Microbiological water quality at non-human influenced reference beaches in southern California during wet weather John F. Griffith a , Kenneth C. Schiff a, * , Gregory S. Lyon a , Jed A. Fuhrman b a Southern California Coastal Water Research Project, 3535 Harbor Blvd., Suite 110, Costa Mesa, CA 92626, USA b University of Southern California, Department of Biological Sciences, University Park Campus, Los Angeles, CA 90089, USA article info Keywords: Fecal indicator bacteria Enterococcus E. coli Total coliform Reference beach Non-human abstract Although urban wet weather discharges may have elevated concentrations of fecal indicator bacteria impacting water quality at swimming beaches, not all of these bacteria may arise from human sources. In this study, the contribution of non-human fecal indicator bacteria was quantified by sampling coastal reference beaches in southern California. Samples were collected at beaches near stormwater discharges from undeveloped watersheds and analyzed for total coliform, Escherichia coli, and enterococci. Surfzone samples exceeded water quality thresholds >10 times more frequently during wet weather than dry weather. Exceedences were greatest <24 h following rainfall, then steadily declined on successive days. Early season storms exceeded thresholds more frequently, and by greater magnitude, compared to late season storms. Large storms exceeded thresholds more frequently than smaller-sized storms, partly due to the breaching of sand berms. When discharges did reach the surf zone, bacterial concentrations in the wave wash were correlated with watershed bacterial flux. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Beaches in southern California are a valuable recreational re- source for swimming, surfing, and other body contact activities. For example, greater than 175 million beach-goers visit southern California beaches annually, more than all other parts of the coun- try combined (Schiff et al., 2001). This year-round activity results in tremendous economic revenue estimated at more than $9 billion annually in ocean related activities for the region (NRC, 1990). Fecal indicator bacteria (total coliform, Escherichia coli/fecal coliform, and enterococci) are used to monitor the water quality of marine beaches because they have been shown to correlate with swimming related illness. For example, Cabelli (1982) demon- strated that increases in concentrations of enterococci correlated with an increase in the risk of highly credible gastrointestinal ill- ness among swimmers on beaches in New Jersey. In Santa Monica Bay, California, Haile et al. (1999) observed an increase in the rel- ative risk for diarrhea with blood and highly credible gastrointesti- nal illness in swimmers exposed to higher concentrations of enterococci. While the water quality at most beaches in southern California meets water quality thresholds established by the State during dry weather, several beaches have impaired water quality based on routine fecal indicator bacteria monitoring. Noble et al. (2000) con- ducted a regional study of all southern California beaches and found that approximately 5% of the shoreline exceeded water qual- ity thresholds for fecal indicator bacteria during the summer of 1998. This level of exceedence was not randomly distributed. More than half of the exceedences occurred near storm drains that dis- charge across the beach. A retrospective analysis of fecal indicator bacteria based on five years of daily beach monitoring during dry weather in Santa Monica Bay found similar results, with over half of the water quality exceedences occurring in front of storm drains (Schiff et al., 2003). The microbial water quality of beaches in southern California drastically changes following rainstorms. Noble et al. (2003a,b) re- peated their 1998 summer study, but sampled following a signifi- cant rainfall event during the winter of 1998–1999. In this case, over half of all beaches exceeded fecal indicator bacteria water quality thresholds. This frequency of impaired water quality jumped to nearly 90% when these beaches were located in front of storm drains. Similarly, Schiff et al. (2003) observed a doubling of microbial water quality exceedences between dry and wet weather, even though wet weather represented less than 10% of the year. There are many sources of bacteria that could potentially be found in storm drains that discharge to beaches. Some of these sources may be of human origin including sewage spills, leaking sanitary sewage systems, faulty septic systems, or illicit discharges and illegal dumping (Geldreich, 1978). However, many bacteria may actually arise from natural sources. Fecal indicator bacteria 0025-326X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2009.11.015 * Corresponding author. Tel.: +1 714 755 3202; fax: +1 714 755 3299. E-mail address: kens@sccwrp.org (K.C. Schiff). Marine Pollution Bulletin 60 (2010) 500–508 Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul