河川水質の統計学的研究-3-木曽川水質への多変量解析の適用
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概要
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We tried to know the characteristics of the water quality and its variation in Kiso river with time series analysis, correlation analysis, principal component analysis and factor analysis. The value from the survey of the water quality of the public water area in Nagano, Gifu and Aichi prefecture from 1973 to 1979 were used and water temperature, pH, DO, BOD, COD and SS were employed as the numerical variables. The following items were summarized: 1. To remove the seasonal variation in regard to water temperature and DO, which were recognized as a twelve month-cycle with time series analysis, the revised values (revised series) were calculated, which were obtained by dividing the original values from the survey (original series) by the seasonal index obtained with transfer mean method. It was recognized that the seasonal variation was removed at all measuring places with the run test on the revised series. 2. From the correlation analysis, substances measured as SS could be mainly associated with the fraction of COD at the upper stream and with the fractions of BOD and COD at the lower stream. The increase of the organic corruption was particularly found at the lower stream. 3. From the principal component analysis, both the eigen value and the ratio of contribution of the first and the second principal component decreased by removing the seasonal variation. The revised series required the fourth principal component to get the 80% ratio of the cumulative contribution. On the eigen vector in the original series, water temperature and DO showed the high value in the first principal component, BOD and SS in the second principal component and BOD in the third principal component. Since in the revised series, water temperature and DO were under the second principal component, and COD and SS showed the high value in the first principal component, the effect of the removal of the seasonal variation was clear. 4. On the revisd series, the factor loading calculated was projected along the axis of the principal components. These projections showed that COD and SS at theupper stream, and BOD and COD at one place of the lower stream were found in each one group. From the rotation by the standard varimax method, the character of every factor became clearer. The difference of the quality between the upper and the lower stream was observed and it became clear that the first factor was the index of the organic corruption, the second was of water temperature, the third was of pH, and the fourth was of SS. 5. From the sqare pattern with the factor examination marks, places of the main stream of Kiso river measured could be classified into three groups: the upper stream where the average water quality was rather good but SS having the COD character was contained, the middle stream where the water quality was stable, and the lower stream where the organic corruption increased.
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