Studies on the characteristic behavior of pollen grains and spores in Lake Hamana on the Pacific coast of Central Japan.

Abstract

The relative abundance of pollen grains and spores in the surface sediments at 22 stations of Lake Hamana was characteristic for each station. The entire area of the lake can be divided into four regions based on the proportions of the following major components, i.e. Pinus, Cryptomeria, Gramineae and fern spores. Type I; The region covering the main lake and Lake Shonai, except the river mouths, where the frequencies of Pinus and Cryptomeria were high, and Pinus was more common than Cryptomeria (St. 3 and 5 through 10, 12, 17 through 19, 21 and 23). Type IIa; The regions at the river mouths flowing into Lake Shonai and of the Shin River, where the frequencies of Gramineae were high, and Pinus was more common than Cryptomeria (St. 1, 2 and 4). Type IIb; The region in Lake Inasahosoe, where the frequencies of both Gramineae and fern spores were high, and Cryptomeria was more common than Pinus (St. 13 through 16). Type IIc; The region in Lake Inohana, where the frequencies of both Gramineae and fern spores were high, but Cryptomeria was less than Pinus (St. 11).The pollen grains and spores in Lake Hamana were considered to be supplied for the most part from the rivers. The frequencies of Pinus and Cryptomeria were high in the sediments obtained from the main lake in contrast to those of Gramineae and fern spores which were relatively high in the satellite lakes as well as at the river mouths. The fact indicated that the sedimentation rates of Gramineae and fern spores were higher than those of Pinus and Cryptomeria. In addition, there was a distributional difference between Pinus and Cryptomeria. With increasing distance from Lake Inasahosoe, the frequencies of Pinus became high in contrast to those of Cryptomeria. In the sucrose density gradient experiment, the specific gravity of Pinus pollen with air-sacs containing water was evidently higher than that of Cryptomeria. Accordingly, it was suggested that the distribution of Pinus pollen grains in the sediments might be mainly affected by the sizes and directions of surface water currents during the period before air was exchanged with water in the air-sacs.