Taxonomic and functional responses of benthic and drifting macroinvertebrates to fine sediment deposition: evidence from an alpine flume-based experiment

Excessive fine sediment deposition is a global pervasive issue in rivers and, in particular, for benthic organisms including macroinvertebrates. However, the assessment of fine sediment effects on the taxonomic and functional diversity of macroinvertebrate communities is challenging because of context-dependent confounding factors, such as river-flow conditions, land-use change, and anthropogenic pressures. By using a set of outdoor artificial flumes, this study examined the immediate (24–48 h) and two weeks post-addition response of Alpine stream macroinvertebrates to experimental deposition of fine sediment (7.5 kg m²). The taxonomic composition of benthic macroinvertebrate communities demonstrated significant differences between control and sediment-affected flumes; while taxonomic composition of drifting macroinvertebrates varied over time, with higher taxonomic heterogeneity for sedimented communities than control flumes. Nestedness was consistently the dominant component that contributed to beta-diversity patterns for both benthic and drifting invertebrates. No differences in taxonomic and functional community metrics were observed between control and sedimented communities, with the exception of a significant reduction in the total abundance of benthic macroinvertebrates in sedimented flumes. This study is one of the first flume-based experiments dealing with the response of Alpine stream macroinvertebrates to fine sediment deposition, and the findings highlight the context specific nature of fine sediment effects.