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

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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.