Isotopic hydrograph separation in the Hydrological Open Air Laboratory, Austria

The rainfall-runoff process transforms a precipitation input to a catchment into runoff output and is an important indicator for river water quality and quantity. Since runoff events are comprised of precipitation event water and stored pre-event water of the catchment, exploring the event and pre-event components of runoff events using the stable isotopes of water (δ18O, δ2H) and two-component and ensemble isotopic hydrograph separation may further our insights into overall catchment behaviour and the origin of water. The aim of this study is to investigate the origin of water for different streamflow gauges in a small agricultural catchment that represent different runoff generation mechanisms. The analysis is performed at the Hydrological Open Air Laboratory (HOAL) in Austria, which is a 66 ha experimental catchment dominated by agricultural land use. One of the main features of this research catchment is that several tributaries of the catchment representing different runoff generation mechanisms are gauged. Two-component and ensemble isotopic hydrograph separations (for both δ18O and δ2H) are conducted for three streamflow gauges (the catchment’s inlet and outlet and a tile drainage system) for multiple events in the warm periods of 2013-2018. The results of the two methods are compared and discussed for different runoff generation mechanisms.