Controls on Spatial and Temporal Variability in Streamflow And

Hydrol. Earth Syst. Sci., 23, 2041–2063, 2019 https://doi.org/10.5194/hess-23-2041-2019 © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License. Controls on spatial and temporal variability in streamflow and hydrochemistry in a glacierized catchment Michael Engel1, Daniele Penna2, Giacomo Bertoldi3, Gianluca Vignoli4, Werner Tirler5, and Francesco Comiti1 1Faculty of Science and Technology, Free University of Bozen-Bolzano, Piazza Università 5, 39100 Bolzano, Italy 2Department of Agriculture, Food, Environment and Forestry (DAGRI), University of Florence, Via S. Bonaventura 13, 50145 Florence, Italy 3Institute for Alpine Environment, Eurac Research, Viale Druso 1, 39100 Bolzano, Italy 4CISMA S.r.l., Via Volta 13/A, 39100 Bolzano, Italy 5Eco-Research S.r.l., Via Negrelli 13, 39100 Bolzano, Italy Correspondence: Michael Engel ([email protected]) and Francesco Comiti ([email protected]) Received: 15 March 2018 – Discussion started: 10 April 2018 Revised: 26 March 2019 – Accepted: 27 March 2019 – Published: 24 April 2019 Abstract. Understanding the hydrological and hydrochemi- imum global solar radiation represented important meteo- cal functioning of glacierized catchments requires the knowl- rological controls, with a significant snowmelt contribution edge of the different controlling factors and their mutual in- when exceeding 5 ◦C or 1000 W m−2, respectively. These interplay. For this purpose, the present study was carried out sights may help in better understanding and predicting hy- in two sub-catchments of the glacierized Sulden River catch- drochemical catchment responses linked to meteorological ment (130 km2; eastern Italian Alps) in 2014 and 2015, char- and geological controls and in guiding future classifications acterized by a similarly sized but contrasting geological set- of glacierized catchments according to their hydrochemical ting. Samples were taken at different space and timescales characteristics. for analysis of stable isotopes in water, electrical conductivity, and major, minor and trace elements. At the monthly sampling scale, complex spatial and tem- 1 Introduction poral dynamics for different spatial scales (0.05–130 km2) were found, such as contrasting electrical conductivity gra- Runoff from glacierized catchments is an important fresh wa- dients in both sub-catchments. For the entire Sulden catch- ter resource to downstream areas (Kaser et al., 2010; Vivi- ment, the relationship between discharge and electrical con- roli et al., 2011). High-elevation environments face rapid and ductivity showed a monthly hysteretic pattern. Hydrometric extensive changes through retreating glaciers, reduced snow and geochemical dynamics were controlled by interplay of cover and permafrost thawing (Harris et al., 2001; Dye, 2002; meteorological conditions, topography and geological het- Beniston, 2003; Galos et al., 2015). This will have impacts on erogeneity. A principal component analysis revealed that the runoff seasonality, water quantity and water quality (Benis- largest variance (36.3 %) was explained by heavy metal con- ton, 2006; Ragettli et al., 2016; Gruber et al., 2017; Kumar centrations (such as Al, V, Cr, Ni, Zn, Cd and Pb) during et al., 2019). Therefore, better understanding the behavior of the melting period, while the remaining variance (16.3 %) high-elevation catchments and their hydrological and hydro- resulted from the bedrock type in the upper Sulden sub- chemical responses at different spatial and temporal scales catchment (inferred from electrical conductivity, Ca, K, As is of uttermost importance in view of water management, and Sr concentrations). Thus, high concentrations of As water quality, hydropower and ecosystem services under the and Sr in rock glacier outflow may more likely result from current phase of climate change (Beniston, 2003; Viviroli et bedrock weathering. Furthermore, nivo-meteorological indi- al., 2011; Beniston and Stoffel, 2014). cators such as daily maximum air temperature and daily max- Published by Copernicus Publications on behalf of the European Geosciences Union. 