Huai Chen

Methane emissions from newly created marshes in the drawdown area of the Three Gorges Reservoir

The study aimed to understand the methane (CH4) emission and its controlling factors in the Three Gorges Reservoir Region and to explore its implication for large dams. We measured CH4 emissions from four vegetation stands in newly created marshes in the drawdown area of the Three Gorges Reservoir, China, in the summer of 2008. The results showed highly spatial variations of methane emissions among the four stands, with the smallest emission (0.25 +/- 0.65 mg CH4 m(-2) h(-1)) in the Juncus amuricus stand, and the greatest (14.9 +/- 10.9 mg CH4 m(-2) h(-1)) in the Scirpus triqueter stand. We found that the spatial variations of CH4 emissions are caused by difference in standing water depth and dissolved organic carbon (DOC). Results also showed a special seasonal variation of CH4 emissions in this area, i.e., maximal emissions in early July followed by a low and steady value before the winter flooding. The seasonality of CH4 emissions was found closely related to temperature and standing water depth. Because of the large area of the drawdown zones for global dam reservoirs and a large CH4 emission rate, such newly created marshes should not be neglected when estimating CH4 emissions from reservoirs.

Diurnal variation of methane emissions from an alpine wetland on the eastern edge of Qinghai-Tibetan Plateau

Alpine wetland is a source for CH4, but little is known about methane emission from such wetland, especially about its diurnal pattern. In this study we tried to probe the diurnal variation in methane emission from alpine wetland vegetation. The average methane emission rate was 9.6 ± 3.4xa0mg CH4 mu2009−u20092 hu2009−u20091. There was an apparent diurnal variation pattern in methane emission with one minor peak at 06:00 and a major one at 15:00. The sunrise peak was consistent with a two-way transport mechanism for plants (convective at daytime and diffusive at night-time). CH4 emission was found significantly correlated with redox potentials. The afternoon peak could not be explained by diurnal variation in soil temperature, but could be attributable to changes in CH4 oxidation and production driven by plant gas transport mechanism. The results have important implications for sampling and scaling strategies for estimating methane emission from alpine wetlands.