Modeling and monitoring pathogen transport through vegetated filter strips

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Contamination of natural waters by microorganisms directly affects public health. Field application of manure can potentially result in surface and groundwater contamination. The objective of this study was to observe and quantify the effects of vegetated filter strips (VFS) on surface and subsurface transport of fecal oviform (FC) surrogates for bacterial pathogens released from a surface - applied bovine/swine manure.

The study included a field-based lysimeter equipped with multi-sensor moisture probes to monitor real-time water content through the soil profile, and with other proper instrumentation to monitor and quantify the spatial and temporal release rates of pathogenic bacteria. Another component of this study involved development and testing of a computer model to predict the surface and subsurface transport of FC.

Results showed that bare plots offered no resistance to surface flow, thus FC were detected in runoff at 600 cm from the ridge of the lysimeter within 10 minutes of the rainfall initiation. Results from vegetated plots showed that vegetation substantially attenuated surface flow of water as compared to bare plots. Unlike the bare soil, the results showed that the vegetated soil surface created a much less uniform transport pattern for FC. Vegetation changed transport patterns and levels of FC concentrations much more significantly than soil texture did.

Results showed that E.coli and Salmonella cholerasuis behaved similarly and resulted in similar transport patterns in both bare plots. Results also showed that both organisms demonstrated a two-stage exponential release rate with a fast release rate in the first 10 minutes of the rainfall simulation.

A one-dimensional convective-dispersive equation using the continuity equation and the Manning's equation were used in MODCHOI model (a modified version of KORMIL2) to predict the surface transport of FC. To simulate the vertical movement of FC, a one-dimensional kinematic wave model was developed and used. Green and Ampt, Philip, and Schmid infiltration models were also applied to the vertical water flow movement. The models simulated the spatial and the temporal distribution of FC in runoff assuming an exponential release of FC from the manure. Simulation results satisfactorily modeled both flow and FC.