北方典型浅水湖泊沉积物有机碳沉积特征研究—以白洋淀为例

Characteristics of organic carbon deposition in sediments of typical shallow lake in Northern China:A case study in Baiyangdian Lake

湖泊沉积物中有机碳是全球碳库的重要组成部分,为明确浅水湖泊沉积物中有机碳的沉积特征,采集了白洋淀的沉积柱样品,利用连续提取的方法,分析了沉积物自然沉积过程中水溶性有机碳(WSOC)、热解性有机碳(THOC)、酸解性有机碳(HHOC)、碱解性有机碳(AHOC)和不溶性有机碳(WISOC)的含量变化规律、光谱组分特征及影响因素.结果显示,各有机碳组分垂直方向上含量变化规律一致,均随深度增加呈下降趋势,表层20 cm左右的沉积物中有机碳组分含量普遍较高,含量特征呈WISOC>AHOC>HHOC>THOC>WSOC.用紫外光谱的特征参数SUVA_(254)、SUVA_(280)来分析溶解性有机碳的腐殖程度和分子量大小变化规律,发现腐殖程度与分子量大小变化趋势一致,WSOC和HHOC随深度增加呈增大趋势,THOC随深度增加呈减小趋势,AHOC在0~21 cm阶段随深度逐渐下降,在21~69 cm范围随深度逐渐上升.用A_(300)/A_(400)表征有机碳分子构成,发现THOC、HHOC主要由富里酸构成,WSOC、AHOC主要成分为胡敏酸.用A_(253)/A_(203)表征芳环取代基的种类,发现WSOC、THOC、HHOC苯环上的脂肪链发生聚合反应转化为羰基、羧基等;AHOC的芳香分子上的取代基被微生物代谢分解或转化为脂肪链.相关性分析结果显示,沉积物有机碳及其各组分之间均呈显著正相关,沉积物中的有机碳组分在沉积过程中受到类似的矿化分解作用,且有机碳及其组分含量与C/N值、pH值呈显著负相关.研究成果揭示了白洋淀区域沉积环境中有机碳组分的分布及部分转化规律,可为进一步明确浅水湖泊的碳源-汇的转换关系结构提供数据支持.

Organic carbon in lake sediments is known as the key component of the global carbon pool.In order to clarify the sedimentary features of organic carbon in shallow lake sediments,this paper collected sedimentary column samples from Baiyangdian Lake.Through the application of the continuous extraction method,we analyzed the variation law of water-soluble organic carbon(WSOC),thermal hydrolytic organic carbon(THOC),hydrochloric acid hydrolyzed organic carbon(HHOC),alkali-hydrolytic organic carbon(AHOC)and water-insoluble organic carbon(WISOC)content,spectral composition characteristics and influencing factors in the process of natural deposition of sediments.The results showed that the variations of organic carbon components in the vertical direction were consistent,and all of them showed a downward tendency with the increase of depth.The organic carbon components in the sediments about 20 cm above the surface were generally higher,and their content characteristics were WISOC>AHOC>HHOC>THOC>WSOC.The SUVA_(254) and SUVA_(280) were used to analyze the variation rule of humus degree and molecular weight of dissolved organic carbon.It was found that the variation trend of humus degree and molecular weight was consistent.WSOC and HHOC showed an increasing trend with increasing depth,while THOC showed a decreasing trend with increasing depth.AHOC decreased with depth in 0~21 cm and increased with depth in 21~69 cm.A_(300)/A_(400) was used to characterize the composition of organic carbon molecules,THOC and HHOC were mainly composed of fulvic acid,while WSOC and AHOC were mainly composed of humic acid.A_(253)/A_(203) represented the types of aromatic ring substituents.The aliphatic chains on WSOC,THOC and HHOC benzene ring were polymerized into carbonyl and carboxyl groups,etc.The substituents on AHOC's aromatic molecules were metabolized and decomposed by microorganisms or converted into fatty chains.Correlation analysis showed that there was a significant positive correlation between the organic carbon and its components in the sediments.The organic carbon components in the sediments were subjected to similar mineralization decomposition during the deposition process,and there was a significant negative correlation between the content of organic carbon and its components and C/N value and pH value.The results revealed the distribution and partial transformation of organic carbon components in the sedimentary environment of Baiyangdian Lake,providing data support for further clarifying the carbon source-sink transformation structure of shallow lakes.