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.
Highlights
Fish and other marine organisms play an essential role in food security and nutrition in the context of climate change (FAO 2018)
Mean near-bed velocities required for faecal pellet saltation and resuspension were extracted from the analysis of synchronized videos and grouped by substrate type and particle age (Fig. 2)
Particle saltation (Fig. 2a) occurred at similar near- quired for resuspension among different substrate bed velocities for all substrates; smooth sur- types (p < 0.001), but not across particle age groups faces showed much less vari- (p = 0.432)
Summary
Fish and other marine organisms play an essential role in food security and nutrition in the context of climate change (FAO 2018). Ecosystems are directly affected by both particulate and suspended metabolism sub-products, such as faeces, pseudo-faeces and fish excretion, as well as excess feeding material not consumed by fish inside the cages (Silvert & Sowles 1996, Brooks & Mahnken 2003, Cubillo et al 2016). All these wastes contain substantial amounts of organic carbon and nutrients that enrich both the water column and the seabed, causing changes in the sediment’s biogeochemistry and Publisher: Inter-Research · www.int-res.com
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