3.2. Isotopic compositions in precipitation, plant water, soil
water, and groundwater
The δ18O and δ2H values in the two
sites varied greatly between water sources and months (Figure 3).
Generally, the average values of δ2H were -53.86‰,
-52.25‰, -45.95‰, and -38.48‰ for groundwater, precipitation, soil
water, and plant water, respectively. The respective average values of
δ18O were -8.83‰, -8.65‰, -6.93‰, and -2.96‰.
Considering groundwater, precipitation, soil water, and plant water, a
progressive enrichment in δ18O or
δ2H existed from groundwater and precipitation to soil
water to plant water for each month. The δ18O and
δ2H in precipitation water enriched initially and then
depleted significantly from May to October (p < 0.05).
Moreover, the trends of δ18O and δ2H
in plant water responded well to the trends of precipitation from May to
July, but not well from August to October. Likewise, significant
differences were observed for δ18O in plant water
between shrub and grassland sites (p < 0.05), but
non-significant differences were observed for δ2H (p =
0.06>0.05). There were no significant differences in the
δ18O and δ2H of soil water and
across months for the two sites (p>0.05). Groundwater isotopes remained
relatively stable during the sampling period.