25 Apr 2022
25 Apr 2022

Disentangling Scatter in Long-Term Concentration-Discharge Relationships: the Role of Event Types

Felipe Saavedra1, Andreas Musolff2, Jana von Freyberg3,4, Ralf Merz1, Stefano Basso1, and Larisa Tarasova1 Felipe Saavedra et al.
  • 1Department Catchment Hydrology, Helmholtz Centre for Environmental Research-UFZ, Halle (Saale), 06120, Germany
  • 2Department of Hydrogeology, Helmholtz Centre for Environmental Research-UFZ, Leipzig, 04318, Germany
  • 3School of Architecture, Civil and Environmental Engineering, EPFL, 1015 Lausanne, Switzerland
  • 4Mountain Hydrology and Mass Movements, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), 8903 Birmensdorf, Switzerland

Abstract. Relationships between nitrate concentrations and discharge rates (C-Q) at the catchment outlet can provide insights into sources, mobilization and biogeochemical transformations of nitrate within the catchment. Nitrate C-Q relationships often exhibit considerable scatter that might be related to variable hydrologic conditions during runoff events at sampling time, corresponding to variable sources and flow paths despite similar discharge rates. Although the origins of this scatter was investigated in individual catchments, the role of different runoff event types on the C-Q relationships across a large dataset of catchments was not yet evaluated.

In order to better understand the role of different runoff events in shaping long-term C-Q relationships, we analyzed low-frequency nitrate data from 184 German catchments, and quantified the deviation of samples collected during different types of events from the long-term power-law C-Q relationships. In most of the catchments, snow-impacted events produce positive deviations of concentrations, indicating an increased nitrate mobilization compared to the long-term pattern. In contrast, negative deviations occur mostly for rainfall-induced events with dry antecedent conditions, indicating lower nitrate concentrations. Pronounced differences in event runoff coefficients among different event types indicate their contrasting levels of hydrologic connectivity that in turn might play a key role controlling nitrate transport due to the activation of faster flow paths between sources and streams. Our study demonstrates using long-term, low-frequency nitrate data that runoff event types shape observed scatter in long-term C-Q relationships according to their level of hydrologic connectivity.

Felipe Saavedra 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 egusphere-2022-205', Anonymous Referee #1, 03 Jun 2022
    • AC1: 'Reply on RC1', Felipe Saavedra, 18 Jul 2022
    • AC3: 'Reply on RC1', Felipe Saavedra, 18 Jul 2022
  • RC2: 'Comment on egusphere-2022-205', Anonymous Referee #2, 15 Jun 2022
    • AC2: 'Reply on RC2', Felipe Saavedra, 18 Jul 2022

Felipe Saavedra et al.

Data sets

WQQDB - water quality and quantity data base Germany Andreas Musolff

CCDB - catchment characteristics data base Germany Ebeling, P., R. Kumar, A. Musolff

Model code and software

Classified runoff events Tarasova L., Basso, S., Wendi, D., Viglione, A., Kumar, R., and R. Merz (2020)

Felipe Saavedra et al.


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Short summary
Nitrate contamination of rivers from agricultural sources is a challenging problem for water quality management. During runoff events of different generation processes, different transport paths within the catchment might be activated, generating a variety of responses in nitrate concentration in stream water. Using data for 184 German catchments we demonstrate that wetness conditions during runoff events at the time of sampling are a key control of nitrate transport from catchments to streams.