Controls on spatial and temporal variability in streamflow and hydrochemistry in a glacierized catchment

Abstract

Understanding the hydrological and hydrochemical functioning of glacierized catchments requires the knowledge of the different controlling factors and their mutual interplay. For this purpose, the present study was carried out in two sub-catchments of the glacierized Sulden River catchment (130 km2; eastern Italian Alps) in 2014 and 2015, characterized by a similarly sized but contrasting geological setting. Samples were taken at different space and timescales for analysis of stable isotopes in water, electrical conductivity, and major, minor and trace elements. At the monthly sampling scale, complex spatial and temporal dynamics for different spatial scales (0.05-130 km2) were found, such as contrasting electrical conductivity gradients in both sub-catchments. For the entire Sulden catchment, the relationship between discharge and electrical conductivity showed a monthly hysteretic pattern. Hydrometric and geochemical dynamics were controlled by interplay of meteorological conditions, topography and geological heterogeneity. A principal component analysis revealed that the largest variance (36.3 %) was explained by heavy metal concentrations (such as Al, V, Cr, Ni, Zn, Cd and Pb) during the melting period, while the remaining variance (16.3 %) resulted from the bedrock type in the upper Sulden subcatchment (inferred from electrical conductivity, Ca, K, As and Sr concentrations). Thus, high concentrations of As and Sr in rock glacier outflow may more likely result from bedrock weathering. Furthermore, nivo-meteorological indicators such as daily maximum air temperature and daily maximum global solar radiation represented important meteorological controls, with a significant snowmelt contribution when exceeding 5 °C or 1000W m-2, respectively. These insights may help in better understanding and predicting hydrochemical catchment responses linked to meteorological and geological controls and in guiding future classifications of glacierized catchments according to their hydrochemical characteristics.