Effects of different pretreatment drying method on sequentially extracted phosphorus forms in marine sediments

The effects of three different pretreatment drying methods (vacuum freeze-drying, oven-drying and air-drying) on the analysis of phosphorus (P) species and their bioavailability were investigated in five typical surface sediments from the Maowei sea in the northern Beibu Gulf.The long-term pretreatment process of air-drying promoted the microbial degradation and transformation of sedimentary P compounds into inorganic P (IP), resulting in the highest concentrations of IP and total P (TP).The highest levels of organic P (OP) were recorded in freeze-drying samples.Among different IP species, the highest concentrations of exchangeable P (Ex-P) and Fe-bound P (Fe-P) were found in oven-drying and air-drying samples, respectively.The variation trend of the extraction concentration of authigenic apatite P (Ca-P) and detrital P (De-P) using different pretreatment drying methods was not significant due to their stable chemical properties.Compared with the other two methods, freeze-drying could reflect the actual composition characteristics of different P forms in marine sediments, and is an ideal method for sample drying.Thus, this pretreatment seems to be the best drying method.Correlation analysis indicated that, in addition to Ca-P, changes of individual samples did not influence the analytical integrity of Ex-P, Fe-P, De-P and OP in extracted solutions from different pretreatment drying methods.The concentrations of bioavailable P (BAP) in the air-drying samples were higher than those of vacuum freeze-drying and oven-drying but, the single factor analysis of variance showed no significant differences on the evaluation potential BAP in surface sediments of the Maowei sea based on the three pretreatment drying methods.