Southern P Indices, Water Quality Data, and Modeling Results: a Comparison

Osmond, D., Bolster, C., Cabrera, M., Feagley, S., Forsberg, A., Mitchell, C., Mylavarapu, R., Oldham, L., Ramirez-Avila, J. J., Sharpley, A., Storm, D., Walker, F., & Zhang, H. (2016). Southern P Indices, Water Quality Data, and Modeling Results: a Comparison. Soil and Water Conservation Society Annual Conference Proceedings. Louisville, KY: Soil and Water Conservation Society.

Phosphorus (P) indices in the south frequently produce different results for similar conditions. After collecting data from benchmark sites throughout the south (6 Arkansas, 1 Georgia, 2 Mississippi, 4 North Carolina, 4 Oklahoma, and 4 Texas site/treatment water quality and land treatment data sets), we compared predictions of each state P-Index assessment tool to water quality data derived from the benchmark sites using RUSLE 2 erosion data as well as actual sediment losses. We also compared predictions of southern (Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, and Texas) P-index assessment tools against calibrated fate and transport water quality models (APEX, TBET, and APLE). We then compared P indices to each other for each data set. Comparisons of the different information sources show dissimilarities between P indices but also water quality data and modeling results. Finally, it is unclear how to assign losses and potential risk since water resources have different sensitivities to phosphorus and typically this is not standardized in P-index loss ratings, including the national nutrient management standard (590 USDA-Natural Resource Conservation Service)