Norgaard, Trine7; Moldrup, Per1; Ferré, Ty P A5; Olsen, Preben7; Rosenbom, Annette E.8; de Jonge, Lis W.7
1 The Faculty of Engineering and Science, Aalborg University, VBN2 Department of Civil Engineering, The Faculty of Engineering and Science, Aalborg University, VBN3 Division of Water and Environment, The Faculty of Engineering and Science, Aalborg University, VBN4 Aarhus University5 Univ Arizona, Dep Hydrol & Water Resources, Tucson, AZ USA6 Geological Survey of Denmark and Greenland7 Aarhus University8 Geological Survey of Denmark and Greenland
The globally-used herbicide glyphosate (N-(phosphonomethyl)glycine) and its most frequently detected metabolite, aminomethylphosphonic acid (AMPA), were studied in a unique 12-year field-scale monitoring program. The leaching of glyphosate, AMPA, and soil particles were studied in a shallow drainage system beneath a 1.26 ha field. Five annual glyphosate applications were applied with different autumn application dates. Solute mass flux from the drain system following the five glyphosate applications were compared to determine how different factors affect the leaching of glyphosate, AMPA, and particles. Glyphosate and AMPA leaching were highly event driven, controlled by the time and intensity of the first precipitation event after glyphosate application. A high similarity in time-accumulated curves for drainage and leached pesticide masses suggests near-constant drainage and leaching rates for approximately 150 days. There was no clear relationship between particle-facilitated transport and the transport of glyphosate or AMPA. However, soil particles, glyphosate, and AMPA, all showed distinct, simultaneous concentration curves, indicating common dominant transport mechanisms. Also, soil- water content at the time of application and the level of the groundwater table relative to the drain depth was essential for whether solutes were detected in the drainage runoff. We present a leaching risk chart to illustrate the dependence of glyphosate, AMPA, and soil particle leaching based on precipitation intensity and the timing of rain events after glyphosate application.