Fig. 3 Daily variations in precipitation, air temperature, evaporation, and humidity in the plot from
May 2018 to Jun 2019. The shaded area indicates the rainy season.
3.2 δ18O and δ2H isotope composition of precipitation in Wuhan
As a direct source of soil water in the test area, precipitation dramatically affects the soil water content. Moreover, the change in the precipitation reflects the shift in air environmental factors (temperature and humidity), which is vital for calculating the isotope composition enrichment limit. Herein, it was used as the basis for analyzing the δ18O and δ2H isotopes in soil water at the test site.
As shown in Table 1, the maximum values of δ18O and δ2H in the local precipitation isotopes continue to increase, whereas the minimum values initially increase and subsequently decrease. The overall average value exhibits an increasing trend. The concentration of the majority of the precipitation isotope samples was negative, and there were only five positive values. The reason for the occurrence of these five positive values may have been that the water vapor of these samples had different sources or experienced intense secondary evaporation during their decrease, thus resulting in the enrichment of heavy isotopes and a lack of light isotopes.