Simulating the water δ18O of a small open lake in the East Asian monsoon region based on hydrologic and isotope mass-balance models

Abstract

• The systematic observations benefit the lake water isotopes (δ L ) simulations. • This study well simulated the temporal variations of δ L of a small and open lake. • The MBM captured the influences of extreme weather events on the δ L . • The sensitivity test well evaluated the influences of weather seasonality on the δ L . Hydrologic and isotope mass-balance models (MBMs) are useful tools for the simulation and quantitative interpretation of lake water δ 18 O (δ L ). Such studies of small, open lakes are important because δ L may show large responses to weather-driven hydrological variability. A δ L sequence was simulated for three-year and five-day interval data from Taozi Lake, a small, open lake in Changsha, in the East Asian monsoon region of China. The MBMs performed well, with the optimal model explaining 90% of the observed δ L variability. However, it was necessary to parameterize the precipitation input by increasing the lake water depth during heavy precipitation events to capture the observed sharp decreases in δ L . We found that the MBMs using air temperature and the equilibrated atmospheric vapor δ 18 O (δ A ) produced a more negative δ L compared to the model using the surface water temperature and the observed δ A , and that the equilibrated δ A was somewhat arbitrary, which introduced a large error in the model output. A sensitivity test highlighted the importance of the seasonal variability of hydrometeorological and isotopic variables to reproduce the observed δ L variability. Additionally, the simulated average δ L showed a similar pattern of variation to the meteorological variables shifted by different ratios, but for the relative humidity, there was only a narrow window within which a realistic δ L series could be reproduced. Our results show that a realistic MBM can be established based on long-term observations, with implications for studies of hydrologic processes and paleoclimate reconstruction.