Study On Phosphorus Forms And Characteristics Of Phosphorus Adsorption And Release Of Sediments In Dongchang Lake

Lake eutrofication is one of the most important problems in China. Moreover,the study on phosphorus behaviors in the interface of sediment-water is veryimportant to help understand the mechanism of lake eutrofication. The distributioncharacteristics of different phosphorus forms, physicochemical characteristics and thecorrelations between them are crucial aspects that can further reveal the mechanism oflake eutrofication. However, the adsorption and release of phosphorus from sedimentsis controlled by many factors, including physicochemical characteristics and otherenvironmental conditions such as the phosphorus concentration of overlying water,disturbance and dissolved oxygen and so on. With the selected Dongchang Lake asthe representative of the eutrophicated and shallow urban lake, the objectives of thisstudy were to examine the characteristics of sediments and the release and adsorptioncharacteristics of phosphorus under different conditions. The results of this studycould provide scientific bases of controlling the lake eutrofication. The main resultsare summarized as follows.Phosphorus forms in the sediments are investigated mainly by using the methodnamed by “SMT protocol”. The total phosphorus (TP), inorganic phosphorus (IP),organic phosphorus (OP), NaOH extracted phosphorus (NaOH-P) and HCl extractedphosphorus (HCl-P) are determined. TP content ranged from381.37mg/kg to626.52mg/kg, the average content is497.76mg/kg in Dongchang Lake. The content ofdifferent phosphorus forms were in the following order: TP> IP> HCl-P> NaOH-P>OP. The correlation between TP and other different phosphorus forms are positive.The correlation between IP, HCl-P and NaOH-P is much better than OP.A pilot experimental study showed that the dynamic process of phosphorus sorption included two stages: a rapid process at first followed by a slow process.Isotherms for phosphorus sorption onto superficial sediments of shallow lake accordwith the Langmuir isotherms. The adsorption capacity of sediments on phosphoruswas relative with the characristics of clay minerals. Modetate doping with kaolinincreased the adsorptive capacity. The adsorptive capacity increased with the contentof bentonite. The adulterated zeolite reduced the adsorption capacity of phosphorus.Moreover, the particle size of sediments was smaller, the sorption capacity ofphosphorus was much better.The phosphorus concentration of the overlying water, disturbance and thedissolved oxygen (DO) affected phosphorus release from the sediments. Thedifference of phosphorus concentration between the overlying water and sediments isthe prerequisite to cause phosphorus release fron sediments. While the overlyingwater was distilled water, the amount of phosphorus release is more than the waterfrom Dongchang Lake. In a certain turbulence intensity (ranging from0r/min to150r/min), the amount of phosphorus increased with the turbulence intensity. But ifexceed the value, the release amount decreased on the contrary. In the process ofsedimentation while disturbance ended, the amount of TP decreased is more than DIPdecreased. In the anaerobic condition, the amount of phosphorus release is more thanin the condition of aerobic and anoxic. So keeping with high DO concentration in theoverlying water is feasible to control phosphorus release from sediments.