Weak Correlation Between Methane Production and Abundance of Methanogens Across Three Brackish Marsh Zones in the Min River Estuary, China

Abstract

Methane production is influenced by the abundance of methanogens and the availability of substrates. Sulfate-reducing bacteria (SRB) also play an important role in the anaerobic decomposition of organic matter. However, the relationships between methane production and abundance of methanogen and pore water substrates in estuarine brackish marshes are poorly characterized, and even to our knowledge, no published research has explored the relationship between methane production rate and pore water dimethyl sulfide (DMS) concentration. We investigated methane production rate, abundances of methanogens and SRB, sediment organic carbon contents, and concentrations of pore water substrates (acetate and DMS) and terminal electron acceptors (SO4 2−, NO3 −, and Fe3+) at a brackish marsh landscape dominated by Phragmites australis marsh, Cyperus malaccensis marsh, and Spartina alterniflora marsh in the Min River estuary, southeast China. The average rates of methane production over the entire 30 cm of the sediment profile (5 cm sampling interval) in the three marshes were 0.142, 0.058, and 0.067 μg g−1 day−1, respectively. The abundance of both methanogens and SRB in the sediment of the P. australis marsh with the highest sediment organic carbon content was higher than in the C. malaccensis and S. alterniflora marshes. Mean pore water DMS concentrations over the entire 30 cm of the sediment profile under the S. alterniflora marsh were higher than those in the C. malaccensis marsh and P. australis marsh. Methane production rate correlated weakly with the abundance of methanogens across the three marsh zones together, but did not correlate with the concentrations of pore water acetate and DMS. Our results suggest that the abundance of methanogens is controlled by sediment organic carbon supply, and further, methane production is affected by the abundance of methanogens in the subtropical estuarine brackish marshes.