Elevated Stream Pathogenic Indicator Bacteria Concentrations in Livestock Grazing Areas across a Single National Forest

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, F 1,210 = 105, p < 0.001; EC, F 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.

Rotational grazing can mitigate ecosystem service trade‐offs between livestock production and water quality in semi‐arid rangelands

“…An explanation for this result is that regardless of stocking rate or rotational treatment, E. coli levels were high on the days cattle were present. (Myers et al, 2017;O'Callaghan et al, 2019). By tracking water quality in relation to regulatory benchmarks across an entire grazing season, and including gradients of duration and timing in our study design, we show that fewer water quality violations occurred when grazing periods were short, and when grazing occurred early or late in the season.…”

Water and Sediment Microbial Quality of Mountain and Agricultural Streams

“…Restricting livestock manure entering into streams is considered to be effective in controlling bacteria loads to streams (Gotkowska‐Płachta et al, 2016; Myers et al, 2017; Pachepsky et al, 2016; Soupir et al, 2006). However, additional measures may be needed for reducing the levels of sediment‐attached bacteria in a stream.…”

The Environmental Impact of Cattle Access to Watercourses: A Review

“…There has been increased concern regarding the impacts of cattle activity near or in watercourses (Muenz et al, 2006; Vidon et al, 2008; Wilson and Everard, 2017), and the practice of allowing unrestricted cattle access to watercourses has been discouraged in some areas including North America and Europe (Bremner et al, 2016; Bragina et al, 2017; Myers et al, 2017). In an effort to reduce the potential environmental impact of cattle access to watercourses, a variety of optional and compulsory mitigation measures are typically available to landowners under agri‐environmental policies.…”

“…Several authors have reported increased fecal contamination in streams impacted by cattle grazing and activity. For instance, Myers et al (2017) assessed the levels of E. coli in watercourses draining areas used for dairy cattle grazing in California, USA, in periods of cattle presence and absence and reported 194 cases of violation of either regional or federal regulatory standards for E. coli in recreational waters, all documented when cattle were present in the grazing fields. The authors observed that E. coli concentrations in waters were generally orders of magnitude higher when cattle were grazing the fields compared with a period of cattle absence (Myers et al, 2017).…”

“…For instance, Myers et al (2017) assessed the levels of E. coli in watercourses draining areas used for dairy cattle grazing in California, USA, in periods of cattle presence and absence and reported 194 cases of violation of either regional or federal regulatory standards for E. coli in recreational waters, all documented when cattle were present in the grazing fields. The authors observed that E. coli concentrations in waters were generally orders of magnitude higher when cattle were grazing the fields compared with a period of cattle absence (Myers et al, 2017). In a study that compared E. coli levels in waters upstream and downstream of cattle drinking sites both before and after the implementation of access restriction measures, Bremner et al (2016) reported E. coli concentrations significantly higher downstream than upstream of an access site when cattle access was unrestricted, with levels often exceeding local irrigation and recreational guidelines (100 and 200 CFU 100 mL −1 , respectively).…”