Heterogeneity in water temperature due to hydropeaking in a mountain river and its implications for macroinvertebrates

This is the authors' abstract. We don't add key points for this paper.

This study examines the hydropeaking-related environmental variability in a regulated mountain river affected by a hydroelectric power (HEP), focusing on thermal and hydraulic conditions, sedimentary characteristics, and benthic organic matter (CPOM), as well as benthic invertebrate communities. The facility generates a hydropeaking flow regime, releasing water 5.5 km downstream from the dam, creating a thermal plume with three distinct zones. These zones exhibit temperature differences of up to 10 °C, alongside marked differences in flow hydraulics, sediment structure, and CPOM availability. In particular, hydraulic conditions vary between stable low-flow areas and more dynamic zones influenced by intermittent hydropeaking releases.Bed sediments vary in size, predominantly consisting of pebbles and cobbles (15–30 mm), with significant differences between zones. Additionally, the Froude number is higher upstream from the release point. Invertebrate communities also differ in density, diversity, and structure, with notable contrasts between the upstream zone and the area immediately downstream. In contrast, the zone opposite the release point, with intermediate temperatures, resembles the upstream zone more closely.Differences in invertebrate communities are associated with the amount of organic matter on the riverbed, as well as with the combined thermal and hydraulic variability across zones, influencing feeding groups and reproductive strategies. The study highlights how small-scale changes in interacting physical habitat conditions (temperature, flow hydraulics, and organic matter availability) can lead to significant variations in aquatic biota, demonstrating the complex interplay between physical and biological factors in hydropeaking-influenced rivers.