[Relationship between water pollution and bacterial flora in river water]

To clarify the relationship between water pollution and bacterial flora in rivers, 132 samples of river water were collected at eleven stations of the Chikuma-Sai river system from April 1985 to March 1986, and 29 biological-physicochemical examinations for indices of water pollution were done using these samples. Species and genus of bacteria in 485 isolates from bacterial flora were identified. Although variations of bacterial flora were seen among sampling stations and sampling seasons, most isolated bacteria were Gram-negative (96.7-100%) with Pseudomonas (25.0-90.0%), Acinetobacter (0-43.8%) and Aeromonas (0-12.5%) occurring predominantly. The principal-component analysis of the data from water pollution indices indicated that the water pollution could be divided into two groups: One was categorized as organic pollution because of the strong relationship to the total plate count, the Bacillus number, coliforms, yeast and dissolved oxygen; the other as visible pollution because of strong relationship to transparency, chemical oxygen demand and suspended solids. Cluster analysis was applied to 19 indices of water pollution with strong relationships to the river pollution, indicating that five stages of river water pollution could be shown visually. The studies on the relationship between water pollution and bacterial flora in river showed that Pseudomonas, the coliform group, Pasteurella, Aeromonas, Acinetobacter, Achromobacter and Bacillus were strongly related to the organic pollution, and Flavobacterium, Moraxella and Pseudomonas (non-growth on MacConkey agar) to the visible pollution. It seemed that the more organic substances exceeded the capacity for self-purification of the river, the more the bacterial populations of Aeromonas, Pasteurella, Pseudomonas and the coliform group increased.