Internal phosphorus loadings and fluxes of surface sediments in four seasons in Shanzi Reservoir

Spatial and temporal variations of different forms of phosphorus of the surface sediments of Shanzi Reservoir were analyzed in four seasons. The Standard Measurement and Test( SMT) and the sediment cores incubation were applied for observing the phosphorus releasing flux in the water-sediment interface. The results showed that the reservoir sediments are rich in phosphorus. The loadings of total phosphorus in surface sediments ranged from 521. 23 ± 7. 60 μg / g to 1255. 54 ± 11. 03 μg / g in four seasons. The amounts of total phosphorus and other phosphorus forms of all samplings were larger in summer than those in other three seasons. The inorganic phosphorus,the dominant phosphorus form in surface sediments,existed in Fe-bound phosphorus forms.The Fe-bound phosphorus and organic phosphorus occupied for 77% to 90% of the total phosphorus. The average releasing rate of dissolved phosphorus ranged from 1. 66-2. 49 mg /( m2·d) in summer and 0. 69-1. 29 mg/( m2·d) in winter. The sediment releasing of dissolved phosphorus mainly occurred in the overlying water in summer due to the water temperature stratification. Water temperature stratification may be destroyed if summer rainstorm came and the dissolved phosphorus releasing from the sediments would have a significant impact on the water quality. The water mixed together due to the water temperature stratification disappearing in winter and the dissolved phosphorus was taken to the top water layer,which could greatly affected the overlying water quality.