Detection methanogens in newly settled sediments from Xuanwu Lake in Nanjing, China.

Sediments from Xuanwu Lake have been dredged in the past 3 years to improve the water quality, but methanogenesis should still exist in the newly settled sediment. Methane production, methanogens, and physiochemical parameters were detected in the surface sediments (0-5 cm) and/or vertical sediments (0-21 cm, segmented at interval of 3 cm). Methane flux at water-air interface varied among five detected sites. Principal component analysis showed that CH(4) flux, content of water and the concentration of total nitrogen (TN), CH(4) and organic matters (OM) weighed most heavily on the component I in surface sediments while different patterns were observed for vertical sediments. The copy number of the 16S rRNA gene for bacteria was lower in the surface sediment (0-6 cm) than that in deeper sediments (12-21 cm), while 16S rRNA genes of Archaea were almost evenly distributed in the vertical sediments. Representatives belonging to the orders Methanobacteriales, Methanomicrobiales, and Methanosarcinales were detected in all samples of the vertical sediments, except that no members of the Methanococcales were detected in the samples at 0-6 cm. The level of Methanobacteriales reached a highest density at 18.1 × 10(4) copies g(-1) dry weight (dw) at 6-9 cm; for Methanosarcinales (76.89 × 10(6) copies g(-1) dw) and Methanococcales (82.70 × 10(3) copies g(-1) dw) at 12-15 cm, whereas for Methanomicrobiales (43.37 × 10(6) copies g(-1) dw) at 9-12 cm. Methanosarcinaceae and Methanosaetaceae reached to their highest densities at 6-9 and 9-12 cm, respectively. These data provided useful information for better understanding the methanogenesis in the newly settled sediments of a recently dredged lake.