Study of chemical forms of phosphorus and their bioavailability in the sediments

Chemical forms of phosphorus in the sediments of the Daya Bay, the Zhujiang River estuary, and the Xiamen Bay are measured with extraction solutions of MgCl₂, NaOH, and HCl. Their availabilities to Chlorella sp. and Isochrysis galbana are estimated by using sediments as the sole source of P in the bioassays. The results show that the contents of total phosphorus (TP) in these sediments are 449.3, 650.1 and 643.9 mg/kg, respectively. The contents of non-apatite inorganic P (NAIP) extracted with MgCl₂ and NaOH from 3 sediments are 168.8, 146.6 and 118.1 mg/kg, respectively, and account for 18.3%-32.6% of TP. The phosphorus extracted with HC1 solution is greater than that extracted with NaOH solution and the lowest extracted P is MgCl₂-extractable P. The greatest relative growth rates of Chlorella sp. and Isochrysis galbana cultured with sediments are in the range of 4.3%-26.9%. The increasing biomasses of these algae correspond to NAIP and AAPP (the estimated algal-available particulate P). AAPP accounts for 42.4%~78.2% of NAIP, 21.1%~27.1% of total inorganic P, and 11.8%~20.3% of TP, respectively.