【作者】 柳勇；

【导师】 徐建明；

【作者基本信息】 浙江大学 ， 土壤学， 2013， 博士

【摘要】 水稻土中五氯酚(PCP)的转化与归宿被广泛研究。PCP在缺氧/厌氧条件下的降解比好氧条件下更快。水稻土的淹水条件创造了好氧-厌氧的兼性环境,致使土-水界面的生物地球化学过程更为复杂,从而有关土-水界面PCP降解过程的研究也变得更加引入关注。本文揭示了水稻土中PCP还原降解与Fe(Ⅱ)累积的关系及其影响因素,阐明了不同种类低分子量水溶性有机化合物(LMW-DOC)和绿肥水溶性有机物(紫云英DOM)两类有机碳源作为电子供体、有机配体或电子穿梭体对PCP还原降解的促进作用及其生物化学机制,评估了绿肥(紫云英和苕子)作为修复调理剂对土壤PCP的转化的影响,取得的主要结果如下：(1)研究了不同种类的LMW-DOC(包括14种低分子量有机酸和8种中性单糖)对土冰界面PCP降解和Fe(Ⅱ)累积动力学的影响。Logistic非线性拟合和聚类分析的结果表明,动力学参数因不同LMW-DOC种类而异,主要表现为因LMW-DOC分子的碳原子数、解离常数和还原度不同,而导致了乙酸钠提取态Fe(Ⅱ)[Fe(Ⅱ)NaOAc]和盐酸提取态Fe(Ⅱ)[Fe(Ⅱ)Hcl]的最大累积量、累积速率常数和最大累积速率明显不同；LMW-DOC分子的还原度不同,也导致了PCP的最大累积量明显不同。相关分析的结果表明,Fe(Ⅱ)NaOAc和Fe(Ⅱ)Hc1的最大累积量与PCP的最大降解率之间存在显著的相关性。根据这一现象,采用生物化学、化学和电化学分析手段并结合相关分析、多元回归分析、冗余分析等数理统计方法进一步研究了微生物参数和环境变量的动态与Fe(Ⅱ)累积和PCP降解动态的关系。结果表明,Fe(Ⅱ)Hc1是对PCP降解起决定性作用的环境变量；pH是影响微生物群落结构分布的关键因子,且因不同LMW-DOC种类而异,总体上pH值的升高有利于Fe(II)NaOAc含量的增加,后者明显促进了PCP的降解,pH值降低和Eh升高时PCP的降解速率也有所下降；Fe(II)/Fe(Ⅲ)电对是对阳极氧化峰电位(Ep)起决定作用的氧化还原电对,在不同LMW-DOC作用下,pH和/或可溶性有机碳(WSOC)变化引起Ep值随时间变化表现出明显的差异,同时也导致Fe(II)Hc1累积和PCP降解的程度有所不同；Fe(II)Hc1和Ep分别比Fe(II)NaOAc和Eh更能反映PCP还原降解的生物化学机制。(2)研究了淹水/好气腐解过程中紫云英DOM的产生、消耗与性质动态变化,评价了不同紫云英DOM的氧化还原容量和氧化还原态的差异性。相关分析和主成分分析的结果表明,在不同的氧化还原条件下,紫云英DOM氧化还原容量和氧化还原态的改变与其替代参数(生物化学物质、原子比、傅里叶红外光谱吸收比、重均/数均分子量、紫外光谱吸收比、还原度、特征性紫外可见光谱吸收等)的变化有关,因此可以用多种仪器分析手段(紫外-可见光谱分析、傅里叶红外光谱分析、凝胶渗透色谱分析、元素分析等)间接量化紫云英DOM的氧化还原性质。(3)研究了不同种类的紫云英DOM(包括新鲜的、淹水腐解7d和14d的及好气腐解7d和14d的紫云英DOM)对土冰界面PCP降解和Fe(Ⅱ)/Fe(Ⅲ)消长动力学的影响。结果表明,不同紫云英DOM处理均可促进淹水土壤中PCP的降解和Fe(Ⅱ)NaOAc或Fe(Ⅱ)NaOAc+HC1(连续提取)的累积,且PCP降解因不同种类紫云英DOM而表现出明显的时段性,而连续提取方法反映了Fe(Ⅲ)与F(Ⅲ)之间的相互转化程度因Fe(Ⅱ)NaOAc占Fe(Ⅱ)NaOAc+HC1的比例大小而异；同时,紫云英DOM性质的多个替代参数与Fe(Ⅱ)NaOAc的最大累积量具有明显的相关关系,但单个替代参数并不能说明多因素共同决定的紫云英DOM的氧化还原反应性。根据这一现象,采用生物化学和化学分析手段并结合相关分析、多元线性回归分析、冗余分析等数理统计方法进一步研究了微生物参数和环境变量的动态与Fe(Ⅱ)累积和PCP降解动态的关系。结果表明,Fe(Ⅱ)NaOAc+HC1是对PCP降解起决定性作用的环境变量；随着WSOC的消耗和pH值的升高,Fe(Ⅱ)NaOAc和Fe(Ⅱ)NaOAc+HC1浓度均有所增加,因而促进了PCP的降解；Fe(Ⅱ)NaOAc+HC1比Fe(Ⅱ)NaOAc更能反映PCP还原降解的生物化学机制。(4)研究了不同添加量(包括1%和3%)的紫云英和苕子对土冰界面PCP降解和Fe(Ⅱ)累积动力学的影响。结果表明,动力学参数因不同绿肥添加量和种类而异,主要表现为DOM的初始紫外-可见参数不同,将导致Fe(Ⅱ)NaOAc的最大累积速率明显不同。根据这一现象,采用化学和电化学分析手段并结合相关分析、多元线性回归分析等数理统计方法进一步研究了环境变量的动态与Fe(Ⅱ)累积和PCP降解动态的关系。结果表明,Fe(Ⅱ)NaOAc是对PCP降解起决定性作用的环境变量；pH值和WSOC含量的变化与绿肥种类关系不大,但因不同添加量而异,紫云英和苕子添加量较低时,pH值的升高和WSOC的消耗有利于Fe(Ⅱ)NaOAc含量的增加,后者明显促进了PCP的降解,pH值降低时PCP的降解速率也有所下降,这在紫云英和苕子添加量较高时表现的尤为明显；Fe(Ⅱ)/Fe(Ⅲ)电对是对Ep起决定作用的氧化还原电对,在不同量紫云英和苕子作用下,Ep值随时间变化表现出明显的差异,同时也导致Fe(Ⅱ)NaOAc累积和PCP降解的程度有所不同；Fe(Ⅱ)NaOAc较能反映PCP还原降解的生物化学机制。更多还原

【Abstract】 The transformation and fate of pentachlorophenol (PCP, C6Cl5OH) in paddy soils have been extensively studied. It is known that the degradation rate of PCP in paddy soils is higher under anoxic/anaerobic conditions than under aerobic conditions. In flooded paddy soils, the biogeochemical processes at the soil-water interface are more complex than those in the bulk soil due to the presence of adjacent anaerobic and aerobic zones. Thus, study of the degradation process of PCP at the soil-water interface has gained increasing attention from researchers. The aims of this study were:1) to examine the relationship and influencing factors of PCP degradation and Fe(Ⅱ) accumulation in a flooded paddy soil;2) to elucidate the promoting effect and associated biochemical mechanisms of different organic carbon sources [low-molecular-weight dissolved organic carbon (LMW-DOC) compounds and Chinese milk vetch dissolved organic matter (CMV-DOM)] as electron donors, organic ligands or electron shuttles on the reductive degradation of PCP in the flooded paddy soil; and3) to