Phosphorus chemical speciation in surface sediments from Cananéia - a non-impacted estuary

ABSTRACT Phosphorus (P) is found in estuarine sediments, which belong to the biogeochemical cycle of this element in aquatic environments. This study examines the distribution of P in different chemical speciations in surface sediments at 14 stations in the southern region of the Cananéia-Iguape Estuarine-Lagoon Complex. P chemical fractions were determined using a sequential extraction method of fractional extraction that measures five P forms: (i) exchangeable P (Pexch), loosely adsorbed or exchangeable; (ii) P-Fe (P-Fe), P-bound Fe oxyhydroxides; (iii) authigenic P (P-CFAP), including carbonate fluorapatite, biogenic apatite (fish debris), and P-bound calcium carbonate; (iv) detrital P (P-FAP), igneous or metamorphic apatites; (v) organic P (Porg); and (vi) total P (Ptotal). The P fractions associated with the sedimentary properties of grain size and organic content can be used as a proxy for understanding environmental conditions. The average percentage of each P fraction of the surface sediments in this region follows the sequence: P-Fe (38%) > Porg (32%) > Pexch (14%) > P-FAP (9%) > P-CFAP (7%). In all stations, P-Fe and Porg were the main fractions of P in the sediments. CaCO3 accounted for less than 30% of it, essentially indicating lithoclastic characteristics, whereas organic carbon (Corg) showed values below 2%. Finally, Ptotal showed concentrations that are consistent with an unpolluted environment, with values below 16 µmol g-1.