The CIEPT: A macroinvertebrate-based multimetric index for assessing the ecological quality of Swiss lowland ponds

Since ponds are limnologically different from rivers and lakes, and as there is a lack of specific methods to assess their ecological quality, we developed a method to assist managers in routine biomonitoring of ponds. For this work, a total of 36 lowland permanent ponds were selected from an existing dataset of 134 Swiss ponds that were classified along a gradient from reference to degraded sites. Site degradation was characterised by seven variables indicative of pond ecological condition: (i) one descriptor of plant communities (macrophyte species richness); (ii) one descriptor of trophic state (total phosphorus and total nitrogen (PN)), and (iii) five anthropogenic stressors linked to land use (percentage of semi-natural areas within a 50-m radius of the site, connectivity with other wetlands within 1km, percentage of agricultural activities and pastures in the pond catchment, and dominant land use in terms of surface area). A total of 55 potential macroinvertebrate and amphibian metrics were tested to assess their relationship to site degradation. The metrics were based on taxonomic richness (total and selected macroinvertebrate groups), intolerance of degradation, conservation values, and biological/ecological traits. The selection of the metrics to be integrated into the index followed a stepwise procedure. To be selected, a metric had to fulfil four criteria. It must have: (1) a significant relationship with at least one of the seven indicators of pond ecological condition; (2) the ability to discriminate between reference and degraded sites; (3) a relative scope of impairment inferior to 1 (low inherent variability of a metric); (4) no redundancy with other metrics used in the index. To produce the index, 18 combinations of selected metrics were tested. The final index (CIEPT) was built using three metrics: genera richness of Coleoptera (C), macroinvertebrate family richness (I), and Ephemeroptera, Plecoptera and Trichoptera (EPT) family richness. The CIEPT responded significantly to pond ecological condition and was tested successfully with an external dataset to confirm suitability. The CIEPT index could be a useful and relatively low cost tool to assist site managers in assessing the ecological quality of ponds.