Characteristics of hydrogen and oxygen isotopes in the groundwater and formation mode of the Beihai springs in the northern Laiyuan Basin

As the source of the Jumahe River, the Juma springs has received the attention of many experts and scholars. Previous studies focused mainly on the chemical and dynamic characteristics of the groundwater and the spring discharge characteristics, the hydrogen and oxygen isotopes characteristics were seldom examined, and the explanation of the causes of the Beihai springs was only a rough qualitative overview. To illustrate the characteristics of hydrogen and oxygen isotopes of the groundwater in the northern Laiyuan Basin and reveal the forming mode of the Beihai springs in detail, groundwater samples in different aquifers were systematically collected for the first time in the study are area and the hydrogen and oxygen isotopic components were determined in this paper. The results show that the values of δD and δ¹⁸O in the water samples fall on or near the regional meteoric water line, indicating that the meteoric water is the main recharge source of the groundwater. The altitude effect is obvious and the groundwater flow path is long for the groundwater in the dolomite aquifer and limestone aquifer, the groundwater flow path is short and the evaporation effect is strong for the groundwater in the unconsolidated sediment aquifer. The deuterium excess of the sample in the dolomite aquifer, limestone aquifer and unconsolidated sediment aquifer are 6.0‰−11.6‰, 4.2‰−11.2‰ and 3.8‰−8.0‰, respectively, much smaller than that in the meteoric water, showing that the karst water and the pore water undergo different processes. When the groundwater in the dolomite aquifer and limestone aquifer flows from the recharge areas to the discharge areas, hydraulic connection and mixing occur in the fault zone near Xiaoxizhuang and Xianglutun. Groundwater rises during the process of flow to the center of the basin because of the resistance effect of the fault, and groundwater in the dolomite aquifer and limestone aquifer is subsequently recharged by the pore water in the unconsolidated sediment aquifer, at last the groundwater emerges on the ground surface in the form of springs as the Beihai springs. Before the pore water joins in, the average recharge comes from the limestone aquifer and dolostone aquifer is about 48.4%−57.6% and 42.4%−51.6%, respectively.