Multi-objective fitting of concentration–discharge relationships (loads and concentrations)

Concentration–discharge (C–Q) relationships are widely used to assess the link between hydrological and biogeochemical processes at catchment scale. They can be fitted to represent either concentrations or discharge-weighted concentrations (i.e., load). In this technical note, we test a multi-objective calibration using both concentration and load, and compare it to a mono-objective calibration applied on either concentrations or load: although widely used in hydrological modeling, multi-objective calibrations are rarely applied to fit C–Q relationships. The multi-objective calibration yielded parameters which were more representative of the concentration behavior during the rarest high-flow events, avoiding issues of under-representation of high-discharge, low-concentration periods. In this technical note, we use the multi-objective calibration on a high-frequency dataset acquired on the ORACLE-Orgeval Observatory (France).