Seasonal Fluctuation in the Number of Bacteria and its Relation to Environmental Factors in the Middle Course of the Tamagawa River

Abstract

A study was conducted on seasonal fluctuations in water quality, environmental factors and bacterial density in the river water and epilithon on the riverbed at Koremasa, marking the mid courseof the Tamagawa River in Tokyo. Water quality and environmental factors at Koremasa were largely influenced by the fluctuation of discharge at the study site. Consequently, the amount of P-compounds was correlated with the discharge summed for 10 days before the sampling day. The amount on the epilithon, however, fluctuated with discharge only on the sampling day. Thus, the turnover of P-compounds was thought to be slower than that of other elements in the river water. Principal component analysis of water quality and environmental factors showed that the first principal component was composed of the TDP, PO4-P, NH4-N, DOC, water temperature and ignition loss of the epilithon. The bacterial density in the river water and epilithon was determined by the acridine orange direct count (AODC), and plate count methodson mediaof three different compositions. In spite of marked fluctuations observed in bacterial numbers determined using these agar media, very slight fluctuations in the AODC were evident throughout the year. The bacterial densities calculated using each plate as a percentage of AODC were larger in the epilithon community than in flowing river water. The bacterial community in the epilithon on the riverbed must therefore be actively growing in the river ecosystem. © 1993, The Japanese Society of Limnology. All rights reserved.