不同来源Cd在稻田土壤中累积迁移的界面过程与模型预测

Remediation of agricultural field suffering from heavy metal pollution is extreme difficult, requires long recovery period and high remediation cost. Therefore, source control is the primary measure to solve this pollution problem in agricultural soils. The current research aims at the existing problems of ambiguous coupling of Cd source and sink in soil-rice system caused by the various Cd pollution sources. On the microscopic level, the Cd adsorption processes onto humic acid (HA) or goethite or goethite-HA complex under different pH conditions will be studied with adsorption experiments using HA and goethite to represent respectively the organic and mineral particles in soils, and a LCD model describing the above adsorption processes will be constructed to clarify the distribution and accumulation mechanisms of Cd from various sources in the source-soil-rice system; On the macroscopic level, different experiments (aging experiments and pot experiments) and analysis (sequential extraction procedures and soil column-Donnan membrane technology) will be used to study the dynamic changes of Cd speciation and bioavailability in Cd fractions in the source-soil-rice system; The spatial variation of Cd contents and its fraction distribution in soil profile will also be studied through comparing Cd distribution in the soil profile with results of leaching experiment, in order to identify the contribution of various pollution sources to Cd accumulated in different soil layers and their variations with time. The ultimate purpose of the project is to clarify how Cd from various sources transports and accumulates in the source-soil-rice system, why deviation between contributions to Cd in the inputs and Cd in soil accumulation occurs, which mechanism underpins the coupling of Cd among the components in this system, and eventually to provide theoretical support for achieving the goal of preventing heavy metal pollution in agricultural soils mainly by source control.

农田重金属污染治理难度大、周期长、成本高，源头治理是防控农田重金属污染问题的关键措施。针对土壤-水稻体系Cd来源多、源汇耦合关系模糊等问题，微观上以胡敏酸和针铁矿代表土壤中有机和矿物颗粒，通过吸附实验研究不同pH下Cd在胡敏酸、针铁矿以及胡敏酸－针铁矿复合体上的吸附过程，构建上述三相上Cd吸附的LCD模型，预测Cd在土壤颗粒表面的微界面反应；宏观上以连续提取、土柱-多南膜技术以及老化实验、盆栽实验研究来源-土壤-水稻体系中Cd的生物有效性及其动态变化特征；以土柱淋滤实验和土壤剖面对比结果为依据，研究土壤剖面的Cd含量及形态分布，判别土壤剖面各投入品的贡献率及其随时间的变化；最终阐明Cd在来源-土壤-水稻体系中的迁移与累积机理，明晰Cd在投入和土壤累积贡献率产生偏差的原因，揭示来源-土壤-水稻系统中Cd的耦合关系和机制，为实现源头预防为主的农田重金属污染控制目标提供理论支持。

农田重金属污染治理难度大、周期长、成本高，源头治理是防控农田重金属污染问题的关键措施。针对土壤中Cd来源多、源汇耦合关系模糊等问题，微观上以胡敏酸和针铁矿代表土壤中有机和矿物颗粒，通过吸附实验研究不同pH下Cd在胡敏酸、针铁矿以及胡敏酸－针铁矿复合体上的吸附过程，构建上述三相上Cd的吸附模型，预测Cd在土壤颗粒表面的微界面反应；宏观上以清单法研究土壤中Cd的主要污染来源及其贡献，以老化实验重点研究有机肥施用稻田土壤中Cd的生物有效性及其动态变化特征；以土柱淋滤实验研究土壤中Cd的淋溶特征以及土壤中Cd赋存形态的空间变化规律，并结合剖面土壤中Cd的含量和赋存形态，对剖面土壤中Cd的污染来源进行解析，最终阐明Cd在来源-土壤体系中的迁移与累积机理，明晰Cd在投入和土壤累积贡献率产生偏差的原因，为实现源头预防为主的农田重金属污染控制目标提供理论支持。本项目的主要研究结果有：（1）Cd在针铁矿表面的形态包括(FeOH)2Cd+1、(FeOH)2Cd2(OH)2+1、(FeOH)2Cd2(OH)30和 (FeOH)2CdOH0，而Cd主要以羟基形态（-OCd+）存在于腐殖酸表面；低pH（pH<6）下，HA和FA均能明显增加针铁矿对Cd的吸附；在高pH（pH>9）下，HA/FA的存在降低了针铁矿对Cd的吸附，且HA对Cd的影响作用强于FA。（2）大气沉降和畜禽粪便是（稻田）土壤中Cd的主要污染来源；施用猪粪和淹水处理能有效降低土壤中的酸可提取态Cd，且随着时间延长，Cd向不活泼形态转变；多表面模型能较好的拟合孔隙水中Cd含量的变化趋势，模型敏感性分析表明影响孔隙水中Cd浓度的主要因子为pH。（3）在特定污染源的影响下，研究区土壤中典型污染重金属的主要赋存形态间呈现明显的相关性，如铅锌矿区附近剖面土壤中可交换态Pb与可交换态Cd和Zn之间呈现极显著相关性，有机肥施用区及沼液灌溉区附近剖面土壤中TOC与可氧化态Cu和Zn间呈显著或极显著相关性，工业区附近则只有可交换态Pb与可交换态Cd呈极显著相关性。