The effects of principal constituents of acid rain on volcanic ash soil.

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The prediction method of ion concentration in soil solutions with repetitive addition of acid solutions that vary in equivalent ratios of nitrate to sulfate in volcanic ash soil was examined in this study. The method for prediction was composed of chemical equilibrium equation, electrical balance and conservation of mass in soil solutions. The results were summarized in the following.1) There was a tendency of HNO_3 solution > acid mixed solution including NO_3^- and SO_4^2^->H_2SO_4 solution on the quantity of dissolved aluminum with equal soil solution pH.2) The model could not simulate well concentration change of basic cations. However, it adequately described cumulative release of basic cations. This shows it is ability to estimate acid buffering capacity of cation exchange and mineral weathering.3) The model less estimated concentration of SO_4^2^- further than the measured value with addition of acid mixed solution, NO_3^- : SO_4^2^- is 0.75 : 0.25. However, it adequately described pH decreasing process and concentration change of basic cations. Therefore, it seemed that NO_3^-, which is difficult to be adsorbed in soil, is dominantly affected release of basic cations and pH decreasing in soil when acid rain including NO_3^- and SO_4^2^- deposited to volcanic ash soil.4) The simulation results agreed well with the measured values of pH and cumulative release of basic cations. These represent the most serious effects of the acid deposition on the soil. Therefore, parameters used in this simulation model are useful for predicting the main effects of the acid deposition on the Kanto loam subsoil.