Abstract
The spatial and temporal distributions of indicator bacteria in a small, multiple-use source drinking water reservoir in Southern California, USA were quantified over the period August 2001–July 2002. High levels of total and fecal coliform bacteria were present in Canyon Lake (annual geometric mean concentrations±SEM of 3.93±0.02 and 3.02±0.03 log cfu/100 mL, respectively), while comparatively low levels of enterococci and E. coli were found (1.16±0.02 log cfu/100 mL and 0.30±0.03 log MPN/100 mL, respectively). As a result, these different indicator bacteria yielded quite divergent indices of water quality, with 72.1% of all surface samples ( n=294) exceeding the USEPA single-sample limit of 400 cfu/100 mL fecal coliform bacteria, while none (0%) of the samples exceeded the single-sample limit for E. coli ( n=194). Regression analyses found a positive correlation between total and fecal coliform bacteria ( R=0.50, significant at p<0.001) and between enterococci and E. coli ( R=0.51, significant at p<0.001), but no correlation or inverse correlations were found between coliform concentrations and enterococci and E. coli levels. External sources responsible for the high total and fecal coliform bacteria were not identified, although laboratory studies demonstrated growth of the coliform bacteria in lake water samples. Enterococci and E. coli were not observed to grow, however. Bacteria concentrations varied relatively little laterally across the lake, although strong vertical gradients in fecal coliform and enterococcus bacteria concentrations were present during summer stratification, with concentrations about 10×higher above the thermocline when compared with surface concentrations. In contrast, total bacteria, total virus and total coliform bacteria levels were unchanged with depth. Seasonal trends in bacteria concentrations were also present. This study shows that the choice of indicator bacteria and sampling depth can both strongly affect the apparent microbial water quality of a lake or reservoir.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.