Large-scale assessment of the impacts of invasive wild pigs on water quality in freshwater streams

Highly competent hosts of zoonotic diseases of economic and epidemiological importance, the highly invasive species, Sus scrofa, has been identified as sources of non-point pollution in North America through small-scale studies of their fecal contamination in surface waters. Their fecal contamination alters natural physicochemical stream characteristics and increases concentrations of fecal bacteria. Providing one of the first-large scale assessments of their impacts, our study identified wild pigs as a source of non-point pollution on both a regional and multi-regional scale within our selected study state through microbial source tracking and traditional water quality assessment. At a multi-regional scale, we found greater median concentrations (mg/L) of nitrate (95.7%; p < 0.001), magnesium (83.3%; p < 0.001), and potassium (84.7%; p < 0.001) in samples from streams with fecal contamination by wild pigs (n = 111) than from streams without (n = 115). Like other non-point pollutants, the effects of wild pigs on water quality are scale-dependent and differ significantly across regions. Finally, at both a regional and multi-regional scale, our study found observably greater Escherichia coli and fecal coliform concentrations in streams with wild pigs, though statistical significance was lost at scale. Future research will be necessary to continue to evaluate the impacts of wild pigs on water quality, especially across different scales. Our findings support continued monitoring of impacts as the density and range of North American wild pig populations continue to increase.