No abstract

1. Today, aquatic biodiversity suffers from many pressures linked to human activities, including climate change, which particularly affects alpine areas. Many alpine freshwater species have shifted their geographical distribution to colder areas, but a reduced availability of suitable habitats is also forecasted. New artificial water bodies could provide habitat enhancement opportunities, including small mountain reservoirs built to overcome a lack of snow during winter.2. To investigate the role of reservoirs as a habitat for freshwater invertebrates, a case study was conducted on eight reservoirs in the Swiss Alps. The study aimed to compare the water quality and freshwater biodiversity of the reservoirs with those of 39 natural and newly excavated ponds. Data were collected on physicochemistry, freshwater habitat structure, and aquatic insects (dragonflies and aquatic beetles).3. The study showed that the mountain reservoirs investigated did not differ from natural ponds in terms of surface area, conductivity, and trophic level. Similarly to natural ponds, reservoirs showed signs of impairment owing to surface run-off carrying pollutants linked to ski tourism. They presented a low diversity of mesohabitats, and in particular lacked vegetation. Compared with natural ponds, the species richness in reservoirs was lower for dragonflies but not for beetles. At the regional scale, the community from the reservoirs was a subset of the natural ponds community, supporting 38% of the regional species richness for these two insect groups. 4. The results suggest that mountain reservoirs are likely to be important for biodiversity in alpine areas, both as habitats and as stepping stones for species shifting their geographical range. These water bodies can be enhanced further by some nature-friendly measures to maximize benefits for biodiversity, including margin revegetation or the creation of adjacent ponds. Ecological engineering needs to be innovative and promote freshwater biodiversity in artificial reservoirs. K E Y W O R D S benthic macroinvertebrates, climate change, freshwater biodiversity, mountain reservoirs, Swiss Alps water bodies, water quality

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Freshwater biodiversity has shown to be highly vulnerable to climate warming. Boreo-alpine species are especially at risk in the Alps because they have to migrate to higher elevations to avoid local extinction. Effects of climate warming could be partly counteracted by creating new freshwater habitats: this would boost the population sizes of the endangered species and would increase the connectivity between Alpine waterbodies to facilitate the species' upward dispersal and colonization of new habitats. Nevertheless, the localization of new habitats has to be carefully chosen, as successful restoration (or habitat creation) depends on many abiotic and ecological variables (e. g. habitats density and quality, connection between bodies of water, presence of targeted species, resistance of landscape to species movements). Furthermore, various socioeconomic drivers and actors determine the land and water uses in the Alps. Therefore we developed an innovative method for prioritization of areas for creation (or restoration) of small bodies of water, taking into account both ecological parameters (from species to landscape) and social ones. The method was developed in a test area (130 km 2 , in Canton Valais, Switzerland) representative of the Swiss Alpine landscapes and their associated socioeconomic activities. The proposed methodological framework consists of four steps which allow refining the geographical area to propose two or three small areas (some hectares) suitable for the creation of small water bodies. The first step investigates the regional scale, often several thousand km 2 , with a focus on environmental considerations: presence of historical or contemporary wetlands and waterbodies, presence of cold stenotherm species, and favourable landscape (in terms of land use) and socioeconomic context. The second step identifies areas of biological connectivity between source ponds and future host ponds for cold stenotherm species, taking into account the distance between source and host ponds and landscape resistance to the movements of pro pagules, finally highlighting the migration corridors. The third step checks the preselected areas with the aim of discarding catchments impaired by selective or diffuse pollutions. The fourth and final step is intended to enhance the probability of the project's social acceptance: qualitative interviews and field observations are conducted on a local scale (often one km 2) and options are evaluated with local stakeholders. Conducting the four successive and complementary steps ensures that the selected areas have a high potential for hosting the alpine biodiversity, and furthermore provide a favourable social framework for success in the short as well as the long term. Such a tool should promote and facilitate actions for conserving freshwater biodiversity in the Alps.