Distribution Characteristics of Organic Phosphorus Fractions and Influencing Factors in Surface Sediments of Lake Erhai

Organic phosphorus fractions and their spatial distribution characteristics in surface sediments of Lake Erhai were investigated by the IVANOFF method,and the impacts of organic matter(OM) on the contents of different organic phosphorus fractions were discussed.The results indicated that the higher OM contents of the sediments,ranging from 2.50% to 11.72%,were distributed in the shallow lake districts in the northern and southern areas of Lake Erhai.However,the higher TP contents,ranging from 710.29 to 1961.22 mg/kg,were mainly distributed in the deep water lake district in the central part of the lake.The average concentration of OP in the sediments from Lake Erhai was 212.71 to 526.23 mg/kg,and its distribution trend was consistent with that of TP.The contents of organic phosphorus with different extraction fractions ranked as follows: Residual-Po Fulvic-P HCl-Po NaHCO3-Po Humic-P.The content of OM was positively associated with the ratio of the content of OP to the content of TP,the content of Fulvic-P and the content of Humic-P(P0.01),and negatively associated with the content of Residual-Po(P0.01) in the sediments.However,the content of OM had no obvious relation with the content of NaHCO3-Po or the content of HCl-Po(P0.05) in the sediments.The main form of OP in the sediments of Lake Erhai was non-labile organic phosphorus(Residual-Po and Humic-P),accounting for 58.74% on average.The percentage of the content of Fulvic-P to the content of OP was higher than that of higher nutrition level lakes,and the percentage of the content of HCl-Po to the content of OP was lower(except for the E7 point).The characteristics of organic phosphorus forms in the sediments of Lake Erhai resulted in lower bioavailability.Accordingly,the distribution characteristics of organic phosphorus forms in the sediments may be the main reason that lower concentrations of phosphorus existed in the overlying water in Lake Erhai.However,the ratio of the content of TOC to the content of OP in the sediments,which was lower than 200,implied a higher potential release risk of organic phosphorus.