ARS | Publication request: Effectiveness of vegetated filter stripsin retentionof E. coli and salmonella from swine manure slurry

Submitted to: Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 15, 2011
Publication Date: June 14, 2012
Citation: Sadeghi, A.M., Cardosol, F., Shelton, D.R., Shirmohammadi, A., Pachepsky, Y.A., Dulaney, W.P. 2012. Effectiveness of vegetated filter stripsin retention of E. coli and salmonella from swine manure slurry. Environmental Management. DOI: 10.1016/j.envman.2012.05.012.

Interpretive Summary: Fecal contamination of surface water resources from animal manure application to agricultural fields is a critical water quality issue, leading to many recent health and environmental concerns. Vegetated filter strips (VFS) are commonly recommended as a best management practice to prevent manure-borne microorganisms from reaching surface water resources. However, relatively little is known about VFS mitigating effectiveness. A field lysimeter study was designed to specifically evaluate the effect of vegetation buffer, compared to bare soil condition, on the retention of swine manure-borne E. coli and Salmonella under various rainfall conditions. Results demonstrate the potential for VFS to mitigate bacterial runoff from swine organic waste sources. No substantial differences were observed in retention of E. coli and Salmonella. Very low bacterial retention was observed in bare plots whereas vegetated plots showed high retention capacity. However, our findings also demonstrated that the effectiveness of VFS can vary dramatically depending on the amount of rainfall required to saturate the VFS, time required for runoff initiation from manured fields, and development of the subsurface flow in VFS. Consequently, VFS recommendations should account for specific soil surface hydrology characteristics such as shallow and fluctuating near surface water table as well as the relative soil storage capacity of the VFS in dictating the filter strips moisture conditions.

Technical Abstract: Vegetated filter strips (VFS) are commonly recommended as a best management practice to prevent manure-borne microorganisms from reaching surface water resources. However, relatively little is known about the efficacy of VFS in mitigating bacterial runoff from land-applied swine manure. Experimental plots (6.5 m x 3.9 m) were set on a 5% slope lysimeter with loamy topsoil, clay loam or loam subsoil and a controllable groundwater level. Three small flow-intercepting miniflumes were installed 4.5 m from the plot’s top, while all remaining runoff was collected in a gutter at the bottom. Plots were divided into bare soil or grass vegetation and upper surface soil moisture before rainfall events was controlled by the subsurface groundwater level. Swine manure slurry inoculated with E. coli and Salmonella, and with added bromide tracer, was applied on the top of the plots and simultaneously initiated the simulated rainfall. Runoff was collected and analyzed every 5 min. No substantial differences between retention of E. coli and Salmonella were found. In initially wet soil surface conditions, there was limited infiltration both in bare and in vegetated plots; almost all bromide and about 30% of bacteria were recovered in runoff water. In initially dry soil surface conditions, there were substantial discrepancies between bare and vegetated plots. In bare plots, recoveries of runoff water, bromide and bacteria under dry conditions were comparable to wet conditions. However, in dry vegetated plots, from 50% to 75% of water was lost to infiltration, while bromide recoveries ranged from14 to 36% and bacteria recovery was only 5%. Substantial intraplot heterogeneity was revealed by the data from miniflumes. GIS analysis of the plot microtopography showed that miniflumes located in the zones of flow convergence collected the majority of bacteria. Overall, the efficiency of vegetated filter strips, with respect to the retention of swine manure bacteria, varied dramatically depending upon the hydrologic soil surface condition. Consequently, VFS recommendations should account for expected amounts of surface soil water saturation as well as the relative soil water storage capacity of the VFS.