三江平原水田排水期氮素输出特征研究

如何系统地把握水田排水期氮素输出特征,已成为控制三江平原区域内规模化水田氮素污染输出的关键。系统地分析在水田排水期内,水田-沟渠系统中氮素的浓度分布特征,并利用同位素示踪技术对沟渠内氮素的削减机制进行探讨。结果表明：泡田排水期是水田氮素输出的主要时期,主要受施肥活动控制,氮素输出负荷占全年输出负荷的40%以上。不同排水期水田沟渠内氮素削减程度及机制具有明显差异：泡田排水期,沟渠内铵态氮浓度下降了46.93%,主要受硝化过程控制;降雨排水期,硝态氮浓度下降了24.00%,而铵态氮浓度上升了26.04%,主要受降雨混合稀释及土壤有机质矿化的影响;晒田排水期,铵态氮浓度下降了52.07%,主要与植被吸收、蒸发等因素有关。

The characteristics of nitrogen output during the paddy field drainage period

Identifying the characteristics of nitrogen output during the paddy field drainage period was critical to control of nitrogen pollution output in the reclamation paddy area. In this study, a paddy field and ditch system in Abujiao basin was selected as the study area. Combined with isotope tracer technique, the characteristics of nitrogen output and the reduction mechanism of nitrogen in paddy fields and ditch systems during the paddy drainage periods were systematically studied. The results showed that ponding drainage period was the most significant period for nitrogen output from paddy fields, mainly controlled by chemical fertilizer application. During this period, total dissolved nitrogen, ammonia nitrogen and nitrate nitrogen discharge load accounted for 42.57%, 69.73% and 54.89% of the year's total amount, respectively. There are distinct differences of nitrogen reduction mechanism in paddy fields and ditch systems for three drainage periods, indicated by results from variation characteristics of nitrogen and nitrate isotopic tracers. During the ponding drainage period, the ammonium nitrogen decreased significantly, almost half ammonium nitrogen reduced during six-day sampling period. Isotopic tracers showed that the removal process was mainly controlled by the nitration process. During the rainfall drainage period, the nitrate nitrogen concentration decreased by 24.00%, while the ammonium nitrogen increased by 26.04%. Mixed with rainfall (high δ ¹⁸O-NO₃ ^- values and low nitrate concentration) might explain the elevated δ ¹⁸O-NO₃ ^- values and linear reduction process of nitrate in the ditch. The fluctuation of ammonium nitrogen might be linked to the input of ammonium nitrogen in paddy fields and the minerali-zation of soil nitrogen. During the sunning drainage period, the reduction processes of nitrogen were more complicated, and isotopic tracer signals were not obvious. The ammonium nitrogen concentration decreased by 52.07%, which might be associated with absorption by vegetation.