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 ≈ 0.06 Pa) than rougher surfaces such as sand (τc ≈ 0.12 Pa) or fragmented rock (τc ≈ 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.

中文翻译：

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基质类型和颗粒年龄对大西洋鲑鱼粪便材料再悬浮的影响

通过在水平流水槽中进行的一组受控实验，模拟了挪威沿海养鱼地点的不同底部条件，研究了底物类型和颗粒年龄对沉积的大西洋鲑鱼鲑鱼粪便物质再动员的影响。颗粒年龄对长达 1 周大的粪便材料的再动员没有显着影响，但重新悬浮粪便颗粒所需的临界剪切应力 (τc) 和速度强烈依赖于底物类型。与沙子 (τc ≈ 0.12 Pa) 或碎石 (τc ≈ 0.32 Pa) 等较粗糙的表面相比，泥土和石板等光滑基质在开始粪便再悬浮时所需的应力 (τc ≈ 0.06 Pa) 较低，在这些表面上有床形和大裂缝保护粒子免受阻力的直接影响。