Experimental and numerical study on nitrate transport process through volcanic ash soil

Column experiments using two Japanese volcanic ash soils (Akahoya and Kuroboku soils) were carried out to improve understanding of solute transport characteristics through volcanic ash soil. As the contaminant source, a mixed solution of KNO₃ and K₂SO₄ was applied from the top of the column. Temporal changes of cations and anions in the effluent were measured at prescribed time intervals. Breakthrough curves (BTC) of anions for Akahoya soil show apparent retardation compared to BTC of anions for Kuroboku soil. Akahoya soil has a higher adsorption capacity of anions than Kuroboku soil. BTC of cations for Akahoya soil show apparent retardation compared to BTC of Kuroboku soil cations. Cations discharged together with anions are relatively strongly adsorbed in Akahoya soil. Cation exchange reactions were observed in both volcanic ash soils. Finally, transport processes of the above column experiment are examined by reactive transport simulations. The numerical results show that solute transport in volcanic ash soil can be reliably simulated with conventional cation exchange and anion retardation.