Integrating Multiple Approaches to Reveal the Spatiotemporal Pattern of Soil Erosion in Mollisol Watershed

Although numerous prediction methods have been developed, scientific estimation of the spatiotemporal pattern of soil erosion at the watershed scale remains challenging. In this study, fallout radionuclides of 210 Pb ex and 137 Cs were used to estimate average annual soil erosion and deposition in a Mollisol watershed in Northeast China. Additionally, the Chinese Soil Loss Equation (CSLE) and source‐sink theory based on fingerprinting techniques were used to trace soil erosion history in the Mollisol watersheds of Northeast China. Results showed that the mean annual soil erosion rates predicted by 210 Pb ex and 137 Cs were inconsistent due to differences in their sources and environmental behaviors, with values of 107.4 t ha −1 a −1 (over 60 years) and 27.3 t ha −1 a −1 (since 1963), respectively. However, the proportion of eroded area to the total watershed area estimated by two methods was similar, ranging from 50.4% to 53.2%. 210 Pb ex showed erosion predominantly on north‐facing slopes while 137 Cs on south‐facing slopes, with only partial agreement on deposition locations. Erosion predicted by the CSLE was significantly correlated with the 137 Cs method ( p < 0.05), but not with the 210 Pb ex method. Combined with remote sensing and source‐sink theory, this study speculated that compound erosion and gully erosion were the predominant type from early 20th century to 1963, while the surface erosion caused by rainfall has been the main type from 1963 to 2021. Soil erosion primarily occurred in the early stages of farmland reclamation before 1963, while second forests were effective to reduce soil erosion. Early land reclamation without soil conservation has led to significant erosion initially, while soil erosion rates tended to stabilize over time as land management practices improved. Overall, the integration of these methods can effectively trace the spatial pattern of soil erosion and determine the shift in erosion types over an extended historical period. This study emphasizes that soil erosion assessment should integrate multiple approaches over extended time scales to scientifically inform soil erosion control strategies in Mollisol regions.