【作者】 刘兆云；

【导师】 章明奎；

【作者基本信息】 浙江大学 ， 土壤学， 2013， 博士

【摘要】 由于黑炭具有特殊的理化性质,使其具有影响全球碳循环、土壤性质和环境中污染物迁移能力等环境意义。研究黑炭在不同土壤中的积累分布规律及其稳定性,可为深入而全面的理解人为活动对黑炭积累分布的影响、土壤中黑炭的稳定性机理、土壤有机碳库对全球环境变化的作用及合理管理土壤提供科学依据。论文在全面评述黑炭在不同类型土壤中的积累分布特点、在土壤环境中的转化及其表面化学性质变化的基础上,采样分析了几种代表性土壤中黑炭的积累与分布规律；利用培养实验和化学氧化方法模拟黑炭进入土壤初期生物与非生物降解过程、不同强度非生物降解过程以及不同时间尺度下黑炭的降解过程,并运用物理、化学和仪器分析方法对降解后黑炭的形貌特征、化学结构、表面性质及其对有机污染物吸附规律的变化进行研究,获得如下主要结果：(1)从浙江省采集了受人类活动不同程度影响的表层土壤和剖面土壤,用化学分析的方法测定土壤中黑炭的含量。结果发现：林地土壤中普遍存在黑炭,枯枝落叶层、表土层(0-10cm)和亚表土层(10～20cm)黑炭数量分别为0.27-67.63,0.83～22.42和0.27～8.72g kg-1,各占有机碳总量的0.12%-13.14%,1.87%～21.40%和3.31%～27.13%。近40年内发生过火灾的样区枯枝落叶层和表土层黑炭质量分数明显高于近期没有发生过火灾的土壤,但近期是否发生火灾对亚表层黑炭积累无明显影响。地形位置对土壤中黑炭的积累也有一定的影响,积累量在山坡坡脚区域明显高于坡顶和上坡。代表性城市土壤黑炭在0～15.22g kg-1之间,平均为3.83g kg-1,变异系数达51.96%,主要集中分布在1～5g kg1之间。城市土壤黑炭平均含量由高至低依次为：工厂厂区土壤>城郊蔬菜地土壤>城市道路附近土壤>城市绿地土壤。黑炭占城市土壤有机碳的比例在0%-53.2%之间,平均为24.83%,该比例由高至低为工厂厂区土壤>城市道路附近土壤>城郊蔬菜地土壤>城市绿地土壤。另外,在水耕人为土壤中,黄斑田土壤有机碳库低于青紫泥田和烂青紫泥田,黑炭占有机碳总量的4.2%-24.6%,在黄斑田和青紫泥田中随深度降低,而在烂青紫泥田中剖面上下差异不大。研究还发现土壤中的黑炭颗粒较小,主要出现在“粘粒”粒级中,随剖面深度增加黑炭颗粒趋向减小。(2)采用直接从不同火灾发生历史记录并有明显黑炭积累的土壤中分离出黑炭样品,并对土壤中黑炭的表面化学性质及其变化进行了初步研究,发现随着黑炭进入土壤后保存时间的延长,黑炭的C含量在67.30%～88.3%之间,逐渐降低；O含量在7.2%～18.6%之间,H含量在1.2%～3.1%之间,有逐渐增加的趋势；同时,CEC在0.17～42.44cmol kg-1之间,逐渐增加;比表面积在48～132m2g1之间逐渐降低。碱性基团在2.65～18.93cmol kg-1之间,也随着形成时间增加趋向减少,而羧基、酸性基团及总基团数分别在16.59-63.24、38.66～124.17和50.80～1298.39cmol kg-1之间,随形成时间的增加而增加。对代表性样品的红外光谱鉴定也表明,随着黑炭进入土壤后保存时间的增加含氧官能团(羧基、羰基、羟基等)均有明显的增加。(3)为了比较生物与非生物降解过程对黑炭矿化速率及其表面性质的影响程度,采用实验室模拟的方法研究了黑炭进入环境初期生物与非生物降解过程对其矿化速率、比表面积、孔隙结构、表面官能团及其对有机污染物吸附能力的影响。结果表明,在30-C培养条件下,添加外源微生物能够促进黑炭的矿化,且累积释放的CO2的量比非生物降解条件下累积释放的CO2的量多；但经生物降解后黑炭表面含氧官能团、比表面积和孔径分布与经非生物降解后黑炭的相比无显著性差异。温度能够影响非生物降解过程中黑炭的矿化速率及其累积释放C02的量,黑炭在70℃非生物降解过程中的矿化速率和累积释放CO2的量均显著大于其在30℃非生物降解过程中的矿化速率和累积释放CO2的量。而且,经70-C非生物降解后黑炭的表面含氧官能团、比表面积、孔径分布和对硝基苯的吸附能力与经30-C生物降解后黑炭的相比均有显著性差异,说明高温条件下空气对黑炭的氧化过程对其表面性质的影响比30℃条件下外源微生物的降解过程对其的影响更加显著。(4)为了更深入的了解不同强度非生物降解过程对黑炭性质的影响,选取了70℃条件下热空气氧化(弱氧化)、双氧水氧化(强氧化)和浓硝酸氧化(极强氧化)等三种不同氧化强度的非生物氧化方法对黑炭性质的影响进行了研究。结果发现,经热空气氧化后黑炭的孔隙被堵塞导致其比表面积和总孔体积减小。而经双氧水和浓硝酸氧化后,黑炭的初始结构被破坏,形成碎片粒子,这些碎片粒子堆积可形成狭缝孔,从而增加了黑炭的比表面积和总孔体积。氧化强度最大的浓硝酸能够将黑炭的孔隙结构破坏的最彻底。而且,经浓硝酸氧化后黑炭的表面形成的含氧官能团的数量最多,元素组成的变化程度最大。(5)由于黑炭具有高度的稳定性,直接开展黑炭在环境中经不同时间尺度降解后其性质变化的研究极具挑战性,因此本研究利用培养试验(培养周期为1年,培养温度为30℃)和浓硝酸剧烈氧化的方法分别模拟黑炭在环境中发生的短期降解过程和黑炭进入环境中极长一段时间后的降解过程。研究结果表明,经短期环境降解后黑炭的比表面积、孔体积及其对有机污染物的吸附能力均有显著变化,但其表面含氧官能团及表面碳氧元素比无显著性变化；经长期的环境降解后黑炭的比表面积、孔体积、表面含氧官能团及其对污染物的吸附能力有显著性变化。在氧化过程中黑炭性质的变化与黑炭的种类(如制备黑炭的生物质及制备温度)和氧化条件有关。由氧化引起的黑炭性质的变化,会对富含黑炭的土壤的性质存在潜在性的影响。更多还原

【Abstract】 Due to its special physical and chemical properties, black carbon can be used to enhance soil fertility, adsorb contaminants and sequester atmospheric C in terrestrial systems to offset C emissions and combat global climate change. Investigating the accumulation and stability of black carbon can provide a scientific basis to better understanding the effect of human activities on the accumulation of black carbon, the stability mechanism of black carbon, the contribution of black carbon on the global climate change and soil management.This dissertation, which is supported by the Natural Science Foundation of China (N0.40771090;4047164), aimed to understand the effect of human activity on the accumulation, the changes in chemical composition and surface