Effects of freeze‒thaw on soil loss under simulated composite upslope inflow and rainfall erosion in the black soil region of northeast China

Abstract

Freeze‒thaw (FT) is the main cause of decreasing soil erodibility and changing hydrological characteristics during spring thawing period in the black soil region of northeast China, which further affects soil erosion. However, there is relatively limited research on the impacts of FT on upslope inflow and rainfall (RRI) composite erosion during this special period. This study simulated three combinations of upslope inflow (RO) rate (0.34, 0.5, and 0.67 L min⁻¹), rainfall (RF) intensity (80, 120, and 160 mm h⁻¹), and RRI (0.34 L min⁻¹‒80 mm h⁻¹, 0.5 L min⁻¹‒120 mm h⁻¹, 0.67 L min⁻¹‒160 mm h⁻¹) under FT and unfrozen (FT_UN) soil condition. The results showed that (1) FT extremely increased the sediment yield rate (SER) of RO and RF by 1750.0% to 5235.6% and 3.1% to 97.7%, respectively, while SER of RRI increased by 12.1% to 70.4%; (2) RRI had a nonlinear superposition amplification effect (SAE) on SER. During FT_UN, the average SAE was 293.9%, which decreased with increasing flow discharge; FT weakened the SAE, and the average SAE was 51.1%, increasing with the increase of flow discharge; (3) The domination force in RRI had been changed from RF during FT_UN to RO during FT; (4) Flow velocity (V) showed the best explanation to SER in RRI. However, the determination coefficient decreased from 0.62 to 0.56 after FT. Under the influence of FT, the critical V of RRI increased from 0.05 m s⁻¹ to 0.08 m s⁻¹. Under the influence of FT, RRI erosion intensified the SER, weakened the SAE, and changed the dominant force. Moreover, the V is the optimal hydrodynamic parameter for predicting RRI erosion. The research results can deepen the understanding of the erosion mechanism of RRI under the influence of FT in the black soil region of northeast China.