title: Differential behaviour of Escherichia coli and Campylobacter spp. in a stream draining dairy pasture.
abstract: The faecal indicator bacterium Escherichia coli and thermotolerant Campylobacter spp., which are potentially pathogenic, were investigated in the Toenepi Stream draining a pastoral catchment dominated by dairying. Bacteria concentrations were monitored routinely at fortnightly intervals over 12 months and intensively during storm events to compare the transport dynamics of bacterial indicator and pathogen under varying hydro-meteorological conditions. Routine monitoring indicated median concentrations of 345 E. coli MPN 100 ml(-1) and relatively low concentrations of 2.3 Campylobacter MPN 100 ml(-1). The bacterial flux was three orders of magnitude greater under elevated stream flow compared with base-flow. E. coli peak concentrations occurred very close to the turbidity peak and consistently ahead of the Campylobacter spp. peak (which was close to the hydrograph peak). We postulate that, under flood conditions, the E. coli peak reflects the entrainment and mobilisation of in-stream stores on the flood wave front. In contrast, Campylobacter spp. are derived from wash-in from land stores upstream and have travelled at the mean water velocity which is slower than the speed of the flood wave. Our findings of different dynamics for E. coli and Campylobacter spp. suggest that mitigation to reduce faecal microbial impacts from farms will need to take account of these differences.
authors.affiliation: National Institute of Water & Atmospheric Research, PO Box 11-115 Hamilton, New Zealand. r.stott@niwa.co.nz
authors.forename: Rebecca
authors.initials: R
authors.lastname: Stott
authors.forename: Robert
authors.initials: R
authors.lastname: Davies-Colley
authors.forename: John
authors.initials: J
authors.lastname: Nagels
authors.forename: Andrea
authors.initials: A
authors.lastname: Donnison
authors.forename: Colleen
authors.initials: C
authors.lastname: Ross
authors.forename: Richard
authors.initials: R
authors.lastname: Muirhead
mesh_terms: D002167:Campylobacter / Q000302:isolation & purification*; D003612:Dairying; D004784:Environmental Monitoring; D004926:Escherichia coli / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology; D055868:Floods; D009520:New Zealand; D045483:Rivers; D014871:Water Microbiology; D014876:Water Pollution / Q000032:analysis* / Q000517:prevention & control