胶州湾盐沼生态系统卤代甲烷的释放与影响机制

Methyl halides are the important carrier of halogens in the atmosphere, and they play an important role in tropospheric and stratospheric ozone depletion. Meanwhile, methyl halides can act as greenhouse gases in the atmosphere, and they are also environmentally significant because of their toxicity. Coastal salt marshes, are the important intertidal ecosystems at the land-ocean interface, have been suggested to be a large potential source for methyl halides. However, the global budget of these trace gas is uncertain, and less study has been conducted on the release of methyl halides from coastal salt marshes so far in China. In order to evaluate the effects of methyl halides emission from coastal salt marshes to the atmospheric environment, the naked beach and three tidal marshes , which were dominated respectively by Spartina, Suaeda salsa and Phragmites and located in different water and salinity gradient of Jiaozhou Bay, are selected as study objects, and the methyl halides flux characteristics, annual change rules and the main affecting factors of coastal wetland will be studied for two years by using static-chamber and gas chromatography-mass spectrometry. To define the responses of tidal to emissions of methyl halides, undisturbed soil column with living plants and sea water samples will be taken from salt marsh and sediment cores will be incubated under the flooding simulation by a simulating device of our own design. The results of the study not only can improve the list of halogenated methane emissions from coastal salt marshes in China, but also can offer important theoretical basis and data which is propitious to assess contribution of methyl halides from salt marshes in china..

卤代甲烷是破坏臭氧层的主要物质，也是重要的痕量温室气体和有机污染物。目前，其源汇的全球预算存在很大的不平衡性。受海陆两相交互作用影响的海岸带盐沼是卤代甲烷重要的自然来源。然而，目前国内非常缺乏海岸带盐沼卤代甲烷气体释放的相关研究。鉴于此，本项目选择胶州湾盐沼位于不同水盐梯度上的光滩、大米草带、盐地碱蓬带、芦苇带作为研究对象，运用静态箱-气相色谱-质谱法，系统研究盐沼卤代甲烷排放的通量特征、时空变化以及关键的影响因素，并采用原状土柱（生长有植被）与现场海水样品，利用自主试制的模拟装置，模拟潮汐不同淹水时间对卤代甲烷释放的影响。探讨潮汐作用（涨落潮过程、淹水时长）对盐沼生态系统卤代甲烷排放的可能机理。研究结果一方面可以完善我国海岸带盐沼卤代甲烷的排放清单，另一方面可以为评估我国海岸带盐沼在全球卤代甲烷气体释放中的贡献提供理论依据和数据支持。

卤代甲烷（CH3Cl、CH3Br和CH3I）是挥发性卤代烃之中最简单的一类化合物，但却是破坏臭氧层的主要物质。近十几年来的研究已表明海岸带盐沼是卤代甲烷重要的自然释放源，国际上关于盐沼卤代甲烷在时间和空间上的数据均十分缺乏，特别是国内关于盐沼卤代甲烷的研究非常有限。本研究以胶州湾盐沼互花米草样带以及光滩为研究对象，通过野外原位观测和室内分析，运用静态箱-气相色谱法，对卤代甲烷排放规律以及关键影响因子进行了研究。研究结果表明：（1）胶州湾盐沼卤代甲烷（CH3Cl、CH3Br和CH3I）的日变化趋势不完全一致。互花米草样带CH3Cl日排放通量峰值出现在13:00，谷值出现在23:00；CH3Br排放通量则在10:00最高，在3:00达到最低值。（2）胶州湾盐沼互花米草样带的卤代甲烷的月排放量高于光滩，CH3Cl的月排放量在4-7月和9-11月期间较高，CH3Br和CH3I的排放量在9-11月相对较高。（3）胶州湾互花米草样带生长季和非生长季三种气体的排放通量均为正值，且生长季的排放量大于非生长季。互花米草样带是卤代甲烷的排放源。光滩中卤代甲烷的释放通量在生长季和非生长季既有正值又有负值，说明光滩既是卤代甲烷的源又是卤代甲烷的汇。（4）植物割除实验和潮汐淹没实验表明植被地上部分是卤代甲烷的源，植被地上部分释放卤代甲烷。潮汐淹没促进卤代甲烷的释放。（5）CH3Cl和CH3Br的排放通量与互花米草叶生物量、总生物量以及土壤中TOC、TS、AS以及盐度呈极显著正相关，CH3I排放通量与大部分指标相关不显著，可能有CH3I不稳定有关。（6）胶州湾盐沼CH3Cl、CH3Br和CH3I总的排放量分别为0.035μmol•m-2•d-1、11.56 nmol•m-2•d-1和5.73 nmol•m-2•d-1，总的来说，胶州湾盐沼是卤代甲烷的排放源，但和世界其他盐沼相比，胶州湾盐沼卤代甲烷的排放通量处于较低水平。（7）胶州湾互花米草湿地CH3Cl与CH3Br排放通量具有显著的相关性（P＜0.01）。 CH3Cl与CH3Br排放通量的摩尔比的平均值为16.64。研究结果一方面可以更好的完善我国海岸带盐沼卤代甲烷的排放清单，另一方面，可更好地了解受人类活动影响较大的海岸带盐沼在全球卤代甲烷气体释放中的贡献。