FIGURE 7. Daily streamflow δ18O values measured at 6 AM, and 6 PM at the Izas gauging station during the years 2017 and 2018. δ18O values measured once a day (12 AM) during the snow free period later in the season are also shown
Comparison between morning and evening streamflow samples (6 AM and 6 PM, respectively) shows higher δ18O values in the latter, coinciding with a major influence of snow melting in the evening sample (Figure 7). This pattern occurred in the large majority of the days, regardless of rainfall events. The observed daily cycle disappears when snow cover depletes from the catchment (early and end June, for 2017 and 2018, respectively).
δ18O values from water samples taken weekly across the catchment (Figure 8) showed a parallel evolution to those measured at the gauging station. The lowest and less variable δ18O values were recorded when the catchment was snow covered. δ18O values progressively increase during the snow free period (July), showing also a higher variability between locations towards the end of the snow season.