Effects Of Iron On Phosphorus Fraction,sorption And Release From Erhai Lake Sediments

The contents and fractions of phosphorus (P) in surface sediments of the Erhai Lake were studied by the Standard Measurement and Test (SMT) procedure. The effects of organic matter (OM), Fe and Mn on P fractions and its release were discussed, and the potential P release risk of the sediments was assessed. The results indicated that the content of total phosphorus (TP) varied in the range of 710.3-1961.2 mg/kg, of which w(Ca-P) the highest (36.9%-59.2%), w(OP) followed by (24.6%-36.9%), and w(Fe/Al-P) the lowest (9.8%-20.7%). The OM content ranged from 25.0 mg/g to 119.6mg/g, which was negatively correlated with TP and Ca-P. The contents of total manganese (Mnt) and total iron (Fet) were 0.8-3.8 mg/g and 34.3-127.2 mg/g, respectively, showing significant positive correlations with the contents of TP and various P fractions. The ratio of w(Fe/Al-P)/w(Ca-P) was lower than 0.5, and that of w(Fe)/w(P) was much larger than 20, indicating the low P release from sediments. However, w(TOC)/w(OP) ratio was lower than 200, indicating the potential release of OP at higher risk. The P-fractions were significantly (p<0.05) positive correlated with the amorphous Fe oxides (Feo-Fep), but the correlation between P-fractions and the crystalline(Fed-Feo) was not significant (p>0.05). And more Fe oxides in the sediments were Feo-Fep while a small quantity was Fed-Feo,which suggested that P release from sediments of the Erhai Lake was mainly controlled by Feo-Fep. Zero Equilibrium P Concentration (EPC0) ranged from 0.023 to 0.065mg/L in sediments from the Erhai Lake. The ratio (Feo-Fep)/(Fe/Al-P), Fep/(Fe/Al-P) and Fe/Al-P were significantly correlated with sorption parameters of P (k,NAP,EPC0) on sediments, indicting that phosphorus sorption and release were mainly controlled by iron oxides and Fe/Al-P.