Saturday, 15 July 2006

Research of Charcoal Particles in Andosols around Lake Biwa, Central Japan.

Jun INOUE, Osaka City Univ, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka, Japan

Andosols are distributed widely in Japan. Previous studies showed black plant particles are included in Andosols that are considered as charcoal particles. However some researcher consider that these black plant particles are related to origin of the Andosols in Japan directly or indirectly, black plant particles has not been examined sufficiently. This study confirmed that black plant particles in Andosols distributed around Lake Biwa are charcoal particles by observation of reflectance microscopy, reflectance measurements and H/C ratio analysis. These black plant particles have white shining under reflectance microscope, higher reflectance (0.2-2.6%) and lower H/C ratio (0.471) similar to modern charcoal. These results provide that these black plant fragments are probably charcoal particles. Therefore, charcoal particles are included in Ando-soils at least in this area. By comparing to previous laboratory experimantal study, the values of reflectance and H/C ratio suggest that charcoal particles were probably generated at a temperature of ca 300 to 500 degree C and were probably generated from forest fire or grass fire. The sizes of some charcoal particles included in Andosols are over 0.5mm. Ohlson and Treyterud (2000) suggests that occurrence of macroscopic charcoal (over 0.5 mm) in forest soils provides a solid evidence for local fire influence. Terefore, fires occurred Andosols distributed around Lake Biwa in a past. The vertical charcoal particles concentration increases from upper than AT Volcanic (dispersed at ca 29,000 cal yr BP) glass-rich stratum to K-Ah Volcanic (dispersed at ca 7,300 cal yr BP) glass-rich stratum. This tendency is almost consistent with that of charcoal concentrations in Lake Biwa sediments. Therefore, some charcoal particles in Lake Biwa sediments are probably derived from fires in Andosols distributed areas around Lake Biwa.

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