Modelling Water Flow and Escherichia coli Transport in Unsaturated Soils Under Drip Irrigation

The HYDRUS-2D/3D model was used to simulate the wetting patterns and distributions of E. coli in unsaturated sandy and sandy loam soils under surface drip irrigation with sewage effluent. The simulated wetting dimensions of soil volume and distributions of E. coli in soil were compared with data obtained from laboratory experiments. The relatively lower values of normalized root mean square error (NRMSE) and relatively larger index of agreement (d) values indicated good performance of the model. Our simulations confirmed that soil texture greatly influenced the adsorption characteristics and played an important role in the migration of E. coli cells. E. coli was transported further in the sandy soil than in the sandy loam soil, while its concentration decreased considerably with distance from the point source in both soil types. In the sandy loam soil, E. coli was mostly concentrated in a substantially smaller volume 5cm from the soil surface. An increasing application rate of water-suspended bacteria accelerated water flux and enhanced the E. coli transport rate, thus resulting in a larger distribution with a higher E. coli concentration in both soil types. In the proximity of the point source, an extremely high concentration of E. coli was recorded under simulated and observed conditions, and the value increased with an increasing input concentration. Copyright (c) 2017 John Wiley & Sons, Ltd.