| Summary: | 碩士 === 國立中山大學 === 海洋地質及化學研究所 === 98 === Methane (CH4) is not only important but also a long-lived greenhouse gas. Scientists estimated that more than half of CH4 is released from the water column. Studies of methane from water column are almost focused on rice fields, wetlands and swamps in Taiwan. There are only limited studies of methane about rivers, lakes and coasts. So this study investigated CH4 distribution in natural waters on and around Taiwan.
The average surface methane concentration in the South China Sea (SCS) is about 5.10±3.61 nM (n=103). The average surface methane concentration in the West Philippines Sea (WPS) is about 3.44±3.89 nM (n=56), lower than in the SCS. The average surface concentration in the Northern and Southern Taiwan Strait are, respectively, 4.72±3.19 nM (n=64) and 4.01±3.19 nM (n=51), and are between the average concentrations in the SCS and the WPS. The sea-to-air fluxes of methane in the SCS and the WPS are 0.38±0.99 μmol/m2/h (n=103) and μmol/m2/h (n=56), respectively. The sea-to-air fluxes of methane in the Northern and Southern Taiwan Strait are, respectively, 0.37±0.55 μmol/m2/h (n=64) and 0.10±0.53 μmol/m2/h (n=51). Although the sea-to-air fluxes for methane is much lower than the flux for carbon dioxide, methane emission in the SCS contributes nearly the same greenhouse effect as carbon dioxide does.
In Taiwan, the average surface methane concentration in rivers is about 3221±12386 nM, and the emission is about 104±337 (μmol/m2/h) (n=179). The average surface methane concentration and flux are, respectively, 2164±5432 nM and 265±1289 μmol/m2/h (n=120) in the water column in China, including the coasts of Hong Kong , Pearl River and Yangtze River. The average surface methane concentration and flux in the natural water are higher than in Taiwan.
In Asia, the average surface methane concentrations of the natural waters are, respectively, 8240±22753 nM (n=27) and 7639±24554 nM (n=50) in Thailand and Indonesia, twice the concentration in Taiwan. The average surface methane concentrations of the natural waters are, respectively, 2841±3358 nM (n=5) and 1939±3694 nM (n=15) in Malaysia and the Philippines, lower than in Taiwan. The emissions of methane in the natural waters are, respectively, 845±2622 μmol/m2/h (n=50), 292±341 μmol/m2/h (n=5) and 181±356 μmol/m2/h (n=15) in Indonesia, Malaysia and the Philippines, also much higher than in Taiwan. The flux of methane in natural waters in Thailand (100±265 μmol/m2/h, n=25) is as the same as in Taiwan.
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