径流变化下雅鲁藏布江生源物质迁移转化过程及微生物作用机制

The transportation process of biogenic matter under runoff regulation is a frontier subject of international scientific problem. Researches into the influencing mechanisms of high dams with large reservoir on the biogenic matter circulation meet the great need of ecological environment protection of water conservancy and hydropower development in China. Studies based on the biogenic matter of nitrogen and silicon transformation process in Yalung Zangbo River are of important value to achieve the goals of grand schemes. In this project, Yalung Zangbo River will be investigated with “The transportation process of biogenic matter under runoff regulation” as the core, systematically studying and identifying the distribution and variation processes of runoff, water temperature, silt, nitrogen, silicon and microorganism; the variant process of multi-material during the inflow and outflow of Zangmu Hydropower and its impact on the flux of nitrogen and silicon; and the response between algae growth process and runoff variation in this special region. The aims of this project are to solve the key scientific problems of the dynamic procedure and interacting mechanism of various substances of water-silt-microorganism-biogenic matter under the extreme environmental conditions (high altitude, low pressure, strong ultraviolet, notable temperature difference between day and night, measurable variation in runoff and oligotropher), which represents the characteristics of highland rivers in our country.The results of this project will provide the basic theory and scientific support for exploiting waterpower resource and protecting ecological environment synergistically in southwest china.

径流变化下生源物质迁移转化过程研究是国际前沿科学问题，开展高坝大库对生源物质循环过程影响机制研究符合国家水利水电开发生态环境保护的重大需求，基于雅鲁藏布江生源物质氮、硅迁移转化过程的研究对重大计划目标实现具有重要价值。本项目拟以“径流变化下生源物质迁移转化规律”这一问题为核心，以雅江为对象，系统研究查明这一重要区域的径流、水温、泥沙、氮、硅和微生物的分布规律与变化过程，藏木水库入库与出库多要素变异过程及对氮、硅通量的影响机理，低温长光照背景下雅江藻类生长过程与径流变化的响应，解决具有高原河流特点的极端环境条件下（高海拔、低气压、强紫外、昼夜温差大、径流变化大、寡营养等）水—沙—微生物—生源物质多要素变化过程及其相互作用机制的关键科学问题，为我国西南地区水能资源开发和生态环境保护协同提供基础理论和科学支撑。

径流变化下生源物质迁移转化过程研究是国际前沿科学问题，开展高坝大库对生源物质循环过程影响机制研究符合国家水利水电开发生态环境保护的重大需求，基于雅鲁藏布江生源物质氮、硅迁移转化过程的研究对重大计划目标实现具有重要价值。本项目以高原河流雅鲁藏布江为主要研究区域，并在梯级水电开发河流澜沧江开展对比研究，探讨了自然条件下雅江不同江段生源物质分布规律及通量变化，分析了藏木水库生源物质迁移转化过程变异及通量变化，阐释了高寒条件下雅江微生物特性及对生源物质转化的作用机理，为我国西南地区水能资源开发和生态环境保护协同提供基础理论和科学支撑。结果表明，生源要素氮在雅江均值达2.01 mg/L（TN），在藏木水库库区显著下降且降幅达36%；生源要素硅在雅江沿程下降且降幅达77.8%（DSi）；生源要素磷在雅江浓度范围为0.04至0.31 mg/L（TP），在藏木水库库区增幅超过120%；生源要素碳在雅江沿程下降48.2%（DOC）。生源物质通量计算结果表明，梯级水电开发显著加剧了单级水电开发对生源要素通量变化的影响且具有空间累积效应。通过微生物16S rRNA基因高通量测序手段发现，雅江藏木水库对微生物群落结构无显著影响，而梯级开发河流澜沧江微生物群落结构发生显著变化。“距离衰减效应”使微生物群落结构相似性均随地理距离和环境异质性增大而降低，且梯级水电开发下微生物群落的距离衰减效应更为显著。微生物基因芯片结果表明，固氮作用功能基因丰度在雅江及澜沧江流域均为最高，且厌氧氨氧化作用对水电开发的扰动最为敏感，其中澜沧江七级梯级水库的影响是雅江单级水库的5倍。室内机理研究表明，强光照下昼夜温差的减小有利于硅藻梅尼小环藻生物量的积累，且其光利用率增加，光合活性上升。强光照还提高了梅尼小环藻对硅的亲和力，较小的昼夜温差下梅尼小环藻对硅的竞争力更高。昼夜温差不断缩小将更有利于梅尼小环藻在低营养盐环境中生存。且在强光环境下硅藻对硅的吸收显著高于弱光环境，其对溶解性硅的固定效率更高。