Analysis of phosphorus fractions in sediments by sequential extraction

The potential release of phosphorus in sediments depends largely on the composition and distribution of organic phosphorus and inorganic phosphorus. To study the release ability and bioavailability of different phosphorous fractions in sediments, the occurrence forms of organic phosphorus and inorganic phosphorus were analyzed simultaneously by sequential extraction using NH4Cl, NaHCO3, NaOH and HCl as extractants. Inorganic phosphorus in sediments was divided into four groups: weakly adsorbed inorganic phosphorus (WA-Pi), potential active inorganic phosphorus (PA-Pi), Fe/Al-bound inorganic phosphorus (Fe/Al-Pi) and Ca-bound inorganic phosphorus (Ca-Pi). Organic phosphorus was also divided into four groups: weakly adsorbed organic phosphorus (WA-Po), potential active organic phosphorus (PA-Po), middle-active organic phosphorus (MA-Po) and non-active organic phosphorus (NA-Pi). The method recovery rate and phosphorus forms in sediment were studied in Lihu Lake. The results showed that: 1) Compared with the SMT method, the recovery rate of the method was satisfactory. The recovery percentages of TP, inorganic phosphorus and organic phosphorus were 93.3%-112.1%, 93.9%-111.5% and 76.4%-119.9%, with mean values of 99.4%, 101.8% and 101.0%, respectively. 2) Inorganic phosphorus was the main phosphorus fraction in surface sediments of Lihu Lake. The content of inorganic phosphorus was 271.29-666.34 mg/kg, with mean value of 441.03 mg/kg, accounting for 62.91% of w(TP). The content of different inorganic phosphorus forms was in the order of w(Ca-Pi)>w(Fe/Al-Pi)>w(PA-Pi)>w(WA-Pi). The content of organic phosphorus was 201.76-368.52 mg/kg. The content of different organic phosphorus forms was in the order of w(R-Po)>w(NANaOH-Po)>w(PA-Po)>w(MAHCl-Po)>w(WA-Po)>w(MANaOH-Po). The chemical forms of inorganic phosphorus and organic phosphorus could be effectively separated by the improved sequential extraction method simultaneously. The analytical needs for testing of bioavailable phosphorus should also be taken into consideration. ©, 2015, Editorial department of Molecular Catalysis. All right reserved.