| Currently, lake eutrophication is one of the major environmental problems facing the world. The continuous accumulation of excessive nutrient is the fundamental cause of eutrophication of lakes. In China, the governance of lake eutrophication has taken a series of means such as sediment dredging, ecological water diversion and aquatic plant reconstruction. Under the condition of exogenous getting controlled, the control of endogenous pollution is the key to control eutrophication of lakes. Studies have shown that phosphorus is an important restrictive nutrient factor of eutrophication process. Phosphorus in the sediment is released to the water body through physical, chemical and biological effect in severely endogenous polluted lakes.This study take Li Lake, one of the urban shallow lakes in China, as the research object; and monitor and analyze water and phosphorus content in the sediment. Simultaneously, this study use Hendly method to conduct grading extraction of organic phosphorus forms in Li Lake. The results showed that TP, DTP and DOP concentration in water in Li Lake was between (0.03～0.31),(0.01～0.11) and (0.00～0.09) mg/L, respectively, with a mean of0.07,0.03and0.02mg/L, respectively. Overall, the results showed an increases distribution trends of total phosphorus pollution from west to east, i.e.,"west Li Lake"<"east Li Lake", and from the center of lake to the coastal area. Particulate phosphorus presented a first rise after falling trend along with the change of seasons. Wherein the concentration in autumn was significantly higher than other three seasons. After2012, TP concentration in water had fluctuated around0.068mg/L. The water quality of Li Lake was basically class IV standard. Multiple regression analysis showed that TP and DTP, SS all showed a significant positive correlation.Research on sediment phosphorus showed that phosphorus content of the sediments is A district<B district<C district<D district under different engineering measures in Li Lake. The overall performance of the zones of retired fish lakes were better than artificial dredging areas. The DTP concentration in interstitial water was between0.013-1.379mg/L, with a mean of0.18mg/L. The TP concentration in sediment of surface layer was between320.52-1929.54mg/kg, with a mean of667.68mg/kg. During the year, the concentration of TP was the highest in autumn. Active and non-active organic phosphorus content were higher in autumn. The bioavailability of phosphorus concentration in sediment was between3.35-60.23mg/kg, with a mean of18.48mg/kg. Correlation analysis showed that Ex-P and DTP in water was a significant positive correlation. The higher Ex-P, the greater DTP released into the interstitial water. Extractable organic phosphorus is closely related to total organic matter as well, but the active organic phosphorus and organic matter are not significantly related.Finally, aiming at the analysis of phosphorus in Li Lake water environment and cutting ability in environmental management projects, according to analysis of part Ⅱ phosphorus pollution of surface sediment and calculated by Warren Wade (Voflenweider) model, Li Lake phosphorus capacity in water environment was2.14t/a, phosphorus sediment fluxes of surface sediment were0.29,0.53,0.41and0.33mg· d-1· m-2in spring, summer, autumn and winter, respectively. Exchangeable phosphorus plays an important role on the release of phosphorus from the sediment to the overlying water. By partitioning sediment contaminated areas and areas suitable for submerged plants recovery, sediment control areas were focused mainly on D district, around ChangGuangXi Park, Bao border bridge and Li Lake bridge. The key control area had reached1.76km2. Suitable areas for recovering submerged plants were mainly in the areas of Jincheng Bay Park, ShuiJu community, Venice park, area around Li embankment and BoGong Island garden areas. In the next step, several major projects are recommended, including the projects of environmentally dredging and covering of sediment, and recovering and adjusting of submerged plants. |
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