Effect of substrate type and pellet age on the resuspension of Atlantic salmon faecal material

Abstract

The influence of substrate type and particle age on the remobilization of settled Atlantic salmon Salmo salar faecal material was studied through a set of controlled experiments in horizontal flow flumes, simulating different bottom conditions present in fish-farming locations along the coast of Norway. There was no significant effect of pellet age on remobilization for up to 1 week old faecal material, but critical shear stresses (τc) and velocities required for resuspending faecal pellets were strongly dependent on substrate type. Smooth substrates such as mud and rock slate required lower stresses for the onset of faeces resuspension (τc %%CONV_ERR%% 0.06 Pa) than rougher surfaces such as sand (τc %%CONV_ERR%% 0.12 Pa) or fragmented rock (τc %%CONV_ERR%% 0.32 Pa), where bedforms and large fractures shield the particles from the direct influence of the drag forces. These newly determined substrate-dependent τc resuspension thresholds will contribute to the construction of more accurate numerical models that include bottom type as a parameter regulating the extent of particle spreading, in contrast to the constant-value approach that has been used to date.

Scenarios of fish waste deposition at the sub-lagoon scale: a modelling approach for aquaculture zoning and site selection

“…Resuspension can pick up previously settled particles and redistribute them over larger areas, thus decreasing organic-matter accumulation and its ecological effects near cages (Keeley et al, 2013;Broch et al, 2017). A seabed's sensitivity to resuspension depends greatly on substrate type and texture (Law et al, 2016;Carvajalino-Ferna ´ndez et al, 2020a), as well as vertical structure, disturbance history and, for sediment substrates, resident biota (Sanford, 2008). Dispersion models with spatially explicit sediment resuspension parameters have been found to be more accurate than those with constant default resuspension parameters or those that ignore resuspension (Carvajalino-Ferna ´ndez et al, 2020b).…”

A Review on Mariculture Effluent: Characterization and Management Tools

“…The critical bed shear stress is one of the main thresholds for resuspension, which depends strongly on substrate roughness and material type. Specifically, smooth substrates typically require lower critical stresses for material resuspension than rough surfaces [75], while the critical shear stress also varies greatly among different particulate materials with varying size and cohesiveness. For instance, smaller-sized particulates tend to have lower resuspension thresholds, and resistance to resuspension increases with increasing cohesiveness, consolidation and biostabilization of the benthic sediment layer [63,76].…”