琵琶湖内湖の底質土の理化学性に気候変動が及ぼす影響

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The total carbon / total nitrogen (C/N) ratio of organic materials, the particle size distribution and the clay mineral composition of the soil horizons which had been sedimented in the bottoms of Lagoons Nisinoko and Syounakanoko during the last 18,000 years were examined by a CN corder method, a laser scattering method, a X-ray diffraction method and thermal analyses. The analytical data were discussed by relating with the changes of past climates. The results are summarized as follows: The C/N ratio of soil horizons formed in the terms of warm climates were lower than that of the cool time. It is suggested that the decomposition rate of organic materials had been accelerated under the condition of relatively high temperature, accordingly. The particle sizes of the horizons corresponded to the terms of cool climates were coarse compared with the warm terms, in the shallow lagoons such as Nishinoko and Shounakanoko. The coarse textures of these horizons should be caused by the following reason, i.e., the lagoons shifted relatively to the part of upper stream in proportion to the decrease of water level in the lake and the lagoons as the decreased of precipitation during the cool term. On the other hand, the lagoons were filled by water in the warm term as the increase of precipitation, and the soil texture became fine in the corresponding horizon. The contents of kaolin minerals are high relatively in the horizons associated with the terms of warm climates, while mica minerals and smectite were rich in the cool terms. It is generally said that the genesis of kaolin minerals is accelerated under the condition of hot or warm climate. The lower soil-horizons were abundant in chlorite compared with upper ones, which suggested an influence of diagenesis. Amorphous materials were especially high in the clay fractions from the horizon of B.P. 6,000, which should be influenced by "Akahoya", the tephra from Kikai Caldera.
日本ペドロジー学会の論文
2000-06-30

琵琶湖内湖の底質土の理化学性に気候変動が及ぼす影響

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