Seasonal Characteristics Of Phosphorus Form And Risk Assessment Of Phosphorus Release In Surface Sediment Of Yunqiao Wetland

Phosphorus is one of the main factor leading to water eutrophication, and wetlands were used to control eutrophication due to the better phosphorus removal, construction of low operating costs, ease of management, etc. And sediment was considered to be the ascription of phosphorus. Yunqiao wetland has become a typical regional of human intervention to restore wetlands ecology, and it plays an important role for alleviating water pollution and protecting water resources. Therefore, this experiment studies the overlying water and surface sediments of Phragmites australis, Cyperus alternifolius, Equisetum arvense, Typha orientalis and a no-plant area in Yunqiao wetland. The different speciations of phosphorus in sediment samples were extracted by chemical continuous extraction. The contents of phosphorus in the overlying waters and chemical properties of the sediments were determined. The seasonal change characteristics of phosphorus form in surface sediments of different vegetation communities were revealed, and the phosphorus release risks were assessed by the phosphorus sorption index (PSI), the degree of phosphorus saturation (DPS) and the eutrophication risk index (ERI). This study has some significance in predicting the risk of phosphorus release and preventing secondary pollution of Phosphorus. And provided a reference value in building wetland, vegetation choice, management of wetlands and management of water resources.The results shown that:(1) The total phosphorus (TP) contents in surface sediments of different vegetation communities of wetland range between 504.42?153.31 mg/kg, which average content was 828.54 mg/kg. The inorganic phosphorus (IP) as the main chemical speciation of TP of sediment, which accounting for over 60% of TP. The calcium bound phosphorus (Ca-P) as the main chemical speciation of IP of sediment, which accounting for over 60% of IP. The contents of TP were characterized by summer, spring and autumn, winter from high to low. And the contents of TP of vegetation lower than the waters in summer and autumn, but the contents of TP of vegetation higher than the waters in spring and winter.(2) The seasonal characters of content and percentage of different forms of phosphorus in the surface sediments show that:The contents and percentage of (Ex-P) in surface sediments were characterized by winter, spring and autumn, summer from high to low. The seasonal characteristics of content and proportion of aluminum bound phosphorus (Al-P), iron bound phosphorus (Fe-P) and organic phosphorus (Or-P) were similar, but there are differences between the vegetation. The contents and percentage of occluded phosphorus (Oc-P) in spring and winter were more than in summer and autumn. The seasonal characteristics of content and proportion of calcium bound phosphorus (Ca-P) wrer not exactly the same, and the large differences between the vegetation.(3) In addition to the winter, planting vegetation can effectively reduce phosphorus in water, but in the winter, the vegetation retention capacity of phosphorus less than self-purification capacity of water. The main factors affecting the Ex-P of sidements was the TP of overlying water. The content TP and Or-P of sediments wrer significantly affected by TP of overlying water also.(4) Vegetation in different seasons are different degrees of boosting the content or proportion of one or several forms of phosphorus, which on Fe-P, Al-P and Or-P were more obvious. The main factors affecting the Ex-P, Fe-P and Ca-P of sidements were the OM, Alox and Feox of sidements. The content of OM, Feox and Alox were increased can promote the formation of Fe-P, and lead to a reduction of the Ca-P.(5) PSI and DPS had a same seasonal variation with summer, spring and autumn, winter from high to low. The PSI range between 504.42-153.31 (mg P/100g)/(?mol/L), and the DPS range between 5.6?26.97%. The main factors affecting the DPS was the contents of Feox and Alox.(6) The ERI of wetland were high throughout the year, and between 9.72?41.28%. Vegetation reduced the risk of phosphorus released from the sediment. Compared with other plants in the same season, P. australis had the control function to phosphorus release.