Purpose: This study aims to evaluate the relationship between pathogens and fecal indicator bacteria (FIB) in fresh water sources over time and the role sediments have in harboring and distributing pathogens in water resources.
Methods: Aquatic mesocosms were used to evaluate the persistence of 14 different pathogens, 5 surrogates, and 2 FIB. Mesocosms were designed to simulate the natural environment and diurnal variations (UV radiation, ambient temperature). Both lake and river systems were used as sources of water and sediments. Microorganisms (MO) were inoculated at 105 per ml for each mesocosm set up (7 liters). Water and sediment samples were collected for up to 28 days to determine MO concentrations. To evaluate the attenuation and release of FIB and surrogate MO in fluvial systems, an indoor fluvarium was used at both base (1 l/s) and high (2 l/s) flow rates.
Results: Mesocosm results suggest that all MO steadily declined in the water column regardless of season; however, winter mesocosms had a less rapid decline overall – most MO detectable out to 14 days – when compared to other seasons when most MO declined by < 7 days. Attenuation and persistence of MO in sediment was greater in the cooler seasons – fall and winter. Finally, Salmonella enterica serovars were more persistent in both water and sediment samples when compared to other MO, and generic E. coli followed a similar pattern as Salmonella whereas enterococci trended with the Listeria monocytogenes strains. Fluvarium results indicate that E. coli persisted at greater concentrations in water for both the base and high flow input phase. Analysis of MO in fluvarium sediment at 24 h showed a significant difference (P = 0.0117) between base and high flow attenuation of MO. During the flushing phase, more MO were resuspended in the water during base flow as opposed to high flow after 4 h. Moreover, E. coli was resuspended into the water column at higher concentrations followed by Salmonella Typhimurium (ATCC 53647) and PRD1 bacteriophage.
Significance: This study will inform the design of risk-based sampling programs and formation of pathogen fate and transport models that better predict potential health risk related to irrigation water quality and fresh produce.