Research Areas > Beach Water Quality > Multi-tiered Approach using Quantitative Polymerase Chain Reaction for Tracking Sources of Fecal Pollution to Santa Monica

Project: Multi-tiered Approach using Quantitative Polymerase Chain Reaction for Tracking Sources of Fecal Pollution into Santa Monica Bay

Background and Objectives

Santa Monica Bay, California, is home to some of the most popular beaches in the world. It is located adjacent to metropolitan Los Angeles where more than 50 million beachgoers visit Santa Monica Bay shorelines every year, more than all other beaches in California combined. However, there are serious concerns about beach water quality in the Bay because of continued exceedences of water quality thresholds based on fecal indicator bacteria such as total coliforms, fecal coliforms or Escherichia coli (EC), and Enterococcus spp. (ENT), particularly in areas impacted by urban runoff. Despite the impairments to water quality and risks to human health, identifying and eliminating the sources of bacteria responsible for the beach warnings remains elusive. The ubiquity of fecal indicator bacteria such as EC and ENT make tracking sources in urban watersheds extremely challenging. In this study, a multi-tiered approach was used to assess sources of fecal pollution in Ballona Creek, an urban watershed that drains to SMB.

Status

This study was conducted in 2004.

Methods

A mass-based design was used at six mainstem sites and four major tributaries to quantify the flux of ENT and EC using traditional culture-based methods. ENT was also quantified using quantitative polymerase chain reaction (QPCR). Additional markers of human fecal contamination that were detected and/or quantified included Bacteroides spp. human-specific marker using conventional polymerase chain reaction (PCR), and enterovirus using quantitative reverse transcriptase PCR (QRTPCR).

Findings

• Sources and concentrations of fecal indicator bacteria were ubiquitously high throughout Ballona Creek, and no single tributary appeared to dominate the fecal inputs.

• The flux of ENT and EC averaged 10⁹ to 10¹⁰ cells hr^-1 and were as high at the head of watershed as they were at the mouth prior to its discharge into Santa Monica Bay.

• The site furthest upstream had the most frequent occurrence and generally the greatest concentrations of enterovirus.

• Ninety-two percent of the samples that tested positive for enterovirus also tested positive for Bacteroides spp. human-specific marker.

• Results indicated the power of using multiple approaches to assess and quantify fecal contamination in freshwater conduits for source tracking in the case of heavily used recreational swimming areas.