Studies into the effects of cadmium and low pH upon methane production

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Investigations into the effects of the heavy metal cadmium (Cd) and low pH upon methanogenesis from anaerobic lake sediments were conducted over the period summer 1978 to early spring 1981 at the Freshwater Institute, Winnipeg, and at the Experimental Lakes Area (ELA), north-western Ontario. Experiments conducted at ELA consisted of both laboratory and field studies, while those at the Institute consisted of developmental and test laboratory studies. The laboratory studies indicated that dropping the pH of the test system below approximately 5.5 would inhibit methanogenesis. The lowering of pH to approximately 3.5 would result in total inhibition of methane production and visible changes in the sediments. The use of Cd water column concentrations as low as 3 µgl−l was found to be sufficient to cause total inhibition of methanogenesis in the laboratory studies. In the field studies acidification of one test system, to a pH of approximately 4.8, resulted in incomplete inhibition of methanogenesis, reducing the rate of production to approximately 50% of that of the controls. In comparison to the control systems, neither the use of Cd nor Cd plus low pH seemed to have any effect on the rate of methanogenesis in these field test systems. The cause of such differences may be due to factors which lay beyond the control of these experiments.