Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2006
Publication Date: 10/14/2006
Citation: Pachepsky, Y.A., Sadeghi, A.M., Bradford, S.A., Shelton, D.R., Guber, A.K., Dao, T.H. 2006. Transport and fate of manure-borne pathogens: modeling perspective. Agricultural Water Management. Online-(doi:10.1016/j.agwat.2006.06.0l0.) Interpretive Summary: Animal manure, if improperly managed, may cause substantial pollution of water or fresh produce. Among other constituents, manure contains pathogenic microorganisms that can cause serious illness and death in humans. Computer models are currently used that predict how these pathogens are transported with water in the overland flow and in streams, and the extent which the pathogens are inactivated while in manure, in soil and stream water and sediment. The objective of this work was to review the status of such modeling and to identify main problem areas. We have evaluated methods that are used to model release of microorganisms from manure, microorganism survival and inactivation, attachment of pathogenic and indicator organisms to soil and sediment particles in runoff, soil, and sediment, and transport and straining or entrapment of microbes in the overland flow and in streams. We found that models are mostly developed using data for so-called indicator organisms that are always present in manure, but it is not known whether indicator organisms are transported and survive in the same way as pathogens. Watershed scale modeling is hindered due to uncertainty in inputs from wildlife and from the background population of microorganisms that do not come directly from applied manure. A better understanding is needed of the effect of manure particulates that can serve as abode, food source and carriers for manure-borne microorganisms. Because it is not possible to experiment with microorganisms in every practically significant case, relating microorganism fate and transport parameters to readily environmental variables, such as soil and vegetation properties and weather parameters is a precondition to successful use of models to address public concern. The scarcity and difficulties in obtaining of microbiological data entails the need for the search for natural manure-borne tracers with the transport behavior similar to that of microorganisms. A substantial knowledge gaps exist in understanding the relative role of resuspension of microorganisms from the stream bottom sediments during strong rainstorm events. Modeling can be a useful tool to explain wide variations in the efficiency of vegetated buffer strips in removal of manure-borne microorganisms that currently are observed. Models provide a useful framework to collect coupled monitoring and experimental data that can be further used for prediction and risk assessment purposes.
Technical Abstract: Among other constituents, manure contains pathogenic microorganisms that can cause serious illness and death in humans. The objective of this work is to review the status and challenges in modeling fate and water transport of manure-borne pathogens (MBP) and organisms-indicators of fecal contamination at pedon, hillslope, and watershed scales. Approaches are critically evaluated that are used to model (a) release of microorganisms from manure, (b) microorganism survival and inactivation in manure, soil, and surface water, (c) partitioning and attachment of pathogenic and indicator organisms to solid particles in runoff, soil, and sediment, and (d) transport with straining or entrapment in the overland flow and in streams. The current challenges and research needs are outlined that include (a) the paucity of experimental data about the transport of pathogenic microorganisms, (b) the need to quantify potential and actual input of pathogens from wildlife, (c) uncertainty in background concentrations of indicator microorganisms, (d) better understanding of the effect of manure particulates on the MBP fate and transport, (e) relating the microorganism fate and transport parameters to environmental variables, such as soil and vegetation properties and weather parameters, (e) evaluating natural tracers with the transport behavior similar to microorganisms, e.g. manure-borne phosphorus, (f) understanding the uncertainty of the stream sampling data, (g) developing a process -based model of microorganism resuspension during the rainfall events, (i) developing upscaling techniques to utilize pedon and hillslope scale measurements and models in the watershed modeling, (j) a better insight into filtering function of vegetated buffer strips and riparian zones. Ensembles of simulations have to be made to estimate the possible distribution of simulation results and risks associated with a specific allocation of manure and manure management practices.