Abstract
Despite the fact that rock glaciers are one of the most common geomorphological expressions of mountain permafrost, the impacts of their solute fluxes on lakes still remain largely obscure. We examined water and sediment chemistry, and biota of two neighboring water bodies with and without a rock glacier in their catchments in the European Alps. Paleolimnological techniques were applied to track long-term temporal trends in the ecotoxicological state of the water bodies and to establish their baseline conditions. We show that the active rock glacier in the mineralized catchment of Lake Rasass (RAS) represents a potent source of acid rock drainage that results in enormous concentrations of metals in water, sediment, and biota of RAS. The incidence of morphological abnormalities in the RAS population of Pseudodiamesa nivosa, a chironomid midge, is as high as that recorded in chironomid populations inhabiting sites heavily contaminated by trace metals of anthropogenic origin. The incidence of morphological deformities in P. nivosa of ∼70% persisted in RAS during the last 2.5 millennia and was ∼40% in the early Holocene. The formation of RAS at the toe of the rock glacier most probably began at the onset of acidic drainage in the freshly deglaciated area. The present adverse conditions are not unprecedented in the lake’s history and cannot be associated exclusively with enhanced thawing of the rock glacier in recent years.
Highlights
Frozen and glacierized high-alpine areas react very sensitively to changes in air temperature and even small differences in temperature determine their frozen status
We examined water and sediment chemistry, and biota of two neighboring water bodies with and without a rock glacier in their catchments in the European Alps
We show that the active rock glacier in the mineralized catchment of Lake Rasass (RAS) represents a potent source of acid rock drainage that results in enormous concentrations of metals in water, sediment, and biota of RAS
Summary
Frozen and glacierized high-alpine areas react very sensitively to changes in air temperature and even small differences in temperature determine their frozen status. The active rock glacier extends on a north-facing slope down to the shore of RAS and occupies ∼18.5% of its catchment area which adjoins the permafrost-free catchment of RPD Both water bodies lacking inflow streams have well-developed outflows. The Bayesian statistical method of the OxCal software package version 4.2.133 was used to produce age-depth models (SI Figure S2) According to these estimates, the RAS and RPD sediment cores span time periods of ∼10 200 years and ∼3200 years, respectively. Larval head capsules of the two most common chironomid taxa, Pseudodiamesa nivosa and Micropsectra radialis-type, found in both dredge and sediment core samples (live specimens and their subfossil remains, respectively) from RAS and RPD (SI Figures S1 and S3) were inspected for deformities of the mentum, a mouth part which is typically well preserved in subfossil material. One-way analysis of variance (ANOVA), followed by Bonferroni post hoc test, was used to determine whether there are any significant differences in the
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