| Lake eutrophication has become one of the major water pollution problems throughout the world. As a major nutrient for aquatic ecology, phosphorus (P) has been regarded as the limiting factor responsible for lake eutrophication. Its concentration in lakes results from both external inputs and internal loading. With the continuous inputs of external P, it could be transferred from water to sediment through biochemical and physical reactions, such as ion exchange, adsorption, and precipitation, and also could be released again from sediments as environmental conditions changes.Nansi Lake (116°34'-117°211'N,34°27'-35°20'E) situated at the southwest of Shandong province, as the sixth largest freshwater lake in china, is an important reservoir of the South-to-North Water Diversion Project(east route). In this study, sediment samplings from the lower Nansi Lake and its inflow rivers were studied, including sedimentary phosphorus fractions, phosphorus adsorption characteristics and phosphorus release characteristics. And phosphorus removal by four submerged macrophytes (Hydrilla verticillata, Potamogeton crispus, Hornworts and Vallisneria) also were investigated.From the results, the contents of NaOH-P in sediments of the lower Nansi Lake range from 76.44 to 161.10 mg/kg, Org-P from 235.79 to 442.79 mg/kg, TP from 758.89 to 895.68 mg/kg, obviously higher than those of its inflow rivers (NaOH-P 13.11-76.89 mg/kg, Org-P 51.01-233.10 mg/kg and TP 366.68-804.8 mg/kg).The contents of HCL-P in lake range from 319.30 to 498.33 mg/kg, IP-P from 419.54 to 644.74 mg/kg, having no obvious difference compared with its inflow rivers (HCL-P 237.61-518.52 mg/kg, IP-P 283.16-614.44 mg/kg).From phosphorus adsorption experiments results, the process involves at least two processes:the fast adsorption process mainly occurs within 1 h, and the slow adsorption process finishes within 2-10 h, at last reaching equilibrium after 10 h. The maximal phosphorus adsorption capacity (Qmax) of lake sediments ranges from 113.46 mg/kg to 159.91 mg/kg, obviously higher than that of its inflow rivers (from 42.78 to 104.37 mg/kg). In addition, the content of native adsorbed phosphorus (NAP), adsorption efficiency, Qmax,TQmax have significantly positive correlations with NaOH-P respectively while no obvious correlation with other phosphorus fractions. It is concluded that NaOH-P whether in lake sediments or in river sediments plays decisive roles in phosphorus adsorption-desorption process.Phosphorus release characteristics from from different functional regions (closed fishing areas, waterway, fish aquaculture and lake shore) of Nansi Lake were investigated. The results show that accumulated amounts of phosphorus release were lake shore> fish aquaculture> waterway> closed fishing areas, up to 89.68,123.60,89.54,87.67 mg/m2 respectively。The researches on phosphorus release control by submerged macrophytes show that the capability is Hydrilla verticillata>Potamogeton crispus> Hornworts> Vallisneria. Submerged macrophytes (10.0g, wet weight) were cultured in Hoagkand nutrient solution (10.0 mg/LKH2PO4-P) for 30d, the contents of phosphorus removal are Hydrilla verticillata> Hornworts>Potamogeton crispus> Vallisneria, up to 2.65,2.35,1.98 and 1.63mg. Further more, rapid phosphorus removal through stems and leaves biosorption were also evaluated, and the results show that maximal phosphorus biosorption amounts of Hydrilla verticillata, Potamogeton crispus, Hornworts and Vallisneria are up to 1.36,1.04,0.71 and 0.24 g/kg, accounting for 32.11%,26.62%,27.26% and 15.07% of the phosphorus bioaccumulation. It is indicated that phosphorus biosorption by stems and leaves plays an important role in phosphorus removal process. |
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