Groundwater recharge mechanism in an integrated tableland of the Loess Plateau, northern China: insights from environmental tracers

Huang, Tianming; Pang, Zhonghe; Liu, Jilai; Ma, Jinzhu; Gates, John

Groundwater recharge mechanism in an integrated tableland of the Loess Plateau, northern China: insights from environmental tracers | Mécanisme de recharge des eaux souterraines dans une zone tabulaire intégrée du plateau de Loess, nord de la Chine: aperçu des traceurs environnementaux Mecanismo de recarga del agua subterránea en una meseta integrada del Loess Plateau, norte de China: conocimientos a partir de trazadores ambientales 基于环境示踪剂的黄土塬区地下水补给机制研究 Mecanismo de recarga das águas subterrâneas em um planalto integrado do Platô Loesse, no norte da China: conhecimentos a partir de traçadores ambientais

2017

Huang, Tianming | Pang, Zhonghe | Liu, Jilai | Ma, Jinzhu | Gates, John

Assessing groundwater recharge characteristics (recharge rate, history, mechanisms (piston and preferential flow)) and groundwater age in arid and semi-arid environments remains a difficult but important research frontier. Such assessments are particularly important when the unsaturated zone (UZ) is thick and the recharge rate is limited. This study combined evaluations of the thick UZ with those of the saturated zone and used multiple tracers, such as Cl, NO₃, Br, ²H, ¹⁸O, ¹³C, ³H and ¹⁴C, to study groundwater recharge characteristics in an integrated loess tableland in the Loess Plateau, China, where precipitation infiltration is the only recharge source for shallow groundwater. The results indicate that diffuse recharge beneath crops, as the main land use of the study area, is 55–71 mm yr⁻¹ based on the chloride mass balance of soil profiles. The length of time required for annual precipitation to reach the water table is 160–400 yrs. The groundwater is all pre-modern water and paleowater, with corrected ¹⁴C age ranging from 136 to 23,412 yrs. Most of the water that eventually becomes recharge originally infiltrated in July–September. 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 shallow groundwater has not been in hydraulic equilibrium with present near-surface boundary conditions. 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.

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