Fecal Indicator Bacteria (FIB) Levels during Dry Weather from Southern California Reference Streams

摘要

High levels of fecal indicator bacteria (FIB) in surface waters is a common problem in urban areas that often leads to impairment of beneficial uses such as swimming or other contact recreation. Once impaired, common management and regulatory solutions include development of Total Maximum Daily Loads (TMDLs) and other water quality management plans. A critical element of these plans is establishment of a reference level of exceedances against which to assess management goals and TMDL compliance. Unfortunately, existing background or reference data on contributions of FIB from undeveloped catchments during dry weather is limited to a small number of locations measured at few time points. The goal of this study was to provide information on indicator bacteria contributions from natural streams in undeveloped catchments throughout southern California during dry weather, non-storm conditions. Specific questions addressed were: (1) What are the background ranges of concentrations of FIB associated with dry weather flow from reference areas; (2) What is the frequency with which reference FIB levels exceed relevant water quality standards: (3) How does seasonality influence stream FIB levels associated with reference areas; and (4) How do the ranges of FIB concentrations associated with reference areas compare with those associated with urban (developed) areas To help establish a regional reference data set, bacteria levels (i.e. Escherichia coli (E. coli), enterococci and total coliforms) were measured from 15 unimpaired streams in 11 southern California watersheds weekly for one full year.