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

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 A mu m), fine silt (8-16 A mu m), medium silt (16-32 A mu m), coarse silt (32-63 A mu m) and sand (> 63 A mu m). 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 45.45x10(8) A mu mol/s during sampling. Of this, about 8.27x10(8) A mu mol/s was associated with the truly suspended fraction. The bio-available particulate P flux was about 13.58x10(8) A mu mol/s. Of this, about 4.24x10(8) A mu mol/s was transported by truly suspended particles.