Rivers run through it – exploring drivers of aquatic macrozoobenthic diversity in an inner alpine dry valley

Abstract Climate change can alter hydrological regimes and intensify drought severity, with consequences for freshwater biodiversity. Mountain regions with naturally low precipitation and strong dependence on meltwater are particularly vulnerable, as shifts in water availability can have cascading effects on these environments. The Vinschgau Valley in the eastern Italian Alps is one of the driest Alpine basins and key headwater area for the Etsch river, which sustains agriculture and biodiversity far beyond the valley. Despite low average annual precipitation, water quantity and availability vary along the pronounced elevational gradient, resulting in heterogeneous hydrological conditions within a climate-sensitive inner-alpine system. Here we investigated how land-use, water balance and environmental factors shape macroinvertebrate diversity across 24 stream sites sampled between 2021 and 2023 along an altitudinal gradient from 800 to 2600 m. We assessed community composition and diversity patterns at local scale, considering water chemistry, nutrient concentrations, streambed stability and substrate composition. On large scale, we considered elevational gradient, land-use cover, and drought indicators derived from high-resolution evapotranspiration and precipitation data. Community clustering revealed that similar assemblages were not geographically proximate, indicating strong environmental filtering. Differences among clusters were associated with water chemistry, substrate composition (with the highest diversity supported by mobile mineral substrates greater than 250 mm), permanent snow cover percentage in the catchment, and prolonged annual precipitation deficits, highlighting the role of hydrological stress in shaping biodiversity. These findings emphasise the vulnerability of Alpine streams to ongoing glacier retreat and drought, with implications for downstream ecosystems, and conservation planning under convergent climate pressures.