庞忠和, 黄天明, 杨硕, 袁利娟. 2018: 包气带在干旱半干旱地区地下水补给研究中的应用. 工程地质学报, 26(1): 51-61. DOI: 10.13544/j.cnki.jeg.2018.01.006
    引用本文: 庞忠和, 黄天明, 杨硕, 袁利娟. 2018: 包气带在干旱半干旱地区地下水补给研究中的应用. 工程地质学报, 26(1): 51-61. DOI: 10.13544/j.cnki.jeg.2018.01.006
    PANG Zhonghe, HUANG Tianming, YANG Shuo, YUAN Lijuan. 2018: THE POTENTIAL OF THE UNSATURATED ZONE IN GROUNDWATER RECHARGE IN ARID AND SEMIARID AREAS. JOURNAL OF ENGINEERING GEOLOGY, 26(1): 51-61. DOI: 10.13544/j.cnki.jeg.2018.01.006
    Citation: PANG Zhonghe, HUANG Tianming, YANG Shuo, YUAN Lijuan. 2018: THE POTENTIAL OF THE UNSATURATED ZONE IN GROUNDWATER RECHARGE IN ARID AND SEMIARID AREAS. JOURNAL OF ENGINEERING GEOLOGY, 26(1): 51-61. DOI: 10.13544/j.cnki.jeg.2018.01.006

    包气带在干旱半干旱地区地下水补给研究中的应用

    THE POTENTIAL OF THE UNSATURATED ZONE IN GROUNDWATER RECHARGE IN ARID AND SEMIARID AREAS

    • 摘要: 在干旱半干旱地区,包气带的溶质和同位素剖面不但可以提供较长时间尺度上的地下水补给信息,而且记录了过去气候变化与环境变化信息。本文基于学科组近10年的研究成果,以鄂尔多斯盆地为例(包括南部的黄土高原和北部的沙漠高原),将包气带和饱和带结合起来,利用多种环境示踪技术,提升了包气带在干旱半干旱地区地下水研究中的潜力,并将其应用到地下水补给历史重建、地下水补给机制确定、植被变化对地下水补给影响评价和地下水污染物全过程示踪中。研究表明,由于在干旱半干旱地区,包气带较厚且补给量有限,地下水和现今的浅表水文过程未达到水力平衡,如在沙漠高原西部,近2 500 a降水尚储存在包气带13 m以浅,地下水是4 000 a以前补给的,其水化学特征与浅部包气带水差异巨大;而在黄土高原,补给量较大,但包气带巨厚,年降水仍需要几十到上百年时间入渗到地下水(但并不意味着没有补给,其土壤水在包气带中平均入渗速率为0.1~0.3 m·a-1),包气带浅部溶质含量较深部和地下水中的高;典型黄土塬区的地下水均不含氚,地下水年龄在几百到上万年。黄土内部层状均匀的土壤质地特征和相对较老的地下水年龄揭示的均匀活塞流入渗是黄土塬区浅层地下水补给的主要方式。黄土高原退耕还林还草和沙漠区植被恢复导致地下水补给呈现不同程度的减少,反映在包气带上表现为溶质含量的增加,可用于定量化确定地下水补给量的变化。本文强化了包气带在干旱半干旱地区地下水补给研究中的作用,在未来地下水资源评价、地下水污染全过程刻画中应得到重视。

       

      Abstract: The solute and isotope profile of the unsaturated zone(UZ)in arid and semiarid areas, can not only provide groundwater recharge information, but also record the past climate and environment changes. Based on the last 10-year's study in the Ordos Basin(including the Loess Plateau in the south part and the desert plateau in the north part), we have combined evaluations of the thick UZ with those of the saturated zone and used multiple tracers to promote the potential of UZ in groundwater study in arid and semiarid areas, including reconstruction of groundwater recharge history, determination of groundwater recharge mechanism, assessment of impact of vegetation changes on groundwater recharge and evaluation of whole processes of groundwater pollution. the results show that shallow groundwater in arid and semiarid areas is often not in equilibrium with near-surface boundary conditions. This is especially the case where the unsaturated zone is thick and recharge rate is limited. A case study from west part of the desert plateau in the Ordos Basin shows that the present diffuse recharge beneath the grassland is 0.11-0.32 mm/year, based on the chloride mass balance of seven soil profiles. the chloride accumulation age is approximately 2, 500 years at a depth of 13 m in the unsaturated zone. the average Cl content in soil moisture in the upper 13 m of the unsaturated zone ranges from 2, 842 to 7, 856 mg·L-1, whereas the shallow groundwater Cl content ranges from 95 to 351 mg·L-1. the corrected 14C age of shallow groundwater ranges from 4, 327 to 29, 708 years. in typical tablelands in the Loess Plateau, the length of time required for annual precipitation to reach the water table ranges from decades of years to hundreds of years with soil moisture velocity of 0.1 to 0.3 m·a-1 and shallow groundwaters are all pre-modern water and paleowater, the Cl and NO3 contents in the upper UZ are considerably higher than those in the deep UZ and shallow groundwater because of recent human activities. the homogeneous material of the UZ and relatively old groundwater age imply that piston flow is the dominant recharge mechanism for the shallow groundwater in the tableland. The"Returning Farmland to Forest and Grassland" project in the Loess Plateau and plantations in desert areas have decreased groundwater recharge and increased solute content in UZ moisture, which can be used to quantitatively determine the changes in recharge rates. the paper has strengthened the role of the UZ in groundwater recharge study in arid and semiarid area, to which should be paid more attention in groundwater resources assessment and groundwater pollution investigation.

       

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