Spectrophotometric determination of phosphate in matrices from sequential leaching of sediments

The speciation of Phosphorus (P) in geologic materials can inform diverse investigations in such as aquatic biogeochemistry, soil sciences, and paleo-oceanography. Here, we describe in detail a set of sequential extraction schemes to measure P concentrations from several operationally defined phases: pore water, exchangeable or loosely sorbed P, Fe-bound P, P associated with biogenic apatite, P associated with authigenic apatite and carbonate forms, P associated with detrital apatite and inorganic forms, and organic P. The two benefits of the procedures we describe compared to prior methodological studies are: (1) fast, simple and inexpensive colorimetric methods have been developed for P determination in all the different matrices; and (2) the Fe-bound phosphorus pool is separated into two fractions, allowing the P associated with most reactive Fe-fraction to be distinguished from P bound to the remainder of the Fe-oxides. Adaptations of these procedures to optimize the characterization of P pools in a range of material types are also outlined.