chemical properties of black carbon in soils due to long-term natural oxidation, the contribution of biotic and abiotic oxidation on the degradation of black carbon, the effects of different intensity of abiotically oxidation conditions (hot air, hydrogen peroxide and nitric acid) on black carbon stability, and the impacts of short-and long-term degradation on the surface properties of black carbon and its potential implications on soil. The main conclusions are as follows:(1) The surface soil and profile soil samples have been influenced by human activities to varying degrees in Zhejiang Province, and deterimined by chemical analysis method. The resuts showed that the mean content of black carbon in litter, surface layer and subsurface layer in the forest soils were3.96,6.91, and3.39g kg-1in that order, accounting for0.96%,8.07%, and11.82%of the soil total organic carbon (TOC), respectively. From40sites experiencing fire events within the last40years, black carbon in the litter and0-10cm soils was significantly higher than soils without a record of fire (p<0.05), whereas in the10-20cm soils fire events had no major impact on black carbon content (p<0.05). In the hilly area, accumulation of black carbon in the soils was generally higher on the low part compared to the top and upper part. The contents of black carbon in urban soils ranged from0to15.22g kg-1, and averaged in3.83g kg-1. Mean contents of black carbon in urban soils for different land uses were in the order manufacture area> vegetable land in suburban area> road in urban area> green space in urban area. Proportion of black carbon in total organic carbon ranged from0%to53.2%with the mean of24.83%. The proportion decreased in the sequence of manufacture area> road in urban area> vegetable land in suburban area> urban green space. In fluvimarine plain, total organic carbon pool in1m soil profile was lower in silty-clayey yellow mottled paddy soil on fluvialmarine than those of blue clayey paddy soil and gleyed blue clayey paddy soil in typical stagnic anthrosols. Black carbon, accounted for4.2%-24.6%of the total soil organic carbon, decreased with increasing depth for silty-clayey yellow mottled paddy soil on fluvialmarine and blue clayey paddy soil, and was even for gleyed blue clayey paddy soil. However, black carbon tended to be richened in clay component. The size of black carbon decreased with increasing profile depth.(2) Black carbon samples were collected from several historical fire-impacted sites from Zhejiang Province and were investigated the changes in chemical composition and surface chemical properties. The results showed that compared with new formed black carbon, soil black carbon exhibited a much lower surface area and alkaline groups, which were in the range of48-132m2g-1and2.65-18.93cmol kg-1, respectively. In contrast, carboxyl, acid groups and total group increased, their contents were16.59～63.24,38.66～124.17and50.80-1298.39cmol kg-1, respectively. Additionally, infrared spectroscopy identification of representative samples also showed that O-containing functional groups increased distinctly with the increase of time. Therefore, above results suggest that soil environments, land use, and formation time of black carbon may all have an impact on soil carbon biogeochemical cycles and soil biological chemistry.