Improving the Estimation of Salt Distribution during Evaporation in Saline Soil by HP1 Model

Restricted by the development of the transient flow and solute reactive transport models for unsaturated soil, empirical functions have been used previously to calculate the mass of dissolved or precipitated salt when they have to be taken into account. Besides, the solute reactive transport process has often been inferred based on measurements that cost lots of time and manpower. HP1 model coupled with PHREEQC provides a suitable tool to improve the estimation of salt distribution during evaporation in saline soil, where the salt dissolution and precipitation cannot be ignored. In this study, we compare the performance of a standard solute transport (SST) model and the HP1 model to examine the improvement of salt distribution estimation. Model results are compared with experimental data sets from four field lysimeters. These columns were exposed to NaCl solution with different concentrations (3, 30, 100, and 250 g/L) and were undergoing the same strong evaporation boundary condition. The pre-existing CaSO 4 , NaCl and Na 2 SO 4 loads were 1.15, 0.47 and 0.23 g/(100 g of soil), respectively. Simulation results show that HP1 ameliorates the overestimation of salt content by SST in deeper soil due to the absence of dissolution of pre-existing soluble salts, and prevents the concentration of the solute from exceeding the solubilities which would occur in SST-result. Additionally, HP1-predicted results can help trace the transport process of each solute. Based on the results, we strongly suggest that the management of fields sensitive to salt content should make use of a coupled flow and chemical reaction model.