Abstract
Longitudinal pattern in the distribu tion of Achnanthes japonica and A. convergens in the Kwang River (Kwangchun), South Korea, and environmental factors affecting their distribution are discussed. Diatom samples were collected from twelve different stations in four times; May, August, October in 1991 and January in 1992. These two species showed different distributional patterns. Achnanthes japonica mainly occurred in the upper reaches with high relative abundance. In the lower reaches, it decreased markedly or disappeared. Achnanthes japonica appears to require relatively high current velocity and not to be able to tolerate salinity, and hence it can be regarded as a typical species in the upper reaches of the running waters, having an oligosaprobic condition and high current velocity. On the contrary, Achnanthes convergens occurred in the whole stations in every sampling time. Requirement for the current velocity of A. convergens appears to be weak, and it can be tolerate somewhat saline water. Thus, A. convergens distributes widely, even in a slightly brackish water.
