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    Particulate matter is important for reserving phosphorus (P) and the removal of phosphorus in marine environments. In this study, particulate P contents, including loosely adsorbed P (Lab-P), ferric bound P (Fe-P), authigenic carbonate fluorapatite and biogenic apatite and CaCO3-associated P (CFA-P), detrital apatite P (Detr-P) and refractory organic P (Org-P), were determined using the SEDEX method in Daya Bay located in the northern South China Sea. The total particulate P (TPP) varied from 2.00 mg g-1 to 9.44 mg g-1 with an average of 4.26 mg g-1. Particulate inorganic P (PIP) and organic P (POP) accounted for 57.7% and 42.3% of the TPP respectively. Lab-P and Org-P constituted the majority of TPP with comparable percentages of 36.3% and 32.6%, followed by CFA-P (21.8%), Fe-P (7.7%) and Detr-P (1.6%). Biological available P (BAP) contents varied from 1.50 mg g-1 to 7.35 mg g-1 with an average of 3.12 mg g-1, which accounted for 73.2% of the TPP. Based on a physical-radioactive model of 234Th, the sinking flux of BAP ranged between 0.04 mmol m-2 d-1 and 1.11 mmol m-2 d-1, averaging 0.45 mmol m-2 d-1. The sinking flux of TPP averaged 0.55 mmol m-2 d-1 (0.06-1.23 mmol m-2 d-1). Combing the sinking of particulate nitrogen (PN), the ratio of sinking flux (PN/TPP) varied from 4.2 to 21.7 (avg. 10.5), indicating that particulate sinking probably result in an increase of N/P ratio in Daya Bay. At some stations, sediment input a large amount of particulate P to the water column via resuspension, corresponding to the TPP fluxes of 0.20 mmol m-2 d-1 to 0.70 mmol m-2 d-1. These results revealed that particulate P plays a crucial role in controlling the cycling and removal of P in coastal waters.

This work was supported by the National Key Basic Research Special Foundation Program of China (2015CB452902 & 2015CB452903).