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Salinisation is a global threat to freshwater habitats and is predicted to worsen with climate change. Increases in salinity can result in substantial modification of freshwater biotic communities through both direct toxic effects and indirect effects such as altering prey resources, competitive interactions, predator abundances, and facilitating the spread of invasive species. Traditional techniques to determine salinity, such as point sampling chemical assessment, are typically periodic and may not reveal intermittent changes in salinity concentration. Halo-stratification and a lack of standardised depth to collect chemical data further complicates using these methods. More importantly, such methods do not show the ecological impacts of salinity increases in freshwater habitats. Complementing traditional techniques with biological assessments may resolve these issues. Pressure-specific biotic indices using aquatic macroinvertebrate community data have long been used to assess aspects of aquatic habitats, although relatively few have focussed on salinity. This paper presents the Salinity Association Group Index (SAGI), a novel aquatic macroinvertebrate index to assess salinity in freshwater habitats. SAGI is compatible with data derived from established survey techniques employed by regulatory bodies and for Water Framework Directive assessments, amongst others. The method integrates taxonomic resolution beyond the family level with taxon abundance weighting in a scoring matrix to increase the efficacy of the tool and make the best use of publicly available data. Application of SAGI in case studies demonstrates a positive, moderate to strong correlation with conductivity used as a measure of salinity. The range of correlations (R2 = 0.57–0.91) compares favourably with pressure-specific, macroinvertebrate-based monitoring tools used in Europe for WFD monitoring. Furthermore, SAGI is shown to be highly effective in comparison to alternative salinity-specific biotic indices.

Rivers are among the most threatened ecosystems worldwide and are experiencing rapid biodiversity loss. Flow alteration due to climate change, water abstraction and augmentation is a severe stressor on many aquatic communities. Macroinvertebrates are widely used for biomonitoring river ecosystems although current taxonomic approaches used to characterise ecological responses to flow have limitations in terms of generalisation across biogeographical regions. A new macroinvertebrate trait-based index, Flow-T, derived from ecological functional information (flow velocity preferences) currently available for almost 500 invertebrate taxa at the European scale is presented. The index was tested using data from rivers spanning different biogeographic and hydro-climatic regions from the UK, Cyprus and Italy. The performance of Flow-T at different spatial scales and its relationship with an established UK flow assessment tool, the Lotic-invertebrate Index for Flow Evaluation (LIFE), was assessed to determine the transferability of the approach internationally. Flow-T was strongly correlated with the LIFE index using both presence-absence and abundance weighted data from all study areas (r varying from 0.46 to 0.96). When applied at the river reach scale, Flow-T was effective in identifying communities associated with distinct mesohabitats characterised by their hydraulic characteristics (e.g., pools, riffles, glides). Flow-T can be derived using both presence/absence and abundance data and can be easily adapted to varying taxonomic resolutions. The trait-based approach facilitates research using the entire European invertebrate fauna and can potentially be applied in regions where information on taxa-specific flow velocity preferences is not currently available. The inter-regional and continental scale transferability of Flow-T may help water resource managers gauge the effects of changes in flow regime on instream communities at varying spatial scales.

Intermittent rivers and ephemeral streams (IRES) are common across Europe and dominate some Mediterranean river networks. In all climate zones, IRES support high biodiversity and provide ecosystem services. As dynamic ecosystems that transition between flowing, pool, and dry states, IRES are typically poorly represented in biomonitoring programmes implemented to characterize EU Water Framework Directive ecological status. We report the results of a survey completed by representatives from 20 European countries to identify current challenges to IRES status assessment, examples of best practice, and priorities for future research. We identify five major barriers to effective ecological status classification in IRES: 1. the exclusion of IRES from Water Framework Directive biomonitoring based on their small catchment size; 2. the lack of river typologies that distinguish between contrasting IRES; 3. difficulties in defining the 'reference conditions' that represent unimpacted dynamic ecosystems; 4. classification of IRES ecological status based on lotic communities sampled using methods developed for perennial rivers; and 5. a reliance on taxonomic characterization of local communities. Despite these challenges, we recognize examples of innovative practice that can inform modification of current biomonitoring activity to promote effective IRES status classification. Priorities for future research include reconceptualization of the reference condition approach to accommodate spatiotemporal fluctuations in community composition, and modification of indices of ecosystem health to recognize both taxon-specific sensitivities to intermittence and dispersal abilities, within a landscape context.