|| 要旨トップ | 本企画の概要 |||日本生態学会第62回全国大会 (2015年3月、鹿児島) 講演要旨
シンポジウム S10-2 (Lecture in Symposium/Workshop)
Although freshwaters are considered to be substantial natural sources of atmospheric methane (CH4), in situ processes of CH4 production and consumption in freshwater ecosystems are poorly understood, especially in subtropical area. To improve our understanding of CH4 dynamics in subtropical lakes, we examined vertical and seasonal profiles of dissolved CH4 and its carbon isotope ratio (d13C) in the deep subtropical Fei-Tsui Reservoir (Taiwan), whose winter vertical mixing varies with the climatic condition. In years with an incomplete vertical mixing and the subsequent strong thermal stratification, resulting in profundal hypoxia, we found increases in sedimentary CH4 production and storage. In contrast, in years with a strong winter vertical mixing to the bottom of the reservoir, CH4 production was suppressed. Diffusive emissions from profundal CH4 storage seemed to be negligible due to the efficiency of CH4 oxidation during ascent through the methane oxidizing bacteria (MOB) activity. Most of the profundal CH4 was rapidly oxidized by MOB in both oxic and anoxic layer, as characterized by its carbon isotope signature, whereas aerobic CH4 production in a subsurface layer, which may be enhanced under high temperature in summer, may account for a large portion of atmospheric CH4 emissions from this reservoir.