Dissolved methane in groundwater of domestic wells and its potential emissions in arid and semi-arid regions of Inner Mongolia, China

Abstract Methane (CH 4 ) is widely present in groundwater. Dissolved CH 4 in groundwater is less understood when compared with that in wetlands. In this study, the concentrations and origin of dissolved CH 4 in groundwater were investigated and the potential importance of groundwater CH 4 emissions in arid and semi-arid regions of Inner Mongolia was discussed. Groundwater was extracted from domestic wells using a submersible pump or manual power and was analyzed for CH 4 concentrations, δ 13 C-CH 4 , and physico-chemical variables. The results show that the concentrations of dissolved CH 4 in groundwater had large spatial variability, ranging from 0 to 0.10 mg L −1 with a mean of 0.01 mg L −1 in Xilingol and from 0 to 8.99 mg L −1 with a mean of 1.44 mg L −1 in Xingan-Tongliao. Substantial CH 4 concentrations of about 2.5–5.5 mg L −1 were found in central areas of Xingan-Tongliao in the winter and the summer. The δ 13 C-CH 4 of about −85‰ was highly depleted while CH 4 concentration was significantly negatively correlated with SO 4 2− concentration, indicating that dissolved CH 4 in groundwater was microbial in origin. This study suggests that groundwater as a source of CH 4 might have great implications in arid and semi-arid regions worldwide and should deserve more research.