2042 M. Engel et al.: Controls on streamflow and hydrochemistry in a glacierized catchment In general, the hydrological response of catchments (i.e., The catchment hydrological conditions, commonly refer- runoff dynamics) is controlled by heterogeneous catchment ring to the antecedent soil moisture, are also a relevant driver properties (Kirchner, 2009), which become more diverse in of the hydrological response (Uhlenbrook and Hoeg, 2003; catchments with large complexity in various landscape fea- von Freyberg et al., 2017). Specifically in high-elevation and tures like, in the case of mountainous, high-elevation glacier- high-latitude catchments, permafrost thawing also affects the ized catchments (Cook and Swift, 2012). In fact, those catch- hydrological connectivity (Rogger et al., 2017), leading to a ments are deemed to be highly dynamic geomorphologi- strong control on catchment functioning as it drives the par- cal, hydrological and biogeochemical environments (Rutter titioning, storage and release of water (Tetzlaff et al., 2014). et al., 2011). The advances in tracer and isotope hydrology In more detail, retreating permafrost may also result in dis- made during the last decades can substantially contribute to tinct geochemical signatures (Clark et al., 2001; Lamhonwah gain more insight into the variability in different runoff com- et al., 2017) and the release of heavy metals being previously ponents of high-elevation catchments (Vaughn and Foun- stored in the ice (Thies et al., 2007; Krainer et al., 2015). As tain, 2005; Maurya et al., 2011; Xing et al., 2015; Penna et those contaminants do not only affect the water quality but al., 2017b), catchment conceptualization (Baraer et al., 2015; also the aquatic biota such as macroinvertebrate communi- Penna et al., 2017a) and sensitivity to climate change (Kong ties in high-elevation and high-latitude environments (Mil- and Pang, 2012). ner et al., 2009), the hydrochemical characterization of per- The main controls on hydrological and hydrochemical mafrost thawing (i.e., from rock glaciers as a specific form catchment responses are represented by climate, bedrock of permafrost) and its impact on stream hydrology deserves geology, surficial geology, soil, vegetation, topography, further investigation (e.g., Williams et al., 2006; Carturan et drainage network (Devito et al., 2005; Williams et al., 2015) al., 2016; Nickus et al., 2015; Colombo et al., 2017). and catchment shape (Sivapalan, 2003). These catchment Although the effect of catchment characteristics and en- properties may affect the partitioning of incoming water and vironmental conditions on stream hydrochemistry at differ- energy fluxes (Carrillo et al., 2011). ent spatial and temporal scales has been studied well in First, a major role is attributed to the global and regional lowland and midland catchments (e.g., Wolock et al., 1997; climate, having strong impacts on mountain glaciers and per- McGuire et al., 2005; Tetzlaff et al., 2009), only few stud- mafrost, streamflow amount and timing, water quality, wa- ies have focused on this aspect in glacierized or permafrost- ter temperature, and suspended sediment yield (Milner et dominated catchments (Wolfe and English, 1995; Hodgkins, al., 2009; Moore et al., 2009; IPCC, 2013). The impact of cli- 2001; Carey and Quinton, 2005; Lewis et al., 2012; Kumar mate is difficult to assess because it requires long time win- et al., 2018). In fact, investigating the geological, meteo- dows (e.g., decades), whereas meteorological drivers interact rological and topographic controls on catchment response at a smaller temporal scales and thus are easier to quantify. and stream water hydrochemistry in high-elevation catch- Among different meteorological drivers, radiation fluxes at ments is essential when analyzing the origin of hydrochemi- the daily timescale were identified as the main energy source cal responses in larger catchments (Chiogna et al., 2016; Na- driving melting processes in glacierized catchments in differ- tali et al., 2016), calibrating hydrological models (Weiler et ent climates (Sicart et al., 2008). Beside radiation, air tem- al., 2017) and analyzing catchment storages (Staudinger et perature variations generally correlate well with streamflow al., 2017). under the presence of snow cover (Swift et al., 2005) and may In this paper, we aim to fill this knowledge gap by analyz- affect the daily streamflow range (Penna et al., 2016; Zuecco ing hydrochemical data from a 2-year monitoring campaign et al., 2018) and streamflow seasonality (Hock et al., 1999; in two nearby glacierized catchments in the eastern Italian Cortés et al., 2011) only after an air temperature threshold Alps, characterized by a similar size and climate but contrast- has been reached. ing geological setting. We hypothesize that the markedly dif- Geology sets the initial conditions for catchment proper- ferent geological properties affect the geochemistry and the ties (Carrillo et al., 2011). The geological setting strongly hydrological response of both catchments. We test this hy- controls catchment connectivity, drainage, groundwater pothesis by sampling different water sources (precipitation, discharge (Farvolden, 1963), runoff response (Onda et stream water, groundwater, snowmelt and glacier melt) for al., 2001), residence time (Katsuyama et al., 2010), hydro- the electrical conductivity (EC), turbidity, and major, minor chemistry

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