Phosphorus chemical speciation and seasonal variations in surface sediments of the Maowei Sea, northern Beibu Gulf

This study presents the distribution, seasonal variations and factors influencing phosphorus (P) forms in surface sediments from the Maowei Sea. P forms were measured using the sequential extraction (SEDEX) procedures. Inorganic P (IP) was the predominant chemical form of total P (TP). Fe-bound P (Fe-P) was the main IP form. Sediment particle sizes, organic matter distribution, terrestrial input and aquaculture activity were responsible for the seasonal variations of different forms of P in sediment. In summer, the average proportions of P fractions in TP followed the order of organic P (OP) > Fe-P > authigenic P (Ca-P) > detrital P (DeP) > exchangeable P (Ex-P); in winter, the corresponding order was OP > Fe-P > De-P > Ca-P > Ex-P. The potential bio-available P accounted for 71.1 +/- 4.9% and 70.6 +/- 6.3% of TP in summer and winter, respectively. Sedimentary organic matter mainly came from land-based sources in winter.