This is a sequential extraction that separates sediment phosphorus by mobility instead of reporting it as a single number. Ten parameters come back: total phosphorus, plus the loosely bound, iron-bound, aluminum-bound, calcium-bound, biogenic, and organic fractions, plus total organic carbon, total solids, and percent water. It runs the Rydin and Welch scheme, with a reporting limit of 2 mg/kg on the phosphorus fractions.

The distinction it draws is the one that decides whether an in-lake treatment is worth doing. Total sediment phosphorus tells you the size of the inventory. Fractionation tells you how much of that inventory can actually return to the water column, which is a different and usually much smaller number.

Note on methodology: Rydin and Welch is a peer-reviewed limnological extraction scheme, not an EPA-approved method. It is the standard approach for this question in lake management practice, and results are intended for management planning rather than regulatory determination.