Study On Form, Migration And Conversion Of Phosphorus In Eutrophic Artificial Lake Sediments

Lake eutrophication is a serious environmental problem worldwide. Currently, most researches focus on natural lakes, whereas artificial lakes that do not have robust ecosystems have not received sufficient attention. Due to the limitation of freshwater resource, some artificial lakes have been supplemented with reclaimed water which contains high concentrations of phosphorus (P), thus increasing the risk of eutrophication and algae bloom. As both the sink and source of P in the water body, sediments play vital roles in the P cycling. Therefore, it is of significance to investigate the distribution and conversion behavior of P in the artificial lake sediments.Seven artificial lakes in a golf course in Beijing were selected as the investigation objectives. Based on the results on P content, binding form and distribution, the mineral fixation and biological conversion capability for P of the lakes was analyzed. A series of simulation experiments were conducted to reveal the influence of different factors for the distribution and conversion of P on the sediment-water interface.As suggested by elemental analysis, the P contents in the artificial sediments reached up to 888~1984 mg/kg, comparable to those of eutrophic natural lake sediments. The disparity of sediment P concentration was correlated to the influence of runoff from lawns. Through fractionation, the NaOH-Al which permanently immobilizes P was found to be in very low level, and the ratio of [NaOH-Al]/[BD-Fe] was less than 3. The capability of these sediments on P absorption and anoxic P release control was limited.After optimizing the extraction strategy, phosphorus-31 nuclear magnetic resonance was employed to characterize the molecular structure and relative quantity of P compounds in the sediment extracts by NaOH-EDTA. The proportion of orthophosphate was 68~89 %, and the rank order of biogenic P species was monoester-P> DNA> pyrophosphate> lipid-P. However, phytate, phosphonates and polyphosphates were not detected. Compared with natural lakes, the quantity and type of P biological conversion were some different.According to the simulation experiment, dissolved oxygen, organic carbon and sediment aluminum content exerted influence on water quality, sediment morphometry, mineral bound form and biogenic-P conversion, with different extents. The high aluminum content had the greatest influence on suppressing anoxic P release. The high dissolved oxygen could suppress P release to some extent. The high organic carbon concentration led to the morphometry change and promoted P release. The conversion of biogenic-P was too complicated to figure out clear conclusion.