[Distribution of Phosphorus Fractions in Surface Sediments of Minjiang Mainstreams]

In recent years, the total phosphorus pollution in Minjiang River was serious, and the surface sediments of the Minjiang River also threatened water quality. To study the spatial distributions of phosphorus in the surface sediments of the Minjiang River, samples of surface sediments were collected upstream (Aba District) and downstream (Yibin District) of the Minjiang River in December, 2016. The sediments were analyzed with the modified sequential extraction method (SEDEX) to obtain six forms of phosphorus, including exchangeable phosphorus (Ex-P), exchangeable organic phosphorus (Org-P), iron-bound phosphorus (Fe-P), authigenic phosphorus (Ca-P), detrital phosphorus (De-P), and refractory phosphorus (Res-P). The results indicated that the contents of total phosphorus (TP) in surface sediments ranged from 522.17 μg ·g^-1 to 979.22 μg ·g^-1, which were far more than the soil phosphorus background values (700 μg ·g^-1). The spatial distribution characteristics of the TP of surface sediments indicated that the TP concentrations in sediments at the Meishan sections (the middle reach of the Minjiang River) were higher than those in the other sections. This was related to the smaller particle size and higher OM contents in sediments in the Meishan sections. The main phosphorus forms in the sediments in the Minjiang River were Ca-P and De-P, with their concentrations accounting for 75% of TP in the sediments. The bio-available phosphorus, which included Ex-P, Org-P, and Fe-P, accounted for 0.31%-29.62% of TP in the sediments of the Minjiang River. The concentrations of bio-available phosphorus in sediments at the Meishan sections and Leshan sections (the middle reach) were highest, indicating that bio-available phosphorus in the surface sediments was high, and its potential environmental impact risks were higher.