台湾地区湖泊甲烷释放量

本研究首次对台湾湖泊的甲烷释放量化评估，以期了解湖泊在台湾地区甲烷总释出量，研究主要利用两种方式进行，一是收集箱实测法，大多运用在交通便利地区，使用甲烷收集箱，定时收集甲烷气，进行浓度分析后，进而估算释放量，另一是利用水汽浓度差估算法，大多运用在交通不便地区，以水体内及接近水体的空气甲烷浓度差，考虑风速及利用理论方程式估算甲烷释放通量，两方法所得到的甲烷释放通量误差在一次方左右。

METHANE ENHSSIONS FROM LAKES IN TAIWAN

Aquatic environments have been postulated to contribute over half of the total global methane flux to the atmosphere. Most investigations of methane emissions from aquatic ecosystems concentrated on rice paddies, salt marshes and freshwater swamps, little attention is focused on the lake, so data on methane flux from (especially Taiwan) lakes are scarce. We do not know of any methane measurements, either on concentration or on flux, for lakes in Taiwan. So this study focuses on evaluating the methane emissions from lakes in Taiwan.

Data were collected by two methods. One was the collection chamber technique. In an area with easy access, we used a plastic chamber to collect methane. From the change of the methane concentration with time, the methane emission rate was calculated. The other method was to calculate the methane emission rate from the methane concentration gradient between the air and water. The results from these two methods differ by one order of magnitude.

The methane emission from the alpine lakes was controlled by the water property; emission rates were generally low, from 0.002 - 1.2 mg/(m²*h) (averaging about 0.07 mg/ (m²*h)). The alpine lakes roughly emit 200 kg of methane to the atmosphere every year. The methane emission from the lakes and reservoirs located below l500m showed larger variations than the alpine lakes. The average methane emission rate was about 0.11 mg/( m²*h). Multiplying by 10000 hectares, the surface area of all lakes / reserviors located below 1500 m, 1.1×10⁵ kg of methane is emitted per year from the lakes and reserviors in Taiwan.

In conclusion, the methane emissions from Taiwan lakes are 0.51 - 0.95 mg/(m²*a), totally the lakes emit 1.1×10⁵ kg of methane to the atmosphere every year. Compared with other emission souces the lakes have fairly low methane emissions. It is evident that the lakes are one of the minor sources of methane emission in Taiwan.