Prediction of Bioavailable Phosphorus Loss in Agricultural Runoff
1993
Sharpley, Andrew N. | Smith, S.J.
The loss of bioavailable P (BAP) in both soluble (SP) and participate (BPP, bioavailable particulate P) forms in agricultural runoff, can accelerate the eutrophication of surface waters. Bioavailable P represents P that is potentially available for algal uptake. Although prediction of BAP loss would provide a more reliable assessment of the impact of agricultural management on surface water eutrophication than just SP or total P (TP), currently no predictive equations are available. Bioavailable P transport in soluble and particulate forms in runoff from 20 agricultural watersheds in the Southern Plains over a 5-yr period, was predicted using kinetic and enrichment ratio approaches, respectively. Measured and predicted SP and BPP concentrations of individual runoff events were similar for all watersheds and management practices over a range of 7 to 3522 and 3 to 4059 µg L⁻¹, respectively. Calculated as the sum of SP and BPP, BAP loss in runoff was predicted accurately, with only a 12% error in measured mean annual loss (662 g ha⁻¹ yr⁻¹). Although BAP loss below 100 g ha⁻¹ yr⁻¹ was underestimated, above this value measured and predicted values closely followed a 1:1 relationship. Inclusion of these equations in comprehensive water quality models will improve the prediction of agricultural management on the biological response of receiving water bodies.
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