10 May 2022
10 May 2022
Status: a revised version of this preprint is currently under review for the journal HESS.

Exploring tracer information in a small stream to reduce the uncertainty and enhance the process interpretation of transient storage models

Enrico Bonanno1,2, Günter Blöschl2, and Julian Klaus3 Enrico Bonanno et al.
  • 1Catchment and Eco-Hydrology Group, Luxembourg Institute of Science and Technology, Belvaux, Luxembourg
  • 2Institute of Hydraulic and Water Resources Engineering, Vienna University of Technology, Vienna, Austria
  • 3Institute of Geography, University of Bonn, Bonn, Germany

Abstract. The transport of solutes in river networks is controlled by the interplay of processes such as in-stream solute transport and the exchange of water between the stream channel and dead zones, in-stream sediments, and the hyporheic zone. Transient storage models (TSMs) are a powerful tool for testing hypotheses related to solute transport in streams. However, TSM parameters are often non-identifiable leading to an unclear understanding of the processes controlling solute transport in streams. In this study, we increased parameter identifiability in a set of tracer breakthrough experiments by combining global identifiability analysis and dynamic identifiability analysis. We compared our results to inverse modelling approaches (OTIS-P) and the commonly used random sampling approach for TSMs (OTIS-MCAT). Compared to OTIS-P, our results informed about sensitivity and identifiability of TSM parameters on the entire feasible parameter space. Our results clearly improved parameter identifiability compared to OTIS-MCAT that often indicated non-identifiability of TSM parameters. Non-identifiable results led to wrong solute retention times in the storage zone and the exchange flow with the storage zone, with a difference respectively up to four and two orders of magnitude compared to results with identifiable TSM parameters. The severe differences in the transport metrics between results obtained from our proposed approach and results from OTIS-MCAT model also resulted in contrasting interpretation of the hydrologic processes controlling solute transport at the study site. Thus, our outcomes point to the risks of interpreting TSM results when even one of the TSM parameters is non-identifiable. Our results showed that there is clear potential for increasing parameter identifiability in random sampling approaches for TSMs and for advancing our understanding of hydrological processes controlling in-stream solute transport.

Enrico Bonanno et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2022-149', Anonymous Referee #1, 20 May 2022
    • AC1: 'Reply on RC1', Enrico Bonanno, 07 Jun 2022
  • RC2: 'Comment on hess-2022-149_3', Anonymous Referee #2, 13 Jun 2022
    • AC2: 'Reply on RC2', Enrico Bonanno, 29 Jun 2022
  • RC3: 'Comment on hess-2022-149', Anonymous Referee #3, 22 Jun 2022
    • AC3: 'Reply on RC3', Enrico Bonanno, 30 Jun 2022

Enrico Bonanno et al.

Data sets

HYDRO-CSI, Project 1.2: In-stream hydrology. Part 2: instantaneous injections Enrico Bonanno; François Barnich; Laurent Gourdol; Jean François Iffly; Jérôme Juilleret; Laurent Pfister; Klaus Julian

Model code and software

BTC_analysis Enrico Bonanno

Enrico Bonanno et al.


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Short summary
There is an unclear understanding of what processes regulate the transport of water, solutes, and pollutants in streams. This is crucial since these processes control water quality in river network. Compared to other approaches, we obtained clearer insights on the processes controlling solute transport in the investigated reach. This work highlight the risks of using uncertain results for interpreting the processes controlling water movement in streams.