Mechanism of groundwater recharge in the thick loess deposits by multiple environmental tracers

The loess−covered region accounts for ∼10 % of global land surface. Because of dry climate and thick vadose zones, the subsurface water flux is low but the water storage is relatively large . As a result, the groundwater recharge mechanism is complicated and currently controversial (e.g., piston flow or dual mode with piston and preferential flow). Taking typical tablelands in China's Loess Plateau as example study area, this study aims to qualitatively and quantitively evaluate the forms/rates and controls of groundwater recharge considering space and time. We collected 498 precipitation, soil water and groundwater samples in 2014–2021 for hydrochemical and isotopic analysis (Cl−, NO3−, δ18O, δ2H, 3H and 14C). A graphical method was employed to determine appropriate model to correct 14C age. Dual model exhibited in the recharge: regional−scale piston flow and local−scale preferential flow. Piston flow dominated groundwater recharge with a proportion of 77 %–89 %. Preferential flow gradually declined with increasing water table depths, and the upper depth limit may be