Natural acid rock drainage causing hydrochemical variations in rock glacier springs in the Austrian Alps

Rock glaciers (RGs) are morphologically distinct landforms of alpine permafrost prevalent in Austria and act as shallow groundwater bodies. Previous studies have shown that some RG spring waters exhibit unexpected low pH values, high concentration of total dissolved solids as well as elevated concentrations of heavy metals due to natural acid rock drainage (NARD). It can be observed that NARD increases and intensifies as permafrost boundaries are shifting towards higher altitudes.

This study aims to show (i) the extreme hydrochemical variation among several springs at a single RG due to NARD and (ii) the temporal evolution of NARD over several years at another RG spring. For this purpose, the active Wannenkar RG in Tyrol and the inactive Klafferkessel RG in Styria are investigated. At the Wannenkar RG, over 15 springs have been identified with large variations in pH values and electric conductivity (EC), which may be attributed to different flow paths and thus hydrogeochemical reactions within an intact RG that is experiencing NARD. In contrast, the Klafferkessel RG features only one spring where over a span of less than 10 years a decrease in pH and a doubling of EC is observed. A detailed analysis of these hydrochemical variations aids to understand the underlying processes. This provides a foundation for water management in this sensitive environment due to climate change.