MICROBIAL BIOMASS IN A SHALLOW, URBAN AQUIFER CONTAMINATED WITH AROMATIC-HYDROCARBONS - ANALYSIS BY PHOSPHOLIPID FATTY-ACID CONTENT AND COMPOSITION

The city of Perth contains a number of sites that have been contaminat ed with hydrocarbons due to leakage from petroleum underground storage tanks. Microbial biomass in groundwater and sediment cores from above and below the water table, and from within and outside a plume of hyd rocarbon contamination, was examined using phospholipid fatty acid met hyl ester analysis. Microbial numbers, calculated from the phospholipi d content, ranged from 0.9 x 10(6) to 7.8 x 10(6) 'Escherichia coli eq uivalent cells' g(-1) dry wt of sediment. Over 96% of the microbial bi omass was attached to the sediment and the proportion of attached cell s did not decrease within the plume of contaminants. The amount of bio mass within aquifer samples seemed to be related more to the proximity of the rhizosphere to the shallow aquifer, and other unknown urban in puts, rather than to the effects of the plume of contaminants. Fatty a cids common to many bacterial groups dominated within the plume, and a s such the analyses gave limited insight into microbial community stru cture. For site assessment of intrinsic remediation of shallow aquifer s in urban areas, estimates of microbial biomass may not provide infor mation that is readily applicable to plume management.