Hydraulic behavior and solute redistribution of saline-alkali black soil: Implications for stormwater source control

Study Region Daqing, northeastern China, has saline-alkali soils, strong evaporation, and shallow groundwater that constrain infiltration-based stormwater source control. Study Focus We examined hydraulic behavior and water and solute redistribution in black soil amended with 0, 0.5, and 2.0% Na 2 CO 3 . Saturated hydraulic conductivity ( K s ) was measured after 0~4 wetting-drying cycles. Soil water retention was determined by the filter paper method, and unsaturated hydraulic conductivity ( K u ) was estimated with the van Genuchten-Mualem model. A complementary column experiment applied sequential rainfall depths of 10, 20, 40, and 70 mm to track soil moisture, electrical conductivity (EC), and gravel layer water EC. New Hydrological Insights for the Region: Na 2 CO 3 addition reduced initial Kₛ from 3.31 × 10 −6 m/s at 0% to 2.49 × 10 −7 and 3.02 × 10 −8 m/s at 0.5% and 2.0%. Wetting-drying caused further declines, while estimated Kᵤ remained lower in Na 2 CO 3 -amended soils over most of the modeled suction range. During sequential rainfall, the 2.0% treatment accumulated more water near the surface and responded more slowly at depth. EC decreased in the upper 20 cm but increased at 20~40 cm, while gravel layer water EC increased by only 8.9%. Low hydraulic conductivity therefore restricted vertical water transmission and promoted solute accumulation within the soil profile.