Chemical and microbiological aspects of acoustically turbid sediments: Preliminary investigations

Abstract

Abstract Chemical, microbiological, and geophysical measurements have been carried out on sediment cores collected from Holyhead Harbour and the Western Irish Sea, where acoustic subbottom profiling has established the presence of large areas of acoustically turbid sediments, commonly referred to as “gassy” sediments. Gas analysis of these cores have shown that the acoustic turbidity was most probably due to high concentrations (>100 nM/mL) of methane occurring at subsurface depths. Microcosm experiments on sediment slurries from Holyhead Harbour confirm that acetate and H2/CO2 are important precursors for methane generation. In sediments from Holyhead Harbour methanogenesis could be slightly stimulated by the addition of H2/CO2 and sulfate (1 mM). This suggested that in surface sediments sulfate reduction and methanogenesis can occur concurrently. Such a situation may explain the appearance of gas plumes and gas pockets detected acoustically at the sediment surface in several regions of the Western Irish...