三峡水库中段泥沙沉降/淤积条件下CH4产汇机制研究

Methane released from reservoirs has gained widespread attention as global warming issue. According to the traditional views, organic matters from inundated soil and vegetations were the main carbon sources of methane. However, as an exterior source, organics which flow into reservoirs by sediments, make the fate and transport of methane complicated. The contribution of exterior organic carbon to the methane release from reservoirs needs to be determined. The mid-reach areas of the Three Gorges Reservoir, which have significant sediment deposition, are selected in this project in order to analyze our hypotheses about both fate and transport way of methane under the influence by sediments. The methane distribution in water, characteristics of sediments and bottom sludge as well as microbial formations, will be studied. The discharge of methane caused by input organic matters by sediments will be calculated and the relationship between sediment and methane will be analyzed. In addition, the possible cooperating metabolism ways by different functional bacteria of methane will be studied. The present proposal will provide a solid basis for future studies of the discharge of greenhouse gases in the Three Gorges Reservoir.

随着国际社会对温室气体的关注，水库CH4释放问题得到越来越多学者重视。传统观点认为，水库蓄水后，受淹土壤、植被等有机质在缺氧或厌氧条件下降解，是CH4释放的重要来源。但外源有机物随泥沙进入库区后，水库CH4的产汇关系变得复杂，外源有机物对水库CH4产汇贡献有待论证。本课题以三峡水库中段为研究区域，针对该区段泥沙沉降/淤积的特殊水文环境，围绕水体CH4时空分布特征、泥沙/底泥特性及微生物区系组成等开展基础研究，评估随泥沙输入的外源有机碳对库区温室气体排放的贡献值，揭示泥沙运动与CH4产汇的相互关系，推导库区水体中各功能菌群可能存在的协同代谢途径，阐释三峡水库中段泥沙沉降/淤积条件下CH4产汇机制，为三峡水库温室气体排放后续研究提供理论基础。

来自陆地大量有机碳源的输入，以及三峡库区调度运行和筑坝蓄水导致 CH4等碳源气体的排放成为近来关注的热点。本研究以三峡库区干流中段为研究对象，针对该区段泥沙沉降/淤积的特殊水文环境，研究期内对忠县（ZX），万州(WZ)，涪陵（FL）进行逐月采样分析，探求水−气界面CH4 通量在水库不同运行工况下的变化特征，研究泥沙/底泥特性及微生物区系组成等，获得以下主要成果：. （1）在观测期间内，三峡库区中段三个采样点上覆水CH4浓度范围为0.02~0.91 μM·L-1，无论在低水位还是高水位运行期间，上覆水CH4浓度峰值均出现在相应低流量时期。低水位运行期间，上覆水CH4浓度倒数与水位呈正相关，通量在水库低水位运行期均表现为“汇”。有机碳呈现明显异源输入特点，并随着有机碳含量增加而促进CH4产生。高水位运行期间，自源性有机碳占比增加，CH4浓度同时受如温度等多种因素影响。通过与国外已有水库监测数据比较分析，CH4扩散通量在全球水库序列中处于中等偏下水平。 . （2）采样点水体秋季的细菌多样性大于春季，上游细菌群落多样性更为丰富。沉积物中细菌群落随时间推移种类更多，且细菌在底泥中种类更加丰富。水体与底泥中细菌群落结构完全不同。水中产甲烷菌多样性指数比泥中低，但群落结构差异不明显。研究区域主要以甲基营养型与氢营养型产甲烷菌为主。甲烷氧化菌丰度逐月递增。水体和泥中甲烷氧化菌群落结构完全不同，且都随时间变化明显变化。. （3）底泥中甲烷通量、TOC和TN显著影响甲烷氧化菌群落结构，水体中硝氮、TOC、DO、水温对甲烷氧化菌群落影响较大。研究区域产甲烷效率高的乙酸营养型占比较少，产甲烷效率很低。且优势菌种Type II型甲烷氧化菌对甲烷利用速率较高，甲烷功能菌群落结构造成研究区域甲烷释放通量低于其他淡水水体。. 本项目执行期间已发表论文7篇，其中境外SCI论文3篇，EI论文2篇，中文核心论文2篇。中英文待发表论文6篇。培养硕士生6名。研究成果为三峡水库温室气体排放后续研究提供理论基础。