Considerations and Implications for Measuring Total Phosphorus and Suspended Sediment in Edge of Field Water Monitoring.

There are several methods and variations of sample preparation reagents as well as analysis procedures for determining runoff total phosphorus. We compared the performance of three persulfate digestion methods (Acid Persulfate, USGS, and Alkaline Persulfate) for total phosphorus percent recovery across a wide range of suspended sediments (SS), and evaluated the ability of using Al and/or Fe in digestion solution to predict SS as a surrogate to the traditional gravimetric method. The Acid Persulfate method was most effective, with an average total phosphorus percent recovery of 96.6%. The second most effective method was the USGS with an average total phosphorus recovery of 76.1%. However, the Alkaline Persulfate method performed poorly with an average 24.5% total phosphorus recovery. As a result application of Alkaline Persulfate digestion to edge of field monitoring may drastically underestimated runoff total phosphorus. In addition to excellent recovery of total phosphorus, the Acid Persulfate method combined with analysis of Al and Fe by inductively coupled plasma atomic emission spectrometry provides a robust estimate of total SS. The implications of accurately measuring total phosphorus are presented and demonstrated using statewide simulations for potential edge of field phosphorus loading in Ohio.