FIGURE 6. Precipitation δ18O (average of the 12 antecedent days; triangles) and streamflow δ18O (average of the morning and evening samples) measured at the Izas gauging station (lines).
During the period April-June, the streamflow δ18O values were noticeably more depleted (ranging from -8 to -12 ‰) than the precipitation (mostly in liquid phase) δ18O values (ranging from -4 to -10 ‰, with most of the values ranging between -6 and -8‰). In general, the evolution of the streamflow isotopy was relatively steady, with slight day-to-day changes. The three years analyzed showed some interannual differences in streamflow δ18O values, likely driven by the snowpack magnitude and duration. The lowest streamflow δ18O values were observed in 2018 (a snow rich year). On the contrary, higher values were found in 2019 and 2020 (low and very low snowpack years, respectively). The differences in streamflow δ18O values remained even weeks after snow cover was completely depleted from the catchment.