Methane release rate and methanogenic bacterial populations in lake sediments

Methane release rates from the sediment in the lake were estimated by a batch culture. The methane release rates were decreased from 6.1 ± 0.7 mgCH4-m−2-h−1 at top 5 cm depth to 2.6 mgCH4-m−2-h−1 at 20–30 cm depth of sediments. Overall methane release rate from sediments was 19.9 mgCH4-m−2-h−1. The maximum specific acetate- and H2-utilization rates, νm, were 5.2 × 10−5 to 7.96 × 10−6 and 0.9 × 10−5 to 1.0 × 10−4 gCOD-gVSS−1-h−1 for the sediments collected in the depths of sediments, respectively. The half-velocity constant, Ks, were from 21 to 65.5 and 27 to 194 mgCOD-1−1 for acetate-and H2-utilizing methanogens in the depths of sediments, respectively. The acetate-utilizing methanogens were enumerated by the most probable number (MPN) technique, and showed the number of acetate-utilizing methanogens increases as the νm increases. The populational distributions were 5.27 × 108 to 2.8 × 108, and 1.2 × 108 MPN-gVSS−1 at the sediments of top 20 and 20–30 cm, respectively. The specific methane production rates of sediments ranged from 1.2 × 10−11 to 3.3 × 10−11 mgCH4-MPN−1-h−1 (average = 2.1 × 10−11 mgCH4-MPN−1-h−1) and are reasonably close to values reported in anaerobic treatment reactors and marine sediments. The sediment of top 20 cm had high microbial activity compared with the deeper section at 20–30 cm depth. In addition, the number of H2-utilizing methanogens was smaller than that of acetate-utilizing methanogens in the sediments.