田间尺度土壤镉吸附动力学及运移机理

Anthropogenic soil Cadmium (Cd) pollution threatens local groundwater environment and human health. Aiming to the questions of undiscovered influence mechanism of soil properties on Cd sorption kinetics, and spatial variability of Cd sorption kinetics, taking Cd-polluted field as the subject, this study will 1) investigate the mechanism of soil properties influencing soil Cd sorption kinetics, relate field soil Cd sorption kinetics with soil properties, and characterize the spatial variability of soil Cd sorption kinetics; and 2) build field-scale model integrating the sorption kinetics and transport process of Cd in soil, illuminate the influence of the spatial variability of soil Cd sorption kinetics on the transport of Cd in soil, and investigate the influence of spatial variability and uncertainty of soil properties on soil Cd transport, and identify the key soil properties and cutoff values which influence the potential risk of soil Cd leaching to groundwater environment.

人为的土壤镉污染威胁着地下水环境和人的健康。针对土壤理化性质对镉吸附动力学影响机理不清、镉吸附动力学存在空间变异问题，以镉污染农田为研究对象，本项目拟 1）研究土壤性质影响镉吸附动力学机理，建立田间土壤镉吸附动力学与土壤性质间的关系，量化田间土壤镉吸附动力学关系的空间变异性；2）建立田间尺度土壤镉吸附动力学与运移模型，阐明田间土壤镉吸附动力学关系空间变异对镉运移的影响机制，分析土壤性质空间变异性和不确定性对镉运移影响，确定影响土壤镉淋溶至地下水环境风险的关键土壤性质及临界值。

农田土壤镉污染威胁人体健康。农田土壤中镉迁移和归趋主要取决于吸附——解吸附过程，然而这一过程的关键步骤与关键影响因子目前并不完全清楚。本项目研究了历史污染镉解吸附过程与土壤性质影响、土壤性质及溶液条件对历史污染镉浸提率影响、以及化学淋洗对土壤性质和镉迁移影响等内容，取得进展如下：历史污染土壤镉两阶段解吸附过程的转折时间为3天，界面反应过程是控制镉解吸附速率的最慢步骤；建立了历史污染镉解吸附速率的土壤转换函数；镉解吸附速率随有机质、粘土含量增加而增加，随无定形氧化铁含量、阳离子交换量（CEC）、溶液pH值、粉粒含量增加而减少。历史污染土壤镉浸提率随着有机质、粘粒含量增加而增加，随粉粒、CEC、无定形氧化铁含量增加而降低。弱有机酸淋洗导致土壤团聚体分散，使细质土壤产生堵塞；土壤堵塞使得吸附镉离子的胶体颗粒在深层土壤积累，导致镉向深层土壤迁移。项目成果对于未来农田土壤镉迁移和归趋相关研究有重要参考意义。