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Subsurface transport of orthophosphate in five agricultural watersheds, USA

January 1, 2011

Concentrations of dissolved orthophosphate (ortho P) in the unsaturated zone, groundwater, tile drains, and groundwater/stream water interfaces were assessed in five agricultural watersheds to determine the potential for subsurface transport. Concentrations of iron oxides were measured in the aquifer material and adsorption of ortho P on oxide surfaces was assessed by geochemical modeling. Attenuation of ortho P in these aquifers was attributed primarily to sorption onto iron oxides, and in one location onto clay minerals. Only one location showed a clear indication of phosphorus transport to a stream from groundwater discharge, although groundwater did contribute to the stream load elsewhere. Subsurface ortho P movement at a site in California resulted in a plume down gradient from orchards, which was attenuated by a 200 m thick riparian zone with natural vegetation. Iron oxides had an effect on phosphorus movement and concentrations at all locations, and groundwater chemistry, especially pH, exerted a major control on the amount of phosphorus adsorbed. Groundwater pH at a site in Maryland was below 5 and that resulted in complete sequestration of phosphorus and no movement toward the stream. Geochemical modeling indicated that as the surfaces approached saturation, groundwater concentrations of ortho P rise rapidly.

Publication Year 2011
Title Subsurface transport of orthophosphate in five agricultural watersheds, USA
DOI 10.1016/j.jhydrol.2011.08.014
Authors Joseph L. Domagalski, Henry M. Johnson
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Hydrology
Index ID 70007517
Record Source USGS Publications Warehouse
USGS Organization California Water Science Center; Oregon Water Science Center