【作者】 黄丹丹；

【导师】 葛滢；

【作者基本信息】 南京农业大学 ， 环境科学， 2008， 硕士

【摘要】 综观淹水及添加有机物料对土壤镉活性有升和降等行为,对淹水稻田硫化镉沉淀机制提出了质疑,为此本文对淹水还原过程中铁氧化物的形态转化带来的镉组分再分配的机制进行了论证,同时提出了此机制能用pe+pH值来表征。本研究采用红壤（pH4.46）和潮黄土（pH7.10）在氮气（N₂）覆盖下进行淹水恒温（25±0.5℃）培养,设置了对照（不加有机物料）、苜蓿、稻草三处理,测定土壤Eh、pH及铁、镉的形态分级分析,再依据化学及电化学平衡原理,对Eh、pH、DOM、铁氧化物等因素与镉活性的关系作数据处理,探讨淹水和添加有机物料后,土壤pe+pH升降与铁组分、镉组分转化之间的关系,初步明确了淹水条件下土壤镉活性行为与氧化还原状况的关系。试验得到以下结果:1.淹水培养60天后,红壤pH上升到5.92,潮黄土在淹水后3天pH降到6.62,然后再上升到6.89。两土壤pe+pH从14.16下降到5.38。pH和pe+pH的升降导致了土壤固相Exc-Fe、Carb-Fe、Oxide-Fe、Org-Fe再分配比例的增长,并使Exc-Cd向Carb-Cd、Oxide-Cd、Org-Cd转化。土壤Exc-Cd与Exc-Fe之间、Exc-Cd与（Carb-Cd+Oxide-Cd+Org-Cd）、（Carb-Fe+Oxide-Fe+Org-Fe）之间都有着显著或极显著的负相关性,由此表明Fe组分的再分配决定着Cd组分的再分配.初步提出了Cd组分再分配的pe+pH、pH范围。2.pe+pH和pH的升降影响着液相中Fe、Cd的浓度.在红壤淹水的1-7天中,固相以Exc-Cd为主,液相中Cd的浓度随pe+pH的下降而增加。在红壤淹水的中后期及潮黄土的整个淹水期,固相以Carb-Cd和Oxide-Cd为主,液相中Cd的浓度随pe+pH的下降而下降。3.土壤淹水后溶液的DOM浓度变化对水溶性Cd浓度的影响不显著。4.苜蓿和稻草处理与对照相比,能使红壤pH平均高出0.39和0.34个单位、pe+pH平均减少2.12和2.52,DOM平均浓度高出19.1倍和3.4倍;能使潮黄土pH平均减少0.27和0.11个单位,pe+pH平均减少0.85和0.65,DOM平均浓度高出3.6倍和1.1倍.pH和pe+pH的升降是不同土壤矿物Fe与有机质之间多个化学和电化学反应作用的结果。Fe组分的再分配决定着Cd组分的再分配.这些反应使红壤有机物料处理比对照的pe+pH下降,pH、Exc-Fe和Oxide-Fe增加,导致苜蓿和稻草两处理的平均Exc-Cd含量比对照分别减少0.101mg·1^-1和0.098mg·1^-1。潮黄土则相反,有机物料处理比对照的pe+pH、pH、Exc-Fe减少和Carb-Fe增加,导致苜蓿和稻草两处理平均Exc-Cd含量比对照分别增加0.441 mg·1^-1和0.10 mg·1^-1.5.有机物料处理的液相Cd²⁺浓度与对照相比,更明显受DOM的配合作用及Exc-Cd的扩散作用的影响。6.有机物料成分的差异直接影响固相Exc-Cd含量和溶液Cd²⁺浓度的降升幅度。更多还原

【Abstract】 Cadmium activity in soil may increase or decrease upon submergence and organic matter addition.Based on the literature review we posed questions to CdS precipitation as the mechanism of controlling Cd activity in flooded rice paddy soils.In this thesis we propose a hypothesis that the redistribution of Cd fractions was controlled by the transformation of iron oxides during the reductive process after submergence.This mechanism can be characterised with the parameter of pe+pH.To prove this,a red soil （pH4.46） and a fluvo-aquic soil（pH7.10） were chosen to be incubated under nitrogen coverage and constant temperature（25±0.5℃）.Three treatments,including control（no addition of organic materials）,clover blossom and straw addition,were set to determine soil Eh,pH,and Fe/Cd fractionation.We studied the relations between Cd activity and Eh,pH, DOM,iron oxides according to the principles of chemical and electrochemical equilibrium to investigate the relationship between transformation of Fe/Cd components and variation of pe+pH in soils after submergence and organic matter addition.The experimental results, which were summarized below,revealed the relationship between Cd behaviors and the redox state in soil under submerged condition.1.The pH of the red soil rose to 5.92 after 60 days of submergence.For the ftuvo-aquic soil,it dropped to 6.62 after 3 days and then increased to 6.89.The pe+pH of two soils descended from 14.16 to 5.38.The variation of pH and pe+pH caused increase of the redistribution ratio of Exe-Fe,Carb-Fe,Oxide-Fe,Org-Fe in soil solid phase,and transformation of Exc-Cd to Carb-Cd,Oxide-Cd and Org-Cd.The negative correlations were significant or highly significant between Exc-Cd and Exc-Fe,between Exc-Cd and （Carb-Cd+Oxide-Cd+Org-Cd） or（Carb-Fe+Oxide-Fe+Org-Fe）.This demonstrates that Fe redistribution controlled Cd redistribution.We also put forward a preliminary range of pe+pH and pH for the redistribution of Cd fractions.2.The variation ofpe+pH and pH affected the concentration of Fe/Cd in solution phase. During the 1-7 days after submergence in the red soil,Exc-Cd was the dominated forms in soild phase,and the concentration of Cd in solution phase increased with the decrease of pe+pH.In the later periods for the red soil and the whole incubation for the fluvo-aquic soil, Carb-Cd and Oxide-Cd were the dominated forms in soild phase,and the concentration of Cd in solution phase decreased with the decrease of pe+pH.3.The change of dissolved organic matter（DOM） concentration following submergence did not significantly affect soluble Cd concentration.4.Compared to the control group,the average pH of the red soil with clover blossom and straw addition increased respectively 0.39 and 0.34,the average pe+pH decreased 2.12 and 2.52,and the average DOM concentration was 19.1 and 3.4 times higher.For the fluvo-aquic soil,the average pH with clover blossom and straw addition decreased 0.27 and 0.11,the average pe+pH decreased 0.85 and 0.65,and the average DOM concentration was 3.6 and 1.1 times higher respectively.The changes of pH and pe+pH were the result of multiple chemical and electrochemical reactions between different Fe minerals in soil and organic matter.Iron redistribution controlled Cd redistribution.These reactions caused pe+pH declined and pH,Exc-Fe,Oxide-Fe increased for the red soils added with organic matter,and the average Exc-Cd with the clover and straw treatments respectively decline 0.101mg·1^-1 and 0.098mg·1^-1.The trend for the fluvo-aquic soil was opposite.Compare to the control group,the pe+pH,pH,Exc-Fe decreased and Carb-Fe increased when adding organic matter,and the average Exc-Cd with the clover and straw treatments respectively increased 0.441mg·1^-1 and 0.10mg·1^-1.5.Compare to the control group,the concentration of Cd²⁺ in soil solution of the organic matter-treated soils was more clearly affected by complexation of DOM and diffusion of Exc-Cd.6.The difference in composition of organic materials directly affected the content of Exc-Cd in solid phase and the variation of Cd²⁺ concentration.更多还原