Understanding hydrological processes in glacierized catchments: Evidence and implications of highly variable isotopic and electrical conductivity data

Abstract

The spatial and temporal characterization of geochemical tracers over Alpine glacierized catchments is particularly difficult, but fundamental to quantify groundwater, glacier melt, and rain water contribution to stream runoff. In this study, we analysed the spatial and temporal variability of δ2H and electrical conductivity (EC) in various water sources during three ablation seasons in an 8.4‐km2 glacierized catchment in the Italian Alps, in relation to snow cover and hydro‐meteorological conditions. Variations in the daily streamflow range due to melt‐induced runoff events were controlled by maximum daily air temperature and snow covered area in the catchment. Maximum daily streamflow decreased with increasing snow cover, and a threshold relation was found between maximum daily temperature and daily streamflow range. During melt‐induced runoff events, stream water EC decreased due to the contribution of glacier melt water to stream runoff. In this catchment, EC could be used to distinguish the contribution of subglacial flow (identified as an end member, enriched in EC) from glacier melt water to stream runoff, whereas spring water in the study area could not be considered as an end member. The isotopic composition of snow, glacier ice, and melt water was not significantly correlated with the sampling point elevation, and the spatial variability was more likely affected by postdepositional processes. The high spatial and temporal variability in the tracer signature of the end members (subglacial flow, rain water, glacier melt water, and residual winter snow), together with small daily variability in stream water δ2H dynamics, are problematic for the quantification of the contribution of the identified end members to stream runoff, and call for further research, possibly integrated with other natural or artificial tracers.

Global Isotope Hydrogeology―Review

“…One or more of these assumptions are frequently invalid (read introduction section of Kirchner, ). For example, (i) event waters and pre‐event waters sometimes have similar isotope compositions (e.g., two occasions in data set published by Berman et al, ); (ii) event water (e.g., rain and snowmelt) isotope compositions often vary substantially through time (e.g., Liu et al, ; Munksgaard et al, ; Xu et al, ; Zuecco et al, ); (iii) pre‐event water (e.g., groundwater) isotope compositions can vary through time (Haiyan et al, ); (iv) soil water discharges can generate substantial streamflow (e.g., Iwagami et al, ); and (v) surface water stores can contribute to runoff (e.g., Gibson, Birks, & Yi, ; Jefferson et al, ). Even where all five assumptions appear valid, end‐member δ 18 O values often vary, yielding large uncertainties in pre‐event water fractions (Bansah & Ali, ; Joerin et al, ).…”

Headwaters’ Isotopic Signature as a Tracer of Stream Origins and Climatic Anomalies: Evidence from the Italian Alps in Summer 2018

“…The year 2018 was extremely warm, with anomalies of air (and seawater) temperature in all months, especially in the spring and summer. Coherently, the observed isotopic values were the least negative ever recorded in Italian Alpine systems of comparable altitude (see for comparison 26,29,33,34,73,74). The isotopic anomaly between the average of the recorded compositions of the Careser basin and that of comparable alpine systems of similar altitude [29,33] was normalized to the annual air temperature anomaly of the "Careser Diga" meteorological station (2600 m a.s.l.…”

“…In this view, the use of dissolved ions as sulfates and silicon can be useful in distinguishing between snow, ice, and groundwater sources in headwaters [23].Stable isotopes are an additional tool used to characterize water sources [24][25][26][27][28]. δ 2 H and δ 18 O are widely used in hydrological studies of high-elevation catchments [25][26][27][28][29]. Improvement of technological techniques, especially laser spectroscopy, helped increase the information of these tracers in different water compartments, especially in sensitive areas such as glacialized catchments, where environmental changes have the most impact [30,31].…”

“…Improvement of technological techniques, especially laser spectroscopy, helped increase the information of these tracers in different water compartments, especially in sensitive areas such as glacialized catchments, where environmental changes have the most impact [30,31]. In recent years, water stable isotopes have been increasingly used to trace water fluxes in the different hydrological conditions of glacial streams in Alpine areas [29,32,33] to characterize spring water [26], as well as to trace snowmelt in mountain streams [32,34,35] and runoff processes [30,34,36]. For instance, they can be used to separate the contribution of each streamflow component [25], although evaporation processes may complicate this framework [25,36,37].…”

Hydrological Functioning of Forested Catchments, Central Himalayan Region, India.

“…Figure 4A and B, indicates that June month was the transition period, when hydrological functioning (Q t activation and generation) of the catchments begins to activate and October was again a transition period when hydrological functioning begins to inactivate. The non-linear behavior is common in hydrological systems (Zuecco et al 2018) and this thresholds can be used as a classi cation tool to better conceptualize runoff response behavior under a range of weather conditions (Ali et al 2013;.…”