冻融作用对棕壤团聚体组成及其重金属镉赋存形态的影响

发布时间：2018-01-01 13:17

本文关键词：冻融作用对棕壤团聚体组成及其重金属镉赋存形态的影响　出处：《沈阳农业大学》2017年硕士论文　论文类型：学位论文

【摘要】：重金属Cd在土壤中的赋存形态直接影响着Cd在土壤中的生物有效性和毒性,在一定程度上决定着Cd在土壤中的真实污染程度。季节性冻融是北方地区常见的气候现象,冻融作用能改变土壤结构、颗粒大小等物理性质,从而间接影响Cd在土壤中的形态转化。本文以沈阳地区的典型土壤—棕壤作为供试土壤,采用人工控温的方法对不同冻结温度、不同含水量条件下的土壤进行冻融交替处理,测定冻融处理后棕壤团聚体的粒径分布及其中重金属Cd的赋存形态,探讨冻融作用对棕壤团聚体稳定性及其中重金属Cd赋存形态转化的影响。得到的主要结论如下:(1)棕壤经过冻融作用后,可变电荷量显著降低(P0.05);但当冻结温度低于-20℃时,可变电荷量降低不明显;冻融作用促进了棕壤有机质含量的增加(P0.05),但冻结温度对棕壤有机质含量影响不显著,当棕壤含水量大于田间持水量的40%时,含水量对有机质含量影响不显著。(2)土壤经过不同冻结温度处理后,2 mm团聚体粒径所占比例显著增加(P0.05),1-2mm、0.25-0.5mm和0.25mm团聚体粒径所占比例明显降低(P0.05),0.5-1 mm团聚体粒径所占比例变化不显著。在一定冻结温度(-20 ℃)条件下,2 mm团聚体所占比例随着土壤含水量的增加而增加,0.5-1 mm和0.25-0.5 mm团聚体所占比例随着含水量的增加而减少,1-2 mm团聚体所占比例在土壤含水量为田间持水量的40%时最大,0.25 mm团聚体所占比例在土壤含水量为田间持水量的30%时最大。(3)棕壤经过冻融处理后,扫描电镜结果显示土体出现了"抱团"现象,增加了土样颗粒之间的团聚能力。当棕壤含水量达到田间持水量的60%时,团聚体稳定性达到最大,但不同冻结温度对团聚体稳定性影响不显著。(4)与未冻融土壤相比,土壤经过不同冻结温度处理后2mm、1-2mm和0.5-1 mm团聚体粒径中重金属Cd的含量明显增加(P0.05),0.25-0.5 mm和0.25 mm团聚体粒径中重金属Cd所占比例明显降低(P0.05),冻融作用促进了 Cd在土壤大团聚体中的富集,降低了 Cd的环境风险。(5)与未冻融土壤相比,经过冻融处理后棕壤中交换态Cd和有机结合态Cd含量降低,铁锰氧化物结合态Cd与残渣态Cd含量增加。随着冻结温度的降低,交换态Cd含量呈现先增加后降低的趋势,铁锰氧化物结合态Cd和有机结合态Cd含量先降低后增加,残渣态Cd含量逐渐降低,但当温度降低到-20 ℃时,残渣态Cd含量不再降低。(6)冻融作用对棕壤团聚体中重金属Cd的形态转化有显著影响(P0.05)。与未冻融土壤相比,在不同团聚体粒径中不同冻结温度均使交换态Cd和有机结合态Cd含量降低,铁锰氧化物结合态Cd与残渣态Cd含量增加。
[Abstract]:Speciation of Cd in soil Cd in soil directly affects the bioavailability and toxicity, to a certain extent determines the real pollution degree of Cd in the soil. The seasonal freezing and thawing climate is common phenomenon in northern areas, freezing and thawing can change the soil structure, particle size and other physical properties. Thus indirectly affect the conversion of Cd in the soil form. The typical soil brown soil of Shenyang area as tested soil, using the artificial freezing temperature of different temperature, different water content under the condition of soil freezing and thawing cycles, measured after freeze-thaw treatment of soil aggregate size distribution and speciation of the the heavy metals of Cd, to investigate the effects of freezing and thawing on soil aggregate stability and the speciation of heavy metals Cd transformation. The main conclusions are as follows: (1) soil after freezing and thawing, the variable charge amount. Reduce (P0.05); but when the freezing temperature lower than -20 DEG C, the variable charge amount decreased; freezing and thawing increased soil organic matter content (P0.05), but the effect of freezing temperature on the soil organic matter content was not significant, when soil water content is greater than 40% of field capacity, influence of water content the organic matter content was not significant. (2) the soil after different freezing temperatures after treatment, 2 mm aggregate size proportion increased significantly (P0.05), 1-2mm, 0.25-0.5mm and 0.25mm aggregate size proportion was significantly lower (P0.05), 0.5-1 mm aggregate particle size proportion did not change significantly in a certain. The freezing temperature (-20 DEG C) condition, 2 mm aggregate proportion increases with the increase of soil water content, 0.5-1 mm and 0.25-0.5 mm aggregate proportion decreased with the increase of water content, 1-2 mm aggregates in the proportion of soil moisture to field water The maximum amount of 40%, 0.25 of the MM aggregates in the largest proportion of soil moisture was 30% of field capacity. (3) soil after freeze-thaw treatment, SEM results showed that the soil appeared "Baotuan" phenomenon, increase the agglomeration ability between the soil like particles. When the soil moisture at field capacity 60% of the water, the maximum aggregate stability, but different freezing temperature effect on aggregate stability is not significant. (4) and non freezing thawing soil compared to soil after different freezing temperature after 2mm treatment, the contents of 1-2mm and 0.5-1 mm aggregate size of heavy metals in a significant increase in Cd (P0.05), 0.25-0.5 mm and 0.25 mm aggregate the particle size of heavy metals in the proportion of Cd decreased significantly (P0.05), freeze-thaw action promoted the accumulation of Cd in soil aggregates, reduce the environmental risk of Cd. (5) and non freezing thawing soil than after freezing thawing treatment after Cd exchange in brown soil Organic state and decreased the content of Cd and Fe Mn oxide bound Cd and residual Cd content increased. With the temperature decrease, exchangeable Cd content increased first and then decreased, Fe Mn oxide bound Cd and organic bound Cd content decreased firstly and then increased, the content of residual Cd decreased gradually, but when the temperature is reduced to -20 degrees, the content of residual Cd was no longer reduced. (6) effects of freezing and thawing on the heavy metal Cd in brown soil under transformation had significant effect (P0.05). And the freezing thawing soil than in different aggregate size in different freezing temperatures were the exchangeable Cd and organic Cd content reduced iron manganese oxide bound Cd and residual Cd content increased.

【学位授予单位】：沈阳农业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X53

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