Origin and Evolution of High Nickel Concentrations in Rock Glacier Springs.

Global warming has accelerated the degradation of alpine permafrost, significantly altering hydrological and hydrogeochemical processes in mountainous catchments. Among these changes, rock glaciers release spring waters with rising solute concentrations, including nickel levels that significantly exceed drinking water limits. This study investigates the geochemical processes driving solute mobilization in five rock glaciers in the European Alps, focusing on nickel enrichment and transport pathways. Geochemical and petrographic analyses show that high nickel concentrations in spring waters originate from sulfide minerals and their weathering products. Sulfur and oxygen isotope analyses of dissolved sulfate confirm mineral weathering as the primary solute source, while inverse hydrogeochemical modeling accurately reproduces the chemical composition of these spring waters. The hydrogeology of rock glaciers plays a critical role in these processes, as deformation and ice melt expose fresh mineral surfaces, while extended residence times of water in the subsurface create favorable conditions for natural acid rock drainage. Our study demonstrates that rock glaciers are active chemical reactors, enriching alpine streams and lakes with metals and raising concerns about water quality and ecological impacts. This work advances understanding of climate-sensitive metal contamination, informing integrated water management strategies in mountain regions.