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.