Methanogenesis in aquatic sediments : inherent variability and effects of environmental contaminants

Studies were conducted on the temporal and spatial variability of methanogenesis and the impact of environmental contaminants on methanogenesis in aquatic sediments. Samples were collected from a variety of freshwater ecosystems including experimental aquatic microcosms; Saucon Creek and the Lehigh River, Bethlehem, Pennsylvania; and Melton Hill Reservoir, Oak Ridge, Tennessee.

In this study on methanogenesis in aquatic sediments, it was found that statistically significant seasonal and spatial variation in the rates of methanogenesis occur in sediments from Melton Hill Reservoir. Significant spatial variation in the numbers of methanogens was also observed; however, there was no detectable seasonal variation in the number of methanogens. Results from a step-wise multiple regression analysis indicated that the amount of organic matter in the sediments and the pH of the sediments explained the greatest proportions of the observed variability in methanogenesis rates. The temperature, redox potential of the sediment, depth of the water column, and the number of methanogens were less important in explaining the variability in methanogenesis.

A multiple classification analysis of variance indicated that significant spatial, but not seasonal, variability occurred in the rates of methanogenesis in sediments from Saucon Creek, a stream recovering from past chronic input of a complex mixture of environmental contaminants in the form of waste effluent from a coking plant. The number of methanogens, and to a lesser extent, the pH, explained a significant proportion of the variability in methanogenesis rates, as indicated by a step-wise multiple regression analysis. Various physical and chemical characteristics and the number of culturable anaerobes were less significant in explaining the variation in rates.

Synthetic fuel oil and the water soluble components of synthetic fuel oil had no statistically significant effect on the rates of methanogenesis in microcosm sediments. Nor was there the significant spatial variation, as indicated by a nested analysis of variance, that was observed for the two natural sediment systems. Treatment effects were observed in toxicant effect studies on Melton Hill sediments. Ten mM methyl viologen, but not 0.0l to 1.82 mM, significantly inhibited the rates of methanogenesis in sediment samples. Concentrations of mercuric chloride ranging from 1.0 to 10.0 mg 1¹ and of Aroclor 1254 ranging from 0.1 to 10.0 mg 1¹ did not inhibit methanogenesis. One hundred mg 1¹ phenanthrene and a 1:30 dilution of coal liquefaction waste effluent produced statistically significant inhibition of the rates of methanogenesis.