Potential physical effects of suspended fine sediment on lotic macroinvertebrates

This study investigates the potential for physical damage caused by suspended fine sediment on gills of three macroinvertebrate species, Hydropsyche siltalai, Ephemera danica and Ecdyonurus venosus. Macroinvertebrate cadavers were exposed to three suspended sediment concentrations (control 3.5, low 83.7 and high 404.0 mg l(-1)) at two velocities (low 0.19 m s(-1) and high 0.37 m s(-1)), for 6 h in a recirculating flume. Tracheal gill surfaces were subsequently examined for evidence of physical damage using scanning electron microscopy (SEM) images. Physical damage predominantly consisted of fine sediment coverage of gill surfaces, appearing as a deposited layer of sediment obscuring and potentially clogging the gill. For E. venosus, suspended sediment concentration influenced gill cover, but velocity had no significant effect. Coverage of H. siltalai gill surfaces increased significantly between low and high sediment concentrations but only at the higher flow velocity. Gill coverage of E. danica did not differ across any sediment concentration. The results were consistent with reported species sensitivities to fine sediment, despite the use of cadavers. However, we found limited evidence of physical abrasion as a direct physical effect of fine sediment under the experimental conditions used.