The Transport and Fate of Microorganisms in Soils With Preferential Flow.

Laboratory and numerical studies were conducted to investigate the transport of E.coli D21g in preferential flow systems with artificial macropores of different lengths and configurations under two solution ionic strengths. The release process of E.coli D21g under transient chemistry conditions was also studied.  The length of an artificial macropore proved to have a great impact on the transport of E.coli D21g, especially under high ionic strength conditions.  The configuration with a discontinuous artificial macropore (Type IV) was found to have less preferential transport of E.coli D21g than configurations with a continuous macropore opened to either top (Type II) or bottom (Type III) boundary.  At low ionic strength, more extensive transport in the preferential path and earlier arrival time were observed for E.coli D21g compared to bromide as a result of size exclusion.  Two release pulses (one from the preferential path and another from the matrix) were observed following a reduction of the solution ionic strength for Type II and III configurations, whereas three pulses (two from the preferential path and another from the matrix) were observed for the Type IV configuration.  Numerical simulations of E. coli D21g under both constant and transient solution chemistry conditions had very high agreement with the experiment data, except for their capability to predict some subtle differences in transport between the various lens configurations.