Looking for metrics to assess the trophic state of ponds: macroinvertebrates and amphibians

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. 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. 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. 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. 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