A comparison of catchment travel times and storage deduced from deuterium and tritium tracers using StorAge Selection functions

Abstract. Catchment travel time distributions (TTDs) are an efficient concept for summarizing the time-varying 3D transport of water and solutes towards outlet in a single function age estimating catchment storage by leveraging information contained tracer data (e.g., deuterium 2H tritium 3H). It is argued that preferential use stable isotopes O H as tracers, compared to tritium, has truncated our vision streamflow TTDs, meaning long tails distribution associated with old tend be neglected. However, reasons truncation TTD still obscured methodological limitations. In this study, we went beyond these limitations evaluated differences between TTDs calculated using only (2H) or (3H). We also mobile (derived from TTDs) each tracer. For this, additionally constrained model successfully simulated high-frequency stream measurements 24 over same period (2015–2017). used forested headwater Weierbach (42 ha) Luxembourg. Time-varying were estimated consistently both tracers within framework based on StorAge Selection (SAS) functions. found similar 2H- 3H-derived estimates, despite statistically significant certain measures storage. The mean was at 2.90±0.54 years, 2H, 3.12±0.59 3H (mean ± 1 SD – standard deviation). Both suggested less than 10 % older 5 years. small previous studies other catchments, contrary prior expectations, more pronounced young water. could explained calculation uncertainties limited sampling frequency tritium. conclude do not seem systematically underestimate times Using radioactive reduced uncertainties. Tritium had ability reveal short streamflow. together better exploited specific about longer inherently contains due its decay. two thus different contents overall. slightly informative analysis, lower number samples. future, it would useful similarly test consistency estimates potential those catchments characteristics, considerable fraction since emphasize role decay discriminating younger