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Research article - Peer-reviewed, 2020

Do stream water solute concentrations reflect when connectivity occurs in a small, pre-Alpine headwater catchment?

Kiewiet, Leonie; van Meerveld, Ilja; Stahli, Manfred; Seibert, Jan

Abstract

Expansion of the hydrologically connected area during rainfall events causes previously disconnected areas to contribute to streamflow. If these newly contributing areas have a different hydrochemical composition compared to the previously connected contributing areas, this may cause a change in stream water chemistry that cannot be explained by simple mixing of rainfall and baseflow. Changes in stormflow composition are, therefore, sometimes used to identify when transiently connected areas (or water sources) contribute to stormflow. We identified the dominant sources of streamflow for a steep 20 ha pre-Alpine headwater catchment in Switzerland and investigated the temporal changes in connectivity for four rainfall events based on stream water concentrations and groundwater level data. First, we compared the isotopic and chemical composition of stormflow at the catchment outlet to the composition of rainfall, groundwater and soil water. Three-component end-member mixing analyses indicated that groundwater dominated stormflow during all events, and that soil water fractions were minimal for three of the four events. However, the large variability in soil and groundwater composition compared to the temporal changes in stormflow composition inhibited the determination of the contributions from the different groundwater sources. Second, we estimated the concentrations of different solutes in stormflow based on the mixing fractions derived from two-component hydrograph separation using a conservative tracer (delta H-2) and the measured concentrations of the solutes in baseflow and rainfall. The estimated concentrations differed from the measured stormflow concentrations for many solutes and samples. The deviations increased gradually with increasing streamflow for some solutes (e.g. iron and copper), suggesting increased contributions from riparian and hillslope groundwater with higher concentrations of these solutes and thus increased hydrological connectivity. The findings of this study show that solute concentrations partly reflect the gradual changes in hydrologic connectivity, and that it is important to quantify the variability in the composition of different source areas.

Published in

Hydrology and Earth System Sciences
2020, volume: 24, number: 7, pages: 3381-3398
Publisher: COPERNICUS GESELLSCHAFT MBH

Authors' information

Kiewiet, Leonie
Univ Zurich
van Meerveld, Ilja
Univ Zurich
Stahli, Manfred
Swiss Fed Res Inst WSL
University of Zürich
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment

Sustainable Development Goals

SDG6 Clean water

UKÄ Subject classification

Oceanography, Hydrology, Water Resources

Publication Identifiers

DOI: https://doi.org/10.5194/hess-24-3381-2020

URI (permanent link to this page)

https://res.slu.se/id/publ/107010