【作者】 党秀丽；

【导师】 张玉龙；

【作者基本信息】 沈阳农业大学 ， 土壤学， 2008， 博士

【摘要】 冻融交替是作用于土壤的非生物应力,前人关于冻融作用对土壤理化性质影响的研究已经取得许多成果,但关于冻融过程对土壤污染物行为的影响及其生态效应方面的研究相对较少,尤其是冻融条件下重金属镉在土壤中迁移转化微观机制的研究目前还鲜有报道。本文选择东北地区代表性土壤之一-棕壤作为试验材料,采用土壤添加外源重金属镉后在不同含水量、不同温度条件下室内冻融培养、测定冻融后土壤中各形态镉含量、土壤对镉的吸附量、解吸量及淋洗液中镉含量的方法,研究了冻融过程对镉在土壤中迁移转化的影响,探讨了冻融过程对土壤重金属镉行为作用的机理。冻融处理及其冻融条件为,冻结温度-30℃,融化温度30℃,冻结和融化各3天即6天为1个冻融周期（次）,冻融次数分别为0、1、3、6、9、12次。这一研究结果,有助于认识季节性冻融地区土壤重金属污染的特点,可为这一地区确定土壤重金属镉的环境容量、评价镉污染土壤的生态环境风险、预测土壤对外源镉污染的缓冲性能和进行镉污染土壤诊断治理提供理论依据。所得主要研究结果如下:1.冻融过程对土壤中重金属镉形态的影响。当添加外源重金属镉含量为10mg kg^-1,对不同含水量(0.21kg kg^-1～0.45kg kg^-1)土壤中交换态、铁锰氧化物结合态、有机结合态、残渣态镉含量的测定结果表明,冻融后土壤中各形态镉含量差异很大,但均以交换态为主,其次为残渣态,有机结合态、铁锰氧化物结合态含量相对较低。土壤含水量和冻融次数对交换态、铁锰氧化物结合态、有机结合态、残渣态镉含量的影响均达到了极显著水平。利用逐步回归分析方法建立的土壤含水量(X₁,kg kg^-1)和冻融次数（X₂,次）与交换态镉含量(Y_交换,mg kg^-1)的关系方程为Y_交换=18.04-62.86X₁-0.48X₂+75.19X₁²+1.49X₁X₂;与铁锰氧化物结合态镉含量(Y_{铁锰-结合},mg kg^-1)的关系方程为Y_{铁锰-结合}=0.46+0.13X₁X₂;与有机结合态镉含量(Y_{有机-结合},mg kg^-1)的关系方程为Y_{有机-结合}=0.74+8.31×10^-2X₂²;与残渣态镉含量(Y_残渣,mg kg^-1)的关系方程为Y_残渣=2.91-0.45X₁X₂。说明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.冻融过程对土壤重金属镉释放的影响。在田间持水量条件下,污染土壤中镉含量为10mg kg^-1～50mg kg^-1时,用NH₄AC和EDTA作提取剂,冻融处理增加了土壤中镉的释放量。与未冻融处理（冻融次数为0次）相比,冻融交替使添加外源镉的土壤中离子态镉的释放率（释放量/添加量）增加,未知态镉的释放率减少,而络合态镉的释放率无显著变化。说明冻融过程具有促进土壤中结合牢固的未知态镉向不稳定的离子态镉转化的作用,即冻融过程有利于镉的释放。3.冻融过程对土壤重金属镉吸附—解吸的影响。当土壤含水量为田间持水量时,在相同的初始Cd²⁺添加浓度下,经过冻融处理的土壤对Cd²⁺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Cd²⁺的吸附量越小,解吸率越大。说明冻融作用降低了土壤对镉的固持能力。Langmuir方程可以很好地拟合冻融土壤与未冻融土壤对镉的吸附,Freundlich方程既可以很好地拟合该土壤对Cd²⁺的等温吸附,也能很好地拟合解吸过程。4.冻融过程对土壤中重金属镉移动性的影响。将镉污染土壤制成土柱,经过冻融作用后用相同数量的去离子水进行淋洗试验,结果表明,水分在经过冻融处理后的土柱中运移的速度明显快于未冻融土柱;Cd²⁺在冻融处理后的土柱中穿透时间较短,而在未冻融土柱中穿透时间较长;冻融处理后的土柱淋出液中Cd²⁺累积淋出量高于未冻融土柱,并且随着冻融次数的增加Cd²⁺累积淋出量也随之增加。用环刀采集原状土样,在不同冻融次数下对土壤孔隙度的测定结果表明,冻融作用使土壤孔隙度增加。说明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。更多还原

