有机质对湖泊沉积物-水界面磷迁移转化的影响机理研究

Phosphorus is a key factor for lake eutrophication, and organic matter is the important component of sediment in the lake, which directly affects the transport and transformation of internal phosphorus in the aquatic ecosystem. Considerable researches have indicated that the organic matter has relative good correlation with phosphorus cycling, and its composition and decomposition play a critical role in the release and absorption of phosphorus between sediment-water interface, but the mechanism that organic matter influnces the phosphorus behavior has not been elucidated. The objectives of this study are to investigate the composition and decomposition characteristics of organic matter in water suspended particles, settlement particles and surface sediments, as well as to analyze quantitatively phosphorus exchange in the sediment-water interface of the eutrophic Lake Taihu through field sampling and laboratory simulaiton experiment analysis. 13C nuclear magnetic resonance spectroscopy (13C-NMR) technology is applied to spatiotemporal distribution of organic matter in water suspended particles, settlement particles and surface sediments, other technologies are used to obtain the characteristic parameters of phosphorus, including 31P-NMR technology，diffusive gradients in thin films technique and oxygen isotopic composition of dissolved inorganic phosphate. Afterwards, the effects of organic matter on phosphorus transport and transformation in the sediment-water interface will be further analyzed together with variation of micro-environment. The resutls may be great useful to understand the biogeochemical process of phosphorus and the theory of lake eutrophication. Furthermore, the study can provide scientific reference for ecological control of lake eutrophication.

磷是湖泊发生富营养化的重要影响因子。有机质作为湖泊沉积物的组分之一，其在湖泊内源磷的迁移转化过程中扮演重要角色，但目前关于有机质对内源磷的影响机理尚不清晰。为此，本项目以典型富营养化湖泊-太湖为研究对象，以有机质和沉积物-水界面磷为研究重点，采用野外采样与室内模拟实验相结合的方法，借助13C核磁共振（13C-NMR）技术获取湖泊有机质组成的时空分布特征及不同来源有机质的分解特征；综合运用31P核磁共振（31P-NMR）技术、薄膜扩散梯度及磷酸根氧同位素技术，确定沉积物-水界面磷的组成、矿化速率及释放通量等特征参数，定量分析沉积物-水界面磷的迁移转化过程，探讨有机质组成及分解对沉积物-水界面磷迁移转化的影响；结合微环境的变化特征，进一步阐明有机质对磷迁移转化的影响机理。研究成果有助于深入理解磷的生物地球化学过程，丰富和完善湖泊富营养化研究理论及方法，并可为富营养化湖泊的生态治理提供科学依据。

开展有机质与沉积物-水界面磷迁移转化过程的关系研究对深入认识湖泊富营养化具有重要意义。本项目以典型富营养化湖泊—太湖为研究对象，以有机质和沉积物-水界面磷为研究重点，采用野外采样与室内模拟实验相结合的方法，利用不同方法获取沉积物有机质组成的时空变化特征；定量分析沉积物-水界面磷的迁移转化过程；探讨有机质组成及分解对沉积物-水界面磷迁移转化的影响。研究结果表明：（1）太湖沉积物总有机质平均含量为1.60%。竺山湾、梅梁湾和胥口湾沉积物总有机质浓度要高于其它湖区。活性有机质占太湖沉积物总有机质的比例为26-39%，而且活性有机质和总有机质空间变化趋势一致。太湖沉积物水溶性有机质占总有机质的比例为9-24%，其空间差异较小。太湖沉积物有机质分子量偏大，腐殖化程度较高。（2）太湖沉积物重组有机质对磷的吸附能力最大，并且对磷元素具有较好的积累。去除部分有机质的沉积物吸附量低于原沉积物。沉积物有机碳组成与其总有机碳含量的关系并不显著。根据化学位移将有机碳分为羧基碳、酚醛基碳、芳香烃、2-烷基碳、氧烷基碳、烷基碳和甲氧基碳，其中烷基碳所占比例最高，好氧条件下所有官能团结合碳与沉积物磷初始值（S0）呈显著负相关；除了酚醛基碳外，其他官能团结合碳均与吸附解吸平衡浓度（EPC0）呈显著负相关，而与最大吸附量（Smax）呈显著正相关；厌氧条件下，所有官能团结合态碳与反映磷吸附解析能力的参数关系均不显著。（3）水华消长期间，沉积物总磷组成相对稳定，污染严重的湖区主要以无机磷为主。竺山湾沉积物内源磷释放通量最大值为26mg/m2/d，峰值出现在7月和8月，且和Fe2+的释放通量呈显著正相关，表明铁价态的变化对磷的迁移影响较大。（4）水生植物分解会导致水体pH值降低，溶解氧含量下降。并且不同的水植物分解对水体pH值和溶解氧含量影响也不相同。水环境的改变会影响到表层沉积物的磷形态以及磷在沉积物-水界面的迁移过程。