瀬戸内海沿岸海域における細菌叢 : Ⅰ. 福山湾における各種汚染指標菌数と有機汚濁の関係

瀬戸内海の水質を評価するために、そこに分布している微生物叢、特に細菌叢の動静を知る必要があると考え、従属栄養細菌全体に注目して、その動静を調ペることを試みた。今回はその第1段階として、福山市沿岸海域に3定点を設けて、一般細菌数を調べ、CODとの関係を検討した。その結果を以下に要約する。1.CODは赤潮発生時を除くと、1.1～7.8ppmと8ppm以下であった。2.pHは全体を通じて7.8～8.5の範囲にあった。3.これらの結果から、赤潮発生という、異常な時を除けば、各採水地点の海水はpH7.8以上8.3以下、COD8ppm以下という環境保全の基準にほぼあてはまっていた。4.CODを季節別にみると、5月～6月に1.9～18.6ppmと高く、7～8月の夏季には3.4ppm以下と逆に低かった。5.一方、細菌学的な面から検討すると.一般細菌数は10⁴～10⁶ と大体一定のレベルにあったが、汚染指標菌数は変動が大きく、特に大腸菌数は0～1.1×10⁴と大きかった。6.CODが3.4ppm以下と低い夏季でも、一般細菌数は10⁵、大腸菌群数は10³～10⁴と高いレベルを維持している。7.CODと細歯数との間には、特に比例関係はみとめられなかった。8.以上の結果から.瀬戸内海に流入する各種汚染物質の濃度に関係なく、一般細菌や汚染指標菌は常にあるレベル以上の量が存在しており、水質評価に物理的-化学的要因の外に、細菌学的な面からの検討を加える必要があることが示唆された。

For the evaluation of the sea water in the Seto Inland Sea, we thought it necessary to investigate first the microbial ecosystem of sea water. Therefore we attempted to check the distribution of heterotrophic bacteria and their activities in the coastal sea water of the Fukuyama bay. The MPN values of viable counts, E. coli, coliforms and enterococci were calculated first then the relation of these values with the COD values in the sea water of three other stations of Fukuyama bay were discussed in this paper. The results obtained in 1980 have been summarized: 1. The pH values were between 7.8 and 8.5 in almost all the sea water samples. 2. The COD values stayed within 8ppm except for the times red tide occured. 3. From these results, it appeared that the quality of the sea water under investigation conformed to the official in Japan of sea water analysis. Indeed this criterion requires a pH amount between 7.8 and 8.3, and COD value within 8 ppm. 4. The seasonal changes of COD values were discussed. It appeared that in May to June the values were higher (1.9 to 18.6 ppm), while those in July to September were within 3.4 ppm. 5. On the other hand, when our bacteriological investigations were made, we found that the viable counts were in levels of 10⁴ to 10⁶ MPN per 100ml, while the values of most of the E, coli, coliforms and enterococci showed in large variation, E. coli, that is, 0 to 1.1 X 10⁴. 6. Although the COD values were within 3.4ppm, the viable counts and coliforms remained in 10⁵ and 10³ - 10⁴ MPN ranges respectively in the hot summer (July to September). 7. The proportion between the COD values and the MPN values of these bacteria was very small. 8. From these results, it could be deduced that considerable numbers of bacteria, mostly fecal indicator organisms, thrown away in the Seto Inland Sea had no relations with quantity of all sorts of contaminants, and consequently a bacteriological investigation was required together with a physico-chemical one for the evaluation of the sea water.