毛乌素沙地包气带气态水同位素特征及其运移规律OA北大核心CSTPCD
Isotopic characteristics and migration of water vapor in the vadose zone of Mu Us Sandy Land
为揭示包气带气态水在大气、土壤和地下水之间交换对内部水与能量传递的响应,该研究应用原位监测、同位素示踪与数值分析相结合的方法,对毛乌素沙地包气带气态水时空变化特征与运移规律进行分析.结果表明,受大气水汽来源和局地循环影响,降水δDL和δ18OL值均表现出春夏富集、秋冬贫化.各深度土壤气态水δ18Oa与液态水δ18OL值呈显著正相关(P<0.01),但在季节上,春夏季为极显著线性正相关(P<0.01),而秋冬季则无显著相关性(P=0.12).表层水汽通量的增大伴随δ18Oa富集,而水汽密度夏季的增大和冬季的减小均表现出表层δ18Oa富集,夏季蒸发比冬季冻结更能引起表层土壤δ18Oa富集.受包气带温度梯度驱动影响,夏季土壤深部气态水接受浅层水汽补给,冬季浅层接受中深层水汽的补给,而春、秋季剖面分别存在温度聚合和发散零通量面,使得补给关系复杂.该研究明确了土壤δ18Oa的变化受水汽迁移模式、大气蒸发能力和土壤冻融的共同控制,表层δ18Oa的富集在冬季受蒸发与向上的水汽传输共同影响,而夏季主要受土壤水的昼夜蒸发与凝结循环作用所致,该结果为厘清土壤水汽迁移机制以及进一步阐明包气带水循环过程提供科学依据.
Vapor-water exchange among atmosphere,soil and groundwater plays an important role in the surface ecological restoration in the vadose zones of arid and semiarid regions.However,it is limited to in-situ monitoring of water vapor flux,due to the complex and uncertain process.The simulation of water vapor cannot be fully verified by the measurement.It is still lacking in the vapor-water migration at different spatial and temporal scales.This study aims to clarify the spatiotemporal variation and migration of vapor-water exchange in the vadose zone of Mu Us Sandy Land by in-situ vapor-water monitoring,isotope tracer and numerical analysis.The results showed that the δDL and δ18OL of precipitation were enriched in spring and summer,but depleted in autumn and winter,due to the atmospheric water vapor source and local circulation.Soil evaporation was enriched in the oxygen isotope(δ18Oa)of surface soil vapor-water in summer more than that of soil freezing in winter.Moreover,there was a significant positive correlation(P<0.01)in the δ18O profile of the soil vapor-water and liquid water at different depths.The reason was that the evaporation intensity source and migration mode of soil vapor-water varied greatly in seasons.The δ18O values of vapor water in spring and summer showed an extremely significant linear positive correlation with the liquid water(P<0.01),while there was no significant correlation in winter(P=0.12).Moreover,there was a positive linear relationship between water vapor flux and δ18Oa.Furthermore,the δ18Oa was enriched in the surface layer at the large water vapor flux,including both downward and upward migration.The surface δ18Oa was enriched in the period of soil freezing in winter,particularly with the decrease of water vapor density(November-March).But the surface layer δ18Oa increased in summer(May-October)as well with the increase of surface water vapor density.Driven by the gradient of soil temperature in the vadose zone,the replenishment relationship of water vapor throughout the profile varied greatly at different periods.The water vapor of shallow soil was the supply source of deep vapor-water in summer,while the recharge was received from the deep layer in winter.But there were the temperature convergence and divergence zero flux planes in spring and autumn,respectively.The recharge characteristics caused the complicated relationship of vapor recharge in the profile.The soil δ18Oa was controlled by the water vapor migration,atmospheric evaporation and soil freeze-thaw in the vadose zone.In winter,the reduced evaporation and upward transport of water vapor can concurrently cause to enrich the surface δ18Oa,thus resulting in a decrease in the correlation between soil water vapor δ18Oa and liquid water δ18OL.While in summer,the dominant effect can be from the diurnal evaporation and condensation cycle of soil water.The findings can provide a scientific basis to clarify the migration of soil water vapor in the water circulation
刘秀花;田书林;马延东;贺屹;石长春;郑策
长安大学水利与环境学院,西安 710054||旱区地下水与生态效应教育部重点实验室,西安 710054||水利部旱区生态水文与水安全重点实验室,西安 710054陕西省林业科学院,西安 710082陕西省林业科学院,西安 710082||陕西榆林毛乌素沙地荒漠生态系统国家定位观测研究站,榆林 719000
农业科学
气态水同位素水汽迁移包气带毛乌素沙地
water vaporisotopeswater vapor migrationvadose zoneMu Us sandy land
《农业工程学报》 2024 (004)
112-120 / 9
国家自然科学基金项目(42372288,42202279);中央高校基本科研业务费专项(300102292904)
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