关键词: 地下水补给河水')">

地下水补给河水, 定量评价, 时空变化, 模型, 马莲河

Abstract: The Malian River,located in the southwestern portion of the Ordos Basin,Inner Mongolia,China,is a secondary tributary of the middle reaches of the Yellow River.It has experienced mounting pressure from exploration and utilization of water resources,so the area has been facing serious water shortages and deterioration of water quality.Finding accurate ways to quantify groundwater discharge to the river is critical for protecting and managing the water resources in the area.To study the spatial and temporal variations of groundwater recharge,we collected 75 samples of surface water and groundwater in the stretch of the river downstream of the Malian River during premonsoon,monsoon,and postmonsoon seasons.A multitracer mass balance approach was applied to identify the location,amount,and seasonal variations of groundwater discharge.We used Cl^- concentrations and electrical conductivity in conjunction with oxygen and hydrogen isotopes.We observed general decreases in Cl^- concentrations (387.20-707.42 mg·L^-1) and EC (1 705.40-3 123.60 μs·cm^-1),as well as δ¹⁸O (-10.41‰--6.30‰) and δD values (-78.25‰--54.88‰) as we moved downstream.The Cl^- concentrations and EC values reached their minimum values during the monsoon season,when δ¹⁸O and δD values peaked.All of the tracers had lower concentrations or isotope ratios in the groundwater than they did in the river water.Groundwater values included Cl^- concentrations (115.92-255.96 mg·L^-1),EC (409.58-196.84 μs·cm^-1),δ¹⁸O (-11.19‰--9.11‰),and δD (-79.80‰--68.28‰).No evident spatial or temporal variations in groundwater tracers were observed.All the groundwater samples had δD and δ¹⁸O values close to the Local Meteoric Water Line,indicating that groundwater was recharged by precipitation and experienced limited evaporation.The river water was generally more enriched in δD and δ¹⁸O,which may have resulted from evaporation.Groundwater discharge rates varied spatially and temporally.Groundwater in the upper and lower segments had much higher discharge rates (accounting for 72.20%-95.07% of the total) than that in middle segment.The percentage of base flow in the river discharge was 68.89% during the premonsoon and 71.19% during the postmonsoon season.Groundwater inflows decreased sharply during monsoon season,with the ratio of base flow only accounting for 29.43% of the total river discharge.In general,the seasonal variations in groundwater discharge to the river were pronounced,while spatial variation was not evident.The extent of interactions between river water and groundwater was mainly dominated by the geological and hydrogeological settings and conditions,such as the aquifer thickness,water hydraulic gradient,and riverbed permeability,so no spatial variations related to the stable conditions in the downstream direction were evident.Uncertainties remain in the model.However,when used correctly,a multitracer method can be applied to provide detailed information on the spatial distribution of groundwater discharge,especially in gaining rivers.This study could provide a theoretical basis and technical support for better understanding the interactions between river water and groundwater,as well as the sustainable development of water resources and ecological and environmental protection.

Key words: groundwater discharge to river,  , quantification,  , spatial and temporal variations,  , model,  , the Malian River