Forms and bioavailability of phosphorus in sediment cores of culture zones in Sanggou Bay

Phosphorus is the most important limiting factor in nutrient cycling, and it is also the key element controlling primary production in aquatic environment. Sediments act as both a sink and a source of phosphorus due to continuous transport of chemical species across the sediment-water interface. Phosphorus is actively involved in both terrestrial and marine biogeochemical cycles. However, not all fractions of phosphorus in sediment are released to the overlying water. Therefore, the effects of phosphorus fractions in sediments for promoting aquatic environment eutrophication can be more efficiently evaluated based on phosphorus fractions, rather than total phosphorus. In this work, forms and bioavailability of phosphorus in the columnar sediments of two sampling sites in Sanggou Bay were analyzed by means of sequential extraction method (SEDEX). According to this method, there are five types of phosphorous:iron-phosphorous (Fe-P), organic-phosphorous (Or-P), detritus-phosphorous (De-P), exchangeable-phosphorous (Ex-P) and autologous-phosphorous (Au-P); The ages of sediment were also used to explore the content change of phosphorous forms in about two hundred years.The results showed that, for two sites, the contents of total phosphorus and phosphorus forms in the core sediments obviously decreased with depth.The main form of total phosphorus (TP) in sediments was organic phosphorus (Or-P) ,which accounted for 59.5 %, 57.6 % of TP in S1 and S2 sites, respectively ,and the percentage of Fe-P was less than 1 % ,which indicated that the environment of Sanggou Bay was less polluted. The contents of various forms in upper layer were all higher than those in bottom sediment and varied greatly in the shell deposition, which suggested that farming activity increased phosphorus sedimentation. In addition, the total phosphorus and contents of phosphorus forms had a tendency to decrease toward the bottom of the core, regardless of the phosphorus species;The distribution of TP and Or-P in time series was almost the same for both two sites;Bioavailable phosphorus in sediments occupied 61.2 % ,71.0 % of the total phosphorus pool,respectively;The content of Ex-P in sediment imposed a greater impact on the primary productivity in culture zones of Sanggou Bay.