Modeling Pathogen Transport in Fragmented Agriculture-Forest Ecosystems.

Livestock operations and wildlife are commonly viewed as major contributors to nonpoint microbial pollution of surface water. Despite the fact that interactions among them substantially increase the chance of contamination especially in fragmented agriculture-forest landscapes, these interactions are typically ignored in risk assessment practices. The objective of this study is to evaluate the effect of interaction between grazing cattle and white-tailed deer on risk of pathogen appearance in surface water for a small mountain watershed.

An add-on module QMRA-SEIR was developed and coupled with SWAT model to simulate transmission of pathogenic and nonpathogenic strains of E.coli between grazing cattle and white-tailed deer, bacteria survival and transport with overland flow. The add-on module includes: deer migration module, Quantitative Microbial Risk Assessment (QMRA) module to simulate cattle and deer infection by pathogens; SEIR module to simulate deer population, deer and cattle infection and recovery; and a module computing pathogen shedding by cattle and deer. Probabilities of deer and cattle infections by pathogens and numbers of infected animals are computed based on a dose-response approach, which includes beta-Poisson and exponential QMRA models. The plant biomass growth predicted with watershed-scale model SWAT used as the input for the deer migration component of the add-on module, while shed pathogen and nonpathogen bacteria concentrations computed by the QMRA-SEIR module are used as the input for SWAT model. The model was qualitatively tested for Little Cove Mountain Creek watershed in PA. The results of simulations indicated an increase in probability of pathogen concentrations in the creek water during summer months, which was associated with overall increased deer population, increased duration and deer population grazing at pastures, and intensive precipitation that initiated runoff and overland transport of bacteria.