Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2008
Publication Date: 3/1/2009
Publication URL: http://hdl.handle.net/10113/41454
Citation: Pachepsky, Y.A., Guber, A.K., Shelton, D.R., Mccarty, G.W. 2009. Size Distributions of Manure Particles Released Concurrently with E. coli Under Simulated Rainfall. Journal of Environmental Management. 90:1365-1369. Interpretive Summary: Animal manures and fecal depositions may contain pathogenic microorganisms that can be released under rainfall and transported to drinking and recreational waters. The microbes are released along with organic particles which may serve as carriers, and as a nutritional source for microbial growth. In spite of the importance of the manure particles in fate and transport of pathogenic organisms, nothing is known about the amounts and sizes of manure particles released during rainfall. Advances in particle size distribution measurements with the help of laser diffractometry have allowed us to obtain the first information on manure particle site distribtuions. We applied bovine manure on soil under live and dead grass, simulated rainfall, and collected runoff from manured surface and leachates through a 2-inch soil layer. Manure particle size distribution, E. coli concentrations, and turbidity were measured in runoff and leachate samples and turbidity. E. coli concentrations and turbidity decreased with time. Particle size distributions in manure runoff and in leachates remained remarkably stable after 15 min of runoff initiation. The released manure particles were of microbial size and varied between 0.2 and 20 um.
Technical Abstract: Manure applied on cropland and animal waste deposited on grazing lands serve as a source of microorganisms, some of which may be pathogenic. These microorganisms are released along with particles of dissolved manure during rainfall events. Relatively little if anything is known about the amounts and sizes of manure particles released during rainfall, that subsequently may contaminate surface waters via runoff or infiltrate into the soil profile. The objective of this work was to obtain and present the first experimental data on the quantity and sizes of bovine manure particles released during simulated rainfall and to compare release rates of manure particles vs. Escherichia coli cells. Experiments were conducted using 200 cm long boxes containing turfgrass soil sod; the boxes were designed so that rates of manure dissolution and subsequent infiltration and runoff could be monitored independently. Dairy manure amended with KBr was broadcast on the upper portion of boxes that contained stands of either live or dead grass. Simulated rainfall (ca. 3.24 cm hr-1) was applied for 90 minutes. Electrical conductivity, E. coli concentrations, turbidity, and particle size distributions obtained from laser diffractometry were determined in manure runoff and soil leachate samples. Turbidity of leachate and manure runoff samples decreased progressively with time until they approached background values. Turbidity of manure runoff samples was on average 20% less than turbidity of soil leachate samples. Turbidity of leachate samples from boxes with dead grass was on average 30% less than from boxes with live grass. Escherichia coli concentrations also decreased with time but not as rapidly as turbidity. The linear regression “log turbidity vs. log E. coli” had the slope of 0.67 and explained 75 % in variation of logarithms of E. coli concentrations. Particle size distributions in manure suspensions remained remarkably stable after 15 min of runoff initiation, although the turbidity continued to decrease. Particles had the median diameter of 3.8 'm, and 90% of particles were between 0.6 and 17.8 'm. The particle size distributions were not affected by the grass status. Because manure particles are known to affect transport and retention of microbial pathogens in soil, more information needs to be collected about the concurrent release of pathogens and manure particles during rainfall events.