Methane levels in five shallow lakes in China: Effect of lake paludification

Abstract

Understanding methane dynamics in lakes is relevant for assessing the natural source of greenhouse gases. Paludification is one of the most common phenomena of lake degeneration, which would have significant influence on CH4 dynamics. However, the actual variety of CH4 dynamics by lake paludification is not yet clear. We investigated CH4 concentrations and production potentials in five shallow lakes located in the east China. The CH4 concentrations and production potentials were significantly higher (approximately 5–10 times) in the lakes with greater paludification degrees and had no significant difference among other lakes with low and similar paludification indexes. High CH4 levels in the paludificated lakes can be associated with the increase of sediment organic matter content and decrease of water depth due to the accelerated sedimentation and outspread of macrophytes during the lake paludification. Similarly, organic matter supply might be a limitation for CH4 production in the lakes with low paludification degrees. These results indicate that lake paludification is probably a main reason for the significant CH4 differences among the studied lakes. This study draws attention to lakes with paludification tendency when making CH4 emission budgets in shallow lakes.