Hydrological Research for Lake Acidification

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Lake water of Joetsu district in Niigata Prefecture have been analyzed for chemical and isotopic compositions in order to know the deciding factors of lake water pH values. Similarly, those of the Pacific coast side lakes have been investigated. The field researches were conducted in November 1999 and May 2000.The results of this study is summarized as follows ;1 There were some acid lakes in this district. But the pH values had a large variation, to be necessary to continue the researches.2 The pH values were low where the residence time of the groundwater inflow was relatively short in teh catchment area.3 The values of electric conductivity was effected by the position and origin of the lakes and was useful to know the mixing ratio of lake water and groundwater.4 There was a week correlation between the pH values and the chemical composition of lake water.5 There was a clear distinction in the isotopic composition between the lakes in the Japan Sea side and those in the Pacific Ocean side.