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题名: 富营养化浅水湖泊氮素分布与硝化作用研究
作者: 陈国元
答辩日期: 2009-06-04
导师: 周易勇
授予单位: 中国科学院水生生物研究所
授予地点: 水生生物研究所
学位: 博士
关键词: 浅水湖泊 ; ; 硝化作用 ; 硝化细菌 ; 限制性片断长度多态性
其他题名: A study on nitrogen distribution and nitrification in shallow eutrophic lakes
摘要: 本文系统研究了我国富营养化浅水湖泊中氮的赋存特征与时空变化规律以及不同营养类型湖泊水体与沉积物中硝化作用自身特点及硝化细菌种群结构的差异,探讨了硝化作用的生物、物理和化学影响因素及其在湖泊富营养化过程中的作用。在所研究的湖泊中,月湖、太湖和滇池等湖泊生态系统中氨氮污染严重,自由氨(NH3)浓度已超过水生动物保护阈值的6-34倍。沉积物间隙水中氨氮占总无机氮的80.1%-97.6%;交换态氨氮占交换态无机氮的71.3%-93.8%。沉积物中大量存在的氨氮为湖水提供了丰富的无机氮源。月湖湖水中无机态氮浓度因季节而迥异,而沉积物中无机态氮含量及其分布则相对稳定。春冬两季湖泊生态系统中无机态氮的浓度显著高于夏秋两季。同时,无机态氮的分布在水平空间上无显著性差异,这说明外源氮输入在月湖这种小型湖泊的无机态氮源分布上不起决定性的作用。水-沉积物界面的氮交换方式存在季节性差异:春冬两季,表层水和上覆水中NO3--N浓度显著高于间隙水中,呈现从湖水向沉积物沉降的趋势;夏秋两季,表层水和上覆水中NO3--N浓度低于间隙水中的含量,呈现从沉积物向上扩散的趋势。NO2--N在水-沉积物界面的迁移规律与之相似。而NH4+-N,一年四季以间隙水中为最高,呈现从沉积物向上扩散趋势。沉积物亚表层(5-10 cm)交换态NO3--N含量最高,而有效态氮与交换态NH4+-N含量最低,故具临界意义。有效态氮多以交换态NH4+-N的形式贮存于表层(0-5 cm)与底层(> 10 cm),且底层含量较高,这种分布与缺氧状态有关。表层沉积物中总氮和有机态氮含量、净氮矿化速率与硝酸还原酶活性均高,间隙水中NH4+-N浓度亦取峰值,而溶解态NO3--N浓度最低,据此提出氮循环的基本过程:有机态氮经矿化产生NH4+-N与NO3--N,同时导致有利于NH4+-N生成的缺氧状态,并促使部分NO3--N异化还原为NH4+-N,二者共同构成表层间隙水中丰富的NH4+-N源。总之,富营养化湖泊表层沉积物富含有机态氮与有效态氮,故为氮生物地球化学循环的最为活跃的层面,而NH4+-N则为最具有效性且含量最高的形态。营养程度较高的湖泊中大量存在的NH4+-N一方面促进了氨氧化菌(AOB)的生长,导致其生物量高;另一方面为氨氧化过程提供了充足的底物,二者共同构成了高氨氧化速率的原因。不同营养类型湖泊水体中,氨氧化和亚硝酸盐氧化过程都是颗粒态活性占主要部分,这有助于硝化细菌抵抗外界不良的环境因子。同时在营养程度较高的湖泊中,氨氧化过程的颗粒态活性部分高于亚硝酸盐氧化过程的颗粒态活性部分。因此, 相对氨氧化过程来说,营养程度较高的湖泊水体中亚硝酸盐氧化过程受到高浓度NH3、高pH值更强烈的抑制,最终导致高氨氧化速率,低亚硝酸盐氧化速率的情况,从而引起水体中NO2--N的累积。AOB和亚硝酸盐氧化菌(NOB)生物量上的差异以及丰富的NH4+-N源是导致沉积物中高氨氧化速率,低亚硝酸盐氧化速率的原因。基于AOB的氨单加氧酶基因(amoA)的限制性片断长度多态性(RFLP)和系统发育分析表明,营养程度高的湖泊沉积物中AOB的amoA序列多样性高于营养程度低的湖泊,同时不同营养类型湖泊沉积物中amoA序列有较大差异。就AOB而言,Nitrosomonas oligotropha- Nitrosomonas ureae和Nitrosospira属于广布种,但是在不同营养类型湖泊中所处地位不一样。N. oligotropha-N. ureae在营养程度高的湖泊沉积物中占主要地位, 而Nitrosospira是营养程度低的湖泊沉积物中的主要种类。N. communis只能在营养程度高的湖泊沉积物中检测到。就NOB而言,Nitrospira是营养程度比较低的湖泊沉积物中的主要种类,而Nitrobacter是高营养型湖泊沉积物中的优势种群。硝化细菌的这种种群结构一定程度上是由湖泊生态系统中的环境因子(如:底物的浓度状况、pH值等)以及硝化细菌自身的生理特性(如:对底物的亲和力、生长速度等)决定的。硝化细菌一方面通过增加种类和功能基因的多样性去适应高营养类型湖泊的复杂环境,另外一方面通过改变优势种群去适应营养程度不同的各种湖泊环境。硝化细菌的这些适应机制保证了不同营养类型湖泊生态系统中硝化作用的稳定性,促进了NH4+-N的氧化和NO3--N的形成,为反硝化除氮提供了底物。 总之,营养程度高的湖泊中的高浓度氨氮一方面促进了硝化细菌的生长,一方面为硝化作用的发生提供了充足的底物,同时增加了硝化细菌种群结构的多样性,使生长速度块,硝化活性强的硝化细菌为优势种群,从而导致高速率硝化作用的发生,加速了氧的消耗。同时,高浓度NH3不仅对水生生物有很强的毒性效应,而且它对NOB的抑制作用又促进了水体中NO2--N的累积。因此,在富营养化湖泊治理与修复过程中必须加强对氨氮的控制。
英文摘要: In order to find out the key biological factors and physichemical variables that govern and influence nitrification, thereby, have a deep insight into the nitrification mechnism and its role in nitrification, we studied the spatial and temporal variations in different nitrogen species, and the difference in nitrification rates and the population structure of nitrifying bacteria in water and sediment in Chinese shallow lakes with different trophic levels. Among the study lakes, Lake Yuehu, Lake Taihu and Lake Dianchi were great polluted by ammonia, and the concentrations of free ammonia (NH3) in water were 6-34 times higher than the threshold above which biota in aquatic environment will be toxified. The concentrations of ammonia accounted for 80.1%-97.6% of total inorganic nitrogen in interstitial water and the exchangeable