咸潮倒灌影响稻田土壤镉活性的化学机制

Salt tidal irrigation with a large number of ions such as Cl-, Ca2+, Mg2+ and so on go into the soil, causing changes in soil and he adsorption equilibrium of heavy metals on soil significantly,which must have an effect on the activity of Cd in soil. The problem is widespread in coastal farmlands, but has not attracted much attention.This project is based on the paddy of coastal filed in Pearl River Delta, and Cd is the main pollutant.It's to study the effect of salt tidal irrigation to the paddy soil of the coastal filed contaminated by Cd, and the environmental factors which affecting the soil available Cd and rice Cd accumulation were studied by simulating the different conditions of salt-tide pouring.The main control factors of soil Cd activity in paddy soil were analyzed by different analysis methods. And the Visual Minteq software and double-layer surface complex model (dlm-2pk) was used to simulate and calculate the combination forms of the main control factors and soil Cd, which to analyze the distribution and content of different Cd species.To understand the change process of soil Cd in in paddy field affected by salty tidal irrigation,so as to analyze the chemical mechanism of the influence of salty tidal irrigation on Cd activity in paddy soil.It provides a theoretical basis for the treatment of Cd pollution in coastal rice fields.

咸潮倒灌引入了海水中大量的氯、钙、镁等离子，显著影响土壤pH值与重金属的吸附平衡，从而影响重金属活性。这一问题普遍存在于滨海农田，但未引起关注。本申请以珠三角滨海稻田为研究对象，镉为主要污染物，重点通过研究咸潮倒灌对滨海镉污染稻田土壤影响的效应和模拟不同咸潮倒灌条件下影响土壤镉活性和稻米镉积累的环境因素，解析出咸潮倒灌影响稻田土壤镉活性的主控因子；并通过Visual Minteq软件，采用双电层表面络合模型DLM-2pK模拟计算主控因子与土壤镉的结合形态，解析不同镉物种分布及丰度，明确咸潮倒灌影响的稻田土壤镉形态转化的关键过程，阐明咸潮倒灌影响稻田镉活性的化学机制。可为我国滨海稻田镉污染治理提供理论依据。

咸潮入侵稻田引入大量的阴阳离子，影响Cd的有效性和Cd的赋存形态。本项目研究了咸潮倒灌对稻田土壤Cd有效性的影响程度与作用机制，通过吸附实验、培养实验和盆栽实验，揭示了盐度控制土壤-水界面Cd有效性的化学机制，明确了铁、碳、氮、硫元素循环对Cd形态的影响机制，并且阐明了Cd在土壤-水稻体系中生物有效性的作用机制，为准确控制咸潮倒灌稻田土壤Cd有效性以及缓解水稻植株Cd吸收提供科学的管理方法。主要结论为：. 建立表面络合模型（SCM）评估不同浓度咸水对土壤Cd有效性的影响，结果表明pH对Cd的吸附行为呈现典型的pH依赖性特征，且随着离子强度的增加，镉氯络合物成为主导形态，促进Cd从土壤颗粒中的释放；通过咸水入侵稻田土壤Cd形态动力学研究表明，随着离子强度的增加，水溶态Cd含量显著增加。这可能是由于在盐度较高的咸水中，零电荷点增加，在土壤表面形成更多的正电荷，从而通过静电斥力抑制Cd的吸附；通过对咸潮入侵稻田土壤Cd解吸特性研究，发现pH值随着盐度的增加而增加，但Cd的释放量也显著增强；通过对水稻土中Cd形态及Fe/N/S/C氧化还原循环动力学研究，表明在厌氧初期和好氧后期，随着盐度的增加，Cd的有效性相对较高，厌氧条件下，有效态Cd含量明显减少，而有机物和铁锰氧化物结合态Cd的保留受到抑制。当转为好氧时，有机物和铁锰氧化物态Cd再固定，硫化物结合态Cd氧化溶解。厌氧条件下，高含盐量（> 30 mmol L–1）显著提高了水稻土Cd的有效性，因此在排水阶段应该尤其注意含盐量；通过盆栽试验发现，水稻根和籽粒中Cd含量随着盐分增加而增加。