湖泊蓝藻暴发期沉积物-水界面氮的昼夜变化规律与机制

Cyanobacterial bloom, which is resulted from lake eutrophication, is a major national and global environmental problem, and nitrogen is one of the key restrictive factors for the cyanobacterial growth. Because of the diel variation of cyanobacteria vital activities, the microenvironment of the sediment-water interface (SWI) is very different between day and night. And nitrogen cycling on the SWI is likely to show regular diel variation. There, on the basis of accurately investigating the diel variation of nitrogen on the SWI, we can deeply understand the release of nitrogen from sediments and its effect on cyanobacterial bloom..This project takes Lake Taihu as the research object, which has cyanobacteria bloom disaster seriously. The advanced technology, including microelectrodes, diffusive gradients in thin films, 15N isotope labelling and functional GeoChip, will be employed to monitor the microenvironment, dissolved inorganic nitrogen, nitrogen flux, nitrogen cycling processes and related functional microbes of the SWI during cyanobacterial blooms in the field and enclosure experiments to characterize the diel variation of the SWI nitrogen cycling. The diel variation of the SWI nitrogen cycling during cyanobacteria blooms will be further studied in the microcosm experiments to explore the mechanism involved. The results of this project will develop the theory of nitrogen cycling in eutrophic lakes and deepen the understanding of the occurrence mechanism of cyanobacterial bloom.

氮是湖泊富营养化的主要限制因子之一。蓝藻生命活动的昼夜变化造成水体环境和沉积物界面微环境的昼夜差异，理论上界面氮循环也将呈现有规律的昼夜变化。因此，在精准把握界面氮昼夜变化规律的基础上，才能深刻认识沉积物氮对蓝藻暴发的影响。.本项目拟以典型富营养化湖泊太湖为研究对象，利用微电极、薄膜扩散梯度、以及15N同位素标记和功能基因芯片等先进技术，通过对湖区和围隔沉积物-水界面氮形态、通量与主要转化过程的昼夜跟踪研究，揭示界面氮循环的的昼夜变化规律；通过条件因子控制实验，考察氮循环过程中界面微环境和相关微生物结构和功能变化，进一步阐明蓝藻水华暴发期间界面氮昼夜变化的主要机制，为发展富营养化湖泊氮营养盐循环理论、制定科学的富营养化治理策略提供科学依据。

研究揭示了典型藻区梅梁湾沉积物-水界面溶解态氮（氨氮、硝氮和亚硝氮）和细菌氮转化过程与其他月份显著不同的时间段，包括蓝藻水华复苏阶段1-2月、蓝藻水华暴发初期4月和蓝藻暴发高峰期6月。在这个时间段，沉积物-水界面溶解态氨氮含量较低，硝氮和亚硝氮含量较高，固氮和尿素水解是较活跃的细菌氮转化过程。模拟实验揭示，蓝藻暴发期沉积物-水界面的溶解态氨氮、硝氮、亚硝氮、DGT可获取态氨氮和硝氮的昼夜变化不明显，但溶解态总氮浓度呈现出白天大于夜晚的变化特征，尿素水解是主要的细菌氮转化过程，且夜晚显著高于白天。总之，研究结果显示蓝藻暴发期，沉积物-水界面的尿素水解过程是主要的细菌氮转化过程，可能为蓝藻生长提供重要氮源。本项目研究为发展富营养化湖泊氮营养盐循环理论、制定科学的富营养化治理策略提供重要科学依据。