[Distribution of enterobacteria in soil following irrigation with waste water]

The filtration of wastewater after irrigation by sandy soil in the area of The Braunschweig Sewage Utilization Association was investigated. For that purpose, the concentrations of gram-negative aerobe rods were determined in soil samples of 15 cm, 30 cm, 45 cm, 60 cm, 75 cm, 90 cm, 105 cm, 120 cm, 135 cm, and 150 cm depth immediately after an irrigation of about 50 mm wastewater during the vegetation (3 series), the vegetationless period (6 series), after one week (3 series) and after two weeks (3 series) during the vegetationless time. All enterobacteria were isolated and identified on the genus or species level (Table 1). Their concentration drops one order of magnitude per 20 cm soil down to a depth of 75 cm. In deeper soil layers the concentration of enterobacteria decreases one order of magnitude about per 60 cm. The enterobacteria penetrated to 60 cm during the vegetation and to 135 cm during the vegetationless period (Fig. 1). There is a relative increase of the fraction of Enterobacteriaceae and a relative decrease of Aeromonas and Plesiomonas as a function of the depth. The non-fermenter, i.e. Acinetobacter, Alcaligenes, and Pseudomonas remain constantly. Down to soil layers of 45 cm the Enterobacter increase relatively. E. coli increase also a little bit, whereas Citrobacter and Klebsiella decrease, respectively (Fig. 2, 3). Downwards, the ratio of Enterobacteriaceae shows no significant changes. Other Enterobacteriaceae, i.e. Proteus, Providencia, and Serratia constitute less than 10 percent. We have found none strains of Salmonella, Shigella, and Yersinia under 5105 enterobacteria identified.