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[MIS14-15] Sulfur denitrification and chemical denitrification in sulfide rich soils in Hachirogata polder
Generally, coastal sediments contain much sulfide which has been formed at seafoor under anoxic condition (Wijsman et al., 1972). Hachirogata polder located at a coastal area in Akita prefecture, was reclaimed from a brackish water lake and have much sulfide in the subsoil. Agricultural activities supply NO3- to the subsoil in the polder. Furthermore, the sulfide exposed under oxic condition can be oxidized, resulting in a decrease of soil pH. Therefore, our hypothesis were (1) sulfur denitrification will occur using sulfide as an electron donor for denitrification and (2) chemical denitrification also may occur under lower pH condition due to an oxidation of sulfide in the soils of Hachirogata polder.
[Method] The soils were sampled at three paddy fields (A-15, A-19, B-4) in Hachiroigata polder on May, 2017. The samples were collected from the depth of 0~50 cm by hand auger at three sites in each field and divided (Layer 1: surface soil, Layer 2: ~25 cm, Layer 3: 25~37.5 cm, Layer 4: 37.5~50 cm). Fresh soils (about 15 g) and 50 mL of treatment water were added to 150 mL bottle. Three treatments water was prepared: IEW(Ion exchanged water), N (KNO3: 5 mgN / L), N+S (KNO3+NaS2O3: 5 mgN / L,10 mgS/L). After adding , the gas-phase was replaced with N2 gas and incubated for 24 hours by shaking. After the incubation, we measured pH, NO3-, NO2-, SO42-, S2O32- in water solution and NO, N2O in the gas phase. The air-dried samples were analyzed for soil pH (H2O, KCl, H2O2), water soluble organic carbon (TOC) and total sulfur (T-S).