Impact of Diversion Boxes on Escherichia coli in Irrigation Waters Intended for Food Crops

Abstract

In recent years, there have been growing concerns about the prevalence of Escherichia coli in Yuma, Arizona, irrigation canals. Certain types of E. coli are pathogenic in humans and when consumed, can cause serious illness. E. coli in irrigation canals in the Yuma area are believed to have been responsible for outbreaks of pathogenic E. coli associated with consumption of leafy greens. The sources of contamination are unknown, although agricultural runoff, animal waste, and defective septic systems are possible contributors. The goal of this study was to assess diversion boxes (structures that redirect the flow of water) and floating debris as potential reservoirs of E. coli in irrigation systems in the Yuma area. Four canal sites were selected and sampled on a monthly basis. Results from comparing upstream and downstream sediment samples indicate that while the E. coli concentration increases in the upstream sediments during warmer summer months, the E. coli concentrations in downstream sediments remain relatively unchanged. The concentrations of E. coli in the water were found to be at least one to three orders of magnitude lower than in the sediments, biofilm and debris. Thus, the biofilm and debris could potentially serve as potential reservoirs for E. coli. Overall, the diversion boxes appeared to have no significant impact on microbial water quality.