High flow event induced the subsurface transport of particulate phosphorus and its speciation in agricultural tile drainage system

Subsurface storm flow of phosphorus (P), including particulate P, has been recently discussed as an important P transport path in contrast to typical surface runoff events. However, P speciation, and P concentration during storm events has not been extensively investigated; therefore, its contribution to the water quality is not clearly understood. In this study, the physicochemical properties of particulate P in tile water samples during a high flow event were investigated in Midwestern agricultural lands using wet chemical methods, 31P Nuclear Magnetic Resonance spectroscopy and P K-edge X-ray absorptions near edge structure spectroscopy. In slightly alkaline pH tile water, total P was ranging from ∼0.06 to 0.22 mg L⁻¹, which is significantly greater than dissolved reactive P (DRP) (∼0.02–0.08 mg L⁻¹). The tile water contains P enriched particulate matters (∼200–660 mg L⁻¹). Total P in the colloidal fraction was from 1013 to 2270 mg kg⁻¹. Phosphate and organic P species, especially monoesters, are sorbed in soil colloids like calcite, and iron oxides, and colloids are effective carriers of P in the subsurface transport process during storm events. The results of this study show that storm events can accelerate the subsurface transport of P with soil particles in addition to DRP.