What impact does the loss of glaciers and permafrost have on the quality of mountain water?
The loss of glaciers and permafrost has significant effects on water quality. In geologically predisposed areas, the loss of the cryosphere is in fact intensifying the so-called ‘acid rock drainage’. This phenomenon involves the oxidation of certain minerals (sulphides, such as pyrite) and results in the release of sulphate ions and heavy metals into lakes and streams, with potential ecological effects and implications for human water use. However, Alpine studies on the phenomenon have so far been scarce and limited to waters fed by glaciers and rock glaciers, structures composed of rock fragments and ice that represent important water resources.
In this study, we examined 80 high-altitude springs in Trentino, South Tyrol and North Tyrol to understand how widespread the phenomenon is and what factors enable it to be predicted on a spatial scale.
We found that acid rock drainage is predominantly associated with specific rock types that are very common in the area, such as paragneiss and mica schist. In areas with these rocks, all glacier springs, 70% of those from rock glaciers and recently formed moraines, 60% of those from rock debris cones and 25% of those originating from vegetated slopes exceed the European quality limits for drinking water. In these valleys, defined as ‘geochemical hotspots’, the probability of ice influence (calculated on the basis of water temperature and the Alpine permafrost probability map) proved to be the main variable allowing contaminated springs to be distinguished from uncontaminated ones.
The study is important because it highlights how acid rock drainage linked to the loss of the cryosphere is not confined to certain areas but affects large swathes of land. The high incidence of water contaminated with heavy metals such as nickel and manganese has potential repercussions for ecosystems and human health.
A B S T R A C T
High mountain areas are experiencing rapid hydrological shifts, due to a decline of meltwater sources and a concomitant increase
of solute concentrations in freshwater ecosystems. While research on water quality is increasing on river systems influenced by glaciers and rock glaciers, very limited knowledge exists on those influenced by other landforms such as moraines and talus slopes. During late summer 2021, we investigated the chemistry and δ18O in the water of 80 high-elevation springs in 6 massifs of the Central-Eastern European Alps. These springs were sourced either by glaciers, young moraines, rock glaciers, talus slopes, or reference slopes mantled with soil. End-member mixing models revealed a large fraction of (snow or glacier) meltwater at all springs (> 60%), even though rainwater had a higher contribution (up to 40%) at lower elevations. Lithology and the likelihood of ice influence, an indicator that we built using the spring water temperature and the Alpine permafrost map, were the most important predictors of water chemistry in regression tree analyses. Springs draining catchments dominated by paragneisses and/or micaschists had high concentrations of sulphate, nickel, manganese, and other metals. In these geochemical hotspots, all glacier springs, 70% of rock glacier and young moraine springs, 60% of talus slope springs, and 25% of reference slope springs had poor water quality (European Union standards for drinking water). In areas with other lithologies, only 13% of springs exhibited poor water quality. For the springs on paragneisses and/or micaschists, the permafrost presence and the motion of different landform
types may enhance nickel concentrations due to acid rock drainage. Finally, we discuss the importance of our findings for water management and freshwater ecosystems.