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Vegetative Filter Strips As a BMP To
Control Microbial Pathogens

Prasanta Kalita
Associate Professor
Department of Agricultural Engineering
(217) 333-0945; pkalita@illinois.edu
Prasanta Kalita

Runoff from animal production facilities often contains high amounts of nutrients, solids, and microorganisms that are potential sources of contamination of the water supply. The principal worries are Cryptosporidium parvum (C. parvum) and Escherichia coli (E. coli) for the hazard they may impose on human health when acquired directly via the fecal-oral route or indirectly as a waterborne infection. There have been outbreaks of C. parvum at places where communities both filtered and chlorinated the water supplies.

Our long-term goal is to control microbial contamination of water resources and provide a safe and sustainable environment for animal production facilities. The overall objectives of this study are to understand microbial fate and transport processes, characterize critical environmental factors affecting microbial transport and control in runoff and near-surface runoff, and disseminate information that will prevent transport of microbial pathogens in the water supply. To design and develop best management practices (BMP) for source control of microbial pathogens, transport processes in surface and near-surface runoff need to be quantified.

Slope
[%]
Rainfall
Intensity
[cm/hr]
Total Percent Recovery in Surface Runoff
Bare-ground Conditions [%] Vegetated Conditions [%]
1st Rain 2nd Rain 3rd Rain 1st Rain 2nd Rain 3rd Rain
1.5 2.54 13.77 0.71 - 1.65 0 -
1.5 6.35 2.53 2.72 - 0.80 0.65 -
3.0 2.54 9.53 4.61 3.84 0.84 0 0
3.0 6.35 5.32 2.90 1.05 0.39 0.18 0.19
4.5 2.54 3.35 0.89 0.13 0.34 0.25 0
4.5 6.35 52.45 3.89 2.67 20.34 4.61 2.20

Table 1. Percent of C. Parvum recovery from vegetated and bare-ground conditions.

Vegetative filter strips (VFS) have been identified as a BMP to help control the movement of solids and nutrients into water sources. These filter strips are designed to reduce runoff velocity, allowing more water detention on the surface. Vegetation can increase soil organic content and local microbial population sizes, enhance soil porosity and soil permeability, increase infiltration capacity, slow down near-surface flow velocities, and provide more organic-rich surfaces for microbial adsorption. Most of these factors tend to cause higher levels of immediate adsorption and increase attenuation of organisms in the plant/soil system. The effects of these factors on microbial fate and transport need to be quantified under different soil, climatic, and watershed conditions; only then can a VFS properly be designed with site-specific criteria for maximum performance. This information must be disseminated effectively for adaptation of design guidelines for understanding and developing BMP to control microbial pathogens.

Experiments have been conducted at a University of Illinois laboratory under a rainfall simulator. A horizontal tilting soil chamber was constructed to investigate the overland and near-surface transport of Cryptosporidium parvum. The soil chamber (12 ft long, 5 m wide, 1 ft deep) was constructed using sheet metal. Experiments were conducted on two soil types, one vegetation, three slopes (1.5, 3.0, and 4.5 percent), and two rainfall intensities (1 and 2.5 in/hr). One compartment of the bed was seeded with vegetation, and the other was left bare. Surface runoff samples were collected for the entire runoff period and analyzed for total recovery of C. parvum oocysts. The total recovery of oocysts in surface runoff compared to the initial application rates for the 1.5, 3.0, and 4.5 percent slopes and for both rainfall intensities can be seen in Table 1. This table shows percent recovery rates from both vegetated and bare-ground conditions. For each slope, the runoff from the vegetated side contained much lower percent recovery rates compared to those from the bare-ground conditions. Each subsequent rainfall applied to the chamber resulted in reduced total recovery rates in surface runoff (Table 1) for both bare-ground and vegetated conditions.

The results from low-intensity rainfall show that almost no oocysts were recovered from second and/or third rainfalls for all three slope conditions from the VFS. The results for high-intensity rainfall indicate that there was less recovery of oocysts at the 1.5 and 3.0 percent slopes as compared to low-intensity rainfall for the same slopes. Bare-ground conditions showed much higher oocyst recovery rates than that from the VFS for the high-intensity rainfall.

These results demonstrate very promising effects of vegetation and vegetative filter strips in controlling pathogen transport in runoff. We will evaluate the effects of a series of rainfall, slope, vegetation, soil, and watershed conditions on pathogen fate and transport in developing BMP design criteria and disseminating the information. Results can be found online at http://www.cvm.uiuc.edu/cryptoweb. The research team members are Prasanta Kalita, Mark Kuhlenschmidt, Ted Funk, and Ronald Smith. This project is partly supported by C-FAR.

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