Methane production in eutrophic Lake Plußsee: seasonal change, temperature effect and metabolic processes in the profundal sediment
Nüsslein, Bernhard; Conrad, Ralf
published: Nov 24, 2000
ArtNo. ESP141014904004, Price: 29.00 €
Rates of CH4 production in the profundal sediment of Lake Plußsee were higher during the summer than during fall, and fairly well explained the CH4 concentration that accumulated in the hypolymnion during summer stratification. Oxidation of CH4 at the oxycline played only a marginal role in the seasonal CH4 cycle. Although the sediment temperature (4 °C) did not change with season, CH4 production rates could be stimulated by incubation at increased temperature (25 °C). At both 4 °C and 25 °C, thermodynamic conditions in the sediment allowed exergonic production of CH4 from either acetate, H2/CO2 or methanol. Inhibition of methanogenesis by 2-bromoethane sulfonic acid (BES) resulted in the accumulation of acetate, but was only detectable at 25 °C. Inhibition of acetoclastic methanogenesis by methyl fluoride resulted in partial inhibition of CH4 and was only detectable at 25 °C. Incorporation of radioactive bicarbonate into CH4 was also only detectable at 25 °C and then accounted for about 25-42 % of total CH4 production. [2-14C] acetate was converted to 14CH4 with turnover times of about 24 and 97 h at 25 °C and 4 °C, respectively, but accounted for only 4-9 % of total CH4 production. The turnover times of radioactive methanol were even larger (about 96 at 25 °C and 153 h at 4 °C) and accounted for < 1 % of total ch4 production. Hence, these processes could account for a larger percentage of CH4 production only if taking place in sediment microniches that did not fully equilibrate with the pore water. Production of CH4 at 25 °C was stimulated by addition of pectin, acetate, methanol or H2, but at 4 °C, it was only stimulated by H2. The stable carbon isotopic composition of CH4 and CO2 in the water column and in incubated sediment slurries indicated that CH4 production was dominated by acetoclastic methanogenesis, with H2/CO2-dependent methanogenesis contributing more at 25 °C than 4 °C. In conclusion, the data are consistent with the assumption that CH4 production at in-situ temperature (4 °C) was due to acetoclastic methanogenesis tightly coupled to acetate production, whereas it was due to both acetoclastic and H2/CO2-dependent methano genesis at 25 °C. This assumption is also consistent with the observation that the sediment fermented added glucose or pectin to acetate as a major product.