Seasonal studies of methanogenesis and desulfurication in sediments of the river saar

Abstract

The interrelation between methanogenic and desulfuricating bacteria was investigated in the anaerobic sediment of the impounded Saar river during a period of 18 months. This interrelation was mainly determined by the water discharge. The carbon and electron flow, normally observed in the river, was altered by high water, which introduced sulfate into the sediment and thus stimulated sulfate reduction and inhibited methanogenesis. On the other hand, low water prevented sulfate from penetrating into deeper sediment layers and thus favoured methanogenesis. Since methanogenic bacteria kept the partial pressure of hydrogen low, sulfate-reducing bacteria were allowed to release hydrogen and thus to remain metabolically active.

The inhibition of methanogenic bacteria by sulfate was overcome by the addition of organic substrates. According to these laboratory experiments, the available organic substrates were limiting and responsible for the observed competition. The same was particularly true in deeper layers of the sediment. Acetate accounted for only 4–13 % of the methane formed in the sediments. The turnover rate of acetate (0,052 μmol · g⁻¹h⁻¹) was comparatively low with respect to other methanogenic environments. Acetate was consumed by sulfate-reducing bacteria as indicated by high colony counts, obtained on acetate medium. In the sediments the major proportion of the methane formed (81–96 %) arose from the reduction of carbon dioxide by hydrogen.