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Gong, Chengcheng

Nom
Gong, Chengcheng
Affiliation principale
Fonction
Doctorant.e
Identifiants
https://libra.unine.ch/handle/123456789/34600

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  • Publication
    Accès libre
    Salix psammophila afforestations can cause a decline of the water table, prevent groundwater recharge and reduce effective infiltration
    (2021-8)
    Zhang, Zaiyong
    ;
    Wang, Wenke
    ;
    Gong, Chengcheng 
    ;
    Zhao, Ming
    ;
    Hendricks Franssen, Harrie-Jan
    ;
    Brunner, Philip 
    Afforestation can reduce desertification and soil erosion. However, the hydrologic implications of afforestation are not well investigated, especially in arid and semi-arid regions. China has the largest area of afforestation in the world, with one-third of the world's total plantation forests. How the shrubs affect evapotranspiration, soil moisture dynamics, and groundwater recharge remains unclear. We designed two pairs of lysimeters, one being 1.2 m deep and the other one 4.2 m deep. Each pair consists of one lysimeter with bare soil, while on the other one a shrub is planted. The different water table depths were implemented to understand how depth to groundwater affects soil moisture and water table dynamics under different hydrological conditions. Soil moisture, water table depth, sap flow, and rainfall were measured concurrently. Our study confirms that for the current meteorological conditions in the Ordos plateau recharge is reduced or even prohibited through the large-scale plantation Salix psammophila. Shrubs also raise the threshold of precipitation required to increase soil moisture of the surface ground. For the conditions we analyzed, a minimum of 6 mm of precipitation was required for infiltration processes to commence. In addition to the hydrological analysis, the density of root distribution is assessed outside of the lysimeters for different water table depths. The results suggest that the root-density distribution is strongly affected by water table depth. Our results have important implications for the determination of the optimal shrub-density in future plantations, as well as for the conceptualization of plant roots in upcoming numerical models.
  • Publication
    Accès libre
    Assessing bare-soil evaporation from different water-table depths using lysimeters and a numerical model in the Ordos Basin, China
    (2019-7)
    Ma, Zhitong
    ;
    Wang, Wenke
    ;
    Zhang, Zaiyong
    ;
    Brunner, Philip 
    ;
    Wang, Zhoufeng
    ;
    Chen, Li
    ;
    Zhao, Ming
    ;
    Gong, Chengcheng 
    In semiarid and arid regions, the evaporation from bare soil is highly sensitive to changes in the depth to the water table. This study quantifies the relation between water-table depth and the groundwater contribution to evaporation in the Ordos Basin in China. In-situ field experiments were combined with numerical simulations of heat, vapor and liquid water flow. Based on lysimeter experiments and a calibrated numerical model, a relation between depth to groundwater and evaporation rate was established for the lysimeter site. In addition, a sensitivity analysis considering the hydraulic conductivity and the inverse of the air-entry pressure (vanGenuchten α) was established. For the field site, the results showed that for the water-table depths less than 52 cm below the ground, evaporation is independent of the water-table depth. For water-table depths exceeding 52 cm, an exponential relation between depth to groundwater and evaporation is observed. No phreatic evaporation occurs for water tables deeper than 105 cm, which is nearly two times the capillary fringe height. The sensitivity analysis showed that the extinction depth decreased with decreasing hydraulic conductivity and increased with α. The field-specific results and the sensitivity analysis provide valuable information to understand the dynamic processes of soil evaporation in the Ordos Basin. From a methodological point of view, the proposed modelling approach and the integration of lysimeter data proved to be a highly efficient combination to study evaporation dynamics in semi-arid and arid environments.