Hydrological and water quality models are fundamental tools for exploring water, nutrient, and pollutant cycles. However, their applications are often limited by considerable uncertainties in model inputs, structures, and observations.

Tracers provide effective means to address these challenges by identifying the sources of water, nutrients, and pollutants, and by constraining their flow paths and residence times. Incorporating tracers into models can therefore reduce uncertainty, improve parameterization and calibration, and enhance the robustness of process-based understanding.

In this session, we welcome contributions on innovative modelling frameworks that integrate tracers into model development, calibration, and applications across spatial and temporal scales. This covers different tracers, including water stable isotopes, hydrochemical tracers, reactive tracers, biological tracers (e.g., eDNA), and physical tracers (e.g., temperature). Tracer studies using lumped, process-based, data-driven, and hybrid models/approaches that advance hydrological and biogeochemical process understanding are all encouraged.

Potential topics include (but are not limited to):
(1) Development or application of tracer-aided hydrological models (lumped or distributed)
(2) Development or application of tracer-aided water quality models (lumped or distributed)
(3) Development or application of data-driven or hybrid approaches incorporating tracers
(4) Introducing tracers to improve model parameterization, calibration, and evaluation
(5) Using tracers to improve understanding of sources, flow paths, and residence times
(6) Using tracers to test existing theories or explore new concepts in hydrology and biogeochemistry