Phosphorus fractions and its release in the sediments of Haihe River, China

The amounts and forms of phosphorus (P) in surface sediments of Haihe River, Tianjin, North China, were examined using a sequential chemical extraction procedure. Five sedimentary P including loosely sorbed P (NH4Cl-P), redox-sensitive P (BD-P), metal oxide bound P (NaOH-P), calcium bound P (HCl-P), and residual P (Res-P) (organic and refractory P), were separately quantified. The results indicated that the contents of different P fractions in the Haihe sediments varied greatly. The total P (TP) contents ranged from 968 to 2 017 mg/kg. NH4Cl-P, BD-P, NaOH-P, and HCl-P ranged from 6.7 to 26.6 mg/kg, 54.5 to 90.2 mg/kg, 185.2 to 382.5 mg/kg, and 252.3 to 425.5 mg/kg, which represented 1.2%-3.2%, 7.7%- 13%, 33.3%-48.9%, and 36.2%-54.2% of the sedimentary inorganic P. For all the sediment samples, the rank order of P-fractions was Res-P > HCl-P > NaOH-P > BD-P > NH4Cl-P. The highly positive relationship between the amounts of P released from the sediments and NH4Cl-P and BD-P, indicated that NH4Cl-P and BD-P were the main fractions that can be released easily.