水位波动带氮素迁移转化规律

Nitrogen migration and transformation in fluctuation belt of water table

为考察水位波动对非饱和-饱和土层中氮素迁移转化的影响,设计土柱实验装置Ⅰ和Ⅱ分别模拟水位稳定与波动两种情景,测定一个水位波动周期内地下水中NO-3-N、NO-2-N和NH+4-N浓度变化情况。结果表明,柱Ⅱ水位第1次下降柱内1#,2#,3#,4#采样点NO-3-N浓度均增大,增幅分别为6.5%、14.9%、15.33%和19.8%。水位上升时结果相反,分别降低17.3%、26.15%、50.29%和44.61%。第2次水位下降至初始位置4个采样点NO-3-N浓度再次增大,幅度分别为7.1%、10.6%、13.89%和7.76%。铵态氮呈相反趋势不同程度的变化。水位波动柱Ⅱ连通水槽内总氮量增加显著高于柱I水槽,即水位波动有利于波动带地下水中氮素垂向迁移,加重波动带以下地下水硝酸盐污染。因此,水位波动对氮素迁移转化的影响不容忽视。

This study was conducted to evaluate the migration and transformation of nitrogen in unsaturated- saturated soil under water table（WT） fluctuation. Soil column I and II with fluctuating and static WT were designed respectively. The concentration changes of NO3- -N, NO2- -N and NH4＋ -N were detected in a cycle of fluctuation. The results showed that the concentrations of NO3--N of 1^#, 2^#, 3^# and 4^# sampling points increased with the first WT descent in column II. The percent of increased concentrations were 6.5% , 14.9% , 15.33% and 19.8% , respectively. When the WT rose, the trend was opposite. And it reduced 17.3% , 26.15% , 50.29% and 44.61%. The NO3- -N concentration of the four sampling points increased again under the second descent of the WT to the initial position, the percent of increased concentrations were 7. 1% , 10.6% , 13.89% and 7.76%. Ammonium nitrogen was an opposite trend. The content of nitrogen in the tank connected with column U was higher than column I significantly under the WT fluctuation. Nitrogen was readily vertical transported in the fluctuation belt of WT. It aggravates nitrate pollution of the fluctuation belt of WT. Therefore,the importance of the WT fluctuation for the migration and transformation of nitrogen can＇ t be ignored.