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Title: Evaluation of phosphorus site assessment tools: Lessons from the USA

item SHARPLEY, ANDREW - University Of Arkansas
item Kleinman, Peter
item Baffaut, Claire
item BEEGLE, DOUG - Pennsylvania State University
item Bolster, Carl
item COLLICK, AMY - University Of Maryland Eastern Shore (UMES)
item EASTON, ZACH - Virginia Polytechnic Institution & State University
item LORY, JOHN - University Of Missouri
item NELSON, NATHAN - Kansas State University
item OSMOND, DEANNA - North Carolina State University
item RADCLIFFE, DAVID - University Of Georgia
item Veith, Tameria - Tamie
item WELD, JENNIFER - Pennsylvania State University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2017
Publication Date: 4/21/2017
Citation: Sharpley, A.N., Kleinman, P.J., Baffaut, C., Beegle, D., Bolster, C.H., Collick, A., Easton, Z., Lory, J., Nelson, N., Osmond, D., Radcliffe, D., Veith, T.L., Weld, J. 2017. Evaluation of phosphorus site assessment tools: Lessons from the USA. Journal of Environmental Quality.46:1250-1256. doi:10.2134/jeq2016.11.0427.

Interpretive Summary: An interpretive summary is not required.

Technical Abstract: Freshwater eutrophication is generally limited or accelerated by phosphorus (P) inputs, with agriculture considered a contributor along with point sources. To help assess the impairments, NRCS incorporated the P Indexing risk assessment tool into the 590 Nutrient Management Conservation Practice Standard approximately 15 years ago, to limit P loss from critical areas of a watershed. States were charged with developing an Index to meet their technical and policy priorities. Because of continued P impairment of surface waters and a disparity among Indices, NRCS funded three regional Conservation Innovation Grants to assess and review P Indices across 22 states. Here we document the outcomes of these regional projects, identify shortcoming, and provide options to refine and improve Indices. Because of insufficient field data to assess the reliability of Indices to identify site risk as a function of land and P management, nonpoint source models (i.e., APEX, APLE, SWAT and TBET) were used to provide surrogate estimates of P loss. From this it was concluded that there are limitations to the predictive capability of field scale models, regarding the effect of nutrient management practices, in particular on P runoff. Hydrology was more accurately simulated. Further, the use of uncalibrated (off-the-shelf) models resulted in poor water quality predictions. While areas for improvement are identified, models remain a power tool to contribute to a better understanding of P loss form agricultural systems. Even so, P Indices were as robust as more data intensive water quality models. However, there was no scientific justification to propose a single P Index that would reliably estimate the risk of P loss across diverse nutrient and land management priorities, landscape properties, climates, and hydrologic processes at a national or regional scale at the present time.