Understanding the relationship between meltwater discharge and solute concentration by modeling solute transport in a snowpack in snow-dominated regions – A review

The release of a disproportionately large fraction of solute into the earliest meltwater fraction, termed the ionic pulse, can be explained by the solute transport mechanisms. To this end, a classical standard advection-dispersion model was developed by Hibberd (1984), but it failed to simulate the long tail following the initial solute arrival. This limitation was overcome by the mobile-immobile water model (MIM) with a single rate-exchange coefficient for the ionic pulse and the negative relationship between meltwater discharge and solute concentration, which was not successfully to reproduce the positive relationship. Hence, the present paper reviews the progress of MIM for describing the solute transport for the two relationships. In addition, the positive relationship has been reported in the snowpack, and this phenomenon was investigated by making the exchange rate constant corresponding to water saturation in the model. This flow-dependent model captured important features of tracer variations but it failed to simulate the magnitude of oscillation of the tracer concentrations, thus implying additional physical processes in immobile water. The characterization of the behavior of both immobile and mobile water in snowmelt calls for either a double-permeability model or a triple continuum model for solute transport through fractured-porous media in groundwater.