Abstract
We constructed a numerical model that simulates a finite system where solute transport and denitrification and isotope fractionation associated with denitrification simultaneously occur. We described the system simply as one dimensional convective-dispersive equation with reaction in finite length, solved the equations numerically by FDM, and examined the effect of dispersion on the change of solute concentration and isotope ratio through the system.
As Peclet number decreases and as the unreacted fraction of nitrate decreases, the relationship between the unreacted fraction and delta-15 value of effluent diverts from the relationship without the effect of solute transport, and the apparent fractionation factor diverts from the true one. The ratio of apparent to true (per mill) enrichment factors decreases as dimensionless reaction rate constant κ14N increases and Peclet number Pe decreases, not the ratio κ14N/Pe but both κ14N and Pe affect the ratio of apparent to true (per mill) enrichment factors, in this point, the apparent fractionation factor calculated by this finite system differs from that calculated from solute and isotope ratio distributions in the semi-infinite system.
