A regional mass balance model for spatially predicting cadmium critical loads in paddy soil under management...

Predicting regional soil Cd changes and corresponding critical loads is crucial for contamination prevention. This study developed a regionalized soil critical load model to estimate spatio-temporal variations in trace metal content and critical load in paddy soil surrounding two industrial cities. The 50-year simulation revealed that soil Cd content remained nearly unchanged in scenario A (default conditions), increased by 9.92 % in scenario B (lime application), and decreased by 55.94 % in scenario C (straw removal). Atmospheric deposition and plant uptake were identified as the primary input and output pathways for soil Cd accumulation. The 90th percentile of regional critical loads for a 50-year protection period was 76.69, 26.57, and 20.91 g ha⁻¹ yr⁻¹ for scenarios C, A, and B, respectively. The critical loads showed high spatial variability, with higher values predominantly occurring at sites with low initial soil Cd content, low pH, or high plant uptake factor (PUF). While lime application reduced the critical load, requiring careful monitoring, straw removal significantly increased it. The model effectively visualized the spatial distribution of output fluxes, evaluated the long-term effects of remediation measures, and provided input flux limit references. This model could support the regional classification and management of soil contamination.