As shown in Fig. 6, along the soil profile, the mean value of
δ18O becomes increasingly negative with increasing
soil depth, and the standard deviation of δ18O
decreases from 1.75 to 0.38 at the surface and stabilizes at 20 cm below
the surface. δ2H exhibits the same trend as
δ18O. It is more of an effect of evaporation on
topsoil. As soil depth increases, the influence of evaporation on soil
water isotope fractionation diminishes. In the same manner as at the low
rainfall point in Hawaii, soil water evaporation intensity is determined
by atmospheric evaporative power and soil water conductivity (Jean C.C
Hsieh,
1998).
Fig. 6 Variation map of
δ18O along the
soil profile, one standard deviation is represented by the
bars.