Multi‐Scale Hydro‐Geochemical Processes Regulating Soil Alkalinity: Evidence From Lake–Land Interactions

Abstract

Soil pH is a key factor influencing ecological security and sustainable agricultural development and serves as a major indicator of soil alkalization. Although the general ‘acidic in the southeast and alkaline in the northwest’ pattern is well documented in China, the spatial organization of regional alkaline hotspots and the relative contributions of climatic, lithological and hydro‐geochemical controls across the continental scale have not been systematically quantified. This study developed a random forest model based on 3382 national floodplain soil samples and 20 socio‐environmental factors to identify the dominant predictors on soil alkalinity. Model interpretation was further supported by SHapley Additive exPlanations (SHAP) analysis and spatial analysis. The results show that calcium oxide is the most important predictor of alkalinity, followed by mean annual precipitation and nitrogen content. Alkaline hotspots are concentrated in the central Qinghai–Tibet Plateau, central and eastern Inner Mongolia and western Jilin Province, showing strong spatial association with lakes larger than 1 km 2 . Soil pH decreases systematically with distance from lakeshores (0.3–1.0 units within 150 km), providing nationwide quantitative evidence that lake systems amplify localized alkaline hotspots across contrasting environmental regions. Through case studies and geographical zoning, dominant alkalization mechanisms were identified and region‐specific ecological management and land‐use strategies are proposed. These findings deepen the understanding of multiscale drivers of soil alkalization and support salinization control and ecological restoration in arid and semi‐arid regions of China.