Abstract

Snow-dominated and glacierized catchments are
important sources of fresh water for biological communities
and for populations living in mountain valleys. Gaining a better
understanding of the runoff origin and of the hydrological
interactions between meltwater, streamflow and groundwater
is critical for natural risk assessment and mitigation as well
as for effective water resource management in mountain regions.
This study is based on the use of stable isotopes of water
and electrical conductivity as tracers to identify the water
sources for runoff and groundwater and their seasonal variability
in a glacierized catchment in the Italian Alps. Samples
were collected from rainfall, snow, snowmelt, ice melt,
spring and stream water (from the main stream at different
locations and from selected tributaries) in 2011, 2012 and
2013. The tracer-based mixing analysis revealed that, overall,
snowmelt and glacier melt were the most important endmembers
for stream runoff during late spring, summer and
early fall. The temporal variability of the tracer concentration
suggested that stream water was dominated by snowmelt at
the beginning of the melting season (May–June), by a mixture
of snowmelt and glacier melt during mid-summer (July–
early August), and by glacier melt during the end of the summer
(end of August–September). The same seasonal pattern
observed in streamflow was also evident for groundwater,
with the highest electrical conductivity and least negative isotopic
values found during cold or relatively less warm periods,
when the melt of snowpack and ice was limited. Particularly,
the application of a two-component mixing model to
data from different springs showed that the snowmelt contribution
to groundwater recharge varied between 21% (�3 %)
and 93% (�1 %) over the season, and the overall contribution
during the three study years ranged between 58%
(�24 %) and 72% (�19 %). These results provided new insights
into the isotopic characterization of the study catchment
presenting further understanding of the spatio-temporal
variability of the main water sources contributing to runoff.