Using stable isotopes as tracer to investigate hydrological condition and estimate water residence time in a plain region, Chengdu, China

The oxygen and hydrogen isotopic compositions (delta O-18 and delta H-2) were measured on river water and precipitation collected from four sub-catchments within the upper Tuojiang River catchment. delta O-18 values of river water and precipitation exhibit significant seasonal variations. These seasonal variations are used for estimating the mean residence time (MRT) for four sub-catchments by an exponential model, ranging from 346 to 493 days. The correlation between catchment MRT and mean slope of the catchment (r(2)=0.29) is weak, while the correlations between catchment MRT, catchment area (r(2)=0.79) and topographic index (r(2)=0.98) are strong. These results indicate that topography and catchment area, both control the catchment MRT and the topographic index may be a reliable parameter for estimating the catchment MRT. Moreover, the relationship between land use types and MRT was investigated. The results show that paddy fields (r(2)=0.95) compared to the other land use types may have a greater impact on the MRT of the irrigation-dominated catchment. This study provides a preliminary exploration of the factors affecting MRT in the plain region and a basis for simulating MRT in the future.

Automated summary

This study investigated the mean residence time (MRT) in the upper Tuojiang River catchment using oxygen and hydrogen isotopic compositions, finding that topography and catchment area significantly influence MRT, with the topographic index being a reliable parameter for estimating MRT. Additionally, the study discovered that paddy fields may have a greater impact on MRT compared to other land use types in irrigation-dominated catchments, providing a basis for simulating MRT in the future.