富营养化湖泊藻积层有机碳积累动态及驱动机制研究

In shallow eutrophic lakes, the benthic bioclastic deposit accumulates abundant organic carbon derived from algae and macrophytes debris. Study on this deposit therefore shows important theoretical and practical significance to the manipulation of endogenous pollution, to the improvement of water quality, and to the slow down of the aquatic ecosystem decline. With typical algal and macrophytic eutrophic lakes as the study area, this project focuses on the bioclastic deposit, covering topics including the source of organic carbon, migration and transformation of the carbon organic pool, and the relationship between humus development and the ecosystem succession in shallow eutrophic lakes. Various investigative and experimental techniques are to be applied for certain set of studies. Specifically, stable specific carbon isotopic labeling and NMR are employed to analyze the organic functional structure of humus in and/or out of the bioclastic deposit; FT-ICR MS, GC-MS and LC-MS are applied to elucidate how much the organic carbon and algal/macrophytes biomass account for the formation of bioclastic deposit and there contribution to the entire carbon cycle. With the aid of study approaches such as field sedimentation rate calculation and lab operating system simulation, our group plans to make quantitative calculation about the turnover of the organic carbon pool in bioclastic deposit. Based on this, we can decipher the extent that biolcastic deposit humification may account for the lake paludification process, based on the migration and transformation rate, flux, partition coefficient and micro dynamic mechanism of humus in lake bioclastic deposit. In addition, during the rapid sedimentation period of bioclastic deposit, we could assess its influence on the balance of organic carbon pool, identify the ecological effect and regulatory mechanism of bioclastic deposit on the function of organic carbon pool, and exploitate the relationship between bioclastic deposit geochemical process and lake ecosystem succession. Our studies are aimed to provide scientific basis for the eutrophic lake management and water quality improvement.

富营养化湖泊藻类和水生高等植物碎屑残体堆积形成的藻积层，对湖泊有机碳积累过程和水质有显著影响。本项目选择典型的藻型和草型富营养化湖泊，研究藻积层有机碳来源、有机碳库迁移转化规律、腐殖质发育与湖泊生态系统演替的关系。运用稳定碳同位素单体标记、核磁共振谱（NMR）技术分析藻积层腐殖质有机物官能团结构；运用傅里叶变换离子回旋共振质谱、气质联用、液质联用分析藻积层有机碳组成及藻\草生物量对碳循环的贡献；结合湖泊原位沉降速率和室内控制系统模拟定量计算藻积层有机碳库周转速率，揭示藻积层腐殖质在藻积层中迁移转化的速率、通量、分配系数及微观动力学机制。评估快速淤积条件下藻积层对湖泊沉积物碳库平衡的影响，辨明藻积层对湖泊沉积物有机碳库功能的生态效应及影响机理，探讨藻积层地球化学过程与湖泊水质的关系，为调控和改善富营养化水体水质提供科学依据。

针对富营养化湖泊大量水华藻类及水生高等植物（水草）碎屑残体聚集堆积在一些特殊区域，形成以黑色淤积物为主的“藻积层”，以太湖为例，根据湖泊水华藻类及水草碎屑残体的时空分布特征，选择太湖西部竺山湾、湖滨带侵蚀漕、植物围挡区、湖滨滩地围塘等作为不同类型碎屑残体堆积区，通过原位调查、原位试验和室内模拟实验，采用稳定同位素示踪、分子生物学等技术，研究湖泊藻积层的形成及稳定性，阐明了藻源性和草源性黑臭物质来源，揭示藻积层中黑臭物质迁移转化过程及驱动机制，提出基于水环境质量控制的黑臭水体调控途径。发表学术论文26篇，其中SCI期刊论文14篇，国内中文核心期刊论文12篇，部分课题成果为近年来太湖治理的清淤工程实施及湖泛防治提供了有力支撑。.（1）阐明了太湖藻类水华聚积堆积形成的藻积层形成及分布特点， 揭示了太湖富营养化藻类水华、气象水文、湖泊岸线形态等对藻积层形成的影响，发现在藻类快速生长、水华爆发的夏季、春夏及夏秋之交，全太湖发生的蓝藻水华在东南季风的驱动下，聚集堆积到西部近岸、湖湾及漕沟中，形成堆积厚度不等的藻积层。.（2）阐明了藻积层的藻类堆积量直接影响藻积层分解速率和分解产物总量，堆积严重的藻积层在特定气象条件下，会产生致黑、致臭物质，并扩散至局部湖区，导致局部湖区水质黑臭（湖泛）。藻积层分解产生的嗅味物质主要有二甲基硫醚（DMS）、二甲基二硫醚（DMDS）和二甲基三硫醚（DMTS）等硫醚类物质，以及β-环柠檬醛（β-cyclocitral）、β-紫罗兰酮（β-ionone）等。.（3）藻积层分解释放温室气体CO2、CH4等，对全球气候变暖有一定贡献；分解释放氮磷营养盐，加重湖水氮磷负荷，对湖泊富营养化有一定贡献；难降解的一些物质，不断沉降到湖底，导致淤积越来越严重。蓝藻衰亡分解导致沉积物腐殖质中富里酸、胡敏酸、胡敏素三种组分结构发生变化，引起沉积物腐殖化程度升高。.（4）揭示了典型区域藻积层有机碳的来源，阐明了藻积层有机碳组成及迁移转化动态变化特征。藻类分解释放大量可溶性有机碳（DOC）于上水体中， DOC在水-沉积物中进一步发生迁移转化，改变了沉积物-水界面DOC浓度梯度，能够影响沉积物-水界面DOC的迁移过程和DOC扩散通量，同时蓝藻聚积生物量和沉积物性质是DOC迁移转化状态重要的影响因素。