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[Phosphorus Fractions and Release Risk in Surface Sediments of an Agricultural Headwater Stream System in Hefei Suburban, China].

A typical water system of agricultural headwater stream in Chaohu Lake basin was selected as the study area, and 17, 16, 14 and 13 surface sediments were collected from the four styles of stream, respectively, including ponds, branches, main channel and mainstream deep pools, in October 2014 (in autumn) and April 2015 (in spring). The forms and space-time variations of phosphorus in the sediments were analyzed. Clustering and variance analysis were conducted on the phosphorus forms data from the four styles of stream by means of multivariate statistical analyses. We quantified the phosphorus release risk (PSI) and identified the main impact factors of PSI via calculating the phosphorus sorption index (PSI) and the correlation analysis. The results showed that: (1) The contents of TP in the surface sediments ranged from 137.517 to 1709.229 mg x kg(-1) with an average value of 532. 245 mg x kg(-1), and the order of the average contents of phosphorus forms was IP (350.347 mg x kg(-1)) > OP (167.333 mg x kg(-1)) > Fe/Al-P ( 78. 869 mg x kg(-1)) > Ca-P (56.343 mg x kg(-1)) > Ex-P (6.609 mg x kg(-1)); (2) The contents of phosphorus forms had the same trend in all the four stream styles, which was deep pool > main channel > branch > pond; (3) In autumn, the deep pool and main channel were clustered into one class, while the pond and branch were clustered into the other class. In spring, branch, main channel and deep pool were clustered into the same class; (4) Variance analysis showed that the differences among the four stream styles were larger in autumn than in spring; (5) The PSI of the surface sediments ranged between 24.49 and 69.94 (mg x L(-1) x (100 g x micromol)(-1). The PSI in spring was lower than that in spring, indicating that phosphorus release risk of surface sediment was higher in spring than in autumn. (6) PSI had a significant negative correlation with Ex-P, IP and pH.