Tracer-based analysis of spatial and temporal variation of water sources in a glacierized catchment

Abstract

Abstract. Snow-dominated and glacierized catchments are important sources of fresh water for biological communities and for population living in mountain valleys. Gaining a better understanding of the runoff origin and of the hydrological interactions between meltwater and streamflow is critical for natural risk assessment and mitigation as well as for effective water resources 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 their seasonal variability in a glacierized catchment in the Italian Alps. Samples were collected from rainfall, snow, snowmelt, ice melt 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 end-members 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 periods of limited melting. Particularly, the application of a two-component mixing model to data from different springs showed that the overall snowmelt contribution to groundwater recharge during the three study years ranged between 58% (±15%) and 72% (±15%). These results provided new insights on the isotopic characterization of the study catchment and the presented approach could offer further understanding of the spatio-temporal variability of the main water sources contributing to runoff in other snow-dominated and glacierized Alpine catchments.