Cascading effects of glacier retreat: Hydro-chemical shifts and macroinvertebrate responses in Andean glacier-fed streams

The retreat of tropical glaciers in the Peruvian Andes, particularly in the Cordillera Blanca, has significantly altered hydrogeological and geochemical processes in mountain watersheds. This study investigates the influence of glacier change-driven acid rock drainage (ARD) upon benthic macroinvertebrate communities in 19 glacier-fed streams of the Santa River watershed over two consecutive dry and wet seasons (2019–2020). The findings reveal that ARD driven by glacier melt and sulphide oxidation has led to increased metal concentrations (e.g., Fe, Mn, Al, Pb) and pH reductions (of 2–3 in some sites), creating a “toxic or treat” scenario for aquatic biodiversity. Statistical analyses, including principal component analysis (PCA), principal coordinate analysis (PCoA), and canonical correspondence analysis (CCA), indicate significant correlations between physical and chemical changes and macroinvertebrate assemblages. Collector-gatherers (e.g., Chironomidae, Baetidae) were dominant in sites impacted by ARD, while sensitive functional feeding groups, such as scrapers and shredders, declined under high metal stress. Seasonal variations also affected taxonomic richness, with greater abundance observed during the dry season. These results highlight the cascading effects of climate-induced glacier loss on freshwater ecosystems and provide critical insights into the ecological consequences of ongoing environmental changes in high-altitude Andean rivers.