青藏高原典型湿地甲烷排放关键控制因子及其模型整合研究

Methane (CH4) is an important greenhouse gas with a global warming potential 28 times greater than that of carbon dioxide. Atmospheric CH4 levels have exhibited a persistent and almost exponentially increasing trend since 1750. Small changes in atmospheric CH4 concentrations can have significant climate impacts because of the gas’s strong greenhouse effects. An improved understanding of the CH4 budget will reduce uncertainties in future climate change projections. Wetlands, as an important component of the terrestrial ecosystem, are considered the single largest CH4 source. CH4 emissions from natural wetlands are the main drivers of the global interannual variability of CH4 emissions with high confidence and contribute largely to interannual variations and anomalies of atmospheric CH4 concentrations. Therefore, it is vital to improve existing CH4 emission quantification methods for wetlands to better understand the global CH4 budget. The Qinghai-Tibet Plateau (QTP) has the second largest natural wetlands areas in China, showing a strong emissions potential of CH4. In this study, different methods including eddy covariance technology, were used to measure the CH4 fluxes from wetlands of the QTP, as well as the key factors that control the wetlands CH4 emissions. Based on the observations, the mechanism between the key control factors and wetlands CH4 emissions were investigated which was then integrated into a processed model of wetlands CH4 emissions. With the support of wetlands distributions map that retrieved from remote sensing data, the temporal and spatial patterns of CH4 emissions from wetlands of the QTP were estimated. This study provides scientific basis for understanding regional carbon budget and for the policy makers.

湿地被认为是最大的单一甲烷排放源，提高对湿地甲烷排放过程及机制的认识与理解对研究区域及全球甲烷收支有着重要意义。青藏高原作为我国自然湿地分布两大区域之一，具有着显著的甲烷源潜力。本研究以青藏高原典型湿地为研究对象，从野外实验入手，利用涡度相关技术与传统静态箱方法对湿地甲烷通量进行观测，并同步对湿地甲烷排放的关键控制因子进行连续的实时监测，以揭示湿地甲烷排放与其关键控制因子之间的相互关系及响应机制；同时利用湿地甲烷排放生态系统过程模型，通过对观测结果的量化分析与模型模块化，实现观测数据与过程模型的整合，在通过遥感解译得到湿地分布状况的基础上，从观测样点向区域水平进行尺度扩展，从而准确估算青藏高原湿地甲烷排放强度和时空格局。该研究将为区域湿地甲烷排放对气候变化的响应机制提供线索，对加深气候变化条件下区域碳源汇过程的理解以及我国温室气体排放清单的制定有着重要的科学意义。

青藏高原作为我国自然湿地分布两大区域之一，提高对青藏高原湿地甲烷排放过程的认识及区域甲烷收支估算精度，对我国温室气体排放清单的制定及全球甲烷收支有着重要意义。项目主要研究内容包括利用遥感影像数据及多源空间数据，给出青藏高原湿地的分布特征及面积测算，并进行不确定性评估；利用野外观测的通量及环境因子数据，分析青藏高原典型湿地甲烷排放的关键控制因子及其响应关系，包括甲烷排放对温度的依赖性，甲烷排放对水位变化的响应，并以这个关系对青藏高原湿地温室气体的排放作区域尺度的外推；对TRIPLEX-GHG湿地甲烷排放模型进行模块改进及参数调校，进行观测数据与模型的整合，对区域尺度上青藏高原湿地甲烷排放进行模拟估算。基于20套多源湿地相关数据的评估表明青藏高原湿地面积及湿地空间分布的不确定性较高；利用CMIP5数据对青藏高原未来的湿地模拟分布表明青藏高原湿地面积在未来排放情景下整体呈现上升趋势，随辐射强度增强，湿地面积的上升趋势有所降低；基于野外观测实验发现青藏高原湿地温室气体排放速率与土壤温度的关系不论数据来自静态箱还是通量塔，指数回归方程较好的拟合了两者之间的相关关系；通过对青藏高原湿地温室气体排放总量的年际动态进行外推显示青藏高原湿地甲烷排放量整体呈增长趋势，在空间格局上，湿地二氧化碳与甲烷排放量的变化趋势无明显空间异质性；基于TRIPLEX-GHG模型的历史模拟结果显示青藏高原湿地年CH4排放量为0.21—0.32Tg，空间格局上来看，大多数湿地区域CH4排放速率为0—6.13 g CH4 m-2 a−1，较高的CH4排放速率分布于青藏高原南部湿地区域，为56.14—74.97 g CH4 m-2 a−1；未来的模型模拟结果显示大气CO2浓度的增加对青藏高原湿地CH4排放具有显著的正反馈作用。