Solid manure as a source of fecal indicator microorganisms: release under simulated rainfall

Authors: BLAUSTEIN, RYAN - US Department Of Agriculture (USDA); Pachepsky, Yakov; HILL, ROBERT - University Of Maryland; Shelton, Daniel

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2015
Publication Date: 5/26/2015
Citation: Blaustein, R., Pachepsky, Y.A., Hill, R., Shelton, D.R. 2015. Solid manure as a source of fecal indicator microorganisms: release under simulated rainfall. Environmental Science and Technology. 49(13):7860-7869.

Interpretive Summary: Release of pathogenic microorganisms from animal manures can affect microbial water quality of water and food. Whereas much has been learned about the bacteria release from liquid manures, the information of bacteria release from solid manures remains relatively scarce. In particular, it remains unknown whether rainfall intensity and surface slope affect the release. It is also unknown whether the bacteria release from solid manure can be simulated under the assumption of simple mixing of rainfall or irrigation water and manure as it often assumed for liquid manures. We carried out experiments and data analysis to address the above research questions. The rainfall intensity varied in a broad range did not affect the release. Surface slope affected the partitioning of released organisms between infiltration and runoff but not the total release. E. coli was released slower than enterococci which in turm were released slower than chloride ion. The bacteria release from solid manure appeared to be a two-stage process. The first stage was dominated by mixing of liquid phase of manure with rain water, whereas the second stage was controlled by dissolution and sloughing of the solid manure components. The Bradford-Schijven model was the suitable mathematical tool to simulate the release since it had an additional parameter controlling the release change as the amount of applied water increased. results of this work will be of use in microbial risk assessment and predictions as they provide insights in bacteria release from solid manure that are currently lacking and are needed in environmental risk assessment and predictions.

Technical Abstract: The objectives of this work were to determine effects of rainfall intensity and slope on release of Escherichia coli, enterococci, total coliforms, and dissolved chloride from solid dairy manure, and to assess the one-parametric exponential model and the two-parametric Bradford-Schijven model on their performance in simulating the observed release. A controlled-intensity rainfall simulator rained on manure in runoff/infiltration partitioning boxes at three rainfall intensities (3, 6, and 9 cm hr-1) and two land surface slopes (5% and 20%) for one hour of release. Initial concentrations of bacteria in release were more than one order of magnitude lower than their starting concentrations in manure. As bacteria were released from manure, they were partitioned into runoff and infiltration at similar concentrations, but in different volumes depending on slope. Bacterial release occurred in two stages that corresponded to different mechanisms associated with release of portions of the manure liquid phase (as indicated by Cl- release) and solid-phases. Parameters of the two models fitted to the bacterial release dependencies on rainfall depth from initiation of release were not significantly affected by rainfall intensity or land slope. Based on the root-mean-squared-error and the Akaike information criterion, the Bradford-Schijven model is recommended to simulate bacterial release from solid manure. These results may be used to advance parameterization of microbial release which is critical for assessing changes in microbial quality of water sources for irrigation and recreation.