灌区沟塘湿地对稻田排水中氮磷的原位削减效果及机理研究

Effect of pond wetland on N and P removal in drainage water from paddy field and its mechanism

沟塘系统是控制农田面源污染的有效措施,本文通过修整灌区内承泄沟塘、重建其水生植物系统,研究了沟塘湿地对稻田排水的原位削减能力及机理。试验结果表明,通过沟塘底泥、水生植物等的综合净化作用,沟塘出流水中总氮TN和总磷TP平均质量浓度分别较入口减小22.01%和9.59%,实现了对稻田排水中氮磷的原位削减,其中氮磷单峰浓度消减均近似服从指数规律。较小的沟塘入流浓度和较长的沟塘净化时间利于获得更大的消减率,因此,建议利用排水沟系对稻田排水进行先期调蓄,初步净化后再排入沟塘,以提高沟塘净化效果。沟塘拦水坝的修建使得底泥吸附在水体净化过程中作用更加明显,0～40cm深底泥在稻麦轮作年TN截留量达1.559kg·m-2、TP累积量达0.394kg·m-2,吸附量可观;水生植物氮磷吸收是沟塘水质净化的重要途径,收割是实现其净化有效性的关键环节,仅移除芦苇和茭草茎叶,可除去氮193.69kg·hm-2和磷33.49kg·hm-2。芦苇和茭草综合对比表明,茭草更适于当地排水沟塘选用。

Ditches and ponds are effective measures to intercept agricultural non-point pollutant.The retention capacity of ditches and ponds for dealing with paddy field effluent was investigated with the renovation and eco-reconstrution of the irrigtion system taken into account.It is found that the pond wetlands are effective in removal of nutrients by synthesis function of sediment and hydrophytes.Comparing with the quantities in inflow the TN and TP in outflow reduced by 22.01% and 9.59%.Both TN and TP concentration in pond wetlands decreases exponentially in disposal period.Lower inflow nutrients concentration and longer disposal time in pond are beneficial to attain higher removal rate.It is suggested that drainage water should be pre-stored in the drainage ditches before it is discharged into the pond wetlands.The effect of sediment absorption in removing N and P from drainage water can be enhanced by outlet control dam constructions.Sediments of the layer with depth 40cm absorbed about 1.559 kg·m^-2 TN and 0.394kg·m^-2 TP for a rice-wheat rotation year.Hydrophytes also play an important role in absorbing N and P from water.Harvesting hydrophytes is key step to prevent from secondary pollution.Harvesting the stems and leaves of Zizania latifolia and Phragmites communis can result in removal of 193.69 kg·hm^-2 TN and 33.49 kg·hm^-2 TP.The Zizania latifolia is more applicable for local ditches and ponds comparing with Phragmites communis in paddy field effluent disposal.