Nanoparticle-Bound P in Runoff From Poultry-Amended Pastures.

Particulate-bound P, traditionally defined as suspended material that will not pass through a 450 nm filter, constitutes a large portion of the potential P pollution. This fraction can be effectively immobilized through the use of vegetative buffer strips and other natural mechanical filtration techniques. P that passes the 450nm filters and reacts with typical molybdate colorimetric reagents (dissolved reactive phosphorous, DRP) is considered “dissolved”. Yet, many of the important colloidal and nanoparticulate carriers of P (e.g., hydrous ferric oxides and micro-crystalline aluminum oxides) are <100nm and likely to pass through the 450 nm filters commonly employed. We analyzed the nanoparticle-composition of runoff generated from rainfall-simulated pasture plots with different amendment levels of poultry manure. Using both cascade centrifugation and asymmetric-flow field-flow-fractionation coupled to ICP-MS detection (AFFF-ICP-MS), we identified Fe-rich alluminosilicate particles in the 50 – 200 nm range that contained significant levels of P. For this presentation, we will characterize the mobile P-rich particles suspended in the runoff before and after passage through pasture vegetation. This work will allow us to assess the relative importance of nanoparticle-bound P to the total P load in runoff. It will also allow us to evaluate the effectiveness of vegetation in retaining nano-particles.