| Environmetal pollution are becoming more and more severe due to over-development of natural resources and population booming. Water pollution, especially eutrophication, turns to be the biggest problems in the world. Although Hangzhou is a world famous tour city with the most beautiful West Lake, heavy eutrophication happened in the lake because of sewage from inhabitants and wastewater discharged from industry and agriculture around the lake before 1980s. Since then, eutrophication in West Lake has been paying more attention and different kinds of lake restoration projects have been put into operation for water quality improvement.Water quality of the West Lake has been monitored and analysed since 1998 with the operation of lake restoration projects, such as sediment dredging, wetland reconstruction and water flushing supported by Hangzhou municipal government. As chlorophyll-a is a main tool in both study and evaluation of lake eutrophication, the chlorophyll-a concentrations in the West Lake were monitored continuously from 1998 to 2007. The spatial distribution of chlorophyll-a concentration and its correlation with water temperature, dissolved oxygen content and the amount of water pumped into the West Lake were also analyzed in detail. Although the West Lake is still under mesotrophic state and some partial area such as North-inner lake is still eutrophied, it is found that the chlorophyll-a concentrations in main parts of West Lake in 2007 decreased by 42.8% to 87.3% compared with those data in 1998, which representing that the comprehensive restoration projects during these ten years have played an important role in the water quality improvement of the West Lake.
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