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 mgCH(4)-m(-2)-h(-1) at top 5 cm depth to 2.6 mgCH(4)m(-2)-h(-1) a t 20-30 cm depth of sediments. Overall methane release rate from sedim ents was 19.9 mgCH(4)-m(-2)-h(-1). The maximum specific acetate and H- 2-utilization rates, v(m), were 5.2 x 10(-5) to 7.96 x 10(-6) and 0.9 x 10(-5) to 1.0 x 10(-4) gCOD-gVSS(-1)-h(-1) for the sediments collect ed in the depths of sediments, respectively. The half-velocity constan t, K-s, were from 21 to 65.5 and 27 to 194 mgCOD-l(-1) for acetate- an d H-2-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 me thanogens increases as the v(m) increases. The populational distributi ons were 5.27 x 10(8) to 2.8 x 10(8), and 1.2 x 10(8) MPN-gVSS(-1) at the sediments of top 20 and 20-30 cm, respectively. The specific metha ne production rates of sediments ranged from 1.2 x 10(-11) to 3.3 x 10 (-11) mgCH(4)-MPN(-1)-h(-1) (average = 2.1 x 10(-11) mgCH(4)-MPN(-1)-h (-1)) and are reasonably close to values reported in anaerobic treatme nt reactors and marine sediments. The sediment of top 20 cm had high m icrobial activity compared with the deeper section at 20-30 cm depth. In addition, the number of H-2-utilizing methanogens was smaller than that of acetate-utilizing methanogens in the sediments.