Differential post-depositional mobility of phosphorus species in lake sediments

Abstract

Historically, paleolimnologists have been cautious about interpreting sedimentary total phosphorus (P) profiles because of the well-documented post-depositional mobility of P. There is recent new attention given to the interpretation of component P fractions that are generally indicative of broad categories of chemical P species in sediments. Using homogenized sediments collected from 5 lakes with differing characteristics, the mobilities of total P, and of NH4Cl-, BD-, NaOH-, and HCl-extractible P were measured in short term incubations (15–24 weeks). Almost all of the observed mobility of total P could be explained by the mobility of reductant-soluble BD–P, with a smaller contribution from NaOH–P. In contrast, HCl–P (apatite) and organic-P showed no significant movement. These results reaffirm that sedimentary TP profiles should be interpreted with caution, and that component P species, particularly NH4Cl-, BD-, and NaOH–P are also prone to post-depositional mobility. In contrast, HCl–P and organic-P appear to be more reliable proxies for paleolimnological reconstructions.