E. coli and enterococci attachment to particles and loading rates in pastureland runoff

Abstract

Limited data on microbial partitioning between the freely suspended and particulate attached phases during transport along overland flow pathways results in high uncertainty in bacterial fate and transport models. The objectives of this work were to partition E. coli and enterococci between the unattached and attached phases at the edge-of-the-field and to identify the particle sizes to which the attached bacteria preferentially associated. The average E. coli PC for all samples collected was 0.06 which corresponded to 4.8% attached and the average PC for enterococcus was 0.18 which corresponded to 13% attached. E. coli and enterococci PC, PAF, and TC did not change significantly between the rising, peak, and recession limbs of the runoff hydrograph. Additionally, no significant correlations were identified between bacteria fractions or total concentrations and TSS. Fifty eight percent of attached E. coli and enterococci cells were associated with particulates retained by an 8 m screen, however, the overall low attachment ratios indicate that designing management practices to trap particulates will not sufficiently reduce transport of pathogen indicators to surface waters. Results of this study indicate that best management practices to reduce bacterial loadings from pasturelands with high vegetative cover should focus on retention of pathogen indicators moving through overland flow pathways in the unattached state.