湘东北地区大气降水和地下水的氢氧稳定同位素研究

Variation of stable hydrogen and oxygen isotopes in precipitation and groundwater in northeast Hunan

深入认识湘东北地区的水文循环过程,对规范该区水资源的有效利用和减缓该区生态环境问题具有重要意义。2021年10月—2023年2月,每月对该区金井镇的大气降水和不同深度(约4.7 m和61 m)井水开展样品采集和测试。该区大气降水稳定同位素值(δ^(18)O、δD)呈现夏半年偏负、冬半年偏正,且氘盈余、水汽通量和HYSPLIT模型分析结果显示,影响该区夏季降水的气团主要来自暖湿的海洋洋面,冬季主要来自稳定的南支西风和局地水汽输送。浅井水和深井水的δ^(18)O和δD与该区大气降水δ^(18)O和δD的均值接近,变幅较小且呈现夏季偏正冬季偏负的特征,说明地下水受到大气降水的补给,但可能滞后于大气降水的变化。然而,不同深度地下水对大气降水的响应机制和滞后时间,还需进一步研究。

Background,aim,and scope There are abundant water resources in the middle and lower reaches of the Yangtze River,where the water resources and ecology problems are becoming more and more prominent.Thus,the research with thorough understanding of the hydrological cycle process is of great significance for regulating the effective utilization of water resources and mitigating the ecological environment problems in northeast Hunan.Here,isotopic monitoring and analysis of atmospheric precipitation and well water with different depths in Jinjing Town,Changsha County,northeast Hunan Province,are carried out to preliminarily explore the hydrological cycle,and to improve the management of water resources and ecological environment in this area.Materials and methods During October 2021 to February 2023,precipitation and well water with different depths(~4.7 m and~61 m)in Jinjing area were collected monthly.And the stable hydrogen and oxygen isotopes(δD,δ^(18)O)in precipitation and well water are tested and analyzed.Monthly precipitation dexcess,are calculated fromδ^(18)O andδD.The meteorological data of Jinjing are downloaded from Changsha Meteorological Resource Sharing Public Platform.The integrated moisture transport flux(from surface to 300 hPa)are from National Climate Centre,China Meteorological Administration Hybrid Single Particle Lagrangian Integrated Trajectory Model is from National Oceanic and Atmospheric Administration,U.S.Department of Commerce.Results The behavior ofδ^(18)O,δD and dexcess in precipitation present significant seasonal variation,with lower value in summer and higher value in winter.Theδ^(18)O andδD in well water is little fluctuation,but with lower value in winter and higher value in summer.Discussion The changes ofδ^(18)O andδD in precipitation are mainly controlled by the source of moisture or associated air mass and the degree of rain removal during its transmission path,in addition to the effect of rainfall amount.Although the original source of groundwater is precipitation,groundwater exhibits little and opposite seasonal variation compared with precipitation.This may be resulted from groundwater recharge by precipitation need the media of surface water,which is a long-term process and could generate a lag response of groundwater to precipitation.Besides,theδ^(18)O andδD in shallow well water show a larger fluctuation than that of deep phreatic water in summer,implied the shallow groundwater is more susceptible to external environment.Conclusions Theδ^(18)O andδD in precipitation present significant seasonal variation,which may be resulted from the change of source of moisture or associated air mass and the degree of rain removal in the upstream regions,in addition to the influence of rainfall amount.There is a strong connection between precipitation and groundwater,although the variation ofδ^(18)O andδD in well water with small range is contrast with that of precipitation.And the shallow groundwater is more susceptible to external environment.Recommendations and perspectives Long-term stable isotopic monitoring of water bodies and improved sampling designments are still needed to better understand hydrological cycle processes.The results of this study show the relationship between groundwater and precipitation,which may be helpful for water resources management in this area.