title: Influence of colloids on the attenuation and transport of phosphorus in alluvial gravel aquifer and vadose zone media.
abstract: Phosphorous (P) leaching (e.g., from effluents, fertilizers) and transport in highly permeable subsurface media can be an important pathway that contributes to eutrophication of receiving surface waters as groundwater recharges the base-flow of surface waters. Here we investigated attenuation and transport of orthophosphate-P in gravel aquifer and vadose zone media in the presence and absence of model colloids (Escherichia coli, kaolinite, goethite). Experiments were conducted using repacked aquifer media in a large column (2m long, 0.19m in diameter) and intact cores (0.4m long, 0.24m in diameter) of vadose zone media under typical field flow rates. In the absence of the model colloids, P was readily traveled through the aquifer media with little attenuation (up to 100% recovery) and retardation, and P adsorption was highly reversible. Conversely, addition of the model colloids generally resulted in reduced P concentration and mass recovery (down to 28% recovery), and increased retardation and adsorption irreversibility in both aquifer and vadose zone media. The degree of colloid-assisted P attenuation was most significant in the presence of fine material and Fe-containing colloids at low flow rate but was least significant in the presence of coarse gravels and E. coli at high flow rate. Based on the experimental results, setback distances of 49-53m were estimated to allow a reduction of P concentrations in groundwater to acceptable levels in the receiving water. These estimates were consistent with field observations in the same aquifer media. Colloid-assisted P attenuation can be utilized to develop mitigation strategies to better manage effluent applications in gravelly soils. To efficiently retain P within soil matrix and reduce P leaching to groundwater, it is recommended to select soils that are rich in iron oxides, to periodically disturb soil preferential flow paths by tillage, and to apply a low irrigation rate.
authors.affiliation: Institute of Environmental Science & Research Ltd., PO Box 29181, Christchurch 8540, New Zealand. Electronic address: Liping.pang@esr.cri.nz.
authors.forename: Liping
authors.initials: L
authors.lastname: Pang
authors.affiliation: Institute of Hydrochemistry, Technische Universität München, Marchioninistr. 17, D-81377 München, Germany.
authors.forename: Mark
authors.initials: M
authors.lastname: Lafogler
authors.affiliation: Institute of Hydrochemistry, Technische Universität München, Marchioninistr. 17, D-81377 München, Germany.
authors.forename: Bastian
authors.initials: B
authors.lastname: Knorr
authors.affiliation: Institute of Environmental Science & Research Ltd., PO Box 29181, Christchurch 8540, New Zealand.
authors.forename: Erin
authors.initials: E
authors.lastname: McGill
authors.affiliation: Institute of Environmental Science & Research Ltd., PO Box 29181, Christchurch 8540, New Zealand.
authors.forename: Darren
authors.initials: D
authors.lastname: Saunders
authors.affiliation: Institute of Hydrochemistry, Technische Universität München, Marchioninistr. 17, D-81377 München, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Baumann
authors.affiliation: Institute of Environmental Science & Research Ltd., PO Box 29181, Christchurch 8540, New Zealand.
authors.forename: Phillip
authors.initials: P
authors.lastname: Abraham
authors.affiliation: Institute of Environmental Science & Research Ltd., PO Box 29181, Christchurch 8540, New Zealand.
authors.forename: Murray
authors.initials: M
authors.lastname: Close
mesh_terms: D004784:Environmental Monitoring; D060587:Groundwater / Q000737:chemistry; D008956:Models, Chemical; D010758:Phosphorus / Q000032:analysis*; D012989:Soil Pollutants / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D010758:Phosphorus
keywords: Adsorption; Alluvial gravel; Colloids; Groundwater; Phosphorus; Transport