不同质地土壤中镉运移的数值模拟与预测

NUMERICAL SIMULATION AND PREDICTION OF Cd TRANSPORT IN SOILS DIFFERENT IN TEXTURE

通过室内土柱实验,采用溶质运移的对流-弥散方程,模拟了饱和条件下重金属镉在不同质地土壤中的运移。结果表明,化学非平衡单点模型(One-site model,OSM)能较好地模拟镉在粉壤土、壤砂土中的运移(R2分别为0.810和0.901),而对镉在砂壤土中运移的模拟效果较差(R2=0.542)。OSM模型准确地模拟了土柱中镉运移的穿透时间,但是对穿透曲线拖尾部分的拟合效果欠佳。土壤对镉运移的阻滞作用与土壤理化性质有关,但是其机理还需要进一步研究。由于上层砂壤土对镉的强烈吸附,使镉的穿透时间较晚(10 pv),且不同土层界面处镉的浓度和吸附量变化明显。

Movement of Cd in soil profiles different in texture was simulated with the advection-dispersion equation for solute transport in an indoor experiment using soil columns. Results show that the chemical nonequilibrium one-site model （OSM） can be used to simulate Cd transport better in silty loam （R2 =0. 810） and loamy sand （R2 =0. 901 ） than in sandy loam （R2 = 0. 542）. The OSM can predict accurately the time for Cd to transport through the soil column, but not fit so well the trailing of the breakthrough curve of Cd. The retarding effect of the soil on Cd transport was related to soil physical and chemical properties, however, its mechanism needs to be studied further in depth. At the end, the parameters obtained from fitting with the aforementioned model were used to simulate transport of Cd in soil profiles consisting of soil layers. The simulated breakthrough curves didn＇t reveal the heterogeneity of the soil profiles. As a result of the strong sorption of Cd by the upper sandy loam layer, it took a long time （ 10 pv） for Cd to pass through the profile. And moreover, the variation of Cd concentration and adsorption quantity at the interface of two soil layers different in texture was obvious.