TITLE:
Elevated Stream Pathogenic Indicator Bacteria Concentrations in Livestock Grazing Areas across a Single National Forest
AUTHORS:
Lindsey Myers, Megan Fiske, Megan Layhee
KEYWORDS:
Cattle, Escherichia coli, Fecal Coliform, Sierra Nevada, Water Quality
JOURNAL NAME:
Natural Resources,
Vol.8 No.10,
October
31,
2017
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.