灌溉水质对污染土壤中重金属迁移及再分配的影响机理

The effect of irrigation water quality on the chemical and physical properties, nutrients condition and compounds accumulation was focused in the past few decades. It is lack of investigation on the mechanisms and effect factors of heavy metals transport influenced by the irrigation in contaminated soil. With the past research results, the PI found that the different types soil colloid significantly affected the migration and solidification of heavy metals. Focused on the significant difference of suspended colloids, pH and redox of irrigation water, and based on the survey of heavy metals accumulation and distribution in soil irrigated with different quality water, this proposal will monitor the special and temporal accumulation of heavy metals in soil. Furthermore, the irrigation condition will be controlled, and the experiment will be carried out with the different quality and quantity of irrigation water, as well as heavy metal contaminated soil will be used in the indoor simulation experiment. This proposal will investigate the ability of irrigation on the cleaning of heavy metals contaminated soil, explore the correlation between irrigation water and heavy metals accumulation and distribution. Furthermore, this project will reveal the impact mechanisms of colloid on the transport and redistribution of heavy metals in soil. It is expected that the success of this project will advance the fundamental migration-solidification theory of heavy metals in irrigation or infiltration; It is also anticipated that the proposed project will provide important theoretical and practical guidance for the remediation of heavy metals contaminated soil in nature condition.

灌溉水质成分不同对土壤理化性质、养分状况及物质累积的影响是科学界早已关注的问题，然而灌溉过程对污染土壤中重金属迁移扩散的驱动机制及影响因素还少见报道。申请者在前期研究中发现，不同类型的土壤胶体对重金属的迁移与固定具有强烈的影响。针对灌溉水中含有不同类型的悬浮胶体以及水体pH、氧化还原条件存在显著差异的实际，本项目在对不同水质灌区土壤中重金属累积、分布调查的基础上，进一步观测重金属的时空动态变化规律，进而通过室内精确控制灌溉条件，以不同灌溉水质和灌溉量为试验处理，以重金属污染的土壤为材料，研究灌溉对污染土壤中重金属的清洗能力、胶体的携带迁移能力和重金属的再分配过程，探寻土壤重金属累积分布与灌溉水质的关系，揭示胶体对重金属在土壤中再分配及扩散迁移的作用机理，为完善农田土壤水入渗和再分布期间重金属的迁移-扩散理论奠定基础，对自然状态下重金属污染土壤修复提供重要的理论与支持。

由于灌溉水中含有大量的胶体物质，导致灌溉过程成为土壤中的污染物在移动胶体与土壤胶体之间的再分配过程。探索不同水质成分对土壤中重金属污染物的作用机理及作用效果，将有助于提高水资源的有效利用及控制土壤污染的范围。本研究以灌溉过程中胶体物质对重金属污染物的竞争吸附与携带运输关系为研究对象，利用在陕西西安沣惠渠灌区和宝鸡峡灌区采集原状土样、剖面土样及室内砂柱、土柱模拟分析等实验手段，对土壤中重金属的分布、累积规律及影响因素进行分析，得到以下结论：（1）关中污灌区农田土壤中重金属Cd、Pb含量超标，不同重金属类型在不同污灌区中的累积程度有所不同，沣惠渠灌区土壤中重金属含量均高于宝鸡峡灌区，且重金属主要富集在0.02~0.002mm和<0.002mm两种粒径团聚体中，重金属含量与有机质含量存在明显的正相关关系；（2）在不同土壤中对重金属Pb、Cd、Ni的吸附能力有所差异，不同水质溶液对其解吸也有所不同，腐殖酸溶液对Pb2+、Cd2+的解吸能力最强，其次是蒙脱石胶体溶液，而对Ni2+解吸能力最强的是天然灌溉水，最弱的则是腐殖酸溶液，在解吸过程中，对重金属的一次解吸率均高于二次解吸率，说明不同介质对重金属的吸附能力不同，但均以表面吸附为主，水质成分会影响重金属的稳定性；（3）不同水质在饱和、非饱和情况下对不同介质中重金属的迁移影响不同，有机型灌溉水（腐殖酸溶液）在不同情况下均能加速土壤中Pb、Cd、Ni的迁移量和迁移距离，其次是复合型灌溉水（天然河水）和无机型灌溉水（蒙脱石溶液）均显著高于对照（蒸馏水）；（4）在饱和多孔介质中，移动胶体对重金属的“解吸迁移”能力不同，在不同影响因素条件下，用stanmod软件能够对运移实验结果进行较好的拟合。