Water Resources Research Act Program

Details for Project ID 2004GU27B

Presence and Survival of Fecal Indicator Bacteria in Soil from the Banks of Major Rivers and Streams on Guam

Institute: Guam
Year Established: 2004 Start Date: 2004-03-01 End Date: 2005-02-28
Total Federal Funds: $38,822 Total Non-Federal Funds: Not available

Principal Investigators: Gary Denton, Roger Fujioka, Annie Leon Guerrero, Harold Wood

Project Summary: The use of fecal bacteria to monitor the hygienic quality of recreational waters has some serious limitations in many tropical and subtropical regions of the world. This is because favorable ambient temperatures encourage extended survival times of these organisms in the environment and dramatically increases the risk of false positives occurring. On Guam, E. coli and enterococci are used to monitor rivers and coastal waters around the island respectively. Both organisms have been observed to survive indefinitely in sediments and soils in Hawaii, Puerto Rico, southern Florida, and northern Australia. Their growth in various environmental media has also been reported in several instances. While the survival, growth and proliferation of E. coli and enterococci is suspected to occur in sediments and soils on Guam, the limited available data is inconclusive because it fails to differentiate between possible contributions from fecal and non-fecal sources. The fact remains, however, that exceedences of the recreational water quality standards are far more frequent during wet weather than they are during dry spells. This strongly suggests that local riverbank soil is a major reservoir for enterococci, and that these bacteria are mobilized into the coastal belt by erosive processes during prolonged periods of heavy rain.The objectives of the study described herein are to demonstrate whether or not E. coli and enterococci are capable of surviving in Guam riverbank soils over extended periods of time, and to elucidate the importance of various soil related factors that might influence the data. To this end, we propose to screen riverbank soils for E. coli and enterococci from all major rivers and streams on island. Sampling sites will coincide with those adopted by Guam EPA for recreational water quality monitoring purposes. Subsequent investigations, at selected sites, will explore any horizontal and vertical variations in abundance of both organism in relation to soil type, organic matter content, nutrient levels, and moisture content. We will also attempt to determine their survivability in the total absence of sustainable sources of fecal bacteria such as storm water runoff and animal excrement.Fecal bacteria will be removed from all soil samples by sonic probe and cultured using Colilert and Enterolert commercial growth media for E. coli and enterococci respectively. Bacterial enumerations will be accomplished using the Quanti-TrayTM MPN method following incubation at 41oC for 24 h 2 h for both organisms. All soils tested during the study will be characterized according to type, and analyzed for organic carbon, nitrate, orthophosphate, total nitrogen, total phosphorus and moisture content. Survival tests will be conducted using closed-jar microcosms.The analytical work will be carried out at the Water and Environmental Research Institute (WERI), Water Quality Laboratory, at the University of Guam, where adequate support facilities, infrastructure and equipment necessary for the study are present. The analytical procedures will adopt USEPA approved methods in all instances. Quality control and quality assurance procedures will be rigidly adhered to. The data obtained should command the attention of water quality managers, environmental regulators and public health officials in tropical and sub-tropical regions throughout the world.