In mountain rivers, long-term observations of water and sediment fluxes are crucial for understanding the dynamics of bedload fluctuations at multiple temporal scales. Here we analyze 7 years of data gathered at a bedload monitoring station in the glacier-fed Sulden/Solda River (South Tyrol, Italy). Continuous seismic data gathered from 8 geophone plates are analyzed to estimate the bedload flux at 1 minute scale. Sixty-five direct bedload sampling were carried out to derive the calibration equations adopted to quantify the transported bedload mass. The signal power is proposed as a more effective metric for calculating bedload mass than threshold-based impulses. Results show: (i) a remarkable variability of bedload rate for the same value of flow discharge; (ii) the joint effect of storm-driven flood events and seasonal changes in sediment supply on bedload rates; and (iii) the strong impact of climatic factors (i.e., temperature and snow cover) on bedload fluxes. Moderate bedload rates occurring in late spring/early summer are likely related to the mobilization of riverbed sediments, while higher bedload peak rates observed in July-August are associated with the activation of glacial and proglacial sediment sources. The dataset shows a complex climatic control on bedload transport at the basin scale, where precipitation, air temperature and snow cover determine flow and glacier melting dynamics. These findings suggest how the effects of the ongoing climatic change (e.g., higher frequency of intense rainfall events and prolonged heat waves) can result in a marked increase in bedload transport in glacier-fed rivers of the Alps.

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.