冻融作用对东北棕壤重金属镉环境行为的影响研究

Freeze-thaw cycles (FTCs) is the typical characteristic of temperate zone. Freezing and thawing affect the soil physical and chemical properties by changing soil structure and hydrothermal movement.It will certainly affect the transformation and transfer of soil elements. Brown soil is located in the northeastern China belt transect of global climate changing research. The intensity of climate chaning and land freeze-thawing are obvious. Combined the effect of FTCs on soil physicochemical properties with the effect of FTCs on Cd transformation, Cd environmental behaviors, such as transformation and transfer were studied as affected by climate changing according to the characteristics of FTCs and the cadmium pollution of brown soil. The relationship between Cd form and the soil water content, freezing temperature and freeze-thaw frequency will be tested using the indoor FTCs experiments and the effects of FTCs on the Cd adsorption/desorption to soil will be studied under different FTCs conditions (water content, freezing temperature and freeze-thaw frequency) by using equilibrium adsorption/desorption isotherms. The effect of FTCs on Cd transferability will be estimated by leaching the soil column filled with Cd polluted soil under different FTCs treatments. Soil physicochemical indexes, such as organic matter, aggregate composition,pH and surface chemical properties will be analyzed under different treatments to determine the mechanisms of FTCs on Cd environmental behaviors in soil. These results will provide valuable theoretical basis for assessing the Cd toxicity, environmental effect and pollution controlling for soil subjected to the process of seasonal freezing and thawing cycles.

冻融交替是温带地区土壤的重要特征，冻结和解冻过程通过改变土壤结构和水热运动而对土壤物理、化学特性产生效应，进而影响土壤中元素的迁移和转化。棕壤位于全球气候变化研究中国东北样带内，是气候变化、土地冻融交替显著的地区。本项目针对该地区冻融交替的气候特点及棕壤重金属镉污染严重的现状，将冻融作用对棕壤理化性质的影响与冻融作用对重金属镉形态转化、迁移等环境行为的作用相结合，采用室内冻融循环试验的方法，建立镉赋存形态与冻融棕壤含水量、冻结温度、冻融频次之间关系的模型；通过吸附/解吸试验，阐明冻融交替条件下棕壤对镉的吸附特性以及吸附态镉的解吸特性；通过土柱淋洗试验，揭示冻融作用对镉在棕壤中迁移特征的影响，并从土壤有机质、团聚体组成、表面化学性质及pH等理化指标的变化阐明冻融作用对镉环境行为的作用机制，为准确评价冻融地区棕壤重金属镉的毒性、环境效应及污染防治提供理论依据。

冻融交替是温带地区土壤的重要特征，冻结和解冻过程通过改变土壤结构和水热运动而对土壤物理、化学特性产生效应，进而影响土壤中元素的迁移和转化。东北地区的棕壤位于全球气候变化研究中国东北样带内，是气候变化、土地冻融交替显著的地区。该地区是我国商品粮的重要生产基地，但由于“三废”排放导致棕壤重金属镉污染较为严重，给粮食安全和人体健康带来巨大风险。因此，研究冻融条件下土壤中重金属镉的环境行为对揭示冻融地区土壤重金属环境风险具有重要意义。. 本项目针对该地区冻融交替的气候特点及棕壤重金属镉污染严重的现状，将冻融作用对棕壤理化性质的影响与冻融作用对重金属镉赋存形态、吸附/解吸、迁移等环境行为的作用相结合，采用室内冻融循环试验的方法，建立镉赋存形态与冻融棕壤含水量、冻结温度、冻融频次之间关系的模型；通过吸附/解吸试验，阐明冻融交替条件下棕壤对镉的吸附特性以及吸附态镉的解吸特性；通过土柱淋洗试验，揭示冻融作用对镉在棕壤中迁移特征的影响，并从土壤有机质、团聚体组成、表面化学性质及pH等理化指标的变化阐明冻融作用对镉环境行为的作用机制，为准确评价冻融地区棕壤重金属镉的毒性、环境效应及污染防治提供理论依据。. 所得结果如下：（1）土壤含水量和冻融次数对不同形态镉含量的影响并不相同，对交换态镉含量作用最显著的冻融条件是土壤含水量，对有机结合态镉含量作用最显著的冻融条件是冻融次数，对铁锰氧化物结合态和残渣态镉含量作用最显著的冻融条件是土壤含水量和冻融次数的共同作用；（2）当土壤含水量为田间持水量时，在相同的初始Cd添加浓度下，经过冻融处理的土壤对Cd的吸附量小于未冻融土壤，解吸率大于未冻融土壤，并且冻融次数越大，土壤对Cd的吸附量越小，解吸率越大；（3）土壤冻融过程可以通过增加土壤孔隙度提高镉在土壤中的移动性，加大镉对土-水系统的环境风险。