Rock glaciers in crystalline catchments: Hidden permafrost‐related threats to alpine headwater lakes

Abstract

A global warming‐induced transition from glacial to periglacial processes has been identified in mountainous regions around the world. Degrading permafrost in pristine periglacial environments can produce acid rock drainage (ARD) and cause severe ecological damage in areas underlain by sulfide‐bearing bedrock. Limnological and paleolimnological approaches were used to assess and compare ARDs generated by rock glaciers, a typical landform of the mountain permafrost domain, and their effects on alpine headwater lakes with similar morphometric features and underlying bedrock geology, but characterized by different intensities of frost action in their catchments during the year. We argue that ARD and its effects on lakes are more severe in the alpine periglacial belt with mean annual air temperatures (MAAT) between −2°C and +3°C, where groundwater persists in the liquid phase for most of the year, in contrast to ARD in the periglacial belt where frost action dominates (MAAT < −2°C). The findings clearly suggest that the ambient air temperature is an important factor affecting the ARD production in alpine periglacial environments. Applying the paleoecological analysis of morphological abnormalities in chironomids through the past millennium, we tested and rejected the hypothesis that unfavorable conditions for aquatic life in the ARD‐stressed lakes are largely related to the temperature increase over recent decades, responsible for the enhanced release of ARD contaminants. Our results indicate that the ARDs generated in the catchments are of a long‐lasting nature and the frequency of chironomid morphological deformities was significantly higher during the Little Ice Age (LIA) than during pre‐ or post‐LIA periods, suggesting that lower water temperatures may increase the adverse impacts of ARD on aquatic invertebrates. This highlights that temperature‐mediated modulations of the metabolism and life cycle of aquatic organisms should be considered when reconstructing long‐term trends in the ecotoxicological state of lakes.

After the peak water: the increasing influence of rock glaciers on alpine river systems

“…This is in line with the literature on rock glacier hydrology stating that these landforms act as unconfined aquifers in mountain slopes (e.g., Jones et al, ; Krainer & Mostler, ). The enrichment of solutes and trace elements in rock glacier outflows is commonly attributed to the thaw of internal ice and to the associated weathering of freshly exposed rock particles (Colombo et al, ; Ilyashuk, Ilyashuk, Psenner, Tessadri, & Koinig, ; Munroe, ; Williams, Knauf, Caine, Liu, & Verplanck, ). Accordingly, the high values of EC, major ions, and trace elements, we observed increasing over the season, are consistent with data reported in the literature on rock glacier hydrology (e.g., Colombo et al, ; Mair et al, ; Millar, Westfall, & Delany, ; Williams et al, ) and suggest that part of the rock glacial baseflow in summer came from permafrost thaw, in addition to the groundwater fraction, and this increased as summer progressed.…”

Prokaryotic Diversity and Distribution in Different Habitats of an Alpine Rock Glacier-Pond System

“…The presence of a localised inflow from the RG has been confirmed [17], but it is important to specify that these meltwater inputs have been described as intermittent, concentrated only in the snow-free season and mainly linked to precipitation events [17,20]. Meltwaters also showed only a moderate increase in solutes concentration if compared with the pond waters [20], differing in this sense from other RGlake/stream systems affected by natural acid rock drainage phenomena [9,14,15]. Nevertheless, beside RG inputs can be limited in frequency and magnitude, microbial communities can quickly react to environmental pressures acting directly or indirectly on them [21], becoming a powerful instrument for the detection of ecosystem perturbations.…”

“…For instance, Thies et al [9] compared the diatom population of RG-influenced and reference streams in the Austrian Alps, highlighting that both diatom species composition and diversity can be negatively affected by the increase in water acidity commonly associated with RG runoff. In the NE Italian Alps, Ilyashuk et al [14,15] reported high concentrations of metals in the waters of RG lakes, which seem to explain the high rate of morphological abnormalities in chironomid population inhabiting lake sediments. Focusing on microbial community, Fegel et al [8] described the bacterial community composition in stream sediments collected close to the terminus of several glaciers and RGs, distributed across three North America mountain ranges.…”

Multi‐temporal 3D point cloud‐based quantification and analysis of geomorphological activity at an alpine rock glacier using airborne and terrestrial LiDAR

“…Being potentially unstable slopes and solid water reservoirs, rock glaciers and their dynamics have gained importance in climate change research in recent decades . Higher mean annual temperatures are expected to induce changes to surface and subsurface dynamics at different temporal scales (e.g., weekly to decadal), depending on site‐specific conditions …”

“…6 Higher mean annual temperatures are expected to induce changes to surface and subsurface dynamics at different temporal scales (e.g., weekly to decadal), depending on sitespecific conditions. [6][7][8][9][10][11][12][13] These surface and subsurface dynamics reflect processes of rock glacier deformation including permafrost creep, permafrost slide, zonal thinning or thickening, advection of surface microtopography, three-dimensional (3D) straining, general mass changes (heaving or settlement), and horizontal shearing and rotation. 14 These processes feature different spatial characteristics, magnitudes and timescales of occurrence.…”