三江平原农田源头排水沟渠截留排水中氮素动态

Dynamics of Nitrogen in Farmland-Originating Drainage Water Retained in Ditches in the Sanjiang Plain

通过小尺度野外原位试验,研究排水沟渠水体、底泥和植物中氮含量的变化规律。结果表明,随水体停留时间增加,沟渠对水体氮素的净化能力增强,认为停留8 d左右较适宜。沟渠对NH4+-N的截留率大于TN和NO3--N。渠水停留11 d时,4条试验沟渠〔氮浓度高、磷浓度低(NHPL),氮浓度高、磷浓度高(NHPH),氮浓度低、磷浓度低(NLPL),氮浓度低、磷浓度高(NLPH)〕对NH4+-N的截留率均达100%,对NO3--N的截留率分别为84.63%、84.35%、75.67%和76.14%,对TN的截留率分别为88.02%、89.89%、90.88%和88.53%。试验结束时沟渠表层(0～15 cm)底泥氮含量降低,植物氮累积量远大于进水TN总量,说明植物生长同时吸收了水体、土壤和底泥中的氮,建议在秋季适时收割植物,以避免植物分解导致二次污染。

A small-scaled in-situ field experiment was carried out to study dynamics of nitrogen in farmland originating drainage water retained in drainage ditches and in sediments and plants in the ditches as well. Results show that the longer the water is retained in the ditch, the more the nitrogen in the water is sequestrated by the ditch, if the water is retained in the drainage ditch for 8 d or so as recommended. The sequestration rate of NH4^＋ -N was higher than that of TN and NO3^- -N. When the water was retained in the ditches for 11 d, NH4^＋ -N sequestration rate reached 100% in all the four ditches with drainage water different in N and P concentrations, i.e. NHPL （high N concentration and low P concentration）, NHPH （high N concentration and high P concentration）, NLPL（ lowN concentration and low P concentration） and NLPH （low N concentration and high P concentration）, whereas NO^3- -N sequestration rate was 84. 63%, 84. 35%, 75.67% and 76. 14%, and TN sequestration rate 88. 02%, 89. 89%, 90. 88% and 88.53%, respectively. At the end of the experiment, it was found that N content in the surface layer （0 -15 cm） of sediments in the ditches decreased and N accumulation in the plants growing in the ditches was much higher than TN in incoming water, suggesting that the plants absorbed N from the waterbody, soil and sediments at the same time for growth. It is, therefore, recommended that the plants in the ditches should be harvested duly in fall to avoid secondary pollution of N from plant decomposition.