Estimation Method of Fractions of Geological Environment and Atmospheric Fallout Based on Long-distance Transport and Domestic Origin of Sulfate in Headstream Water in Mountainous Area, Shikoku Island

Abstract

Temporal-special distribution of dissolved major anions at 64 sites in headstreams without any direct human activity of the Shikoku mountainous area in Japan was investigated from autumn to early winter from 2009 to 2012. It was proposed in this work that sulfate ion (SO₄²⁻) concentration in the headstream water was differentiated into fractions of geologic environment and atmospheric fallout consistent with long-range transportation and domestic origin. The geologic environment SO₄²⁻ was obtained to be 2-3 μmol L⁻¹ in metamorphic rock belts, limestone and granite areas, 21 μmol L⁻¹ in sedimentary rock belt, and 10 μmol L⁻¹ in chert areas. In the sites above phase boundary layer height and with less effect of domestic origin, a correlation of the fallout fraction of SO₄²⁻ increased exponentially against the elevation between the sampling site and the highest point in the catchment area. It was considered that the accumulation phenomena of SO₄²⁻ was caused by deposition from the upper atmospheric layer accumulating PM_2.5. The domestic origin of SO₄²⁻ under 480 m alt. of sampling site was increased in the order of categories faced to East Seto > West Seto > Bungo Channel > Kii Channel > Tosa Bay.