Habitat‐Specific Response of Macroinvertebrate Drift to Flow Pulses: Implications for Hydropeaking Management

ABSTRACT Flow pulses play a vital role in maintaining the ecological functioning of natural river systems. However, anthropogenic flow regulation, particularly from hydropower operations, can introduce rapid and unnatural pulses that negatively impact aquatic biota. This study investigated the effects of hydropeaking‐induced rapid fluctuations on macroinvertebrate drift at the patch scale. Using a portable flume, we simulated rapid flow pulses on 45 patches characterised by either slow or fast current habitat conditions, within a prealpine river reach that supports an unimpacted macroinvertebrate community. This in situ experimental approach allowed us to bridge the gap between laboratory flumes and observational studies in regulated rivers. Current velocity (V40—mean current velocity at 40% of the water depth from the bottom) was the primary driver of increases in drift intensity when no distinction was made between habitat type. In patches with slow current (V40 < 0.5 m/s), drift intensity was primarily influenced by V40, whilst in patches with fast current (V40 > 0.5 m/s), the change in current velocity (V40% – percentage change in V40 between baseline and stress phases of experiment) was more influential. V40% significantly shaped drift composition in patches with slow current. Our findings show that flow pulses, such as those caused by hydropeaking, significantly affect macroinvertebrate drift, with responses varying at the patch scale according to habitat‐specific hydraulics and local benthic assemblages. This study advances river management by emphasising the importance of patch‐scale processes for effective hydropeaking mitigation. By highlighting habitat‐specific sensitivities, our findings support the development of more spatially targeted conservation strategies to enhance biodiversity and ecosystem resilience in flow‐altered river systems worldwide.