Isotopic and geochemical variability of rock glaciers spring waters in the eastern Italian Alps

Due to the rapid shrinkage of mountain glaciers, subsurface ice, including ground ice stored in periglacial landforms such as rock glaciers (RGs), is expected to become a significant shallow groundwater reservoir under future climate warming. However, there are still many open questions about the ice volume stored inside RGs, its melting rates, its hydrological significance and the quality of the water flowing out from RGs. In this work, we aim at: i) characterizing the geochemistry of RG springs, and ii) evaluating the variability of environmental tracers in spring waters collected downslope of intact and relict RGs.

During summer 2024, two sampling campaigns (in late July and early September) were conducted to measure spring-water temperature, electrical conductivity (EC), pH and collect water samples for the analyses of stable isotopes of hydrogen and oxygen, major ions and trace elements. One spring from an intact RG and one spring from a relict RG were sampled every 48 hours using automatic samplers to investigate the temporal dynamics of the different tracers.

Spring waters downslope of relict RGs had lower EC compared to spring waters from intact RGs. A seasonal isotopic enrichment was found, which was likely due to the decreasing snowmelt contribution, and it was more evident at high elevations. Intact RG springs had higher EC and concentrations of sulphates, when compared with relict RGs and reference springs. This difference was more evident during September and at locations with acidic metamorphic lithologies.

These initial analyses revealed substantial geochemical differences between springs from intact RGs and those from relict RGs and reference locations. At some springs from intact RGs, sulphate concentrations exceeding the indicator parameters for drinking water quality suggest potential issues related to the use of RG water for human purposes. Analyses of trace elements will provide a clearer picture of the geochemical characteristics of the spring waters, expanding the still limited knowledge on RGs and their springs.

 

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).