ИСТИНА

Shallow groundwater is an important source of water for the maintenance and restoration of ecosystems in arid environments, which necessitates a deeper understanding of its complex spatial and temporal dynamics driven by hydrological processes. This presentation explores the dominant hydrological processes that control the shallow groundwater dynamics in the Gobi Desert-riparian-oasis system of the lower Heihe River, a typical arid inland river basin located in northwestern China. The dynamic behaviour patterns of the groundwater level at most sites are characterized by a declining trend during the period from spring to autumn and a slightly increasing trend in the winter months. The seasonal variations of the water table are determined by the rate of evaporation and lateral groundwater recharge via riverbank filtration. Further, the water table fluctuation (WTF) method was used to investigate groundwater evapotranspiration (ETg) processes at two sites dominated by phreatophytes (Tamarix ramosissima and Populus euphratica). The average ETg rate during the summer months (June–August) of 2010-2012 was estimated to be 0.63-0.73 mm/d at the site dominated by Tamarix ramosissima and 1.89-2.33 mm/d at the site dominated by Populus euphratica, depending on climatic conditions, vegetation status, and depth to water table. Additionally, a coupled river-aquifer numerical model was used to calculate the river leakage in the main stream of natural rivers from April 20, 2010 to April 21, 2012. The results showed that the amount of river water leakage was about 2.51×108 m3, which accounted for approximately 32% of the amount of river flow. The river filtration rate is mainly determined by the streambed vertical hydraulic conductivity, which is highly dependent on the river water temperature that varies from 0 to 20 °C.