Abstract:

In order to understand the conversion processes between the surface water and groundwater in a.pngicially recharge lakes in Ningxia Plain, a monitoring profile of the Mingcui Lake shore zone was established to analyze its hydrodynamic, hydrochemistry, and stable isotopes, and to further investigate the source and depth of the groundwater recharge in the lake shore zone. The results of hydrodynamic analysis show that the Mingcui Lake is a typical saturated flow-recharge wetland and the high-water head is the direct driving force for the transformation of lake water to shallow groundwater. Under the influence of regional hydrodynamics, the dynamic response of lake water is close to that of groundwater in the west bank, but relatively weaker than that of groundwater in the east bank. The hydrochemistry results show that the chemical compositions of the shallow groundwater in the flood season is different from that in the dry season in the west bank, while the east bank is relatively stable. The Piper diagram shows that the chemical type of the shallow groundwater is consistent with the surface water during the flood period due to that abundant surface water recharges groundwater. With the decrease of recharge of surface water in dry season, the distribution of groundwater samples is discrete, particularly the difference of chemical compositions between surface water and groundwater at the depth of 30 m. The δD and δ¹⁸O isotopic analysis show that the surface water has clear recharge effect on the groundwater buried less than 10 m in the nearshore area, and the groundwater below 30 m in depth is enhanced by direction-finding runoff. The shallow groundwater above 10 m in the shore zone of the Mingcui Lake is supplied by the lake water and irrigation water accounting for more than 80%. Through comparing the local flow field and stable isotopes at different depths (5m, 10m, and 30m) within various lakeshore zones across the southern, central, and northern regions of Ningxia Plain, we conclude that the exchange depth between the surface water and groundwater in the lakeshore zone of the a.pngicial recharge lake is less than 10 m. Additionally, under a.pngicial recharge conditions, there is a unidirectional and fixed relationship between the groundwater and surface water.

Key words: Ningxia Plain, a.pngicial recharge lake, surface water to groundwater conversion, hydrochemistry, stable isotope