Ehj 1(1)-1

The survival of the faecal indicator organism Escherichia coli (E. coli) in recreational coastal water and sediment was investigated using laboratory based microcosms. Intact sediment cores from three distinct coastal sites in metropolitan Adelaide were inoculated with known concentrations of E. coli and incubated at temperatures of 10°C, 20°C and 30°C. Enumeration of E. coli in sediment and overlying water was undertaken by the membrane filtration method on Days 0, 1, 2, 7, 14 and 28 following inoculation. Under all conditions studied, the decay rate of E. coli was greater in overlying water compared with the rate in sediment. E. coli survival was found to have an inverse relationship with temperature. Sediment characteristics (particle size and organic carbon content) were found to influence the decay of E. coli. The decay rate of E. coli was demonstrated to be lowest in sediment consisting of small particle size and high organic carbon content. Resuspension of E. coli into the water column was demonstrated when the top 10-20 millimetres of sediment was stirred immediately prior to enumeration, mimicking recreational activity. Greatest resuspension of E. coli was observed from sediment consisting mainly of sand when incubated at 10°C.