Aquatic macroinvertebrates as indicators for hydropeaking : development and validation of specific multimetric indices

Hydropeaking imposes sub‑daily discharge fluctuations that, among others, alter hydraulics, wetted area, and benthic communities. Benthic habitat sampling and analyses are well suited to detect long-term changes in faunal composition resulting from cumulative hydropeaking effects. In this study, we developed and validated a hydropeaking‑sensitive multimetric index (MMI) using macroinvertebrate assemblages at 54 sites on 11 Swiss rivers spanning hydropeaked, residual‑flow, and (near‑)natural reaches. Standardized field‑screening (12 kick samples per site; 500 µm) was conducted in March–April 2022–2023; a subset of 31 sites (370 samples out of the total 648 samples) underwent laboratory identification for quality control. 42 environmental variables were compiled, and recent sub‑daily hydrology (15‑min, prior six months) was summarized, including eight hydropeaking-specific hydrological variables and a multimetric hydrological index. 25 suitable macroinvertebrate candidate community metrics were pre-selected and calculated for each study site located in reaches with a hydropeaking or a (near-) natural flow regime. These metrics were then evaluated based on their variability between laboratory and field-screening datasets, their indicative quality regarding hydropeaking sensitivity and natural variability, and how they were influenced by environmental variables such as morphological alterations and pollution. The MMI developed from the obtained results integrates individual metrics that best represent the established aquatic macroinvertebrate community, while specifically reflecting hydropeaking-related hydrological and hydraulic impacts and minimizing the influence of natural variability and other environmental factors. This MMI allows for the comparison of different river reaches regardless of river type and can therefore be applied not only to assess hydropeaking impacts, but also to evaluate the effectiveness of hydrological and/or morphological mitigation or restoration measures through a pre- and post-implementation comparison of the benthic macroinvertebrate community – serving, in this sense, as an efficient monitoring tool.