(3) In order to compare the importance of biotic and abiotic degradation on the properties changes of black carbon, the laboratoty simulated studies were used. The results showed that the labile fractions and stability of black carbon depend on the type of black carbon. In the condition of incubation at30℃, additional microbe can promote the mineralization of black carbon caused more CO2is released than abiotic degradation. However, in this condition, there is no significant changes in the surface oxygen-containing functional groups, surface area, and pore distribution after biotic degradation compared to abiotic degradation. The amount and rate of released CO2of70℃abiotic oxidation is more than that of30℃biotic oxidation. Additionally, surface oxygen-containing functional groups, surface area, pore distribution, and adsorption properties changed significantly after70℃abiotic oxidation. These results indicated that the severe oxidation provide more contribution to the black carbon degradation than microbe oxidation.(4) We used chemical oxidation method to investigate the effects of oxidative intensity on the changes of black carbon properties. The results showed that the changes of black carbon properties significantly depended on oxidative intensity. Hot air oxidation could cause blockage in pores of the original black carbon, which may explain the decrease in surface area and total pore volumes. While these parameters increased dramatically after nitric acid and hydrogen peroxide oxidation, as the structure of the original black carbon was severely destroyed, and the smaller size particles formed the slit-like mesopores. The data of FTIR spectra and zeta potentials indicated that nitric acid fixed the most oxygen-containing functional groups. These oxidation led to changes in elemental composition of black carbon. The nitric acid oxidized black carbon was shown to have highest oxygen content. These findings suggest that the changes of properties of black carbon oxidized by abiotic processes may affect black carbon environmental behavior.(5) A simulated oxidation technique was used to examine the impacts of degradation on the surface properties of biochar and the potential implications of the changes in biochar properties were discussed. To simulate the short-and long-term environmental degradation, mild and harsh degradation were employed. Results showed that after mild degradation, the black carbon samples showed significant reductions in surface area and pore volumes. After harsh degradation, the black carbon samples revealed dramatic variations in their surface chemistry, surface area, pore volumes, morphology and adsorption properties. The results clearly indicate that changes of black carbon surface properties were affected by black carbon types and oxidative conditions. It is suggested that black carbon surface properties are likely to be gradually altered during environmental exposure. This implies that these changes have potential effects for altering the physicochemical properties of black carbon amended soils.更多还原