Chemical studies of a 200 meter core sample from Lake Biwa-ko
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A deep core sample of 197.2 meters in length was obtained by the technical assistance of MIZUNO and AOKI from the bottom of about 65 m in water depth at the central part of Lake Biwa-ko. Chemical analyses were conducted about the organic components and the inorganic elements in the core sample and the following results were obtained :<BR>1). The content of total carbon (Ct) ranges from 4.4 to 14.7mgC/g of dry sediments and varies with core depth periodically showing four remarkable peaks at 15m, 90m, 140m and 180m. The vertical profile of the content, however, shows a decreasing tendency with depth.<BR>2). Ratio of total carbon (Ct) to total nitrogen (Nt) ranges from 4.3 to 9.8 and fluctuates with core depth showing two remarkable peaks at 130m and 180m.<BR>3). Total carbon (CH<SUB>2</SUB>O<SUB>2</SUB>) and total nitrogen (NH<SUB>2</SUB>O<SUB>2</SUB>) in the samples treated with H<SUB>2</SUB>O<SUB>2</SUB> indicates carbonate carbon and ammonium nitrogen included in clay mineral lattices respectively. Ratio of CH<SUB>2</SUB>O<SUB>2</SUB> to NH<SUB>2</SUB>O<SUB>2</SUB> fluctuates vertically in a range from 1.8 to 8.9. This vertical distribution shows four remarkable peaks at 56m, 85m, 130m and 180m in core depth. Each of the former three peaks corresponds to each of the palaeomagnetic reversals of Blake, Biwa I and Biwa II discovered by KAWAI <I>et al</I>. (1972) respectively. These peaks also correspond to the peaks of percentage of sediment particles coarser than 44μ, which were found by YAMAMOTO.<BR>4). The contents of organic carbon (Corg.) and organic nitrogen (Norg.) were estimated as follows : Corg.=Ct-CH<SUB>2</SUB>O<SUB>2</SUB> and Norg.=Nt-(NH<SUB>2</SUB>O<SUB>2</SUB>+NNH<SUB>4</SUB>), where NNH<SUB>4</SUB> denotes ammonium nitrogen.<BR>The content of Corg. varies similarly to Ct showing four remarkable peaks at 15m, 90m, 140m and 180m. The former three peaks correspond to the warm periods which were recognized by FUJI through his palynological study (FUJI and HORIE, 1972). The four peaks also correspond to the minimum values of Corg./Norg. ratio. This fact suggests that the four sediment layers corresponding to the four peaks are rich in proteinous substances, thus relatively high production of this substances has arisen in the lake water in the warm periods.
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日本陸水学会 | 論文
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