三峡水库碳排放机制研究

Governments pay more and more attention to the fact that reservoirs cause carbon emission on different degree, and it also becomes a hot issue attracting scientists recently. The natural geographical conditions and water environment situations of the Three Gorges Reservoir are clearly different from lakes or reservoir reported previously. Methods of the in situ observation and indoor physical model simulation will be adopted in this project to study the carbon emission resulted from the Three Gorges Reservoir. Based on high resolution and frequency sampling and analysis for sediment, sediment-water interface, water and water-air interface (organic matter content and form, the concentration and fluxes of CO2 and CH4, and stable carbon isotopic composition of organic matter and CO2 and CH4), and monitoring environmental physical, chemical and hydrology factors synchronously, this project try to reveal the releasing fluxes of CO2 and CH4 from water-air interfaces of the mainstream and distributaries, and their respective principles. Relationship between the CO2 and CH4 fluxes and the main factors will be analyzed. It is expected that the formation mechanism of CO2 and CH4 for the organic matter in sediments and waters can be exposed by this project, and the migration and transformation mechanism of CO2 and CH4 diffusing toward the water surface can be clarified, especially of the situation of these processes during different water level and its variation range of the Three Gorges Reservoir. The mineralization rate of organic matter in sediments and future trend of carbon emission for the reservoir will be analyzed preliminarily. In addition to contributing science knowledge about carbon emission about large reservoirs of river-type, the results of this study can also provide scientific basis for carbon emission evaluation of the similar reservoirs, and for reducing carbon emission with changing water environment factors through ecological operation of reservoirs.

水库存在不同程度碳排放的事实越来越受到各国政府的重视，水库碳排放也成为科学家新近关注的热点问题。三峡水库自然地理状况和水环境条件等明显不同于已有研究报道的湖泊或水库。本项目拟采用野外原位观测和室内沉积物培养模拟相结合的方法，利用碳稳定同位素分析和沉积物微电极系统观测技术等，通过对沉积物、沉积物-水界面、水体和水-气界面的观测与分析（有机质含量与形态、CO2和CH4浓度与通量及碳稳定同位素组成等），同步监测环境理化因子和水文因子，分析三峡水库干流、支流库湾各界面CO2和CH4通量、规律、影响因素，揭示沉积物中和水体中CO2和CH4生成、迁移与转化机制，特别是相关过程在水库不同水位与变幅下的情景，并初步评估新生沉积物有机质的矿化速率与未来碳排放趋势。研究成果可提升对河道型大型水库碳排放问题的认识，并为评价类似水库的碳排放、及如何使用生态调度改变水体环境因子分布状况从而减少水库碳排放等提供依据。

水库存在不同程度碳排放的事实越来越受到各国政府的重视，水库碳排放也成为科学家关注的热点问题。三峡工程是世界上最大的水利枢纽工程，水库的修建使土地利用方式改变，导致碳排放问题，水库自然地理状况和水环境条件等明显不同于已有研究报道的湖泊和水库。本项目采用野外原位观测对三峡水库典型支流库湾和干流等水域进行连续的水-气界面CH4和CO2通量的原位监测和环境调查，研究水体内CH4和CO2的生成与迁移转化，通过室内柱状沉积物培养模拟实验，分析沉积物内CH4和CO2的形成与迁移、转化机制，研究沉积物有机质矿化速率，初步定量化评估未来碳排放趋势，丰富科学认识自然的意义，同时为科学评价三峡水库调蓄运行初期的碳排放和未来趋势，使用生态调度改变库湾水体的环境因子分布状况从而减少碳排放等提供科学依据。结果表明：干流监测点郭家坝水-气界面CH4和CO2昼夜性通量不仅在一个昼夜变化很大，不同季节的平均值变化也很大，各个季节昼夜性CH4通量变化幅度均大于相应的CO2通量，观测期间内季节性CH4和CO2通量分别在0.01～0.12mg·m-2·h-1、8.96～263.56mg·m-2·h-1，均值分别为0.05mg·m-2·h-1、104.43mg·m-2·h-1，月平均的CH4和CO2通量与昼夜性通量的均值十分接近；支流香溪河库湾年内CH4通量在-0.120～31.008mg·m-2·h-1，其昼夜性通量在4月和10月变化大，8月变化相对较小，10月CH4昼夜性通量平均为0.081mg·m-2·h-1，与8月相接近，而远小于4月，4月昼夜性通量平均值分别为8月和10月的3.6倍和3.8倍。2014年11月至2015年1月，CO2和CH4分压在不同的月份有明显的变化，2013年9月至2013年11月神农溪表层水体溶解CO2浓度在165.33～510.54μmol·L-1，CH4浓度在0.04～0.32μmol·L-1，监测点处表层水体CH4与CO2浓度随着水位的变化具有明显的波动与平稳交替变化特征。埋藏于海水环境的沉积物释放的CH4和CO2通量均高于埋藏于淡水沉积物，海水环境下平均CH4和CO2通量分别为淡水的2倍和1.87倍，相同温度下沉积物在海水环境中降解速度更快，另外表层沉积物中51.8%的CH4被氧化，当温度达到35℃时77.4%的CH4被氧化，甲烷的产生与氧化与温度呈明显的正相关，随着