Author(s): Lloyd H. C. Chua; Peter Shanahan; Edmond Y. M. Lo; Ban Shuy; Janelle Thompson; Cameron C. Dixon; Kathleen B. Kerigan; Jean Pierre Nshimyimana; Jessica M. Yeager; Li-Jun Lee; Yu-Ling Por
Linked Author(s): Eng-Ban Shuy
Keywords: Dry Weather; Bacteria Monitoring; E. coli; Enterococci; Land use
Abstract: An initial assessment of bacteria concentrations under dry weather conditions was made for the Kranji catchment in Singapore. Under Phase 1 of the study, high counts of E. coli and Enterococci were observed at 5 sampling locations, which were monitored for a period in excess of 1 year. The USEPA (1986) guideline concentration for E. coli of 235 per 100ml was exceeded for almost all samples collected. Comparing between the 5 sampling locations, it was found that E. coli and Enterococci concentrations were highest at KC02, which had a sub-catchment with the highest percentage development, compared to the other 4 monitoring sites. Limited storm sampling showed evidence of elevated concentrations of E. coli and Enterococci contained in storm runoff. Phase 2 of the study saw an expansion of the monitoring program to obtain a wider spatial coverage of sites being monitored. The drainage system upstream of KC02 was progressively sampled which led to the identification of a possible source, where an E. coli concentration of 2 x 10 6 per 100ml was measured about 1.4 km along the drainage network, upstream of KC02. An analysis of the data obtained from Phase 2 showed that E. coli varied according to land use, in increasing order according to the following sequence of land use categories: Undeveloped→Farm→Residential→Sewage Treatment Plant (STP). DNA analysis revealed that the locations where the human factor (HF) marker was detected generally corresponded with locations at which high coliform concentrations were found and which were known or suspected to be associated with sanitary wastewater. Nonetheless, numerous locations at which coliform counts were well above USEPA water-quality criteria often did not show human factor presence. Others have questioned whether coliform may grow naturally in tropical waters and more analyses are needed to investigate the possible contributors to observed coliform counts in Kranji catchment.
Year: 2010