Mobilization of Escherichia coli and fecal source markers from decomposing cowpats

• Published in: The Science of the total environment 2022-12, Vol.853, p.158509-158509, Article 158509
• Main Authors: Devane, Megan, Dupont, Pierre-Yves, Robson, Beth, Lin, Susan, Scholes, Paula, Wood, David, Weaver, Louise, Webster-Brown, Jenny, Gilpin, Brent
• Format: Article
• Language: English
• Subjects: Aged fecal sources; Bovine; Fecal contamination; Fecal sterols; Microbial source tracking
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.158509

In rural environments, the sources of fecal contamination in freshwater environments are often diffuse and a mix of fresh and aged fecal sources. It is important for water monitoring purposes, therefore, to understand the impacts of weathering on detection of the fecal source markers available for mobilization from livestock sources. This study targets the impacts of rainfall events on the mobilization of fecal source tracking (FST) markers from simulated cowpats decomposing in situ for five-and-a-half-months. The FST markers analysed were Escherichia coli, microbial source tracking (MST) markers, fecal steroids and a fecal ageing ratio based on the ratio between counts of river microflora and total coliforms. There was a substantial concentration of E. coli (104/100 mL) released from the ageing cowpats suggesting a long-term reservoir of E. coli in the cowpat. Mobilization of fecal markers from rainfall-impacted cowpats, however, was markedly reduced compared with fecal markers in the cowpat. Overall, the Bacteroidales bovine-associated MST markers were less persistent than E. coli in the cowpat and rainfall runoff. The ten fecal steroids, including the major herbivore steroid, 24-ethylcoprostanol, are shown to be stable markers of bovine pollution due to statistically similar degradation rates among all steroids. The mobilizable fraction for each FST marker in the rainfall runoff allowed generation of mobilization decline curves and the derived decline rate constants can be incorporated into source attribution models for agricultural contaminants. Findings from this study of aged bovine pollution sources will enable water managers to improve attribution of elevated E. coli to the appropriate fecal source in rural environments. [Display omitted] •Decomposing cowpats on pasture are a long-term source of fecal marker contamination.•A substantial E. coli reservoir is maintained in aged cowpats for five months.•Bovine MST markers are less persistent than E. coli counts in ageing cowpat runoff.•Rainfall mobilizes less bovine fecal markers than runoff from aged cowpats.•Rainfall mobilization decline rates could be used in models of contaminant runoff.