【Abstract】 Freeze-thawing cycles is a kind of non-biological impact on soil.Its effects on soil physical-chemical properties have been studied comprehensively but its effects on soil pollution and its ecological significance was not concerned enough,particularly the mechanism of Cd element transfer and transformation in soil under freezing-thawing cycles was still remained elusive.This paper used burozem which is a typical soil in the northeast region of China to determine the effects of freezing-thawing cycles on Cd transfer and transformation in soil with indoor culture under different soil water content and different frequency of freeze-thawing cycles.These results provide a scientific basis for establishing of Cd environmental capacity in soil,assessing of Cd eco-environmental risk,evaluating of soil ability to buffer exogenous Cd and diagnosing of soil pollution in the northeast region.The condition of the freezing-thawing cycles was adopted as the temperature of freezing and thawing being-30℃and 30℃,respectively,both freezing and thawing were lasted for 3 days （as 6 days for one freeze-thawing frequency）,the frequency of freeze-thawing was 0,1,3,6, 9,12,respectively.The main results of this study are presented:1.Effect of freeze-thawing cycles on the form of Cd.The difference of concentration among exchangeable Cd,Fe/Mn-Oxide binding Cd,bound-organic Cd,and residual Cd was big under freeze-thawing cycles after added Cd 10mg kg^-1to soil with water content 0.21kg kg^-1～0.45kg kg^-1,and exchangeable Cd was the main form,second was residural Cd,the amount of bound-organic Cd and Fe/Mn-Oxide binding Cd were relatively low.The content of soil water and the frequency of freezing-thawing cycles significantly influenced the content of each Cd form（p＜0.01）.The optimum regression equations for the relationship among the content of soil water（X₁）,the frequency of freezing-thawing cycles （X₂）,and the content of each Cd form（Y）were as followed: For exchangeable Cd,Y=18.04-62.86X₁-0.48X₂+75.19X₁²+1.49X₁X₁;for Fe/Mn-Oxide binding Cd,Y=0.46+0.13X₁X₂;for bound-organic Cd,Y=0.74+8.3l×10^-2X₂²;and for residural Cd,Y=2.91-0.45X₁X₂.This means that the effects of soil water content and freeze-thawing frequency on Cd concentration of four forms were not the same.The results showed that soil water content has significant effect on exchangeable Cd,frequency of freeze-thawing has significant effect on bound-organic Cd,the interaction effect of soil water content and frequency of freeze-thawing has significant effect on Fe/Mn-Oxide binding Cd and residural Cd.2.Effect of Freeze-thawing cycles on Cd release from soil.Freezing-thawing cycles increased Cd release from soil under these conditions of soil water content equal to field moisture capacity and soil Cd content between 10mg kg^-1～50mg kg^-1.The release rate of ion-state Cd from soil under freeze-thawing conditions was larger than that observed under no freeze-thawing conditions but the release rate of unknown-state Cd was smaller than that observed under no freezing-thawing conditions.However,the release rate of complex-state Cd was not significant different with or without freezing-thawing cycles.Those results demonstrated that some unknown-state Cd originally bound firmly to soil colloids could be transformed into ion-state Cd under freeze-thawing cycles so that it was easily to release from soil.3.Effect of Freeze-thawing cycles on the ability of Cd absorbed to soil and desorbed from soil.The ability of soils treated with freeze-thawing cycles to absorb Cd was smaller and their ability to desorb Cd became larger as compared to the untreated soil at the same content of added Cd under field capacity water of soil.The treated soils with freeze-thawing cycles exhibited less ability to absorb Cd and more ability to desorb Cd with the increase of freeze-thawing frequency.These results suggest that freeze-thawing cycles can reduce the ability of soil to keep Cd.Langmuir and Freundlich equations could fit well to the ability of soils to absorb Cd with or without freeze-thawing cycles（p＜0.01）.The desorption capacity of Cd in soil with or without freeze-thawing cycles could be well described by the Freundlich equation（p＜0.01）. 4.Effect of Freeze-thawing cycles on Cd transferability.Soil porosity was determined after original soil sampled by cutting ring and treated by Freeze-thawing cycles.Results showed that freeze-thawing cycles increased the soil porosity.Experiments showed that deionized water transferred faster in the earth column filled with Cd polluted soil under freezing-thawing conditions than that of no freezing-thawing cycles when use the same amount deionized water to leach the earth column.Similarly,Cd ion transferred faster in the earth column with freeze-thawing cycles treatment as compared to that of no freeze-thawing cycles treatment.The concentration of Cd ion in leacheate from the column with freeze-thawing cycles treatment was higher than that observed in the untreated soil.The total amount of Cd ion leaching from the column increased with the increase of freeze-thawing frequency.Those data suggest that freeze-thawing cycles increase the ability of Cd to transfer in soil so that enhance the harm of Cd to soil-underground water system.更多还原