藏木电站蓄水运行对雅鲁藏布江河流生源物质输送的影响

Zangmu hydropower station is the only large hydropower project in the main stream of Yarlung-Zangbo River now, which is running in November 2014. Through systematical observations and analyses of hydrology, water chemistry of upstream, reservoir, and downstream profile of Zangmu hydropower station, form composition and concentrations changes change feature of important biogeochemical substances (carbon, nitrogen, phosphorus, and silicon) in river after dam reservoir regulation would be clarified. Internal driving mechanisms about the influences of reservoir sedimentation and catagenesis on source or sink transformation of fluvial biogenic substances would be revealed by environmental sedimentology study of the reservoir area. Nutrition dynamas of phytoplankton community succession were studied after impoundment to explore coordinated variation mechanisms between primary productivity during transformation from river to lake and paludification and transportation of river biogeochemical substances. Combined with the related historical data, quality equilibrium relationship among biogenic elements in river-reservoir system would be built up, and total effects of anthropogenic damming in plateau river on geochemical process variations of biogenic elements would be quantitatively evaluated. New scientific cognitions in the aspect of basic theory of effects of river dammings in plateau cold regions would be acquired, which would be the vital basis for profoundly understanding and thorough evaluating the influences of hydropower development on ecology and environment of the Yarlung-Zangbo River, and is the important content of important scientific programs in the major rivers in southwestern China.

藏木电站2014年11月投产运行，是目前雅鲁藏布江干流唯一建成的大型水电站。项目通过入库、库区水体及坝下控制断面水文和水化学的系统观测，明晰藏木电站蓄水后河流重要生源物质（碳、氮、磷、硅）的浓度及形态组成变化特征；通过库区环境沉积学研究，揭示水库沉积作用、沉积物水界面反应与河流生源物质“源-汇”转化的内在联系；通过水库浮游植物演替的营养动力学研究，探索水库湖沼化进程与生源物质迁移转化的协同演变机制；结合历史观测资料，建立河流-水库系统生源物质的质量平衡关系，定量评估藏木电站建设运行对河流生源物质影响的总体效应。项目实施，将在筑坝拦截对高原寒区河流影响的基础理论方面取得新的科学认知，可为深刻认识和全面评价雅鲁藏布江水电梯级开发生态环境影响提供支持，是西南径流重大科学计划的重要内容。

以藏木水库为主要研究区域完成了雅鲁藏布江流域及阿里河流水系的连续观测，2018年重点完成了前期观测成果的总结分析，完成了项目任务的要求。数据分析与文章发表工作也将继续深入，相关成果将继续署名本项目资助完成。本项目取得了如下三个方面的研究成果：.第一，通过两年的野外观测，以藏木水库为重点，完成了雅江及阿里水系3次系统采样调查工作，获取了两个水期（丰水、枯水）水化学、生源物质、微生物、沉积物数据集。形成了雅鲁藏布江及阿里水系河流基础水化学特征的总体认识。在弱碱环境下，雅江大部分采样点都处于方解石的平衡过饱和状态，水体无机碳同位素值（13CDIC）为约为-9.873‰至-1.644‰，证实了水体CO2浓度主要来源于岩石风化带入的DIC转化。雅江水-气界面碳排放通量为1.445×1010 mol yr-1，占流域碳总输入的16.6%，雅江CO2脱气作用较弱。.第二，在原位观测的基础上，通过对数据的分析研究定量评估了藏木电站建设运行对河流生源物质影响的总体效应。.第三，由于土地利用类型的多样性，河流受地理位置、地形地貌、气候及人类活动等因素的影响，其氮转化机制也呈现多样性。西藏湖泊中的氮转化机制受人类活动影响相对较小，硝氮主要来源于土壤有机氮和大气干沉降。硝化作用和反硝化作用则是湿地生态系统中氮转化的主要机制。藏木水库内存在反硝化脱氮作用增强的趋势，水库氮转化机制的变化同样可能影响河流水体中氮的通量和组成。. 项目执行期间，培养博士研究生1名，硕士研究生3名，发表论文4篇，申请发明专利2项，获大禹奖二等奖1项。