Grantee Research Project Results
Phosphorus Leaching in Riparian Floodplains: Preferential Flow and Scale EffectsEPA Grant Number: FP917333
Title: Phosphorus Leaching in Riparian Floodplains: Preferential Flow and Scale Effects
Investigators: Heeren, Derek M
Institution: Northwestern Oklahoma State University
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 2011 through July 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Water Quality: Hydrogeology and Surface Water
Information is needed on the potential significance of connectivity between phosphorus in surface runoff and groundwater and phosphorus movement from the soil to groundwater in watersheds with cherty and gravelly soils. The potential for phosphorus leaching commonly is estimated based on point-measurements of soil test phosphorus (STP) or measurements of the sorption capability of disturbed soil samples representing the soil matrix. However, in these areas, gravel outcrops and macropores (visibly observed in previous research activities) occur on the floodplains and lead to extremely high infiltration rates. This research project will investigate how macropores and gravel outcrops in alluvial floodplains create a scale-dependent impact on contaminant leaching through soils through innovative field studies by: (1) quantifying the spatially variable phosphorus transport capacity of heterogeneous, gravel soils, and (2) evaluating the influence of experimental scale on observed phosphorus leaching.
The subsurface heterogeneity in the alluvial deposits at three riparian floodplain sites in Oklahoma and Arkansas first will be investigated using electrical resistivity imaging techniques by producing a three-dimensional map of the alluvial floodplain subsurface at each proposed field site. This three-dimensional image will allow the determination of areas of localized gravel outcrops that may lead to increased leaching potential. Phosphorus leaching will be measured at the point scale in the laboratory using flow cell experiments of disturbed soil samples and at plot scales (approximately 1, 10 and 100 square meters) with replicated infiltration experiments at the three riparian floodplain sites. The injection tests in the field will be imaged using innovative electrical resistivity techniques. Through numerical modeling, the research will be extended beyond the three specific floodplain sites by estimating the phosphorus concentration and load entering gravel subsoils for various topsoil depths, storm sizes and initial phosphorus concentrations for the Ozark Ecoregion.
It is expected that measured leaching will generally increase as the scale increases from point to plot scales. Leaching potential should not be quantified based on disturbed, small-scale samples of floodplain sediment. This research has wide-reaching implications for how riparian floodplains throughout the world are managed. Future management recommendations for gravelly riparian floodplains may be altered as a result of these research findings.
Potential to Further Environmental / Human Health Protection
Billions of dollars are spent annually through governmental programs in North America and Europe to mitigate surface runoff, sediment, pesticide and nutrient loads through conservation and restoration of riparian buffers. Although these management plans can be effective, this research hypothesizes that leaching and subsurface phosphorus transport also could be a contributing factor in certain conditions with this transport occurring along focused as opposed to diffuse pathways. Broad-reaching implications extend beyond phosphorus; this research will affect the use of riparian buffers for mitigating other contaminants such as nitrogen, pathogens and pesticides to stream systems.