Reaserch And Assessment On Eutrophication Characteristics Of Wanfeng Lake Guizhou

Reservoir and lake water resource issues together with water pollution, emerged with the rapid initialization of reservoirs, have caught increasing public attentions. Water eutrophication is one of the hot research areas of this field today. Wanfeng Lake, located in the upper reach of Nanpan River, was of a channel type built by river blocking method in 1998.It covers an area of 176km~2, and has a capacity of 1.026 billion m~3, yielding 1.424 billion m~3 of water each year. In these years, Wangfeng Lake has gradually developed into eutropication with a water quality far below TypeⅢstandard the function area requires, which makes an all-around entropication management as of top concern.During Aug 2005 to Dec 2006 , This paper has conduct investigation and assessment towards the concerned factors of the Wanfeng Lake area and its flow-in rivers such as the physical and chemical factors, the quality and aspects of water and the eutrophication level of water. It studies how much each factor may contribute to water eutrophication and initiates with basic management solutions. Main conclusions achieved are as follows: (1) The characteristics of the physical and chemical factors of the Wanfeng Lake include:Temp of a year 19.7℃(realtime Tem.below 20℃in three seasons except summer),transparency 0.44m to 5m,Ave.pH 7.92(slightly alkaline),COD 2.86 mg/L,chl.a 5.40mg/m,TN 2.34 mg/L,TP 0.20 mg/L,ratio of N to P 12.01.From those data,we can conclude that the overall water quality of Lake Wangfeng is worsen than class III of Water Quality Standard of Surface Water,and can only be classified as class IV,V or V-minus.Among all these pollutants,TP and TN are the major standard-violating factors, while others (organic) can satisfy the standard.90% of Lake Wanfeng are of moderate level of nutrition , and are changing into euthophication,the amount of TP and TN have go beyond its capacity largely.The result of the ratio of N to P also means Lake Wanfeng is a P-polluted lake.(2)We assess the extensity of euthophication in Lake Wanfeng by comparing each indicator.It comes out that the sum of weighed index is 49.19,we can get the conclusion that Lake Wanfeng in general is in a transient status from moderate level of nutrition to slight euthophication.(3)We use some mathematical tools,such as correlation, partial correlation,principle component analysis, and general component analysis to deal with the data,and get the result like,there is strong evidence proving the existence of positive correlation between chl.a and TP,chl.a and TN respectively, and the former one is stronger.The significant and positive correlation also existed between TP and TN,transparency and TP,transparency and TN, while the COD only has correlation with water temperature.This means the euthophication here is closely related with TP,TN,and transparency,and less with organic materials.The partial correlation analysis revealed that chl.a has significant positive correlation with TP, rather than with TN.The principle component analysis indicated that the number one contributor to the euthophication of Lake Wanfeng is at Sanjiangkou which accepted rivers from outside of Guizhou province.The cause can be explained in two points,one is because the rivers from outside themselves have a bad quality,class V or V-minus,with pollutants violating standards significantly; two is because Sanjiangkou is located at the bay of Lake Wanfeng,it means it has a bad exchange capacity,that is not good for pollutant dispersion,subsequently impairs the self-purification function of the lake.(4)We monitored the input rivers of Lake Wangfeng,and found the parameters of those rivers are,pH 8.18(alkineline),COD1.74 mg/L,TN 2.989 mg/L,TP 0.128mg/L.Four of these rivers are classified as class V-minus,with TP and TN as the dominating pollutants.(5) Comprehensive solutions to manage Wanfeng Lake's eutrophication problem include:①To strengthen the control of industry pollution resources, urban livehood sewage water emission and agricultural production wastes;②To further control and manage the pollutants inside of the lake such as the wastes from fishery, tourism, shipping and bottom silts;③To add efforts to bring the Lake area biological rehabilitation project into effect...