Inactivation of Escherichia coli During Storage of Irrigation Water in Agricultural Reservoirs

Abstract

Microbial contamination of surface waters is one of the most important water quality issues affecting the agricultural sector in Nova Scotia, Canada. Most farmers who irrigate in the province draw their source water directly from streams and rivers. One mode of pathogen transmission is the irrigation of horticultural crops with contaminated water. The extended storage of irrigation water prior to crop application could minimize this risk. Natural inactivation processes could, depending on the source water characteristics and length of storage time, reduce bacteria levels to acceptable use standards. The purpose of this project was to study bacterial population dynamics, specifically those of Escherichia coli, in shallow irrigation water reservoirs. Experiments, involving a series of dialysis tube survival studies, were conducted from May through September of 2006 in an operational farm reservoir to examine microbial inactivation kinetics. It was found that E. coli populations in the cool, lower layer (depth ≈ 3 m) did not decline, while populations in the warm upper layer (depth ≈ 1.0 m) experienced significant reductions over a period of several days. An inactivation model was calibrated and used to develop conservative estimates of T 90 , T 99 , and T 99.9 values for environmental conditions typical of the Annapolis Valley of Nova Scotia. If a shallow reservoir was well mixed to prevent gradients in temperature and dissolved oxygen, storage of irrigation water for a period of at least two weeks would reduce bacterial numbers by at least three logs during the growing season in Nova Scotia.

The effect of anthropogenic pressure shown by microbiological and chemical water quality indicators on the main rivers of Podhale, southern Poland

“…These are enteric microorganisms, which have evolved to exist in relatively stable environment, therefore their exposure to unfavorable conditions which can be encountered in rivers and water reservoirs can be a significantly limiting factor. Studies by Murphy et al ( 2010 ) demonstrated that populations of E. coli can be inactivated within a warm upper layer of a shallow reservoir, but they can also survive for long periods of time within a cool, oxygen depleted environments in lower layers of these same systems. The range of factors affecting microbial fate and transport in a reservoir is wide and complex, and their detailed analysis is beyond the scope of this paper.…”

Irrigation Waters as a Source of Pathogenic Microorganisms in Produce: A Review

“…The inactivation rate of E. coli under direct sunlight was about an order of magnitude larger than in darkness in an irrigation pond (Maϊga et al, 2009); the value of the k 1 rate constant was about 19 d 21 , which is much higher than anything shown in Fig. Inactivation of E. coli and enterococci declines with depth (Barcina et al, 1990;Maϊga et al, 2009;Murphy et al, 2010). Inactivation of E. coli and enterococci declines with depth (Barcina et al, 1990;Maϊga et al, 2009;Murphy et al, 2010).…”