a b s t r a c tPhosphorus (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 CaCO 3 -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.Ó 2014 Elsevier Ltd. All rights reserved.As an important biogenic element in the ocean, phosphorus (P) directly affects the primary productivity of the ocean and has a significant impact on the marine carbon cycle (Lui and Chen, 2011;Yu et al., 2012); P is also directly related to the global climate and environmental changes (Krom et al., 2004). Hecky and Kilham (1988) pointed out that P might be the element which controlled the global marine biological productivity during a long geologic time scale (>1000 years). As an important reservoir of P in marine environment, sediment not only has a buffering effect on the P content in the overlying water, but also is an important source of P in seawater (Giblin et al., 1997;Zabel et al., 1998). Fisher et al. (1982) reported that sediments provided 28-35% of P needed in the primary productivity of coastal marine ecosystems.Both organic and inorganic forms of P are present in marine sediments. Inorganic forms of P may be adsorbed onto the surfaces of minerals, or be bound to aluminum, iron, or calcium (Föllmi, 1996;Benitez-Nelson, 2000;Łukawska-Matuszewska and Bolałek, 2008;Song, 2010). The binding forms of P in sediments have major influences on transportation, degradation, and the ultimate fate of P in marine ecosystems. Only certain forms of P can be transformed into bio-available ones after being affected by physical, chemical and biological factors, including desorption, dissolution and reduction processes (Song, 2010). After that, the bio-available forms of P are released into the overlying water. These certain forms of P become important factors affecting the trophic status of water or causing eutrophication (Eijsink et al., 2000). Therefore, research on the geochemical forms of P in sediments may help researchers understand the dynamic cycle of P in seawater and sediments, such as migration and transformation between sediments and the overlying water, and subsequent diagenesis and other geochemical processes (Zabel et al., 1998;Eijsink et al., 2000).The Laizhou Bay and the surrounding marine area of the Zhangzi Island (hereafter referred to as the Zhangzi Island for short) are important mariculture zones in China, and they are located in the B...