5 Conclusion
Stable isotopes (δD and δ18O) of precipitation,
surface water, and groundwater were used to determine the groundwater
recharge mechanism and the spatial-temporal variation pattern in the
Loess hilly region. The hydrogen and oxygen isotopes of precipitation
was most enriched, followed by surface water and then groundwater(this
having the most depleted isotopes). The hydrogen and oxygen isotopes of
the three water bodies were all gradually enriched from the gully head
to the downstream in the small watershed. The transmission time of the
precipitation and surface water to groundwater were 443.16 d and 64.58
d, respectively; and the corresponding groundwater recharge ratio were
29.22% and 70.78%, respectively. The main recharge source of
groundwater in the Loess hilly region was surface water. The connection
between precipitation and groundwater in the rainy season was stronger
than that in the dry season, and the ratios of recharge were 32.83% and
25.60%, in the rainy and dry season, respectively. The groundwater
recharge ratio by precipitation in upstream was larger than downstream.
Meanwhile, the recharge ratio by surface water in upstream was smaller
than the downstream. At the same time, the main recharge area for
groundwater was
located
upstream in the small watershed of loess hilly region, while the main
discharge area for groundwater was located downstream.