Variations of Indicator Bacteria in a Large Urban Watershed

The Santa Ana River (SAR) in southern California, USA is an impaired stream with historically high fecal coliform counts. This study evaluated the presence of indicator bacteria in 13 sites in the middle Santa Ana River watershed (MSAR). The objectives of this study were to: (i) examine spatial and temporal characteristics of fecal bacteria loading during dry (low or baseline) flow, storm flow (wet), and recessional flow along two creeks, two wastewater treatment plants (WWTP) outlets, and a control site in the middle Santa Ana River watershed (MSAR), and (ii) develop tests to fully quantify how the various sampling locations and water flow conditions affected indicator bacteria concentrations in the watershed. Total coliform (TC), fecal coliform (FC), E. coli, enterococci, and total bacterial concentrations were monitored in 13 locations in the watershed over a two year period. Analysis of covariance (ANOCOVA) model was used to test each specific set of bacteria counts, site effects, water flow conditions, and the four water quality covariate effects. Our results show that the control site (S1) and WWTP estimates always show significantly lower indicator bacteria than the channels influenced by urban runoff and agricultural activities. The water flow effects indicated that the recessional water flow transported significantly lower bacterial counts into the watershed than either the dry weather flow or the storm or wet weather flow. Also, bacterial counts estimates changed far more significantly across different sites, in comparison to estimates across seasonal flow estimates or time. These results imply that total TC, FC, E. coli, and enterococci bacterial counts in the two tributaries were strongly influenced by spatial location effects with contamination due to local agricultural and/ or urban run-off, in contrast to elevated up-stream contamination and/ or discharge contamination associated with the two WWPT. Therefore, this study has provided for the first time useful information that could be used in constructing watershed management plans for a mixed watershed.