Biomonitoring of intermittent rivers and ephemeral streams in Europe: Current practice and priorities to enhance ecological status assessments

Abstract

Intermittent rivers and ephemeral streams (IRES) are common across Europe and dominate some Mediterranean river networks, supporting high biodiversity and providing ecosystem services in all climate zones. 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 document national IRES biomonitoring activity. 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 the reconceptualization of the reference condition approach to accommodate spatiotemporal fluctuations in community composition, and modification of indices of ecosystem health to recognize taxon-specific sensitivity to intermittence and dispersal abilities, within a landscape context.