不同数学模型模拟非均质土壤溶质大尺度运移的对比分析

Comparison of alternative models for simulating solute transport in heterogeneous soil at large scale

利用长度为1250cm的非均质土柱中NaCl运移的试验资料,分别应用对流-弥散方程(CDE)、两区模型(TRM)、对流对数正态传递函数模型(CLT)、分数微分对流-弥散方程(FADE)和连续时间随机游走理论(CTRW)等数学模型对长土柱中溶质的运移过程进行模拟,对比各个模型的模拟结果,并从模型机理上分析模拟结果差异的原因,探讨各种模型描述非均质土壤中溶质大尺度运移的适用性。结果表明:CDE、CLT和FADE难以描述非均质土柱中的不规则穿透曲线,但FADE对穿透曲线尾部的模拟精度比CDE和CLT有所提高;与CDE、CLT和FADE相比,两者的模拟结果与实测值吻合更好,在穿透曲线尾部CTRW的模拟值略大于TRM的模拟结果;两者不仅较好地描述了穿透曲线的提前穿透和拖尾等不规则特征,而且捕捉到了非均质土柱中溶质不规则运移程度随着尺度增加而减弱的变化趋势。尽管TRM和CTRW均能很好地模拟长土柱试验所研究的饱和非均质土壤中保守性溶质的一维运移问题,但对于复杂的溶质运移问题的模拟,TRM和CTRW各有其优缺点。

This study compared five different models for simulating solute transport in a 1 250cm long and highly heterogeneous soil column. The five models were：the convection-dispersion equation（CDE）,two-region model（TRM）, convective lognormal transfer function model（CLT）,fractional advection-dispersion equation （FADE） and continuous time random walk（CTRW）. The results indicated that the CDE, CLT and FADE were all unable to describe the anomalous measured BTCs adequately, and FADE provided somewhat better simulation results at the tailing part of the anomalous BTCs than CDE and CLT. The TRM and CTRW provided nearly similar good simulation results except that the modeling results of CTRW were somewhat larger than those of TRM at the tails of the BTCs. With respect to CDE, CLT and FADE, both TRM and CTRW were better to capture the full evolution of the measured BTCs at different travel distances, especially for the early and long tailing parts. Moreover, the degree of anomalous transport behavior in the heterogeneous soil column was reduced with transport scale, and TRM and CTRW detected this trend adequately. To compare the applicability of the TRM and CTRW in evaluating more complex solute transport issues in heterogeneous soils, the strengths-weaknesses analysis of them was presented in this study.