Process of Formation of Potentially Acid Sulfate Soils from Central Kyushu, Japan : Sulfur Isotopic Approach
2000 年 44 巻 1 号 p. 15-20
詳細
2000 年 44 巻 1 号 p. 15-20
The potential acid sulfate soil formation from central Kyushu, Japan was studied using stable isotope technique. Subsurface soil horizons developed from fluvio-marine sediments around Chikugo river estuary and from peaty sediments within Aso Caldera contain significant amounts of sulfide-sulfur of which a part is easily oxidized to form active acid sulfate soils (pH: around 3 in water suspension) upon aerial oxidation. Sulfur isotope composition (^<34>S/^<32>S ratios, commonly designated as δ^<34>S) of air-dried materials for water-soluble sulfate-sulfur and sulfide-sulfur fractions oxidizable with warm hydrogen peroxide showed distinct δ^<34>S values ranging from -32.0 to +8.1‰ which are lighter than those of seawater-sulfate (Chikugo river estuary; δ^<34>S=+21‰), local groundwater (within Aso Caldera; δ^<34>S=-2.3 to +23‰), fresh volcanic ash (δ^<34>S=+3.0‰), and hot spring (δ^<34>S=+0.8 and +2.0‰) sulfates. Sulfate-reducing bacteria are responsible for formation of active sulfide with such low δ^<34>S values. Sulfides which are easily oxidized into sulfuric acid upon air-drying tend to be depleted with heavy sulfur (^<34>S), relative to unoxidized sulfides and elemental sulfur.