evaluate the effect of green manures (Chinese milk vetch and bird vetch) as amendment on the transformation and fate of PCP in the flooded paddy soil. The primary findings are summarized as follows:(1) The effect of different LMW-DOC compounds (fourteen organic acids and eight neutral monosaccharides) on the kinetic parameters of Fe(Ⅱ) accumulation and PCP degradation at the soil-water interface. Logistic curve fitting and cluster analysis showed that the kinetic parameters of Fe(Ⅱ) accumulation and PCP degradation significantly varied with different organic ligands and/or electron donors as well as carbon sources for Fe(Ⅲ) reduction and PCP degradation. The large variations in the number of carbon atoms per molecule, dissociation constants, and degree of reduction of the LMW-DOC led to substantial differences in the maximum capacities for accumulation, accumulation rate constants, and maximum accumulation rates of NaOAc-extractable Fe(Ⅱ)[Fe(Ⅱ)NaoAc] and HCl-extractable Fe(Ⅱ)[Fe(Ⅱ)HCl]-Different degree of reduction of the LMW-DOC also caused significant changes in the maximum capacities for accumulation of PCP. Correlation analysis demonstrated that there was a significant relationship between the maximum capacities of Fe(Ⅱ) accumulation and PCP degradation. Based on the above results, the relationship of microbial parameter (phospholipid fatty acid, PLFAs) and selected environmental variables with the kinetic parameters of Fe(Ⅱ) accumulation and PCP degradation was examined using biochemical, chemical and electrochemical analysis tools in combination with correlation analysis, regression analysis and redundancy analysis. Results showed that Fe(Ⅱ)HCl was the key environmental variable that played a decisive role in PCP degradation. The pH value, which varied with different types of LMW-DOC, was a key factor that determined the structure and distribution of soil microbial communities. Overall, the increase in pH promoted to Fe(Ⅱ)NaOAc accumulation and further significantly enhanced PCP degradation. The pH decreases and Eh increases were associated with decreases in the degradation rate of PCP. Fe(Ⅱ)/Fe(Ⅲ) was the redox couple that determined the anodic peak potential (Ep). In the presence of different LMW-DOC, the changes in pH value and/or WSOC content led to significant differences in the Ep value over time as well as different degrees of Fe(Ⅱ)HCl accumulation and PCP degradation. As compared to Fe(Ⅱ)NaOAc and Eh, Fe(Ⅱ)HCl and Ep were more indicative of the biochemical mechanism of the reductive degradation of PCP.(2) The dynamic changes in CMV-DOM production, consumption, and properties during decomposition under continuously-flooded (CF) and non-flooded (NF) conditions, and the differences in the redox capacity and redox state of CMV-DOM between fresh and CF-/NF-decomposed samples. Correlation analysis and principal component analysis showed that under different redox conditions, the changes in the redox capacity and redox state of CMV-DOM were related to large variations in the surrogate parameters (biochemical index, atomic ratio, Fourier transform infrared absorption ratio, weight-average/number-average molecular weight, ultraviolet absorbance ratio, degree of reduction, and ultraviolet spectral absorbance ratio). Thus, it is possible to indirectly predict the redox properties of CMV-DOM through a variety of instrument analyses (ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, gel permeation chromatography, and elemental analysis).