島根県湖陵町蛇池の環境地質

Geochemical amlyses of bottom sediments and cored samples have been carried out to evaluate environmental changes of the non-marine Lake Jaike of San'in district．Soils of surrounding areas and sediments of the Lake Jinzai of brachish environment are also examined for comparative study．Cored samples with 70cm length showed gradually increasing concentrations of arsenic（from 12 to 31 ppm），lead（from 24 to 31 ppm），zinc（from 95 to 144 Pppm），phosphorous（P_2O_5，from O.09 to O.28 wt%）and total iron（from 8.20 to 11.15 wt%）but with relatively consistent values in chromium（75-83 ppm）and thorium（11-12 ppm）suggesting that the variations were caused by environmental change related to the land modification．Abrupt projection of total sulfur（TS）contents in this profile is suggestive of an excess supply of common fertilizer such as sulfate ammonium，of which the event was coincident to an extinction of fishes in 1988．In contrast to the decline of TS，phosphorus increased steadily indicating switching of aglochemicals．