Impacts of Soil Disturbed Depth on Variations in Soil Erosion and Solute Loss Processes

Abstract

Soil erosion‐induced solute loss contributes to nonpoint source pollution (NPS). Existing NPS models employ a static effective mixing depth (De) for multi‐scale solute loss prediction, while fundamentally neglecting both the governing role of runoff layer depth (Dr) in solute transport dynamics and the spatiotemporally dynamic nature of De itself. Bromide (Br) has high solubility and low reactivity; therefore, this study employed Br as the solute, with KMnO4 and Br tracer methods used to quantitatively determine the dynamic variations of Dr (0.04–0.59 cm) and De (0.08–10.35 cm) under varying rainfall intensities (60, 90, and 120 mm h−1) and overland flow rates (0, 1, and 2 L min−1). The investigation focused on elucidating the effects of soil disturbed depth (Ds, comprising Dr and De) on soil erosion and solute loss processes. Additionally, runoff coefficient (Rc), sediment concentration (Cs), sediment yield rate (Sy), Br concentration in runoff (CBr), Dr, and De were determined at 2‐or 3‐min intervals. The power function effectively captures the temporal dynamics of De and Dr during rainfall processes. Significant differences were observed in soil erosion (including runoff initiation and sediment yield) and solute loss processes across different Ds (F > 3, p < 0.01). Sy, Cs, and CBr demonstrated increasing trends with rising Ds, though the magnitude of these increases varied across different Ds (R2adj > 0.55). Furthermore, a notable linear correlation was identified between cumulative runoff generation, sediment yield, bromide loss, and mean Dr and De (R2adj > 0.75). Collectively, Ds accounted for 64.9% and 46.2% of the variation in soil erosion and Br loss, respectively. These findings enable optimized NPS modeling and tillage practices to mitigate nonpoint source pollution.