资源环境科技发展态势分析平台

Isotope-based hydrograph separation (IHS) is a widely used method in studies of runoff generation and streamflow partitioning. Challenges in choosing and characterizing appropriate tracers and end-members have, however led to presumably highly uncertain IHS results. Here we tested the effects of end-member definitions and tracer choices on IHS results in nested Prairie watersheds of varying size and landscape characteristics. Specifically, the consideration of eight potential new water end-members, eight potential old water end-members, and two stable water isotope tracers led to 80 potential IHS results for each stream water sample. IHS-related uncertainty was evaluated using a Gaussian error propagation method. Results show that choosing an appropriate new water end-member is most challenging during the freshet: highly variable old water fractions associated with high uncertainties were attributed to changing conditions from melting snow only to rain-on-snow. In summer and fall, it was rather the choice of an appropriate old water end-member that was most problematic. IHS results obtained using O-18 versus H-2 as a tracer were significantly different except in the flattest and most wind-sheltered watersheds examined. Overall, H-2-based IHS results were more uncertain than their O-18-based counterparts. Recommendations are therefore made toward careful selection of a tracer and a sampling strategy aimed at characterizing the most appropriate end-members for IHS, especially when dealing with seasonally cold watersheds.