富营养化湖泊藻沉降与氧调控对内源氮循环的协同效应与机制

The cycle of endogenous nitrogen is the key factor leading to the eutrophication and algal blooms in lakes. Algae sedimentation not only directly affects both the transportation and transformation of endogenous nitrogen by uptake or release, but also triggers a synergistic effects combining with oxygen variations, leading to changes of redox conditions and carbon sources, which are vital factors affecting the microbial nitrogen cycling processes. In this proposal, a quantitative study on revealing the cooperative interactions between algae sedimentation and oxygen regulation will be carried out by using stable isotope tracing (15N and 13C) and high resolution microelectrode monitoring in both lab simulation and field experiments. The dynamic characteristics of functional microorganisms (communities) will be identified by combining DNA-stable isotope probing and high-throughput sequencing (i.e., 16S rRNA and metagenomics) to elucidate the microbial nitrogen cycling processes and mechanisms. Moreover, synchrotron-based STXM-XANES will be used to characterize the chemical speciation and microstructure of nitrogen on the sediment-water interfaces to explore the intermediates produced in the key nitrogen cycling processes. The project is expected to establish a scientific basis for the study of endogenous nitrogen cycle and provide new insights into the development of sustainable methods for controlling eutrophication.

富营养化湖泊中内源氮素的循环过程是影响富营养化发生和藻华形成的关键。藻类沉降过程不但会通过吸收/释放直接影响内源氮的迁移转化，而且会与底部氧环境变化过程产生协同效应，导致氧化还原条件和碳源发生变化而影响氮循环的微生物途径。本研究拟通过室内模拟和野外实验相结合，应用稳定同位素示踪（15N和13C）、高分辨微电极监测等技术，定量揭示藻沉降与氧调控之间的相互响应过程与机制，结合DNA同位素标记和高通量测序技术对氮代谢功能微生物（群）的动态特征进行定性和定量研究，揭示藻沉降过程与氧调控过程协同效应下对氮循环微生物途径的影响过程与机制，同时借助同步辐射STXM-XANES技术探测氮素在界面上赋存的化学价态和微观结构，从分子水平解析氮循环的关键过程产物。本课题可以为探究富营养化湖泊中内源氮的循环过程与机制奠定科学基础，同时能为发展长效治理水体富营养化的有效技术提供科学支持。

富营养化湖泊中内源氮素的循环过程是影响富营养化发生和藻华形成的关键。藻类沉降过程不但会通过吸收/释放直接影响内源氮的迁移转化，而且会与底部氧环境变化过程产生协同效应，导致氧化还原条件和碳源发生变化而影响氮循环的微生物途径。本项目采用自主研发的“载氧+吸附”复合功能材料结合絮凝除藻技术对藻华水体进行修复后，能够快速逆转底部厌氧环境，并持续数十天之久（受本项目实验周期限制，仅开展35天），并在水-底泥界面形成好氧-兼氧-厌氧的环境梯度，在水-底泥界面形成关键的好氧隔离层，通过氧化、吸附和物理隔离三个方面的耦合效应，防止底泥和沉降藻中的还原性污染物和氮磷向上覆水中的释放。通过厌氧修复、氧环境梯度的形成以及沉降藻作为碳源和营养物质的供给源，显著改变了水-底泥界面微生态过程，包括参与氮、碳循环过程的功能微生物群落结构。此外，为沉水植被的恢复创造有利条件，促进沉水植物生长过程中有效利用沉降藻中释放的营养盐物质如藻源氮素等，进一步降低了藻源性污染物的二次释放风险，能够为有效控制富营养化和藻华暴发风险提供技术支持。