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C-1.1.3 Research on critical load estimation with soil response models to acidic substances

[Contact Person]

Junko Shindo
Global Agro-Environment Research Team, National Inst, of Agro-Environmental Sciences, Ministry of Agriculture, Forestry and Fisheries
3-1-1 Kannondai, Tsukuba. Ibaraki 305 Japan
Phone +81-298-38-8356. Fax +81-298-38-8199
E-mail shindo@ss.niaes.affrc.go.jp

Total Budget for FY1996-FY1998

22,928,000 Yen (FY1998; 6,9 10,000 Yen)

Abstract

To evaluate the acid buffering capacity of chemical processes, the following models were developed l) An extended constant capacitance model was valid to simulate SO₄^2- adsorption to soils, assuming protonation of surface hydroxyl groups and formation of outer sphere complex with SO₄^2-. 2) Dissolution rate constants of volcanic glasses were derived from dissolution experiment data and introduced into a existing mineral weathering model (PROFILE model). 3) A dynamic model was applied to the field condition and changes in soil solution chemistry agreed with the observations. According to the field measurements, base cation budget was investigated. Net production of base cation in soil was negative and contribution of plant uptake and release from soil were evaluated. Measurement of Sr isotope ratio made it possible to give tentative estimation of mineral weathering rate in the field. Comparison of measured weathering rate to the estimation with modified PROFILE suggested that the base cation is mainly supplied from sandy fraction of soil.

[Key Words]

Soil acidification model, Mineral weathering, Sulfate adsorption. Ion budget