Diatom assemblages of lake bed sediments in Lake Koyama-ike, Tottori Prefecture, western Japan

摘要

Lake Koyama-ike, located in Tottori Prefecture, western Japan, is a coastal brackish lake facing the Japan Sea. Since 1983, this lake has been characterized by artificial fluctuation of its lacustrine water quality. We collected lake bed surface sediments from 25 sites of the lake on July 10, 2010, corresponding to a period when the water salinity had been controlled to be in the range 150–1,000 mg/l. The diatom assemblages in the samples comprised a total 137 diatom species belonging to 38 genera. Among them, the major 11 species belonging to 8 genera, i.e., Aulacoseira granulata , A. ambigua , Cyclostephanos dubius , Cyclotella atomus complex (C. atomus var. atomus and C. atomus var. gracilis ), C. meneghiniana , Cyclotella sp., Diploneis sp., Fallacia florinae , Lindavia praetermissa , Thalassiocyclus lucens , and Thalassiosira lacustris , occupied more than 70% of all samples. Results of the clustering analysis indicate that similar diatom assemblages were found at most sampling sites and their distribution pattern was unclear. We interpreted the axes of the principal component analysis as water salinity (axis 1) and distance from the lake's shore (axis 2), respectively. Totally, seven of the predominant diatom species, except for L. praetermissa , F. florinae , and two unidentified species (Cyclotella sp. and Diploneis sp.), were common in the periphytic diatom flora near the lake's shore.