珠三角典型红树林湿地碳收支及环境耦合机制研究

By releasing about 22% CH4 in the total release volume of CH4 in the world, wetlands become the largest natural release source of CH4. CH4 not only contributes about 20% greenhouse gas to the globe, but also produces a greenhouse effect 24 times CO2; therefore whether the wetlands act as the “carbon source” or “carbon gathering place” can’t be identified simply from the figures of “carbon sequestration” and “carbon release”; the greenhouse effect variation caused by carbon of different states should also be taken into consideration. Mangrove wetland is a typical kind of coastal wetlands; it is one of the areas in the world with the highest productivity, which impacts carbon balance in the coastal area and the whole world significantly. Mangrove wetland in the Pearl River Delta, as the wetland ecosystem that is nearest to large-scale urban agglomeration, has extremely active carbon exchange with the urban area, whose healthy state has strong coupling relationship with human activities. In this paper typical mangrove wetlands in the Pearl River Delta were taken as the study subject; the carbon budget in the mangrove wetland was studied quantitatively based on field survey, ecology observation, and laboratory tests in combination with 3S technology and mathematical model, so as to identify the role that mangrove wetlands play in carbon release and sequestration, to explore the factors and conditions that lead to its role transfer between the two, to investigate the coupling effect of environmental factors of mangrove wetland – urban complex ecosystem, and to provide scientific basis for restoration and protection of mangrove wetlands.

湿地的CH4释放量占全球CH4释放总量的22%左右，是全球CH4的最大自然释放源。CH4对温室气体的贡献达20%左右，其温室效应又是CO2的24倍。因此湿地的固碳及释碳不能简单的从数值的收支上对比得出“源”或“汇”的身份，还应考虑不同形态的碳所造成的温室效应差异。其中红树林湿地作为典型的滨海湿地类型，是地球上生产力最高的区域之一，对海岸区及全球碳平衡有着重要影响。珠三角地区的红树林湿地作为与大型城市群最为接近的红树林湿地生态系统，与城市碳交换活动极为活跃。本研究以珠三角典型红树林湿地为研究对象，以野外调查、生态学观测、室内实验为基础，融合3S技术、数学模型对红树林湿地碳收支进行定量研究，甄别红树林湿地在温室效应上“源”或"汇”的身份，探索导致红树林湿地“源”“汇”身份转化的因子及条件，探索红树林——城市复合生态系统环境因子的耦合效应，为恢复和保护红树林湿地提供科学依据。

本研究以珠三角典型红树林湿地为研究对象，以野外调查、生态学观测、室内实验为基础，融合3S技术、数学模型对红树林湿地碳收支进行定量研究，甄别红树林湿地在温室效应上“源”或"汇”的身份，探索导致红树林湿地“源”“汇”身份转化的因子及条件，探索红树林——城市复合生态系统环境因子的耦合效应，为恢复和保护红树林湿地提供科学依据。研究结果表明：（1）研究区的红树林生态系统（土壤碳库为0-30 cm）碳储量为130483.28 MgC。其中植物碳储量为89234.40 MgC，植物碳密度在27.48-174.44 MgC·ha-1之间，平均储量为95.49 MgC·ha-1，远高于全国乔木林的碳储量平均值。。0-30 cm土壤碳含量在 6.01-132.95 g·kg-1之间，平均值为34.29 g·kg-1；0-30 cm土壤碳储量为40555.04 MgC。红树林凋落物碳库为693.84 MgC，凋落物的原位归还能力对土壤碳含量的增加有显著影响，是土壤碳含量由陆地至海洋递减的原因之一。（2）研究区土壤的固碳速率为447.20 MgC·a-1，植被的固碳速率（净初级生产力）为5422.83 MgC·a-1，土壤碳排放速率为1875.83MgC·a-1。研究区现阶段为碳汇，总固碳速率为3815.17MgC·a-1。根据增温潜势将CH4、N2O换算为CO2当量后，研究区红树林在减缓温室效应和全球变化上仍起到积极的作用，但实际的固碳效果减少到2096.52MgC·a-1。因CH4和N2O排放量造成研究区的红树林生态系统阻止全球变暖的效果下降了47.51%，CH4对温室气体实际效果的贡献从2.73%上升到了53.26%，占据了总贡献的一半以上。因此，CH4的排放速率是决定红树林在温室效应上身份的关键因子。（3）室内模拟和野外原位监测结果都表明重金属污染越严重的样点，CH4 排放通量越高，但CO2却与之相反，即整体上重金属污染越严重的样点，CO2 排放通量越低。室内模拟实验下，不同重金属污染程度下的土壤N2O通量没有显著差异，但是深圳福田红树林湿地土壤N2O通量显著高于珠海淇澳岛。在室内模拟实验中，淹水和未淹水两种不同的处理对CH4通量未产生显著影响，但CO2通量在未淹水处理时显著高于淹水处理，而N2O通量与之相反。