【摘要】：濕地碳循環(huán)中,土壤有機碳不僅能轉化為氣體形式(CO2、CH4)直接釋放到大氣中,也能夠以水溶物形式即可溶性有機碳(DOC),被地表徑流攜帶進入水體,構成碳循環(huán)的另一重要環(huán)節(jié)。目前關于濕地碳循環(huán)的研究主要集中在CO2與CH4的排放規(guī)律,對于DOC在濕地土壤中的遷移轉化則少有關注。本文選取中國亞熱帶季風氣候區(qū)的三種典型濕地(城市次生濕地-杭州西溪濕地、湖泊灘涂濕地-湖州下渚湖濕地、人工濕地-余杭區(qū)徑山水稻田)作為研究對象。通過野外采樣分析觀測濕地土壤DOC含量的分布特征；通過實驗室常規(guī)吸附模擬實驗,得出較短時間尺度上濕地土壤對DOC的吸附特性；借助多種表征手段,進一步揭示濕地土壤對DOC的吸附機理。研究結果表明：1、土壤DOC的含量變化范圍在125.72～512.92 mg·kg-1之間,平均含量為269.72±119.01mg·kg-1,約占TOC平均含量的2%,含量較為豐富。其在土壤剖面中的分布整體呈現出隨土層深度增加而降低的趨勢。三種濕地DOC平均含量的大小順序為：水稻田城市次生濕地湖泊灘涂濕地。土壤理化性質對DOC的分布有一定影響。土壤TOC作為DOC的來源,其含量與DOC含量呈極顯著正相關；高含水率的土壤有利于DOC的產生與積累；土壤全氮、堿解氮與DOC三者之間存在協(xié)同促進關系。通徑分析結果表明：TOC和堿解氮是影響DOC含量分布的兩個相對重要因素,其中TOC的直接影響更大。2、當吸附質初始濃度介于0～45 mg·1-1范圍內時：IM isotherm、Freundlich、 Temkin三種等溫吸附模型都能較好的擬合吸附過程,其中IM isotherm方程的擬合效果最佳。IM isotherm方程中的分配系數m可反映吸附能力強弱,m值越大,吸附能力越強,各采樣點底層土壤均表現出最強的吸附能力。水稻田與城市次生濕地土壤的吸附能力相近,強于湖泊灘涂濕地。土壤吸附DOC的能力受多變量共同影響,其主控因素為土壤pH值、物理性粘粒和活性鋁含量,而土壤TOC、活性鐵及含水率等因子對吸附過程影響不顯著。3、掃描電鏡和比表面積分析表明土壤表面的孔隙結構是決定土壤吸附能力的關鍵因素,孔隙越多,比表面積越大,比表面能越大,對DOC的吸附能力就越強,進而推測土壤吸附DOC過程存在物理吸附機制。傅里葉-紅外測試證實了化學吸附機制的存在,即DOC與土壤礦物羥基之間的配位體交換作用。顆粒物中的脂肪族或芳香族等大分子有機物可能不利于吸附過程的進行。
[Abstract]:In wetland carbon cycle, soil organic carbon can not only be transformed into gas form (CO2,CH4), but also be transported into water by surface runoff in the form of soluble organic carbon (DOC),). Another important part of the carbon cycle. At present, the study on the carbon cycle of wetland is mainly focused on the emission of CO2 and CH4, but little attention has been paid to the migration and transformation of DOC in wetland soil. In this paper, three typical wetlands (urban secondary wetland-Hangzhou Xixi wetland, lake beach wetland-Huzhou Xizhu lake wetland, artificial wetland-Jingshan paddy field) in the subtropical monsoon climate region of China are selected as the research objects. The distribution characteristics of DOC content in wetland soil were observed by field sampling analysis, and the adsorption characteristics of DOC to wetland soil on a short time scale were obtained by conventional adsorption simulation experiment in laboratory. The mechanism of DOC adsorption on wetland soil was further revealed by various characterization methods. The results showed that: 1. The content of DOC in soil ranged from 125.72 to 512.92 mg kg-1, and the average content of DOC was 269.72 鹵119.01mg kg-1, which was about 2% of the average content of TOC. Its distribution in soil profile decreased with the increase of soil depth. The order of average DOC content of the three kinds of wetland is: the secondary wetland lake tidal flat wetland in paddy field city. The physical and chemical properties of soil have a certain effect on the distribution of DOC. As a source of DOC, soil TOC content was significantly positively correlated with DOC content; soil with high moisture content was conducive to the production and accumulation of DOC; and there was a synergistic promotion relationship among soil total nitrogen, alkali-hydrolyzed nitrogen and DOC. Path analysis results show that TOC and alkali-hydrolyzed nitrogen are two relative important factors affecting the distribution of DOC content, among which the direct influence of TOC is greater. 2. When the initial concentration of adsorbate is in the range of 0 ~ 45 mg 1-1: IM isotherm,Freundlich, The three isothermal adsorption models of Temkin can fit the adsorption process well. The best fitting effect of IM isotherm equation is that the partition coefficient m of. IM isotherm equation can reflect the strength of adsorption ability, the larger the value of m, the stronger the adsorption ability. The bottom soil of each sampling point showed the strongest adsorption ability. The sorption capacity of paddy field and urban secondary wetland is similar, which is stronger than that of lake beach wetland. The ability of soil to adsorb DOC is affected by many variables. The main controlling factors are soil pH value, physical clay and active aluminum content, but the factors such as soil TOC, active iron and moisture content have no significant effect on the adsorption process. 3. SEM and surface area analysis showed that the pore structure of soil surface was the key factor to determine the adsorption ability of soil. The more pores, the larger specific surface area and specific surface energy, the stronger the adsorption capacity of DOC was. Furthermore, the physical adsorption mechanism of soil adsorption DOC was inferred. The existence of chemical adsorption mechanism was confirmed by Fourier transform infrared spectroscopy (FTIR), that is, ligand exchange between DOC and soil mineral hydroxyl groups. Macromolecular organic compounds such as aliphatic or aromatic compounds in particulate matter may not be conducive to the adsorption process.
【學位授予單位】：浙江大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：X53

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本文編號：2401585