Characteristics of Water Quality and Evaluation of Eutrophication for Reservoirs in Kunsan

Recently, eutrophication or lake and reservoir has become serious problem to man who want use that water for several purpose. In order to solve the eutrophication problem, the trophic state of that eutrophic lake and reservoir should be measured properly. For the purpose of this, various method to indicate the trophic state of lake and reservoir was developed by many researchers. This research was conducted to evaluate characteristics and eutrophication of water qualitymfor small scale reservoir in Kunsan. On-site investigation to 5 reservoirs and laboratory experiment were carried out during four seasons from November, 2003 to July, 2004. Twelve items measured field ana a laboratory. Measured data was analyzed to quantitative method by multivariate approach and eutrophication index. The result is summarized as following. 1) Showing the characteristics of water quality for reservoir in Kunsan, Okgu reservoir and Oknua reservoir was exceeded 4 grades of agricultural water standard in TP, TN and COD. This means that eutrophication was gone much, therefore, water-purity control of reservoir need. While, Mije reservoir that is used to Kunsan citizens' recreation was good in water quality. But, water quality exceeded 4 grades of agricultural Dater standard sometimes. 2) As a results of correlation analysis between variables of water qualify, Interrelation between variables which is connected with eutrophication was expressed good relationship as above 6.000 in correlation coefficients. The correlation coefficient(r) between COD and chlorophyll-a, total phosphorus and chlorophyll-a, total nitrogen and chlorophyll-a were 0.750, 0.720 and 0.600 respectively. Therefore, Change of water quality can grasp according to eutrophication progress degree. 3) If do evaluate to eutrophication by quantitative method which is proposed by OECD, US-EPA and Forsberg & Ryding, in the case of chlorophyll a, Okgu, Oknua and Daewi reservoir was eutrophic state and Mije and Geumgul reservoir was mesotrophic state. But, estimation by TN and TP showed highly eutrophic state (hypereutrophic) in all reservoirs. 4) If do evaluate by eutrophication index which is Carlson's TSI, revised carlson TSI and Walker's index, in the case of chlorophyll a, TSI values of Okgu, Oknua and Daewi reservoir is eutrophic state more than 50 and Mije and Geumgul reservoir was mesotrophic state as range of $40{\sim}50$ in TSI value. But, in the case of TP as nutrients, all reservoirs showed highly eutrophic state which was exceed to 70 in TSI value. According to above results, the water quality for small scale reservoirs in Kunsan is progressing by trophic state. therefore, for continuous use as agriculture water, we had better do establishment of management plan about water quality.