Fine sediment in streams and rivers is one of the most globally widespread of all freshwater pollutants. However, the ecological implications are still poorly quantified, and field experiments to assess likely functional and structural effects are scarce.We assessed the response of stream invertebrates to fine sediment (i.e. inert sand) added to trays (n ¼ 65) containing otherwise natural substrata over a three-week period in three replicate streams in the Usk catchment, Wales.Sediment addition to 0.6-18 kg m À2 affected both the structure and functional composition of invertebrate assemblages while also reducing overall abundance and in some common species (Baetis rhodani, Ecdyonurus sp. and Leuctra geniculata).Sediment also reduced richness and overall trait diversity (TD), while different life-history traits were either favoured (polivoltinism, tegumental respiration and burrowing behaviour) or disfavoured (swimmers, attached taxa, gill respiration). Moreover, sediments appeared to promote a nested subset pattern in species composition, with generalists favoured at the expense of specialists either through exclusion or impaired colonization. Effects were due largely to the loss of five taxa that contributed to the significant nestedness across the sand gradient: B. rhodani, Ecdyonurus sp., Leuctra geniculata, Simuliidae and Ephemerella ignita.This short-term experiment supports recent surveys in indicating how sedimentation can change the structural and functional composition of stream invertebrate assemblages even at low to moderate rates of deposition. In revealing direct effects on trait adversity, trait representation and nestedness, the data are also consistent with survey data in indicating that sediments have potentially important ramifications for conservation by removing organisms systematically according to life-history features.

Although anthropogenic degradation of riverine systems stimulated a multi-taxon bioassessment of their ecological integrity in EU countries, specific responses of different taxonomic groups to human pressure are poorly investigated in Mediterranean rivers. Here, we assess if richness and composition of macroinvertebrate and fish assemblages show concordant variation along a gradient of anthropogenic pressure in 31 reaches across 13 wadeable streams in central Italy. Fish and invertebrate taxonomic richness was not correlated across sites. However, Mantel test showed that the two groups were significantly, albeit weakly, correlated even after statistically controlling for the effect of environmental variables and site proximity. Variance partitioning with partial Canonical Correspondence Analysis showed that the assemblages of the two groups were influenced by different set of environmental drivers: invertebrates were influenced by water organic content, channel and substratum features, while fish were related to stream temperature (mirroring elevation) and local land-use. Variance partitioning revealed the importance of biotic interactions between the two groups as a possible mechanisms determining concordance. Although significant, the congruence between the groups was weak, indicating that they should not be used as surrogate of each other for environmental assessments in these Mediterranean catchments. Indeed, both richness and patterns in nestedness (i.e. where depauperate locations host only a subset of taxa found in richer locations) appeared influenced by different environmental drivers suggesting that the observed concordance did not result from a co-loss of taxa along similar environmental gradients. As fish and macroinvertebrates appeared sensitive to different environmental factors, we argue that monitoring programmes should consider a multi-assemblage assessment, as also required by the Water Framework Directive.

Summary The unique information provided by multiyear data sets can aid in detecting major long‐term trends and making predictions with respect to environmental and biological variables. These trends are expected to differ among climatic regions but little information exists concerning long‐term variability within a particular climate region. We analysed the long‐term (14‐year time span) patterns in species richness and composition of aquatic insects (EPT: Ephemeroptera, Plecoptera and Trichoptera) in relation to changes in temperature, precipitation and discharge in two reference streams in Catalonia (north‐east Spain). Our study sites were located in the Mediterranean macroclimate region but in different mesoclimatic areas, one in the Wet Mediterranean climate area and the other in the Dry Mediterranean climate area (WM and DM, respectively). At the macroclimate scale, precipitation decreased and the frequency of drought events increased during the 14‐year period. Although the mean number of taxa in each of the two sites remained similar, there was a replacement of species characteristic of riffle‐like conditions by species characteristic of pool‐like conditions over time in both sites. EPT composition differed between sites at the mesoclimate scale, demonstrating the importance of regional factors. In particular, changes in EPT composition were less variable in WM than in DM both in the short term and in the long term, indicating that the WM site was less constrained by climate than the DM site. Such differences between mesoclimates are related to differences in flood magnitude (higher in WM) and drought frequency (more frequent in DM) as well as local hydromorphological differences. Our findings indicate that the streams responded similarly to long‐term patterns in large‐scale variables (i.e. those affecting the overall macroclimatic region), but differed with respect to the effect of local‐scale variables (i.e. those differentially affecting each mesoclimatic area). Predictive bio‐assessment models that use reference conditions must incorporate long‐term variability to accurately assess the ecological status of Mediterranean climate streams.

River impoundments and waste water discharge are a serious threat to the integrity and biodiversity of river ecosystems, especially in central Italy. Benthic macroinvertebrates were sampled in autumn and summer along the Aniene River to assess the cumulative biological effect of the numerous dams and sewage treatment plants that affect its middle and lower course. We hypothesized that (i) increasing habitat impairment would promote the formation of nestedness in species assemblage, where species poor locations support only a sub‐set of organisms from richer sites; (ii) specific life‐history traits would confer sensitivity to habitat degradation. Patterns of macroinvertebrate richness and diversity along the river tracked the distribution of dams and sewage treatment plants. Partial Mantel test showed that dissimilarity in assemblages increased with the number of dams and treatment plants between reaches after controlling for longitudinal distance. Assemblages were significantly nested, and nestedness appeared related to both water quality gradients (phosphorous, turbidity) that reflected anthropogenic inputs, and to natural gradient in altitude. Reaches with nested assemblages (supporting a sub‐set of the species pool) were characterized by greater representations of taxa with shorter life cycles, while, in contrast, species rich sites supported taxa with longer life cycles and lower dispersal ability. These results suggest that the cumulative effect of dams and sewage treatment plants promoted the formation of nested subsets in species distribution. Moreover, it appeared that certain functional traits that conferred sensitivity also dictated the progressive non‐random loss of taxa in face of multiple anthropogenic stressors. These findings have conservation implications in the regions, but need to be considered preliminary since anthropogenic and natural factors co‐varied systematically along the study river precluding the identification of single factor effects.

High quality water is vital for human life, and ensuring its availability is a basic requirement and a major societal aim. The Water Framework Directive (WFD; 2000/60/EC) is a key piece of legislation for the protection and sustainable use of water in the European Union. In this work we briefly review the WFD directive and the current status of European inland surface waters. Additionally, we summarize major challenges and threats for the biological assessment of inland surface waters under climate change effects and invasion by alien species, and highlight the emerging tools and approaches that might help improve biological assessments, including molecular indices based on environmental DNA (eDNA), to new data from the Earth Observation programmes, and data-sharing platforms. Finally, we present recommendations to improve monitoring systems and assessments in the context of the WFD. Developments in this field may increase the likelihood of assuring high quality water for society.