was simulated using the Benthic Boundary Layer Transport model (BBLT). Four waste classes were considered: fines, flocs, fecal waste and feed pellets, each with distinct settling velocities and critical erosion shear stresses. The resulting concentration of each class within the cage site varied by approximately 5 orders of magnitude with higher concentrations of fines and flocs in the far field as compared to fecal material and pellets.