Analysis of aquatic insect data
Analysis
Data from the NAWA (National Surface Water Quality Monitoring) and BDM (Biodiversity Monitoring of Switzerland) monitoring programs were used for the analysis. Both programs examine around 600 watercourses in Switzerland at intervals of four and five years respectively. Both monitoring programmes record the biological status of watercourses using aquatic insects in accordance with the standardized IBCH method, whereby mayflies, stoneflies and caddisflies are determined at species level. In addition, the two indicators “external aspect” and “ecomorphology” are recorded, which describe the abiotic water quality and the quality of the water structure. While the external aspect indicator provides information on silt, turbidity and waste, for example, ecomorphology describes structural characteristics such as the degree of obstruction and the naturalness of the banks. A total of 578 sampling sites from the two monitoring programs from 2010 to 2022 were analysed in the study. The data was evaluated separately by monitoring program and altitudinal stage, with temporal trends for the IBCH index and the external aspect and ecomorphology indicators being examined. In addition, photo documentation was used to check whether revitalization measures had been carried out at sampling sites with altered ecomorphology.
Results and conclusion
The results show a slight increase in the IBCH index in both monitoring programs (see graph). The external aspect and ecomorphology indicators remained largely unchanged overall. In places where targeted restoration measures were implemented (approx. 3 % of the data), however, improvements in ecomorphology and the IBCH index were observed. Some of these positive individual cases are described in the publication of the study, such as the restoration of the Ruisseau de Boécourt in the canton of Jura, which is reflected positively both in the structural assessments and in the numbers of aquatic insect species.
The main conclusion of the study is that after almost 15 years, the first indications of the positive effects of the water protection measures can be seen in the national monitoring programmes. However, these improvements are selective and are overshadowed by the effects of climate change. One of the main reasons for this is that the proportion of watercourse sites with structural improvements is still relatively low. This is not surprising, as only 4% of the planned revitalisation projects have been implemented to date. In order to achieve a measurable effect throughout Switzerland, further major efforts are therefore required. The long-term goal is to revitalise 4,000 km of watercourses by 2090 - at present, only 160 km have been implemented. Interestingly, beavers could also contribute to the improvement of watercourses. In six places where the animals have newly settled, all indicators have improved.
