Purpose: The purpose of this study is to evaluate the influence of events that may result in episodic contamination of agricultural pond water.
Methods: Water samples (500 ml) from six ponds in Central Florida were collected weekly, November - May, weekly and every other day after rain exceeding 2.0 cm within 24h, and freeze protection. Samples were collected 20 cm below surface within a 304.8 cm radius of the water intake. Microbial populations (total coliforms, generic Escherichia coli, and Enterococci) were enumerated by MPN. Environmental variables measured included, water and ambient temperature, pH, conductivity, oxidation and reduction potential, and turbidity; observed animal activity was noted.
Results: Escherichia coli populations were ≤ 2.4 log MPN/100 ml in 247/276 (89.5 %) and geometric means were ≤ 2.1 log MPN/100 ml in 252/276 (91.3%) of samples. Following rain events, populations increased up to 4.2 log CFU/100 ml from the previous sampling. Populations of coliforms and Enterococci ranged from log 2 to 8 and 1 to 5, respectively. Microbial populations varied within ponds varied up to 4 log MPN/100 ml between sample points. Pearson product moment correlation coefficients (r) among microbial indicators were above 0.61 (P < 0.0001). Microbial indicators were not correlated with environmental variables, except pH (P < 0.0001). Animal activity during sampling included amphibians, fish and birds.
Significance: Surface waters tested in Central Florida met the current recommendations for microbial water quality 85.5% (236/276) of the time. Environmental factors may change the microbial quality of surface water; understanding the effects will allow targeted sampling of surface water to reduce food safety risks.