Study on the precipitation-silty soil moisture-groundwater transformation of Quaternary Upper Pleistocene stratum in the northern margin of the Jianghan Plain

In recent years, researches on soil moisture transport in vadose zone around the world mainly focus on sand, loam, clay loam and loess in arid or semi-arid areas but little research on moisture transport in silty soil in humid climate areas. It is generally believed that vertical infiltration recharge of precipitation in plain area is the main recharge mode of shallow groundwater over the last decades, but whether the soil moisture can transport through thick silty soil to shallow confined aquifer or not and what is the recharge mode of the shallow confined aquifer covered by thick silty soil (fig. 1) in subtropical monsoon climate plain area just like Jianghan Plain are still unknown. We built a field test site in 2018 with different probes to monitor factors including rainfall, evaporation, groundwater level and soil moisture, soil water potential, soil temperature, soil salinity at different soil layers. All the data except groundwater level are collected through wireless transmission and processed by using Excel 2010, Origin 2017 and Auto CAD 2007. We found the maximum depth of silty soil affected by evaporation. We divided the silty soil into five layers from top to bottom: the sensitive layer of rainfall infiltration, the delayed layer of rainfall infiltration, the migration layer of rainfall, the stable layer of soil moisture and the groundwater affected layer. There is a positive correlation between the dynamic change of groundwater level and the lower interface elevation change of soil moisture stable layer. In my opinion, it is not precise enough to evaluate the recharge just by using surface hydraulic conductivity of soil, we should take the structural heterogeneities into consideration. The reaction of soil moisture in different layers to rainfall and groundwater level reveals the movement of soil moisture, it is of great theoretical and practical significance for groundwater recharge evaluation and groundwater pollution prevention in subtropical monsoon climate plain area.