Abstract
Livestock presence in proximity to forest streams has been shown to contribute pathogenic bacteria in excess of water quality standards established to protect human health. However, the degree to which livestock fecal contamination in streams on national forest lands is either a limited or a potentially widespread occurrence is still debated. This study provides additional insight into the matter. We analyzed water in small streams near known cattle grazing areas within the Stanislaus National Forest in the Sierra Nevada, California from 2012 to 2016. Fourteen stream sites were sampled before and after cattle were released onto the forest (four of these sites were sampled across multiple years) to compare indicator bacteria concentrations (fecal coliform—FC, Escherichia coli—EC) to standards established for recreational contact for surface waters. One control site was also sampled. There were 194 water quality violations of either state or federal regulatory standards for recreational contact, all of which occurred once cattle were on the forest. Mean (max) FC and EC concentrations were on orders of magnitude higher after cattle were released onto the forest [FC 1307 (30,000) and EC 1033 (17,000) MPN/100 mL] than during the time period before cattle were on the forest [FC 19 (220) and EC 17 (220) MPN/100 mL; FC, F1,210 = 105, p 1,210 = 85.5, p 0.001]. In addition, the presence of cattle, visual evidence of recent cattle-related disturbances, and sampling week were important predictor variables of FC and EC. These findings support the link between cattle presence and increased levels of stream pathogenic bacteria, and also demonstrate that stream pathogenic bacteria pollution occurs widely across the forest. This research indicates the need to consider alternative range management practices to better protect water quality and human health.
Highlights
National forests in the United States are managed for diverse and often competing purposes such as providing habitat for wildlife and water supplies for downstream urban users, while managing for wood production, livestock grazing, and recreation
Fourteen stream sites were sampled before and after cattle were released onto the forest to compare indicator bacteria concentrations to standards established for recreational contact for surface waters
The results of this study demonstrate that fecal coliform and E. coli were detected at orders of magnitude higher once cattle arrived on the forest than during the period before cattle were on the forest
Summary
National forests in the United States are managed for diverse and often competing purposes such as providing habitat for wildlife and water supplies for downstream urban users, while managing for wood production, livestock grazing, and recreation. Research has demonstrated that livestock activities near aquatic habitat have the potential to diminish water quality, lead to soil compaction, cause stream channel erosion, and alter vegetative structure, as summarized in several reviews including [3] [4] [5]. Such impacts can affect recreational use and create potential for the risk of human illness through bodily contact with contaminated water or ingestion of polluted water. Recreational use on national forest lands is projected to rise [6], increasing the need for land managers and the public to understand the extent of water quality pollution on forest lands, and the relationship between livestock grazing on national forest lands and pathogenic bacteria pollution
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