Quantitative Analysis of the Rate of Geochemical Weathering of Sulfur from Sedimentary Rocks Using Atmospheric Deposition, Concentration and River Discharge Data

Quantitative analysis of the rate of geochemical weathering of sulfur (S) from sedimentary rocks (GeoS) was conducted using concentration (Cs) and discharge (Qs) data from the Tedori River and atmospheric deposition (AtdepS) in the basin. First, S fluxes were calculated using 16 years of Cs and Qs data. The annual average discharge of S (TotalS) was estimated at 8597 ton·year-1 (117.3 kg·ha-1·year-1). Of this, 1331 ton·year-1 was AtdepS (18.2 kg·ha-1·year-1) and another 7266 ton·year-1 was GeoS (99.1 kg·ha-1·year-1). Monthly changes in TotalS were investigated, which showed that GeoS was highest in summer, because of the air temperature, while AtdepS peaked in winter because of seasonal wind. Using Qs and AtdepS corrected for altitude, TotalS, AtdepS and GeoS were estimated at six sites, and among these sites we found that the TotalS per unit area values were random, depending on the site characteristics. In particular, the discharge from the Kuwajima site was remarkably high suggesting that the sedimentary rocks at this site had higher pyrite content than at the other sites. Finally, we also assessed the relationship between the characteristics of sedimentary rocks and GeoS in a range of rivers in the Hokuriku Region, and found that there was a close relationship between concentrations of SO42- greater than 10 mg·l-1 and sedimentary rocks containing the pyrite group. In addition, we estimated that the influence of GeoS was present when the concentration of SO42- in river water was greater than 2 - 3 mg·l-1 in the Hokuriku region.