Study On Exogenous Pollutants Flux In East Taihu Lake, Yangcheng Lake And Ecological And Economical Evaluation Of Fish Multiplication

In order to control eutrophication of East Taihu Lake and Yangcheng Lake, water quality and water flux of the inlet and outlet of the two lakes were monitored to estimate exogenous pollutants flux. Besides, ecological and economical evaluation of fish multiplication was conducted in West Yangchen Lake.1. Study on the exogenous pollutants flux of East Taihu Lake. Water quality and flux were monitored in inlets of the junction between the East Taihu Lake and West Taihu Lake,Daqugang,Shihegang,Jiaobaigang,Dajugang and outlets of Zhangjiabang,Xinliangang,Shuilugang,Qianggang,Tingzigang,Shengjiagang,Taipu river,Dingjiagang,Qidu,Xinkailuzha,Miaogang once every 2 months from March, 2009 to March, 2010. Results showed the average concentration of total nitrogen (TN), total phosphorus (TP) and chemical oxygen demand (CODMn) in inlets were 1.65mg.L^-1,0.10 mg.L^-1 and 5.62 mg.L^-1, respectively, and in outlets the value were 1.27 mg.L^-1, 0.10 mg.L^-1 and 5.47 mg.L^-1 respectively.The water quality meet grade IV when they were compared with the water quality standards. The flux of TN, TP, and CODMn input by monitored inlets were 9010.5t, 1052.6t and 49621.4t, respectively. The pollutants flux from West Taihu Lake was the largest among inlets, with 8924.0t of TN (occupied 99.0% of total input N), 1046.0t of TP (occupied 99.4% of total input P),and 49276.8t of CODMn (occupied 99% of total input CODMn).The flux of TN, TP, and CODMn output by monitored outlets were 2956.3t, 174.8t and 8037.9t, respectively. The pollutants flux from Taipu river was the largest among outlets,with 2134.6t of TN (occupied 72.2% of total input N), 96.9t of TP (occupied 55.4% of total input P), and 4187.5t of CODMn (occupied52.1% of total input CODMn). Compared with the different seasons, the pollution loaded was higher in winter than summer.2. Study on the exogenous pollutants flux of West Yangchen Lake. Water quality and flux were monitored in inlets of Sanjiacun,Baitujing,Zhangjingyan,Maozhuanghe,Lianzigang,Qitugang,Daweigang,Guanjingqiao,Nanxiaojing and outlets of Xishagang,Qingshuigang,Hongmiaogang,Nanyuanmu,Guanjinggang,Tianjinggang,Zhonghukouzi once every 2 months from April, 2009 toDecember, 2010. Results showed the average concentration of TN, TP and CODMn in inlets were 3.42mg.L^-1,0.25mg.L^-1 and 6.33mg.L^-1 and in outlets the value were 2.40mg.L^-1,0.16mg.L^-1 and 6.25mg.L^-1 respectively.The water quality meet grade V when they were compared with the water quality standards.In two years, the flux of TN, TP, and CODMn input by monitored inlets were 3183.3t, 224.4t and 5687.1t respectively. The flux of TN, TP, and CODMn input by monitored inlets in 2010 were 1934.5t, 123.2t and 3138.6t respectively. The flux of TN, TP, and CODMn output by monitored outlets in 2010 were 1516.6t, 65.5t and 3513.2t respectively.This results indicated that the exogenous pollutants flux in Yang cheng Lake are increasing. Compared with the different seasons, the pollution loaded was higher in winter than summer.3. Study on ecological and economical evaluation of fish multiplication in Yang cheng Lake.Water quality in 7 inlets, 6 outlets, and 6 fish multiplication areas were monitored once every 2 months from April, 2009 to December, 2010, and economic benefit was calculated. Results showed the average concentration of TN and TP of enclosures is 0.21mg.L^-1 and 0.11 lower than those of inlets respectively.The level of Chlorophyll a is 17.52-77.93ug.L^-1. These results suggested that fish multiplication improve waterquality and control algal blooms effectively. Planktivorous fishes culture brought economic benefit of 29.68 million yuan. Meanwhile, 79.8 tons of N and 23.0 tons of P were removed from the lake by fisheries.Conclusion:The exogenous pollution is serious in East Taihu Lake and Yangcheng Lake.The positive measures must be adopted to reduce the importation of exogenous pollutants. Our results suggested that planktivorous fishes culture control waterquality and algal blooms very well.