ammonium concentrations accounted for 71.3%-93.8% of total exchangeable nitrogen. The large amount of ammonia in sediment offer a abundant supply for nitrogen in water. The inorganic nitrogen concentrations in water were liable to the change of season, while sediment was a relatively stable system. The inorganic nitrogen concentrations in winter and spring were higher than those in summer and autumn. There was no significant difference in spatial distribution of nitrogen, which indicates that external nitrogen input was not a crucial factor determining the inorganic nitrogen distribution in Lake Yuehu. The nitrogen exchange between water-sediment interface had a seasonal variation. In winter and spring, the NO3--N concentrations in surface and overlying water were higher than those in interstitial water, which indicated that NO3--N tended to sink from water into sediment. In summer and autumn, the NO3--N concentrations in surface and overlying water were lower than those in sediment, indicating that NO3--N tended to release from sediment to water. NO2--N had the same trend as NO3--N between water-sediment interface. But, NH4+-N concentrations in interstitial water were always higher than them in surface and overlying water in the four seasons, which revealed that NH4+-N diffused up to water from sediment all the time. The subsurface sediment (5-10 cm) was a critical layer in which exchangeable nitrate contents were the highest and exchangeable ammonium and available nitrogen contents were the lowest. Available nitrogen stored mainly in the form of exchangeable ammonium in both surface (0-5 cm) and the deep layers (> 10 cm) where its content was higher, this distribution can be explained with anaerobic conditions. The surface sediment not only showed higher contents of both total and organic nitrogen, rates of N-mineralization and nitrate reductase activities, but also gave the highest ammonium and the lowest nitrate concentrations in interstitial water. Therefore, as a nitrogen cycling mode, it is proposed that organic nitrogen was remineralized to ammonia and nitrate with the former being nitrified into the later, resulting in anaerobic conditions that contributed to ammonia accumulation by the production of its own and nitrate reduction in interstitial water of surface sediment. Shortly, enriched by organic nitrogen, the surface sediment in eutrophic lakes is the most active dimension for the biogeochemical cycling of nitrogen with ammonia being the major and most effective form. The large amount of ammonia in the lake with high trophic level not only accelerate the growth of ammonia-oxidizing bacteria (AOB), in term of significantly enhanced biomass, but also supply enough substrate for nitritation, leading to the high nitritation rates. In the water of lakes with different trophic levels, particle-associated nitritation and nitratation rates were the main part of total nitritation and nitratation rates, which can help nitrifying bacteria to resist the bad environmental factors. In the lake with high trophic level, the proportion of particle-associated nitritation was higher than that of