Densities of Fecal Indicator Bacteria in Tidal Waters of the Ballona Wetlands, Los Angeles County, California
Densities of fecal indicator bacteria (FIB) represented by total coliforms, E. coli and enterococci were measured within tidal channels of the Ballona Wetlands (Los Angeles County) to see if the wetlands act as a sink or source for these bacteria and to measure increases in FIB densities during wet weather. Samples were collected on 10 days over a 1-yr period beginning February 2003 at four sites within the wetlands and one site in Ballona Creek opposite the west tide gate. Incoming flood and outgoing ebb tides were sampled during each sampling event at each station. Water from Ballona Creek may be a significant source of indicator bacteria in the wetlands. Within the tidal channels, densities for total coliforms typically ranged from 103–104 MPN/100 ml, but ranged up to 106 during runoff events. Densities of E. coli and enterococci were orders of magnitude less than those measured for total coliforms, generally ranging from 101–104 for E. coli, and 101–105 for enterococci; greater densities were associated with runoff events. Densities of FIB tended to be up to three times greater during flood than ebb tide conditions depending on the tidal range. This result suggests that more FIB may be entering the wetlands on flood tides than leaving during ebbs, so that these bacteria either are being destroyed, sinking into the tidal channel sediments and plant surfaces, or both. This hypothesis needs to be tested by further identifying other possible FIB sources within the wetlands, and increasing the study design’s statistical power to better characterize the flux of these bacteria entering and leaving the wetlands.