Ion sources and seasonal recharge characteristics of groundwater around Dali Lake in semi-arid region of Inner Mongolia Plateau, China

The interaction between groundwater and surface water around an inland lake in semi-arid regions creates a unique ecological pattern and is a key link in the regional ecohydrological cycle. In this paper, the major ions and hydrogen and oxygen isotope characteristics of groundwater, lake water, river water, and rain water were analyzed, which were sampled in Dali Lake and its surrounding areas in the dry and wet seasons. The ion ratio method and the end-member mixing analysis (EMMA) based on principal component analysis (PCA) were applied. The causes of the major ions in groundwater during the dry and wet seasons were analyzed. The temporal and spatial recharge sources and characteristics of groundwater were identified and quantified. The hydraulic relation between groundwater and surface water was clarified. The main hydrochemical type of groundwater was Ca-HCO₃ with changed to Ca-Mg-Cl type in some areas in the wet seasons. Rock weathering was the main genetic mechanism of groundwater hydrochemistry which mainly from the dissolution of silicate. River water and precipitation were the main sources of groundwater recharge. However, there was a large difference in spatio-temporal distribution and recharge contribution. Gongar River water and precipitation were the main recharge sources of groundwater during the dry season with a contribution rate of 49 % and 48 % respectively. Haolai River water and Liangzi River water together became the main recharge sources of groundwater during the wet season with a contribution rate of between 83 % and 92 %. Rain water covered from 7 % to 13 % of groundwater recharge during the wet season. Overall, compared with river water and precipitation, the contribution of lake water to groundwater recharge was almost negligible, ranging from 0 % to 6 %.