working on freshwater lakes in Texas, and by Vilks and Rashid (1977), working on the
sediments of St Margarests Bay in Canada, that the major component of the gas bubbles
causing acoustic scattering in the sediments under study was methane.
The complete anaerobic breakdown of organic matter involves a number of metabolically
separate microorganisms interacting to yield carbon dioxide and methane as end products. Intermediate products of anaerobic metabolism are fatty acids and hydrogen,
which then act as substrates for the sulphate-reducing and methane-producing bacteria,
the terminal organisms in the anaerobic microbial food chain. Considerable interest in the
nature of the interaction between sulphate-reducing and methane producing bacteria has
been shown over recent years (Cappenberg and Prins, 1974 ; Oremland and Taylor, 1978 ;
Winfrey and Ward, 1983) specifically in the way that sulphate concentrations influence
both microbial groups (Oremland and Polcin, 1982 ; Lovley, Dwyer and Klug, 1982 ;
Lovley and Klug, 1983 ; King, Klug and Lovley, 1983 ; Kristjansson, Schonheit and
Thauer, 1982 ; Schonheit, Kristjansson and Thauer, 1982).
Analysis of the methane concentrations within acoustically turbid sediments from the
Western Irish Sea and Holyhead Harbour are reported below. Microcosm experiments
demonstrating the potential for biogenic methane production causing the acoustic turbidity are also described.
Figure 1 : Map of Holyhead harbour and sampling stations.
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