particle-associated nitratation. So, the high pH values and high concentration of ammonia in the more eutrophic lakes had more adverse effects directly on the nitratation activity that was less protected via particle association, which will inhibite nitratation step in concert, leading to a transient NO2--N build-up. And in sediment, due to both the larger amount of AOB relative to nitrite-oxidizing bacteria (NOB) and the abundant ammonia as its substrate, nitritation rates were significantly higher than nitratation rates. Additionally, restriction fragment length polymorphism(RFLP)targeting the amoA and phylogenetic analysis revealed that AOB in the sediment of lakes with high trophic levels had greater diversity of amoA gene than them in the sediment of lakes with low trophic levels, and there were significant difference between the amoA genes in lakes with different trophic levels. Nitrosomonas oligotropha- Nitrosomonas ureae and Nitrosospira were ubiquitous, but they had different distribution in lakes with different trophic levels. N. oligotropha-N. ureae dominated in the sediments of Yujia Basin, while, Nitrosospira dominated in the sediments of Tuanhu Basin. N. communis was only detected in the eutrophic Yujia Basin. For NOB, Nitrospira dominated in the sediments of Tuanhu Basi, while, Nitrobacter dominated in the sediments of Yujia Basi. This characteristic of nitrifiers population structures can be explained by the sharp differences in environmental conditions (e.g. substrate concentrations, pH values and et al.) between the two basins and heterogeneity in physiological characteristics (e.g. substrate affinity, growth rates and et al.) among the dominant nitrifiers species. In the lakes with high trophic level, nitrifying bacteria increase diversity of amoA genes and species to adapt to the complex environment, furthermore, they can chang dominant species to adapt to the varying environment in the lakes with different trophic levels, which facilitate the stabilization of nitrification in different trophic lakes, accelerating the oxidation of NH4+-N and production of NO3--N that supply the substrate for denitrification. Conclusively, the high NH4+-N concentrations in lakes with high trophic level accelerate the growth of nitrifiers and supply abundant substrate for nitrification. On the other hand, the large amount of NH4+-N increase diversity of nitrifiers species and the species with high growth rates and oxidation activity are the dominant nitrifiers, which lead to high nitrification rate and accelerate the consumation of dissolved oxygen. At the same time, high NH3 concentration has strong toxicity to aquatic organisms and the inhibition to NOB accelerates NO2--N build-up in water. So, it is very important to control ammonia for the improvement and restoration of eutrophic lakes.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.ihb.ac.cn/handle/342005/12498
Appears in Collections:中科院水生所知识产出(2009年前)_学位论文

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Recommended Citation:
富营养化浅水湖泊氮素分布与硝化作用研究.陈国元[d].中国科学院水生生物研究所,2009.20-25
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