西南地区水库的碳效应及其地球化学调控机制

Recently, much attention is payed to effects of reservoirs on the local and global carbon cycles, and amounts of emissions and burials of carbon in reservoirs and behaviors of acting as a carbon source or sink are disputed extensively and intensely. In this proposal we will conduct a study on the carbon balance of emssions and burials in the reservoirs in Wujiang watershed and its tributary, Maotiaohe river, and Chishuihe watersheds in Guizhou. We will carry out the invesgation of CO2 and CH4 concentrations and emission rates in the reservoirs and further discovers the pathways and regulating factors of the gas emssions. Based on the reservoirs' purposes, sizes, shapes, geographical condiations, CO2 and CH4 concentrations, and relationships with catchments, 7-10 resevoirs will be chosen from the investaged ones, in which the monthly and diurnal variations of CO2 znd CH4 concentrations will be observed and emisson flux will be measured with flux chamber technique. Sediment cores will be collected in these erservoirs, and C, N, and P concentration will be measured for the sediment samples. On the basis of dating with 137Cs and 210Pb, the amouts of carbon stored in the reservoirs will be estimated, and the balance of carbon emssions and carbon burial in the reservoirs will be assessed. The chemical composition, carbon isotope of dissolvbed inorganic carbon, pH and O2 variation in a high resolution will be measured in the pore water of the sediment cores. Accordingly, diagenesis of organic and inorganic carbon on the interface of sediment and water, which is significantly afffect by the high sedimentation rate, will be discussed, and the dynamical parameters of organic carbon decomposition will be analyzed. And the mechanism by which diagenesis regulates the carbon balance in the reservoirs will be studied. The coupling of carbon balance in reservors with carbon origin, export, exchange of carbon in watersheds will be disscussed with principle of geochemical cycles. Therefore, the net effect of the reservoirs on the local carbon cycles will be analyzed, by which environmental effect of reserviors will be scientifically and objectively assessed. Finally, the findings that could be obtained in this proposal will provide power means and solid theoretical foundation to discover the effects of the reservoirs in southwestern China on the local and global carbon cycles.

水库对区域乃至全球碳循环的影响是最近一个受到高度关注的热点问题，在水库的温室气体释放量、沉积物碳埋藏量，以及水库到底是一个碳源还是碳汇等方面都存在非常大的争议。本申请将在贵州乌江流域以及支流猫跳河流域，赤水河流域分季节调查不同类型水库CO2、CH4的浓度变化和释放通量，分析水库碳释放的主要途经和影响因素。选择7－10个典型的代表性水库，在核素计年基础上分析沉积物碳埋藏量，阐明水库碳源－碳汇的总体碳效应。结合沉积物孔隙水分析，揭示水库高沉积速率条件下，沉积物－水界面的成岩作用反应，有机质降解的动力学过程以及对水库碳效应的调控。结合流域的研究成果，运用地球化学原理，综合分析流域－水库在碳输出、碳交换过程中的耦合关系，分析水库净的碳效应，进而科学地评估水库在温室气体排放方面的环境效应。研究成果最终为阐明我国西南地区水库对区域碳平衡乃至全球碳循环的影响提供坚实的理论基础。

水库对区域乃至全球碳循环的影响是一个受到高度关注的热点问题，在水库的温室气体释放、有机碳埋藏，以及水库到底是一个碳源还是碳汇等方面都存在非常大的争议。本课题在贵州乌江以及红枫湖流域，通过对地下水、河水、湖（水库）水以及沉积物系统采样，分析了CO2、CH4浓度和释放通量，以及沉积物有机碳埋藏。.结果发现，西南地区碳酸盐岩溶蚀加速了流域碳输出，无机碳输出的速率（8.3 g C m-2 a-1）几乎是有机碳（1.1 g C m-2 a-1）的8倍。水库在释放CO2（1.0±0.2 g C m-2 a-1）的同时又在沉积物中保留有机碳（0.9±0.2 g C m-2 a-1）。水库温室气体释放在不同类型水库中具有明显不同的特征，干流上较大的水库，温室气体释放通量较小，水动力作用较强，水体含氧量比较充分，因而CH4的产率较低，不构成重要的CH4释放源。在支流的一些分层水库中，底层缺氧水体中存在较高的CH4浓度，在水库的下泄过程中会产生较大的下泄水CH4释放。在一些小水库中，存在高的CH4释放，因而具有较大的环境影响。.从流域-湖库系统而言，碳交换的质量平衡显示湖泊水库中的碳主要来自于土壤CO2，属于无机碳，这与已有的观点完全不同。一般的观点认为水体Co2释放主要来自流域输出的有机质在水体内部的降解。无机起源的湖泊水体CO2释放在本质上是土壤CO2回归大气的一个途径，因此湖泊水库CO2释放不属于大气CO2的源。相反，沉积物中有机碳埋藏把大气中的CO2转变为有机碳永久保存在沉积物中，因而这个过程是一个净的大气碳汇。因而现有的观点可能高估了湖泊水库CO2释放的影响，低估了作为碳汇的重要意义。湖泊Co2的无机起源使得常用的评估的碳效应的碳释放/碳埋藏的比值法也不再适用，我们提出用碳埋藏与流域NEP差值可能是更适合的代用指标。在全球尺度上，我们提出评估水体碳效应时应首先区分的来源，否则会得出错误的结论。这一成果已投到地学领域的top期刊，目前正在修改中。