The future responses of surface water and groundwater to environmental changes, including land management and climate change, remain subject to high uncertainty due to limited understanding of how water is stored and mixed within the land phase of the hydrological cycle. Isotopes of water and some soluble hydrochemicals can be used as natural tracers to provide greater understanding of how water has been transported and stored from the time that it reaches the land as precipitation until it reappears in surface water streams. An important attribute of these tracers is that they provide a spatially integrated measure of catchment behaviour and responses. Isotopes in water, δ18O and δD can be used to estimate proportions of old and new water in catchment runoff and to estimate the mean residence times of waters in catchments. Hydrochemicals such as DOC and SiO2 and isotopes of Sr are dissolved in water as it is transported through soils and groundwater and can therefore be used to characterise the flow pathways that the water has travelled before reaching streams.

Our research uses solute tracers to help gain understanding of transport processes. We have undertaken monitoring of tracers in nested sub-catchment systems where we have sampled water from precipitation, soil water through-flow, springs and streams. A particular objective of our studies has been to integrate the tracers within hydrological models enabling the complex inter-relationships between spatially and temporally varying processes to be numerically interpreted. The tracer data provide an additional objective function for the models and can therefore help to improve both model structures and their parameterisation.

Our research in this area focuses on:

• Monitoring a range of hydrochemical and isotopic tracers in the field
• Integrating the tracer data within catchment models
• Using the data and models to develop hypotheses of key transport processes and catchment functioning

Who is working in this area?

• Sarah Dunn
• Jeff Bacon
• Pat Cooper

Keywords

• isotope, hydrochemical, tracer, residence times, flow pathways