Effects of Water Path Flow and Evaporation on Nitrate Nitrogen Movement through Unsaturated Soil

通过实验、计算机模拟和地下水水质观测，研究了径流和蒸发对非饱和土壤中硝态氮(NO3-N)运移的影响。地下水水质的时间变化为了了解自然气候条件下天然盆地中NO_3-N的运移情况，观测了地下水中NO_3-N浓度的时间变化。观测结果表明：(1)地下水水质对降雨事件的响应；(2)地下水水质对降雨事件的快速响应，反映了水流等急流的影响；(3)响应的时间和大小受土壤含水率和降雨量的影响。通过模型多孔介质实验和计算机模拟，研究了非饱和介质中水路形成的机理和条件。结果表明：(1)水路具有分形性；(2)毛管力和重力的共同作用决定了水路的形状；(3)毛管力和重力的综合作用受孔隙大小和方向的影响；(4)降雨量对水路形状的影响是可变的。土壤入渗和蒸发引起的硝态氮运移通过模型土壤试验和计算机模拟，研究了入渗和蒸发引起的硝态氮运移。结果表明：(1)硝态氮在多孔介质中的可移动性小于水分；(2)蒸发导致硝态氮向土壤表面迁移，但对硝态氮的渗流深度影响不明显；(3)降雨量影响大颗粒在暴雨中的渗流深度；(4)小颗粒向土壤表面的迁移明显。

Effects of water path flow and evaporation on nitrate nitrogen (NO_3-N) movement through unsaturated soils were investigated by experiments, computer simulations and observations of groundwater qualities.1. Temporal Changes of Groundwater QualitiesTo get some informations on NO_3-N movements in natural basins under natural weather conditions, the temporal changes of NO_3-N concentrations of groundwaters were observed. Observed results showed that (1) groundwater qualities responded to rainfall events, (2) quick responses of the qualities to the events suggested the influence of such quick flow as water path flow, and (3) the timing and magnitude of the responses were influenced by water contents of soils and rainfall amounts.2. Water Path Flow through Unsaturated MediaThe mechanisms and conditions of water path formation in unsaturated media were investigated by experiments using model porous media and by computer simulations. The results showed that (1) the water path developed fractal patterns, (2) the combined effect of capillary force and gravity determined the shape of water path, (3) the combined effect was influenced by sizes and directions of pores, and (4) the effect of rainfall amount on the water path shape was changeable.3. Nitrate Nitrogen Movement Caused by Infiltration and EvaporationNO_3-N movement caused by infiltration and evaporation were investigated by experiments using the model soil and by computer simulations. The results showed that (1) NO_3-N was less mobile than water in porous media, (2) evaporation caused NO_3-N movement toward soil surface but did not make remarkable chage of the depth of NO_3-N percolation, (3) rainfall amount influenced the depth for big particles with heavy rainfalls, and (4) NO_3-N movement toward soil surface was remarkable for small particles.