Effect Of Submerged Macrophytes Together With Sediments On The Circulation Of Phosphorus Of Eutrophic Lakes

The water-sediment interface is the transformation-zone between water and sediments, a special and important area of aquatic environment. As the concernful composition in the ecosystem, submerged macrophytes have a dominative effect on the removal and transformation of phosphorus between the water-sediment interface. In this work, Jingye lake, a water-submerged macrophyte-sediment ecosystem, was selected as the sampling field to investigate the effect of submerged macrophytes together with sediments on the circulation of phosphorus of eutrophic lakes, and further lab-simulating experiments was also carried out.During the sampling period, the concentrations of TN and TP of overlying water of Jingye lake ranged from 6.21 mg/L to 2.70 mg/L, and 0.18 mg/L to 0.12 mg/L respectively, and both of which were beyond the limiting concentration of eutrophication. When the Potamogeton crispus was growing, the concentrations of TN, TP, PP, TDP and SRP of overlying water except DOP decreased with the increase of biomass of Potamogeton crispus, while increased when the biomass of Potamogeton crispus began to decline. The same change trend was also found with the alkaline phosphatase activity in surface and pore water, and the alkaline phosphatase activity in surface was higher than that in the pore water, sugesting that restraint in the alkaline phosphatase activity by submerged macrophytes is an important characteristic of decontamination of water.During the sampling period, the concentrations of Ex-P, Fe-P and Ca-P of algae type sediments were higher than that of grass type sediments of Jingye lake, whereas the concentrations of Oc-P, De-P and Or-P were reverse. Al-P was not detected in both type of sediments. So it can be concluded that Potamogeton crispus absorbs the bioavailable phosphorus from overlying water and surface sediments and accelerates the accumulation of propagation residues and its phosphorus in the surface sediments (TOC: 6.26～8.89 %; organic phosphorus: 25.4～62.8 mg/kg). Meanwhile, by changing the physical and chemical characteristics of surface sediments, Potamogeton crispus restrains the desorption process of bio-unavailable phosphorus, decreases the phosphorus concentration of overlying water indirectly. Consequently, we can decrease the phosphorus concentration in water by removing the dead Potamogeton crispus termly. The live plant makes the sediment-bound phosphorus, which made great contribution to the eutrophication, exist in the sediments steadily. Therefore, Potamogeton crispus plays the role to some extent in controlling the degree of eutrophication of Jingye lake by influencing the circulation of the phosphorus of water-sediment interface.Lab-simulating investigation indicated that organic matter can accelerate the P desorption process greatly, and the desorption capacity had the same trend as TOC concentration. Meanwhile, cyanobacteria worked better by compared with humous acids. It is because that humous acids accelerated PO4- and SO42- desorption, as well as reacted with bioavailable phosphorus.