Behavior of different phosphorus species in suspended particulate matter in the Changjiang estuary

Abstract: Suspended particulate matter (SPM) collected in the Changjiang (Yangtze River) estuary in June 2006 was separated into five fractions via water elutriation: clay-very fine silt (<8 µm), fine silt (8–16 µm), medium silt (16–32 µm), coarse silt (32-63 µm) and sand (>63 µm). The SPM and fractionated particles were sequentially analyzed by a modified SEDEX sequential extraction method to obtain six species of phosphorus: exchangeable or loosely-sorbed P, organic P, Fe-bound P, authigenic P, detrital P and refractory P. The results indicated that all particulate phosphorus species except for detrital P were negatively correlated to particle size; a high detrital P content was found in coarse silt and very coarse silt. From the inside of the river mouth to the gate of the river mouth, organic P, Fe-bound P and refractory P in the suspended particles decreased and a higher amount of exchangeable P appeared around the gate of the river mouth. From the gate of the river mouth to the sea, exchangeable P and organic P in suspended particles increased distinctly. The total particulate P flux into the estuary from the Changjiang River was about 45.45×10⁸ µmol/s during sampling. Of this, about 8.27×10⁸ µmol/s was associated with the “truly suspended” fraction. The bio-available particulate P flux was about 13.58×10⁸ µmol/s. Of this, about 4.24×10⁸ µmol/s was transported by “truly suspended” particles.