Tracer characterization of rock glaciers spring waters in the Eastern Italian Alps

The rapid melting of alpine glaciers is expected to make subsurface ice, including that stored in periglacial formations like rock glaciers (RGs), an important shallow groundwater source for the downstream areas. However, many open questions remain about the ice volume in RGs, its melting rates, hydrological importance, and the quality of water flowing from RGs. This study aims to: i) characterize the geochemistry of RG springs, and ii) assess the variability of environmental tracers in spring waters downstream of RGs with different degree of activity.

We studied springs from intact (ice-embedding) and relict (without ice) RGs, as well as reference springs not influenced by RGs, in six mountain catchments of the Eastern Italian Alps. Sampling campaigns were carried out during two years with different snow and hydrometeorological conditions. While the hydrologic year 2023/2024 was characterized by higher snow cover accumulation and duration, the year 2024/2025 had a shorter accumulation season and most catchments were snow free already in June.

During summer 2024 and 2025, from late June to late September, we conducted sampling campaigns to measure spring water temperature, electrical conductivity (EC), pH, and collect water samples for analyzing stable isotopes of hydrogen and oxygen, major ions, and trace elements. We used automatic samplers to collect samples every 48 hours from one intact RG spring and one relict RG spring to study the temporal dynamics of different tracers.

Springs downstream of relict RGs exhibited lower EC than those from intact RGs. A seasonal isotopic enrichment was observed, likely due to decreasing snowmelt contribution. This seasonal enrichment was more pronounced at higher elevations. Intact RG springs had higher EC and sulphate concentrations compared to relict RGs and reference springs, especially in late summer (September) and in areas underlain by acidic metamorphic rocks (micashists). Water samples collected in 2025 from intact RG springs exhibited higher EC and ion concentrations than those collected in 2024. This contrast underscores the role of seasonal snow and snowmelt in the dilution of solutes released in high-elevation areas, where subsurface ice is likely present.

These initial findings reveal significant geochemical differences between springs from intact RGs and those from relict RGs or reference sites. At some intact RG springs nichel, manganese and sulphate concentrations are not suitable for drinking water, suggesting potential issues for human consumption.

These preliminary results contribute to the limited knowledge of RGs spring water chemistry, stimulating further investigation also including biogeochemical processes eventually involved in the rock-water interface.

This study was carried out within the project PRIN 2022 “SUBSURFICE – Ecohydrological and environmental significance of subsurface ice in alpine catchments” (code no. 2022AL7WKC, CUP: C53D23002020006), which received funding from the European Union NRRP (Mission 4, Component 2, Investment 1.1, D.D. 104 2/2/2022).