The role of resuspension in enterococci distribution in water at an urban beach

Abstract

This study investigated the process and effects of bacterial resuspension on microbiological water quality in a small urban embayment. Water and sediments were sampled for enterococci at a small urban bay, on both irregular and intensive time scales, with a focus on the potential sources of faecal contamination to the system. Distribution of enterococci in sediments was influenced by the location and microbiological quality of major sources of enterococci to the embayment. Stream and storm water contributed the greatest numbers of enterococci and, consequently, high numbers of enterococci were found in both water and sediments surrounding discharge points for these sources. To investigate bacterial resuspension, water samples were collected from within the surf zone (at water depths of 1-1.5 m) as a wave crest passed. Two samples were collected simultaneously at each sampling location at 10 cm above the seabed and 10 cm below the water surface. Samples were analysed for enterococci and data compared with bacterial numbers in adjacent sediments as well as in stream and storm water sources. Vertical distribution data for enterococci in the water column revealed evidence of spatial and temporal variability in bacterial resuspension and the role of wave action was demonstrated. Bacterial resuspension under waves was directly related to weather and wave conditions. The resuspension of enterococci was not detected beyond the surf zone suggesting that wave action was the main cause of resuspension at the study site.