15In this work, we studied Trichoptera assemblages in different rivers in NW Spain 16 affected by hydroelectric power stations, and assessed the influence of environmental 17 variables on the distribution of species. Twenty sites in four rivers were sampled during 18 eight sampling campaigns (2001)(2002). The fauna was collected with a quantitative 19 Surber sampler. In addition, several physical, chemical and habitat variables were 20 measured at each site. A distance-based redundancy analysis (dbRDA) was done to 21 investigate the relationship between the assemblages and the environmental variables. 22Assemblage composition was analyzed by non-metric Multi-Dimensional Scaling 23 (NMDS) and differences between groups were tested using the analysis of similarity 24 (ANOSIM) considering two grouping variables, the river basin and the position of the 25

This paper studies the effect of wastewater discharges on benthic macroinvertebrates in the Furnia River (Pontevedra, NW Spain). Semiquantitative surveys were carried out in spring 2008 and 2017 in three different locations, upstream and downstream of a sewage treatment plant built in 2013. Different indexes were calculated based on benthic macroinvertebrate assemblages: abundance, richness, Shannon-Wiener, EPT, IASPT, IBMWP and several physicochemical variables were measured concurrently. Although the indexes values decreased slightly along the water course, the results indicate an optimal water quality of the Furnia River, supporting a very diverse community of aquatic macroinvertebrates.

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We analysed the microhabitat preferences of caddisfly species in four rivers in north-western Spain. In each river, we sampled five sites with different types of substrate. These sites were characterised in situ according to the predominant material type (macrophytes, moss, pebbles and sand). A one-way ANOVA was used to test for significant differences in species abundance among substrates, and a nested ANOVA was used to test for significant differences in physical and chemical variables among rivers and sampling sites. A similarity percentage-species contribution analysis was performed to estimate the contribution of each species to the characterisation of each substrate. We observed significant differences in the abundance of seven species (Drusus bolivari, Glossosoma privatum, Larcasia partita, Micrasema longulum, M. servatum, M. gr. moestum and Sericostoma sp.) among substrates, confirming that these species have substrate preferences. According to similarity percentage-species contribution, the species that contributed most to differences were as follows: for sand, Sericostoma sp.; for macrophytes, Rhyacophila adjuncta, Hydropsyche ambigua, Sericostoma sp.; for moss, Micrasema gr. moestum, M. servatum, M. longulum, Hydropsyche tibialis and R. adjuncta; and for pebbles, Sericostoma sp., Larcasia partita and H. tibialis. These preferences can be explained by the fact that different species use different materials from the substrate to build their cases and also as a source of stability, protection and food.

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