Permafrost degradation affects hydrochemistry of surface waters. In particular, evidence of modifications in water quality has been collected in mountain headwaters impacted by rock-glacier thawing. Rock glaciers are slowly flowing mixtures of debris and ice-rich permafrost, and can represent a reservoir of water. Melting ice inside them has been reported to affect surface water hydrochemistry, in some cases causing ecological damages. Investigating the mechanisms for this, however, requires understanding how, where and when rock glaciers and water bodies interact. Moreover, it is necessary to understand how atmospheric forcing can affect the export of physicochemical fluxes from rock glaciers. Different hypotheses have been proposed to explain the main driving weather-climate processes, nevertheless, they are still unclear.
With these goals, hydrology and structural setting of a rock glacier-pond system located in the NW Italian Alps were elucidated using waterborne geophysics (ground penetrating radar, electrical resistivity tomography and self-potential) and heat tracing. An integrated study of atmospheric parameters (air temperature, snow cover duration, rainfall) and physicochemical characteristics of water (water temperature as a proxy of rock-glacier discharge, stable water isotopes, major ions and trace elements) was also performed in the pond on a high-resolution temporal basis (weekly) for two consecutive ice-free seasons.
The advancing movement of the investigated rock glacier has progressively filled the valley depression, creating a dam that could have modified the level of impounded water. A subsurface hydrological window connecting the rock glacier to the pond was also detected, where an inflow of cold underground waters from the rock glacier was observed. Here, greater water contribution from the rock glacier occurred following intense precipitation events during the ice-free season. An outflowing mechanism of the pond is hypothesised and might be associated with the presence of a subsurface seepage.
An intra-seasonal behaviour of solute export from the rock glacier into the pond was found, with increasing solute export associated with higher rock-glacier hydrological contributions. The key finding was the rainfall (after snowmelt depletion) as primary driver of solute export from the rock glacier during the thawing season after warm atmospheric periods, with the flushing of solutes stored in the rock glacier.