Phosphorus forms and distribution in the sediments of Poyang Lake, China

The forms and distribution of phosphorus in the sediments of Poyang Lake were studied using chemical extraction methods to understand the potential release and adsorption of phosphorus. The results showed that phosphorus in the sediments mainly consisted of inorganic phosphorous species, including iron bound phosphorus, calcium bound phosphorus, aluminium bound phosphorus and dissolved phosphorus, as well as organic phosphorous species. The spatial distribution of phosphorus species in surface sediments showed a decreasing trend from the outlet to the entrance of Poyang Lake. The content of total phosphorus in the surface sediments ranged from 688.29 to 825.36 mg/kg, and inorganic phosphorous was the major phosphorus species. Iron bound phosphorus was the dominant form of inorganic phosphorous, accounting for greater than 40% of the total phosphorus, while calcium bound phosphorus and aluminium bound phosphorus accounted for more than 20%, and dissolved phosphorus accounted for less than 5%. The content of organic phosphorus in surface sediments was lower, accounting for less than 15%. Total phosphorus was positively correlated with iron bound phosphorus, aluminium bound phosphorus, calcium bound phosphorus and organic phosphorous, while organic phosphorous was positively correlated with iron bound phosphorus and aluminium bound phosphorus, but only weakly related to calcium bound phosphorus. For all six sites, the contents of total phosphorus and phosphorus forms in the core sediments obviously decreased with depth, while they were significantly enriched in the surface sediments. The total phosphorus and phosphorus forms contents were significantly higher in the upper layers and had a tendency to decrease toward the bottom of the core, regardless of the phosphorus species. In addition, the average contents of total phosphorus and various phosphorus forms decreased rapidly with sediment depth from 0-20 cm, and then decreased slightly from 20–30 cm.