Geochemical characteristics of phosphorus in surface sediments of two major Chinese mariculture areas: The Laizhou Bay and the coastal waters of the Zhangzi Island

•Phosphorus in surface sediments of ZI was more mobile than that of LB.•Phosphorus in sediments of LB was mainly from physical weathering and/or erosion.•Grain size and TOC co-affected the behaviors of phosphorus in sediments of LB and ZI.•LB and ZI stand for Laizhou Bay and the coastal marine area around Zhangzi Island. Phosphorus (P) in surface sediments of the Laizhou Bay (LB) and the coastal waters around the Zhangzi Island (ZI) was analyzed. Six forms of P were separated — exchangeable or loosely sorbed P (Ads–P), aluminum-bound P (Al–P), iron-bound P (Fe–P), authigenic apatite plus CaCO3-bound P plus biogenic apatite (Ca–P), detrital apatite plus other inorganic P (De–P) and organic P (OP). The average contents of P in the LB were in the order: De–P>OP>Ca–P>Fe–P>Ads–P>Al–P; in the ZI, the corresponding order was De–P>OP>Fe–P>Ca–P>Ads–P>Al–P. Due to the high nutrient loadings from the surrounding rivers, TP contents in sediments of the LB were higher than in those of the ZI. The potential bio-available P (Ads–P and OP) accounted for 14.7% and 24.2% of TP in sediments of the LB and the ZI, respectively.