title: Retention and remobilization dynamics of fine particles and microorganisms in pastoral streams.
abstract: Both microbial metabolism and pathogen retention and remobilization are dependent on downstream transport of fine particles, which migrate in a series of deposition and resuspension events. All fine particles, including clay minerals, particulate organic carbon, nutrients and microbes, are often considered to be transported similarly in the environment because of a lack of specific observations comparing their relative transport. We conducted a tracer injection study to compare the transport and retention of the fecal indicator bacterium Escherichia coli, synthetic inert fluorescent fine particles, and a dissolved conservative tracer. We found that the fluorescent fine particles and bacteria were transported similarly, with both having greater retention than the solute tracer. We used a stochastic model to evaluate in-stream retention and migration of the solute, fluorescent particles, and E. coli. The best-fit model parameters indicate that different stream reaches had varied retention characteristics, but always showed greater retention of fluorescent particles and E. coli compared to the solute tracer. Direct measurements within known retention areas after the injection showed that the majority of the fluorescent particles and E. coli were retained near the sediment-water interface in macrophyte stands or filtered within the top 3 cm of the streambed sediment. Both the tracer particles and E. coli were retained within these regions for multiple months following the injection experiment. The stochastic model properly captured the wide range of storage timescales and processes we observed in the stream. Our results demonstrate the importance of the streambed sediment and in-stream macrophytes as short- and long-term reservoirs for fine organic particles and microbes in streams.
authors.affiliation: Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL 60208, USA; NIWA (National Institute of Water & Atmospheric Research Ltd.), Hamilton 3216, New Zealand. Electronic address: j-drummond@u.northwestern.edu.
authors.forename: J D
authors.initials: JD
authors.lastname: Drummond
authors.affiliation: NIWA (National Institute of Water & Atmospheric Research Ltd.), Hamilton 3216, New Zealand.
authors.forename: R J
authors.initials: RJ
authors.lastname: Davies-Colley
authors.affiliation: NIWA (National Institute of Water & Atmospheric Research Ltd.), Hamilton 3216, New Zealand.
authors.forename: R
authors.initials: R
authors.lastname: Stott
authors.affiliation: NIWA (National Institute of Water & Atmospheric Research Ltd.), Hamilton 3216, New Zealand.
authors.forename: J P
authors.initials: JP
authors.lastname: Sukias
authors.affiliation: NIWA (National Institute of Water & Atmospheric Research Ltd.), Hamilton 3216, New Zealand.
authors.forename: J W
authors.initials: JW
authors.lastname: Nagels
authors.affiliation: NIWA (National Institute of Water & Atmospheric Research Ltd.), Hamilton 3216, New Zealand; University of Waikato, Hamilton 3216, New Zealand.
authors.forename: A
authors.initials: A
authors.lastname: Sharp
authors.affiliation: Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL 60208, USA.
authors.forename: A I
authors.initials: AI
authors.lastname: Packman
mesh_terms: D004926:Escherichia coli / Q000302:isolation & purification*; D005243:Feces; D005434:Flow Cytometry; D005456:Fluorescent Dyes / Q000737:chemistry; D019015:Geologic Sediments / Q000382:microbiology; D010316:Particle Size; D045483:Rivers / Q000382:microbiology; D013269:Stochastic Processes; D014865:Waste Disposal, Fluid / Q000379:methods*; D014871:Water Microbiology; D014872:Water Movements; D014873:Water Pollutants
chemical_list: D005456:Fluorescent Dyes; D014873:Water Pollutants
keywords: Escherichia coli; Fine particle; Microorganisms; Particle retention; Particulate organic carbon; Remobilization