Some thoughts about shoreline bacterial monitoring and implications for public health warning systems

Stephen B. Weisberg
Southern California Coastal Water Research Project

 Friday, July 12, 2002
12:00 Noon–Pacific Forum

Implementation of Assembly Bill 411 enhanced beach water quality monitoring programs throughout California, but it also increased reliance on single sample bacterial standards. Use of single sample standards is confounded by variability in bacterial measurements, and studies were conducted to quantify temporal, spatial, and laboratory variability. Laboratory variability was found to be high. Most samples on which health warnings are based were within measurement error of state standards. Spatial variability was found to be low, except near storm drain outlets where rapid dilution away from these high concentration sources was found to depend on oceanographic conditions. Temporal variability was also large, with nearly 70% of high bacterial concentration events lasting less than the 24 hours necessary for laboratory sample processing. Thus, most public health warnings are out-of-date when they are issued. Several research and management alternatives for improving the health warning systems will be presented.