非均质包气带三氮累积转化模拟砂箱试验

Sandbox experiment on the accumulation and transformation of nitrogen in the heterogeneous unsaturated zone

为研究包气带非均质结构对氮素迁移转化的影响,采用室内砂箱实验模拟了1.72mm/h降雨强度下NH4-N污染非均质包气带的过程。通过观测出水及土壤溶液中NH4-N、NO2-N和NO3-N质量浓度变化,分析探讨了NH4-N在含有两个亚粘土透镜体的非均质包气带介质中的迁移转化和累积时空分布特征。结果表明:经过89d物理吸附和微生物作用,出水NH4-N首先迅速增加然后逐渐减小,而出水NO3-N含量持续增加,其间NO2-N出现累积峰,系统最终达到平衡稳定状态;土壤溶液中NH4-N在两亚粘土透镜体上表面累积较多,NO3-N和NO2-N在上透镜体中的累积含量大于下透镜体;而砂槽上部土壤中出现明显的NO3-N累积,NH4-N和NO2-N则在下部土壤和亚粘土透镜体中累积较多。包气带介质质地、粗-细交互结构及降雨淋溶、水分运移对"三氮"的迁移转化和富集有重要影响。

Laboratory experiments were conducted using a sandbox to investigate the influence of unsaturated zone heterogeneous structure on the nitrogen transport and transformation.The circumstances of unsaturated zone contamination by ammonia-N were simulated under the rainfall intensity of 1.72 mm/h.Concentrations of ammonia-N,nitrate-N and nitrite-N were measured for the tested soils as well as the leaching water at different experimental times.Results indicated that the dynamic equilibrium was reached after 89 days＇ absorption of soil particle and biodegradation.Ammonia-N concentrations of the leaching water decreased after the peak in the beginning of the experiment,nitrate-N though was increased.The accumulated apices of nitrite-N were also observed during this period.An accumulation of ammonia-N in the upper surface of two sandy-loam interface was observed while concentrations of nitrate-N and nitrite-N in the upper clay lenses were higher.Nitrate-N was accumulated in the topsoil while an accumulation of ammonia-N and nitrite-N were found in the submerged soil.The results obtained from the study suggest that the unsaturated zone soil texture,layered-structure and water leaching were very important to the nitrogen transport and transformation.