Recognition on recharge of Shaizhudong spring in the central Weibei, Shaanxi Province, China

Shaizhudong spring is located between middle-low mountains and Weibei loess tablelands. The overall terrain trend of the study area is that it is higher in the northwest than in the southeast.The north area is mainly middle-low mountains with elevations of about 1 200 to 1 600 m, and it mainly consists of exposed or concealed carbonate rocks. In the southwest the terrain gradually decreases, with altitudes of 800 to 1 000 m, and a series of Tangwangling synclinal fold structures consisting of Ordovician clastic and carbonate rocks. The terrain of the southeast area shows a ladder-like decrease and the elevation of the piedmont zone is between 400 and 500 m, which is located between exposed carbonate area and piedmont alluvial-pluvial fan sector. Shaizhudong spring is the largest karst spring in central Weibei, Shaanxi Province, China. Its supply source has been the topic of a lot of research, and it was thought that Jinghe leakage was the main recharge source, and it was the main discharge point in the hiden karst system of shaizhudong spring area. In this paper, we have a different understanding of the recharge of Shaizhudong spring, based on research into hydrogen, oxygen and strontium isotopes, combined with hydro-geochemistry and karst hydrogeological conditions. Isotope hydro-geochemistry study showed that the recharge was given priority to karst groundwater outside southwest of the Shaizhudong spring area. The proportions of atmospheric precipitation, river water and karst water were 11 %, 37 % and 52 % of all the supply source, and proportion in the southwest, northwest and the dam site area karst water were 77.9 %, 19.7 % and 2.4 % in the karst water supplies, respectively. On this basis, this paper also estimates that the average residence time of Shaizhudong spring karst water is 62-64 years based on tritium isotope data.