Linking river discharge and macroinvertebrate communities under climate change in a glacier-fed stream

Glacier retreat driven by climate change is expected to alter hydrological and chemical conditions in glacier-fed streams, with consequences for macroinvertebrate community structure and function. To assess long-term community responses to changing runoff regimes, we revisited the glacier-fed Vestari-Jökulsá River in Iceland, originally studied in 1996/97, and compared historical data with new measurements collected in 2022.Macroinvertebrate species richness, Shannon diversity, and evenness declined at several sites, while total organism density remained relatively stable. Analyses of community composition based on Bray-Curtis dissimilarities revealed higher similarity among sites in 2022 compared to 1996/97, suggesting increasing homogenization of assemblages with glacial retreat. As runoff regime has been identified as a key driver of future community change, we examine hydrological dynamics in the catchment in relation to observed ecological changes and predicted runoff scenarios. Ongoing analyses focus on trends in annual discharge and seasonal dynamics, including the timing of melt onset and potential changes in winter and summer runoff.By integrating long-term ecological, hydrological, and chemical perspectives, this study enhances understanding of climate-driven changes in glacier-fed stream ecosystems.