洪泽湖不同植被类型湿地甲烷排放规律及其影响机制研究

Lakes are important atmospheric methane (CH4) emission sources, and CH4 emissions from lakes are being increasingly attentioned by scientists. Hongze lake is one of the most important wetland resources in Huaihe River Basin, which is greatly affected by anthropogenic activities. However, methane emissions from Hongze lake and the microbiological mechanism are still indeterminate. In this study, Phragmites australis, Nymphoides peltatum, Potamogeton malaianus in the littoral zone, and open water in the littoral zone and the pelagic zone are selected for the measurement of CH4 fluxes. The object of this study to (1) understand the CH4 emission intensity of the artificial type wetlands, natural wetlands in the littoral zone, and open water in the littoral zone and pelagic zone; and (2) evaluate the effects of different wetland types on CH4 emission from Hongze lake. Meanwhile, we will measure the temporal variation of soil redox, dissolved CH4 concentration in pore water of soil, dissolved organic carbon (DOC), dissolved oxygen, in order to reveal the key factors controlling the variation of CH4 emission rates. Laboratory incubation experiments, by using 13C isotope trace technique and molecular biotechnology, are carried out to investigate the association of dynamic variation of CH4 production potential with dominant communities of methanogens and methanotrophs among different wetland types. This study will reveal the methane-related microbial community variation of different wetland types and the effects on CH4 emissions from Hongze lake, then provide basic scientific data for evaluation of CH4 emissions from lakes.

湖泊是重要的大气甲烷排放源，其甲烷排放越来越被关注。洪泽湖是淮河流域重要的湿地资源，受工农业活动影响较大。然而，洪泽湖不同植被类型湿地甲烷排放及其影响机制如何，尚不明晰。本项目拟选取洪泽湖湖滨芦苇、荇菜、马来眼子菜及湖滨和湖心开放水面等典型湿地为研究对象，连续监测不同植被类型湿地甲烷排放通量，定量估算湖滨和湖心的甲烷排放强度，通过对比分析，明确不同植被类型湿地对洪泽湖甲烷排放的贡献；同步测定土壤和水中甲烷浓度、水溶性有机碳、溶解氧、氧化还原电位等动态变化，甄别甲烷排放季节性变化的关键驱动因子；运用13C同位素示踪和分子生物学技术，研究不同湿地甲烷产生潜力、产甲烷功能菌与甲烷氧化菌群落特征，阐明洪泽湖不同植被类型湿地甲烷排放的微生物机制，为准确评估洪泽湖甲烷排放量提供科学依据。

项目围绕洪泽湖不同植被类型湿地甲烷排放规律及其影响机制展开研究，重点研究了：（1）洪泽湖不同植被类型湿地甲烷和氧化亚氮排放通量的差异及其影响因素；（2）评估了洪泽湖不同植被湿地的综合增温潜势（GWP）及其产甲烷途径的差异；（3）洪泽湖不同植被湿地产甲烷潜力的变化特征及其微生物机制。研究工作紧紧围绕项目计划任务书的内容展开，已经达成预期目标。共发表研究论文4篇，获得授权实用新型专利1项，培养研究生2名，获批省级大学生创新创业项目2项。主要进展如下：（1）洪泽湖不同植被类型湿地的CH4排放呈现出明显的较为一致的季节变化，CH4排放通量的大小表现为开放水面＜空心莲子草＜芦苇＜荷花，年平均值依次分别为0.72、0.87、0.89和1.15 mg CH4 m-2 h-1；不同植被湿地N2O排放的季节变化并不显著，其年平均排放通量为23.62-26.58 μg N2O m-2 h-1，空心莲子草湿地N2O排放通量最高，但不同植被湿地差异不大；主成分分析结果表明，气温、水位、NH4+-N浓度是控制CH4和N2O排放通量季节变化的关键因素。（2）洪泽湖不同植被湿地CH4年累积排放量为44-91 kg CH4 ha-1 yr-1，N2O年累积排放量为1.53-2.36 kg N2O ha-1 yr-1，洪泽湖湿地GWP为1818-2813 kg CO2-eq ha-1 yr-1，CH4排放的贡献率达67.94%-79.39%；相对于CO2+H2的产甲烷途径，乙酸产甲烷途径对洪泽湖不同植被湿地甲烷产生的贡献可能更大，但其贡献大小随植被类型的不同而变化较大。（3）洪泽湖不同植被湿地冬夏两季的产CH4潜力具有明显的差异，冬季产CH4潜力均远低于夏季，夏季产甲烷潜力是冬季的112-167倍；洪泽湖的产CH4潜力均随着底泥土壤SOC和DOC含量的增加而逐渐增加，不同植被湿地产CH4潜力与CH4年平均排放通量大小表现出不一致的变化规律，这可能与产甲烷菌的群落结构有关；洪泽湖不同植被湿地的产甲烷菌均以氢营养型为主，而甲基营养型和乙酸营养型产甲烷菌的比例较小；不同植被湿地的优势产甲烷菌目均为甲烷微菌目（Methanomicrobiales），但开放水面湿地甲烷杆菌目（Methanobacteriales）的相对丰度是有植被湿地的1.7-2.0倍。