Environmental magnetic-study of irrigation ponds sediment

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1. The method of sampling sediment up to I m in depth from bottom of a lake to about 4 m, without disturbing the surface was established.2. The existence or nonexistence of magneto tactic bacteria has clarified by the pond, and it does not depend on sediment. Moreover, magneto tactic bacteria were distributed in the surface sediment centering on the depth of about I cm, and in many cases, 3 cm, even if they were deep, they were not observed by 5 cm or less.3. The method for separating contribution of the magnetic mineral particle currently not fixed (movable component) and contribution of the magnetic particle already fixed (fixed component) by freezing samples was developed. Although a fixed component may decrease greatly when a fixed component transformed into a movable component in 'the process of defrosting and a freeze, the possible increase in the fixed component deduced by the process is ten or less percent of both sum total in general.4. The movable component was only about 30 - 600/0 even at the surface. In comparatively many cores, the value was seen decrease as it became deep until it became in depth of 10-20 cm.5. There was two cores in which the movable component increases 2000 or more in the depth of 20 cm or deeper. By these cores, the partial inversion phenomenon of the acquisition time of detrital remanent magnetism may arise. A certain amount of correlation between a frequency dependence of initial susceptibility and the movable component was seen in these cores. It is thought that this is because the rate of small magnetite particle of stable single domain is changed and it has contributed to the change of a movable component by change of deposition environment.