Effect of weir impoundments on methane dynamics in a river.

We measured CH4 concentration, CH4 oxidation in the water column and total CH4 emissions to the atmosphere (diffusion and ebullition) in three weir impoundments and river reaches between them, in order to understand their role in river methane (CH4) dynamics. Sediment samples were also collected to determine CH4 consumption and production potentials together with the contribution of individual methanogenic pathways. The CH4 surface water concentration increased 7.5 times in the 16km long river stretch. Microbial CH4 oxidation in the water column reached values ranging from 51 to 403nmoll-1d-1 and substantially contributed to the CH4 removal from surface water, together with CH4 emissions. The total CH4 emissions to the atmosphere varied between 0.8 and 207.1mmolCH4m-2d-1 with the highest values observed upstream of the weirs (mean 68.5±29.9mmolCH4m-2d-1). Most of the CH4 was transported through the air-water interface by ebullition upstream of the weirs, while the ebullition accounted for 95.8±2.0% of the total CH4 emissions. Both CH4 production and oxidation potential of sediments were higher upstream of the weirs compared to downstream of the weirs. The contribution of hydrogenotrophic methanogenesis to total CH4 sediment production was 36.7-89.4% and prevailed upstream of the weirs. Our findings indicate that weirs might influence river CH4 dynamics, especially by increased CH4 production and consumption by sediments, followed by increasing CH4 emissions to the atmosphere.

Dominance of Methanosarcinales phylotypes and depth-wise distribution of methanogenic community in fresh water sediments of Sitka stream from Czech Republic.

The variation in the diversity of methanogens in sediment depths from Sitka stream was studied by constructing a 16S rRNA gene library using methanogen-specific primers and a denaturing gradient gel electrophoresis (DGGE)-based approach. A total of nine different phylotypes from the 16S rRNA library were obtained, and all of them were clustered within the order Methanosarcinales. These nine phylotypes likely represent nine new species and at least 5-6 new genera. Similarly, DGGE analysis revealed an increase in the diversity of methanogens with an increase in sediment depth. These results suggest that Methanosarcinales phylotypes might be the dominant methanogens in the sediment from Sitka stream, and the diversity of methanogens increases as the depth increases. Results of the present study will help in making effective strategies to monitor the dominant methanogen phylotypes and methane emissions in the environment.