Nanoparticle-Facilitated Transport of Phosphorus in Runoff of Poultry-Litter Amended Grassland.

Managing P loss from poultry litter amended pastures has regional importance to the health of sensitive ecosystems. Standard sampling methodology includes separating particulate-bound P from “dissolved” P using a 0.45 μm filter. However, many of the particles that strongly sorb P are less than 0.45 μm, and if present, would be incorrectly lumped with “dissolved” P. Since these particles exhibit very different reactive-transport behavior than truly dissolved aquo-ions, incorrect classification could lead to large errors in predictive models. We assessed the contribution of nanoparticle-bound P (nPP, <0.45 μm) to runoff P for a four month period following a litter application (Nov. 2009) in six 0.8-ha fescue watersheds that had typically received bi-annual poultry litter applications since 1995. Samples were size fractionated by differential centrifugation, ultrafiltration, and field flow fractionation (FFF) and analyzed for Molybdate-reactive P (MRP), total P, Fe, Al, Mn, Si, Ti and As. Selected samples were visualized via transmission electron microscopy (TEM). We found an average of 10% (maximum of 21 ± 2.5%) of <0.45 μm runoff P present as nPP. These nano-particles had a mean diameter of 250 nm and were composed of aggregates of ~50 nm aluminosilicate flakes with clusters of <10 nm Fe and Ti-oxide phases and possibly some organic matter. The P was overwhelmingly associated with nanometer sized Fe and Ti-oxide phases. In most cases this nPP was effectively measured by the molybdate reaction and thus it is likely previous studies characterizing “dissolved” P as MRP passing through a 0.45 mm filter, have included nPP. Experiments are underway to determine the source of this nPP in the runoff. The effects of anoxia, pH changes, and carbon additions on the soil and litter are being evaluated in laboratory incubations.

 

Abbreviations:  FFF, field flow fractionation; MRP, molybdate reactive phosphorus; nPP, nanoparticle-bound phosphorus; TEM, transmission electron microscopy.