Fluctuations in Bacterial Community and Environmental Factors at the Urban Spring Masugata

Abstract

Fluctuations in the density of heterotrophic bacteria, an acridin orange direct count (AODC) and environmental factors were studied every two weeks from March 1993 to October 1994 at the urban spring Masugata in the upper reaches of the Nogawa River in Tokyo, Japan. Although water temperature was a constant at 16°C throughout the year, the density of heterotropic bacteria in water fluctuated between 2.6×10 and 1.6×10³ CFU ml^-1, and the density of AODC ranged from 1.8×10³ to 5.5×10⁴ count ml^-1. These fluctuation patterns of bacterial density did not follow seasonal changes. Different fluctuation patterns were observed between the density of heterotrophic bacteria and that of AODC, and the values of the density of AODC were 2 to 3 orders of magnitude higher than those of heterotrophic bacteria. Annual changes in the density of heterotropic bacteria appeared to be affected by the rainfall. The fluctuations in AODC and the concentration of NO₃^--N had a significant positive correlation (p<0.01). Nitrifying bacteria were not detected, and the density of proteolytic bacteria, deaminating bacteria and nitrate reducer were lower than that of heterotropic bacteria.