Submitted to: Proceedings of the Symposium on Watershed Management
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2007
Publication Date: 3/10/2007
Citation: Guber, A.K., Pachepsky, Y.A., Sadeghi, A.M. 2007. Evaluating uncertainty in E. coli retention in vegetated buffer strips in locations selected with SWAT simulations. Proceedings of the Symposium on Watershed Management, March 10-14, 2007, San Antonio, Texas. pp.286-293. ASABE Publication 701P0207. Interpretive Summary: Vegetated buffer strips (VFS) separate fields and pastures from streams and other water bodies and can serve as barriers that prevent sediment and agricultural chemicals from entering waterways and polluting them. Growing concern about manure-borne pathogens as water pollutants defines the need to evaluate the efficiency of VFSs with respect to pathogens. The functioning of VSF as barriers for manure-borne pathogens is to a large extent dependant on vegetation status, soil infiltration capacity, and rainfall intensity and duration. These factors cannot be defined accurately and time-independently for a particular VFS. Only probability distributions can be inferred for those factors. This creates an unavoidable uncertainty that cannot be ignored and has to be factored into efficiency estimates. We have developed the model STIR to simulate the overland transport and loss to infiltration of manure-borne pathogens in VFS. This model was used in Monte Carlo simulations in which the input parameters of vegetation, soil, rainfall, and pathogen load were drawn from probability distribution functions. The result of such simulations was also the probability distribution of the VFS efficiency. For the example of our experimental 6-m long VFS at the 20% slope, The VFS efficiency was less than 100% in 5% of cases, and less than 75% in 2.5% of cases. Relatively long high-intensity rainfalls, low hydraulic conductivities, high soil moisture contents before the rainfall, and high spread of surface water velocities were the main sources of the VFS partial failure. Analogous simulations can be done for any other VFS with site-specific soil and weather properties, and the results in terms of efficiency probabilities can be useful in making decisions on VFS placement with respect to manure-borne pathogens
Technical Abstract: Vegetated fulter strips (VFS), as a best management practice, have become an important component of the water quality improvement in watersheds. The SWAT model allows for a comprehensive description of agricultural practices, and has proven to be efficient in applications to watershed with a substantial agricultural component. The REMM, KINEROS, and other models have recently been suggested to use SWAT output to evaluate the VFS retention capacity with respect to nutrient and sediment loads. The concern about the manure-borne pathogens in waterways and water bodies has to be addressed in more details by estimating the efficiency of VFS in pathogen retention. The existing knowledge base shows that the functioning of VSF as barriers for manure-borne pathogens to the large extent depends on vegetation status, soil infiltration capacity in VFS, and rainfall intensity and duration. The effect of these factors on the pathogen breakthrough in VFS needs to be researched at the time scales smaller than the computation interval of one day that SWAT uses. The downscaling of the SWAT output to the smaller time scales, however, introduces an uncertainty. We have developed the model STIR to simulate the overland transport and loss to infiltration of manure-borne pathogens in VFS. This model was used in Monte Carlo simulations to evaluate the possible variability in pathogen breakthrough in VFS with inputs from SWAT. The simulations show that probabilistic characterization of the VFS efficiency with site-specific soil and weather properties can be useful in making decisions on VFS placement with respect to manure-borne pathogens.