Hydrochemical and isotope characteristics of spring water discharging from Qiushe Loess Section in Lingtai, northwestern China and their implication to groundwater recharge

The loess plateau in northwestern China with an area of 640000 km², which has developed the loess deposits with a thickness up to 200 m in typical areas, is regarded as a huge carbon stock like the karst area in southwestern China, and plays an important role in regional (even global) carbon cycle. But the spring discharging from loess is poorly known compared with karst spring so far. The objective of this study is to ascertain the characteristics and origin of spring at Qiushe Village, Lingtai County, Gansu Province by hydro-chemical and isotopic methods. The results show that the springs including LGQ, HMQ, YYQ and CZQ are the depression spring and belong to the same shallow aquifer with the well water JZJ. There are not distinct seasonal/diurnal-scale variations on the hydro-chemical characteristics of the spring water (LGQ, HMQ, YYQ, CZQ) and groundwater (JZJ). The hydro-chemical type of groundwater is Ca·Mg-HCO₃. The D and O isotope ratios indicate that the precipitation is the main recharge source of groundwater in study area. And the results of tritium (TU) and Cl concentration suggest that the recharge cycle of groundwater may be more than 60 yrs. Our study shows that the water cycle in loess plateau including rainfall, infiltration, recharge and discharge exerts a continuous impact on carbon stock in loess, which should be paid more attention to in future research on the quantitative reconstruction of paleoclimate.