ABSTRACT1. The aim of this study was to identify the environmental variables correlated with biodiversity in alpine ponds.2. Twenty alpine ponds in Switzerland were chosen to examine the relationship between the species (or family) richness of five biological groups and a selection of eight environmental variables.3. Altitude, pH, conductivity, macrophyte presence, fish presence and trophic state, showed significant relationships with the diversity of at least one biological group. On the other hand, pond area and depth demonstrated no significant correlations with biodiversity.4. Most highlighted relationships between biodiversity and environmental variables were different from those seen in lowland ponds, reflecting the distinctive nature of alpine water bodies. The results of the study suggest that there is a need to establish specific biodiversity evaluation tools for alpine ponds, which differ from those already used for lowland ponds.

ABSTRACT1. Ponds are particularly rich habitats and play an essential role in the conservation of aquatic biodiversity. Therefore it is necessary to develop a specific method for evaluating their biological integrity, and particularly their water quality. Metrics have proved to be efficient for studies on running waters. Such an approach would be particularly useful for ponds and therefore needs to be tested.2. Eight metrics based on the richness of invertebrates and amphibians and 73 others derived from the biological/ecological trait categories linked to Coleoptera, Odonata and Gastropoda were tested for their potential as indicators of the trophic state of 94 ponds in Switzerland. The relationships between these metrics and the state of water eutrophication were explored.3. Four metrics based on richness responded to excessive nutrient levels in the colline vegetation belt. These were: aquatic Coleoptera species richness; the pooled species richness of aquatic Coleoptera, aquatic Gastropoda, adult Odonata and Amphibia (COGA); the family-level richness of macroinvertebrates and the family-level richness of the combined Megaloptera and Odonata groups (MO). At altitudes above 800 m (i.e. montane-subalpine and alpine vegetation belts), two to four other metrics were identified as pond water-quality indicators.4. Furthermore, many trait categories were sensitive to excessive nutrient levels. In the colline belt, 13 out of the 33 metrics derived from the biological/ecological traits responded to an increase in the trophic state (i.e. at least one metric for each of the three invertebrate groups tested). However, the patterns of the relationships are unclear and further investigations are required to identify and select the relevant metrics for an assessment of water quality.5. In conclusion, for the future assessment of pond quality, four metrics derived from richness could be taken into consideration. Nevertheless, further investigations are required to identify the biological/ecological traits that could be combined with these richness metrics.

Despite increasing awareness of global biodiversity loss, we lack quantitative data on local extinctions for many species. This is especially true for rare species, which are typically assessed on the basis of expert judgment rather than data. Revisiting previously assessed populations enables estimation of local extinction rates and the identification of species characteristics and habitats with high local extinction risk. Between 2010 and 2016, in a nationwide revisitation study, 420 volunteer botanists revisited 8,024 populations of the 713 rarest and most threatened plant species in Switzerland recorded between 1960 and 2001. Of the revisited 8,024 populations, 27% had gone locally extinct. Among critically endangered species, the local extinctions increased to 40%. Species from ruderal and freshwater habitat types showed the highest proportion of local extinctions. Our results provide compelling evidence for rapid and widespread local extinctions and suggest that current conservation measures are insufficient. Local extinctions precede and provide early warnings for global extinctions. The ongoing loss of populations suggests that we will lose species diversity unless we scale up species-targeted conservation and restoration measures, especially in anthropogenic landscapes.

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In Swiss ponds, eutrophication represents one of the major threats to biodiversity. A biological method to assess the trophic state would, therefore, be particularly useful for monitoring purposes. Macrophytes have already been successfully used to evaluate the trophic state of rivers and lakes. Considering their colonizing abilities and their roles in pond ecosystem structure and function, macrophytes should be included in any assessment methods as required by the European Water Framework Directive. Vegetation survey and water quality data for 114 permanent ponds throughout Switzerland were analysed to define indicator values for 113 species including 47 with well-defined ecological response to total water phosphorus (TP). Using indicator values and species cover, a Macrophyte Nutrient Index for Ponds (M-NIP) was calculated for each site and assessed with both the original pond data set and a limited validation data set. The resulting index performed better when considering only species with narrow responses to TP gradient and was more applicable, but less accurate when including all species. Despite these limitations, the M-NIP is a valuable and easy tool to assess and monitor the nutrient status of Swiss ponds and was shown to be robust and relatively sensitive to slight changes in phosphorus loading with a validation subset.