『Abstract
Knowledge of the transport and deposition behavior for pathogenic
Escherichia coli is needed to assess contamination and
protect water resources. We evaluated the effects of repacked
(R) and physically and biologically weathered (PBW) columns of
sandy loam and clay loam soils on the transport and retention
of E. coli and bromide under saturated and unsaturated
flow conditions. PBW soil columns were weathered outdoors by exposure
to wetting, drying, freezing and thawing cycles during the winter
of 2008 and spring and summer of 2009. These physically weathered
soil columns were subjected to additional 6 months of biological
weathering by 20 earthworms placed onto each soil columns. Nalidixic
acid-resistant E. coli (E. coli NAR) and bromide
(Br) were employed as pulse tracers and their temporal and spatial
variabilities were monitored in the leachate samples. The flow
regimes (inlet suction 0 for saturated and 5 hPa for unsaturated)
were controlled using a tension infiltrometer. Cumulative percentage
and maximum concentrations (Cmax) of Br and
E. coli NAR and filtration coefficients (λf)
of E. coli NAR were assessed. In the repacked soil columns,
average bacterial concentration and Cmax
in leachate were lower, likely due to enhanced pollutant/soil
particle interactions at low water fluxes. The largest λf occurred in the repacked clay loam soil. Accelerated
water velocities through preferential flow pathways were likely
responsible for the smaller filtration coefficients in the PBW
columns. Unsaturated flow conditions resulted in larger λf values for E. coli NAR and smaller Cmax values for both tracers.
Keywords: Repacked soil; Weathered soil; Filtration coefficient;
Preferential flow; Tension infiltrometer』
1. Introduction
2. Materials and methods
2.1. Soil preparation and treatments
2.2. Tracers and leaching setup
2.3. Filtration and transport parameters
2.4. Statistical analysis
3. Results and discussion
3.1. Cumulative percentage of recovered E. coli NAR
and Br
3.2. Maximum concentration (Cmax) of E.
coli NAR and Br
3.3. Filtration coefficient
4. Conclusions
Acknowledgments
References