Ecological Security Assessment and Pollution Research of the Drinking Water Source Area in Cixi City
|Keywords||drinking water source Cixi City safety assessment eutrophication sediment countermeasure|
China is facing dual challenges of pollution and shortage of drinking water resources.Reservoir lakes are the main type of drinking water sources in town of China,especially in southern China. With the rapid development of industry and agriculture,national ecological damage and water quality deterioration in reservoir lakes has emerged,and water quality security in cities taking reservoir lakes as main source of water supply becomes increasingly serious.Cixi City,located in southeast coast in China,is a typical small and medium-sized city with developed economy and a large population.It takes hillside reservoir as source of drinking water mainly.At present,serious problem of water sources has become the bottle-neck for the national economical and social development.Based on survey of status of drinking water source in Cixi City,assessment of ecological security of drinking water source is carried out.Pollutant exchanges across sediment (soil)-water interface in Shanglin Lake is studied.A set of countermeasure suitable for Cixi Citys is put forward directed at the main water ecological security problems in this area.The results are as follows.In Cixi City,the average comprehensive polluted index of the past two years of drinking water sources is between 1.8 and 3.0,and the water quality safety level is safely basically or safety accordingly.Compared with the results in 2004,the water quality safety level falls to safety basically now from safely in 2004,the water quality deteriorated obviously.The eutrophication index is at a high level generally.Index of TN and TP is high.Based on analysis of project water supply capacity and the water supply guarantee rate in dry year,the water quantity safety level is safely basically on the whole,but the level of Shaoao Reservoir and Mei Lake is unsafely.The study on pollutant exchanges across sediment(soil)-water interface in Shanglin Lake shows sediment in reservoir lakes in Cixi City can cause secondary pollution easily.①Sediment in Shanglin Lake contains more active phosphorus than other lakes.②Total content of Exch-P,Al-P and Fe-P which can be released easily reach up to 21.27%.③The pollution of Cd and Hg is the most serious in sediment of Shanglin Lake.Besides,the two metals’ toxicity coefficient is high.So the ecological risk level of Cd and Hg has reached medium and high level respectively.④The non-point pollution from agriculture in the water resource area should be paid more attention.The content of available phosphorus in waxberry soil is high in rain-collecting area of Shanglin Lake. Phosphorus loss during the rainfall process has influenced the water quality and aggravates the eutrophication. Several comprehensive countermeasures for ecology safety of water source area are put forward directed to the above problems.Integrated treatment on internal pollution sources in water-collecting areas and inside reservoir,construction of ecological buffering and conservation areas,control of non-point pollution from Agriculture are concluded.Besides,to improve the environment management system,to establish monitoring system and early warning system in water source area are needed urgently for preventing and dealing with the water pollution accident.