|Shober, Amy - University Of Delaware|
|Turner, Kathryn - University Of Delaware|
|Fiorellino, Nicole - Collaborator|
|Andres, Alan - Collaborator|
|Mcgrath, Joshua - University Of Maryland|
|Sims, James - University Of Delaware|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2017
Publication Date: N/A
Interpretive Summary: Evaluating the predictions of phosphorus site assessment tools is challenging when information on runoff phosphorus losses is unavailable. In this study, we selected Phosphorus Indices from Delaware, Maryland, Virginia, and North Carolina and evaluated their projections of subsurface phosphorus movement against a comprehensive soil phosphorus dataset from artificially drained sites on the Delmarva Peninsula. With the exception of North Carolina’s Phosphorus Index, assessment tools from Delaware, Maryland, and Virginia generally agreed about a site’s potential for subsurface phosphorus loss, owing to similarities in their phosphorus source and transport formulations. Findings from this study highlight the value of soil phosphorus data to assess Phosphorus Indices in areas lacking data on phosphorus loads in subsurface runoff.
Technical Abstract: Phosphorus (P) Indices are important tools for nutrient management planning in the U.S. whose evaluation often has been deemphasized in favor of research and development. Assessing P Indices in artificially drained agroecosystems is especially important, as subsurface flow is the predominant mode of P transport, but its representation in most P Indices is often inadequate. In this study, we leveraged detailed characterizations of 124 soil cores (sites) collected from 12 agricultural fields across the Delmarva Peninsula to assess subsurface P loss routines of five P Indices from Delaware, Maryland (2), Virginia, and North Carolina. The subsurface P risk scores of each P Index were initially compared using Pearson correlation and then regressed against soil water extractable P near the depth of the seasonal high water table (WEPWT), which was used a proxy for subsurface P loss risk in the absence of observational data on subsurface P fluxes. Subsurface P loss risk scores from the four semi-quantitative Delmarva P Indices generally agreed in direction but not in magnitude, and adequately predicted soil WEPWT concentrations (r2 = 0.51 to 0.72). In contrast, subsurface P risk scores from the North Carolina P Loss Assessment Tool (NC-PLAT) were poorly correlated with scores from other P Indices and did not predict soil WEPWT concentrations (r2 = 0.00). Our results support the use of WEPWT as a valuable metric for providing interim insight into the directionality of subsurface P loss risk scores. Findings also highlight the need for standardized monitoring of subsurface P fluxes to further improve P Index refinement and harmonization in artificially drained landscapes.