(3) The effect of different CMV-DOM (fresh, NF-decomposed for7d and14d, or CF-decomposed for7d and14d) on the kinetic parameters of PCP degradation and Fe(Ⅱ)/Fe(Ⅲ) accumulation and disappearance at the soil-water interface. Addition of fresh or CF-/NF-decomposed CMV-DOM significantly enhanced the degradation of PCP and the accumulation of Fe(Ⅱ)NaOAc or Fe(Ⅱ)NaOAc+Ha (sequential extraction) in the flooded paddy soil. Results of sequential extraction showed that the degree of transformation between Fe(Ⅲ) and Fe(Ⅱ) varied with the ratio of Fe(Ⅱ)NaOAc to Fe(Ⅱ)NaOAc+HCl·In addition, most surrogate parameters of CMV-DOM properties were significantly related to the maximum capacity for Fe(Ⅱ)NaOAc accumulation. However, a single surrogate parameter could not explain the variations in the redox reactivity of fresh and CF-/NF-decomposed CMV-DOM that were jointly determined by multiple factors. Based on the above results, the relationship between selected microbial parameters as well as environmental variables and the kinetic parameters of Fe(Ⅱ) accumulation and PCP degradation was examined using biochemical and chemical analysis tools in combination with correlation analysis, regression analysis, and redundancy analysis. Results showed that Fe(Ⅱ)NaOAc+Hcl was the environmental variable that played a decisive role in PCP degradation. The consumption of WSOC and the increases in pH led to increases in the Fe(Ⅱ)NaOAc and Fe(Ⅱ)NaOAc+HCl concentrations, thus contributing to PCP degradation. As compared to Fe(Ⅱ)NaoAcl Fe(Ⅱ)NaOAc+HCl is more indicative of the biochemical mechanisms involved in the reductive transformation of PCP.(4) The effect of different dosages (1%and3%) of Chinese milk vetch (Astragalus sinicus L.) and bird vetch (Vicia cracca L.) on the kinetic parameters of PCP degradation and Fe(Ⅱ) accumulation at the soil-floodwater interface. The kinetic parameters of PCP degradation and Fe(Ⅱ) accumulation significantly varied with the dosage and type of green manures. The variations in the initial ultraviolet-visible spectral parameters of DOM led to significant changes in the maximum rates of Fe(Ⅱ)NaOAc accumulation. Based on the above results, the relationship between selected environmental variables and the kinetic parameters of Fe(Ⅱ) accumulation and PCP degradation was examined using chemical and electrochemical analysis tools in combination with correlation analysis and regression analysis. Results showed that Fe(Ⅱ)NaOAc was the key environmental variable that played a decisive role in PCP degradation. The changes in pH value and WSOC content significantly varied with the dosage rather than the type of green manure added into the soil. At a low dosage of Chinese milk vetch or bird vetch, the pH increase and WSOC consumption greatly enhanced Fe(Ⅱ)NaOAc accumulation and thus contributed to PCP degradation. The degradation rate of PCP decreased with pH decreases, especially at a relatively high dosage of Chinese milk vetch or bird vetch. Fe(Ⅱ)/Fe(Ⅲ) was the redox couple that determined Ep. At different dosages of Chinese milk vetch or bird vetch, the Ep value significantly varied over time, leading to different degrees of Fe(II)NaOAc accumulation and PCP degradation. Fe(II)NaOAc could well explain the mechanisms involved in the reductive transformation of PCP.更多还原