湖滨带复合型人工湿地氮磷的去除效果

Removal efficiency of nitrogen and phosphorus in integrated constructed lake-side wetlands

湖滨带是连接湖泊水域生态系统与陆地生态系统的一个功能过渡区,是湖泊的最后一道保护屏障。在河流的入湖口建造湖滨湿地,可有效净化入湖径流中携带的部分有机污染物、营养盐等。以云南抚仙湖北岸的湖滨湿地—马料河复合人工湿地为研究对象,探讨了湿地不同功能区去除氮磷的效果。研究表明,沉淀池除氮效果最不明显,在该区内有机氮可能发生矿化作用而转变为氨氮。有植物系统的潜流和表流区除氮效果较为明显,潜流区对氨氮、硝氮和总氮的平均去除率分别达18.0%、19.7%和22.6%;表流区对三者的平均去除率分别达50.4%、35.9%和43.5%。沉淀池对磷有一定的截留作用,且在进水污染物质量浓度较高时表现明显,平均截留率为14.9%。潜流和表流区除磷效果不明显,可能是因为湿地运行了两年多,土壤吸附交换达到平衡,影响了表流区的除磷效果。潜流区除磷效果受降雨影响较大,雨季时,总磷的平均截留率为12.1%,主要是不溶性磷的吸附和沉积;雨季末期,湿地流量较小,水体流动性差,系统内处于厌氧状态,出现磷释放现象。

The lake riparian zone,which connects the lake aquatic ecosystem and the terrestrial ecosystem,is the last protection barrier of lakes. Constructed wetlands in the riparian zone can decontaminate certain organic pollutants and nutrients in surface runoff effectively. The integrated constructed wetland of Maliao River,at the north bank of Fuxian lake,Yunnan province,is selected as the studied area. The removal efficiency of nitrogen and phosphorus of different function units of the wetland has been studied. Results show that,nitrogen removal rate in the sedimentation tank （ST） unit is not apparent,where the mineralization of organic nitrogen to NH4^＋ may happen. But the subsurface flow unit （SSF） and the free water surface （FWS） unit with macrophytes have noticeable effect on nitrogen removal. The removal efficiencies of NH4^＋,NO3^-and TN are 18.0%,19.7% and 22.6% respectively for SSF,and are 50.4%,35.9% and 43.5% for FWS. In the ST unit phosphorus retention happens,which is more apparent for higher pollutant input concentrations,with an average retention rate of 14.9%. The removal effect of phosphorus in SSF and FWS units is not noticeable,probably due to the saturation of soil adsorption after more than two years operating for the FWS unit. Rainfall has evident effects on the phosphorus removal efficiency of the SSF unit. In wet seasons,there happens particle phosphorus adsorption and deposition with a removal efficiency of 12.1%. Under the anaerobic condition resulting from small discharge rates at the end of wet seasons,phosphorus may release from the wetland soil.