Assessment of Escherichia coli Leaching in two Acidic Soils

Manures are used to increase pH and fertility of acidic soils in Gilan province. Although they are useful, but contain coliform bacteria that can reach the groundwater resources and lead contamination. This study aimed to investigate an indicator bacterium; Escherichia coli transport in two acidic soils. Two soil samples with pH vlues of 5.88 and 3.99 were taken from Amlash and Lahijan area respectively. For leaching experiment, air dried soil was freely packed in Polyvinyl chloride sylinders (with diameter of 4.8 and height of 14.92 cm). A 0.1 pore volume (PV) of bacteria (1× 108 CFU mL-1) and bromide (0.008 mol L-1) as a pulse flow was applied on the top of the soil columns after water flow rate reached steady state condition and leaching experiment was followed with distilled water. Leachate sampling was carried out in regular time intervals till 4.5 PV and E. coli and bromide concentrations were measured in the leachate. Resident E. coli number were also determined in each cutted 3 cm section of soil after leaching experiment endup. C/C0 peak of E. coli in the leachate of Amlash and Lahijan soil columns was observed at 0.7 and 0.9 PV repectively, while the C/C0 peak of bromide was occurred at 0.8 and 1.8 PV respectively. Early occurance of E. coli bacteria rather than bromide in the leachate of both soils was attributed to preferential water flow path which was dominant in the Lahijan soil column due to more clay and organic carbon content. The most resident E. coli number was determined in the surface layer of both soils which was greater in Amlash soil and decreased by 0.9 and 1.44 (log unit) in Amlash and Lahijan soil columns respectively. Overall, not only the cumulative number of E. coli bacteria was higher in the leachate of Amlash soil column, but also it contained more resident E. coli bacteria rather than Lahijan soil column due to greater pH value.