Abstract
Alpine riverine ecosystems are highly sensitive to climate change and anthropogenic pressures, yet they provide critical ecosystem services, including downstream water resources. Glacier-fed streams, such as the Saldur/Saldura stream in the Italian Central-Eastern Alps, are particularly vulnerable due to their dependence on snow and glacier melt. The Saldur/Saldura catchment (ca. 100 km²), one of the driest areas of the Alps and part of an LTSER platform, is a unique study area due to its dry conditions, low anthropogenic stressors, and the presence of a glacier that sustains the hydrology of this inner-Alpine valley. Since 2010, a long-term biomonitoring program has been assessing the effects of climate and anthropogenic factors - specifically the construction of a small run-of-river (ROR) hydropower plant in 2015 - on stream macroinvertebrate communities. Monthly monitoring during the snow-free period (April-September/October) was initially conducted at three altitudinal sampling sites and was expanded to six sites after the construction of the ROR hydropower plant. This high-resolution temporal dataset allowed us to analyse the spatial and temporal dynamics of macroinvertebrate assemblages in response to natural and anthropogenic drivers.
Our findings provide insights into the key dynamics shaping macroinvertebrate communities, highlighting the predominant influence of seasonal melting processes driven by snow and glacier dynamics on their structural and taxonomic characteristics. Increased runoff during peak melt periods corresponds to a decrease in faunal density, taxa richness and functional diversity. Longitudinal gradients also emerged, with taxa distribution patterns reflecting variations in temperature, discharge, and suspended sediment load along the stream. We also observed that seasonal glacial melt dynamics appeared to overshadow the potential impacts of hydropower operations, suggesting that the Saldur/Saldura stream's hydrology and benthic communities remain primarily shaped by climatic drivers.
This study highlights the value of long-term, high-resolution monitoring in disentangling the complex interplay between natural processes and anthropogenic factors in sensitive Alpine ecosystems. By combining long-term biomonitoring approaches with advanced statistical analyses, our work demonstrates the resilience of glacier-fed stream macroinvertebrate communities to localised human impacts, while emphasising their vulnerability to climate-induced changes in glacier and snowmelt dynamics. The results contribute to a broader understanding of the ecological implications of small hydropower plants in low-impacted valleys and highlight the importance of sustained monitoring efforts for effective management, conservation and future water scarcity scenarios in Alpine regions.