SWAT-SIR Model for Predicting Fate and Transport of Manure-borne Pathogens in Fragmented Agriculture-Forest Ecosystems

The objective of this study was to develop and qualitatively evaluate a model predicting transmission of manure-borne pathogens between co-grazing cattle and wildlife. The developed addon module SIR that we coupled with SWAT model included the following new components: wildlife population changes, resource selection, dose-response, compartmental susceptible-infectiousrecovered (SIR) module and pathogen shedding. Probabilities of the wild and domestic animal infection by pathogens and numbers of infected animals were computed based on a dose-response approach, which included beta-Poisson and exponential models. Land use and plant biomass predicted with watershed-scale model SWAT were used as the input for the deer resource selection and foliage consumption. Pathogen shedding by wild and domestic animals was computed in the addon module SIR based on the number of infected animals, daily shedding rates and duration of grazing. The developed model was implemented to define scenarios and identify mechanisms of E.coli O157:H7 transmission between co-grazing white-tailed deer and cattle for a small watershed. Introducing SIR component into SWAT model allowed prediction of increasing E.coli O157:H7 load on farmlands in spring and summer months as a result of increasing numbers of infected cattle and deer. This increase can potentially be caused by the infection spreading among cattle due to grooming as well as deer infection by pathogens ingested with foliage after surface manure application or released to foliage from cattle fecal deposits. The model output linked with ARC-GIS allowed spatial and temporal analysis of pathogen distribution across the watershed for specific weather and management scenarios. Overall, the developed SWAT-SIR model is a useful tool for assessment of pathogen transport and for development of better management practices in mixed agriculture-forest ecosystems.