Effect of Phytoplankton on Escherichia coli Survival in Laboratory Microcosms.

Fecal contamination of water sources is an important water quality issue for agricultural irrigation ponds. Escherichia coli is a common microbial indicator used to evaluate recreational and irrigation water quality. Nuisance algae commonly grow in low- or no-flow irrigation water sources. The objective of this experiment was to test whether phytoplankton collected from irrigation ponds impacts survival of E. coli in fresh water. Samples of water containing phytoplankton from one irrigation pond in Maryland were placed in Erlenmeyer flasks and inoculated with cultured E. coli. Flasks were kept at room temperature under full spectrum fluorescent lights with 12 hr light and dark cycles. E. coli concentrations and environmental covariates (pH, redox potential, and DO) were measured daily for a week. Water samples were collected daily and preserved for algal community identification. The exponential die-off of E. coli was observed both in absence and in presence of phytoplankton. The survival rates appeared to be statistically different in the absence and in presence of phytoplankton. Both pond water source and initial E. coli concentration in the inoculum appeared to be significant survival factors. Results of this work indicate that that site-specic relationships can be developed to characterize the water environment conditions for E. coli survival based on planktonic algae concentrations which in turn can be estimated from chlorophyll a measurements. More information and research is needed regarding the survival of E.coli in planktonic algae.