Contrasting physical and chemical conditions of two springs fed by
active rock glaciers
Abstract
Rock glaciers are increasingly influencing the hydrology and water
chemistry of Alpine catchments, with important implications for drinking
water quality and ecosystem health under a changing climate. During
summers of 2017 - 2019, we monitored the physical and chemical
conditions of springs emerging from two active rock glaciers (ZRG and
SRG) with distinct geomorphological settings in the Eastern Italian Alps
(Solda/Sulden catchment). Both springs had constantly cold waters (1.4 ±
0.1 °C), and their ionic composition was dominated by SO42-, HCO3-, Ca2+
and Mg2+. Concentrations of major ions and trace elements, and values of
water isotopes (δ18O, δ2H), increased towards autumn with an asymptotic
trend at SRG, and a positive unimodal pattern at ZRG, where
concentrations peaked 60 - 80 days after the end of the snowmelt.
Wavelet analysis on electrical conductivity (EC) and water temperature
records revealed daily cycles only at SRG, and significant
weekly/biweekly fluctuations at both springs attributable to
oscillations of meteorological conditions. Several rainfall events
triggered a transient (0.5 - 2 hrs) EC drop and water temperature rise
(dilution and warming) at SRG, whereas only intense rainfall events
occasionally increased EC at ZRG (solute enrichment and thermal
buffering), with a long-lasting effect (6 - 48 hrs). Our results,
supported by a limited but emerging literature, suggest that: i) the
distinctive composition of the bedrock drives different concentrations
of major ions and trace elements in rock glacier springs; ii) pond-like
and stream-like springs have distinct fluctuations of water parameters
at different timescales; iii) peaks of EC/solute concentrations indicate
a seasonal window of major permafrost thaw for rock glaciers feeding
pond-like springs. These results provide a first quantitative
description of the hydrological seasonality in rock glacier outflows,
and their hydrochemical response to precipitation events, bringing
relevant information for water management in the European Alps under
climate change.