京杭运河常州段泥水界面无机氮交换过程模拟研究

分别在枯水期、平水期、丰水期利用原柱样静态释放实验对京杭运河常州段4个点位的无机氮界面交换过程进行模拟,并借助模拟结果对运河不同形态氮的界面循环过程进行了初步探讨。结果表明,全年NH+4N界面交换特征均表现为底泥向上覆水体释放,平均交换速率比较结果为平水期182.3mg/(m2·d)]>丰水期94.0mg/(m2·d)]>枯水期29.5mg/(m2·d)],而底泥污染严重的下游点位释放通量高于其他断面;丰水期底泥为上覆水NO-3N的源,平水期和丰水期则成汇,且平水期底泥平均吸附速率若为枯水期的6倍;全年NO-2N交换过程表现底泥吸附的特征,枯水期交换速率极低,全年底泥DIN(总无机氮)输入量>输出量,底泥对高浓度上覆水NO-3N的吸附作用可能是底泥污染逐渐加重的原因。

Simulated Study on the Exchange of the Inorganic Nitrogen （IN） at the Sediment-water Interface in Changzhou Segment of the Grand Canal

The behavior of different nitrogen forms at sediment-water surface was studied, based on the simulated experiments on the release of IN at 4 sites in high flow period, mean flow period and low flow period in Changzhou segment of the grand canal. Results showed that NH＋4-N was released from sediment to overlying water all the year. The exchange rates were 182.3mg/（m^2·d） during mean flow period, 94.0mg/（m^2·d） during high flow period and 29.5mg/（m^2·d） during low flow period following descending order, while the flux mass of downstream sites that was seriously polluted was proved to be higher than those at other sites; sediment was acted as the main source of NO-3-N in overlying water in high flow period, while it became the sink in the mean and low flow periods. In addition, the adsorption rate during mean flow period was 6 times as that in low flow period. The exchange behaviors of NO-2-N were represented as the characteristics of sediment adsorption, while an extremely low exchange rate occurred in low flow period. Generally, the amount of DIN inputs into the sediment was much higher than the output from the sediment. Sedimentary adsorption on the NO-3-N with high levels in the overlying waters might be the reason why the sediment pollution aggravated gradually.