The Nanxiaohegou basin is a typical watershed in the gully region of the Loess Plateau, China. The stable isotopes of hydrogen and oxygen and the hydrochemistry of the surface water and groundwater in the region were characterized in this study. The interaction between the surface water and groundwater in the region was demonstrated based on stable isotopes and hydrochemical methods. Results show that the δD and δ18O values of precipitation change according to the seasons with high values in spring and summer and low values in autumn and winter. The δD and δ18O values of the reservoir water are higher in summer and autumn, while they are lower in the winter and spring. The seasonal variation of δD and δ18O in groundwater is not significant. The surface water and groundwater in the watershed mainly belong to Na·Mg-HCO3-type water. The hydraulic conductivity of surface water and groundwater is characterized by high values in winter and low values in summer. Results on stable isotopes and hydrochemistry indicate that local precipitation and deep groundwater may be the main recharge sources of surface water (reservoir water, channel water) and spring water in the Nanxiaohegou basin. The perennial spring in the basin may be mainly replenished by deep groundwater, while seasonal springs are replenished by deep groundwater and local precipitation, such as the springs of Dongzhuanggou and Yangjiagou sub-basins. This study provides a greater understanding of the hydrological processes in the gully region of the Loess Plateau.
Keywords: electric conductivity; gully region of the Loess Plateau; hydrochemistry; hydrogen and oxygen stable isotopes; surface water and groundwater.