Forms, Transfer And Conversion Of Phosphorus In Sediments Along Vertical Section In The West Lake

Superfluous phosphorus in lake ecosystem plays the key role in eutrophication. More and more researches have focused on the inner loadings of sediments since recent years. To understand the phosphorus cycle and its transfer/conversion is very important to the water quality control. The changeability and complexity of phosphorus forms in sediments lead to the stagnant progress of the phosphorus geological chemical cycle. Different forms of phosphorus usually differ greatly in ecological significance, which is the foundation to learn the behaviors of phosphorus. Known as the world famous scenery, the water quality of the West Lake has being in the awful condition.For the first time, the thesis investigated and analyzed entirely with the concentrations and forms of phosphorus in sediments due to the new distributions in the West Lake after the western advance project was executed. The concentration of TP in sediment was in the medium level while the relative content of OP was especially high. In the composition of phosphorus forms along vertical section, the concentration of O-P was relatively stable while other forms showed the similar transformation regularities with TP, which meant the outer input and the complex nutrients transform processes in the sediment-water surface. The exchange of phosphorus between sediments and water has been in the homeostasis. Ca-P might be the final foreordination of phosphorus by the diagenesis, the decrease of contents of other forms suggested the invert processes to the much stabler form.In addition, the infection to the forms, distributions and behaviors of phosphorus along the vertical section of sediments by the mineralization and degradation of organic matter and alkaline phosphatase activity were studied either.The concentration of organic mass in the West Lake was very high, and the contents varied in different lake zones which was related to the organic pollution inputs, human movement influences, primary productivity levels, sediment fluxes and so on. The concentration of TP along the vertical section was controlled by the functionary of organic mass mineralization and degradation to a large extent. OP, DP, Fe-P, Ca-P had well correlations with organic mass. The concentration of organic mass and the functionary of mineralization and degradation influenced the distribution and transform/ conversion of phosphorus in sediments.The alkaline phosphatase activity was especially high of the samples. The characteristics of APA distributions in the vertical section had similar regularities in the whole lake coverage. The surface layer in sediments was the most active area of the phosphorus cycle under the function of alkaline phosphatase. There were always other active areas under anoxic circumstances either in the middle or bottom of the sediments. The actuality of lacking of phosphorus in sediments led to the higher activities of alkaline phosphatase. Extent of OP mineralization had an affinity with APA.The West Lake has been rebuilt cosmically for several times, in which the sludge dredging was thought to be the common instrument. Study of the effects of the latest dredging showed that, the enrichment of nutrients in the surface layer has not been changed, the concentrations had few transformations between sediment layers, distribution of inorganic phosphorus was more similar to the estate before dredging. As a tool in controlling the eutrophication of the West Lake, the actual efficient time of dredging was less than 2 years.