Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
4577479 | Journal of Hydrology | 2011 | 15 Pages |
SummaryConcentrations 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.
► Phosphorus transport in groundwater was assessed at five agricultural watersheds. ► Phosphorus subsurface movement was controlled by sorption onto iron oxides or clays. ► Water chemistry and soil types affected phosphorus transport to the aquifers. ► Low pH conditions within an aquifer in Maryland prevented phosphorus transport. ► Geochemical modeling was used to assess adsorption.