Seasonal fluctuation in the number of bacteria and its relation to environmental factors in the Tamagawa River

Summary

A strong, positive relationship was found between bacterial density and chlorophyll concentration in the epilithon on the riverbed at Unazawa, on the upstream part of the Tamagawa River. However, at Koremasa, in the middle part of the river, the number of bacteria in the epilithon was related to the concentration of DOC, P-compounds and NO₃-N in water flowing on the riverbed. Environmental factors had no effect on bacterial density in the river water at either sampling site. The fact that the number of bacteria in the epilithon at a particular site was related to environmental factors at that site suggests that the bacteria on the upper surface of the stones of the riverbed form an autochthonous community. Most of the bacteria in the river water may be allochthonous species flowing in water.