人工湿地生态根孔技术及其应用

人工湿地亚表层介质的堵塞问题一直是湿地系统持续有效运行的障碍,极大地限制了人工湿地技术的大规模工程应用.通过白洋淀自然湿地现场研究,发现由大型水生植物所形成的根孔异常发达,径级不等的死活根孔混合在一起,组成了庞大的湿地根孔网络.人工湿地生态根孔技术通过模拟白洋淀湿地自然的芦苇根孔系统,以人为填埋的植物秸秆作为湿地的填料/介质,有效地改变了土壤亚表层大孔隙结构,为人工湿地建设和应用开辟了一条新途径.通过构筑根孔和自然根孔之间的过渡和湿地根孔的不断更新,实现湿地填料/介质的自我更新,克服了一般潜流人工湿地其填料/介质易发生堵塞的缺点.构筑根孔有效填补了人工湿地运行初期大量自然根孔尚未形成的空白期.该技术在小试湿地中获得了成功应用.以玉米秸秆和地肤秸秆作为小试模拟湿地的填埋介质,其填埋量体积比为2%～4%.与未填埋秸秆的基质土壤处理单元相比,填埋秸秆处理单元其导水效率和营养盐去除能力都得到了有效提高.研究结果表明:填埋秸秆腐烂后形成的构筑根孔其水分侧向入渗率是基质土壤的20倍左右.在中、低营养盐负荷情况下,填埋秸秆处理单元对溶解性总氮(DTN)去除率平均提高4.5%～27.1%;对溶解性总磷(DTP)去除率平均提高7.0%～20.4%.

The constructed root channel technology and its application in constructed wetlands

Clogging problem of subsurface layer media has increasingly been an obstacle to the long-term effective operation of constructed wetlands, which greatly limits their practical application and sustainability. In the field experimental study in Baiyangdian Lake, we found that the aquatic macrophytes could form root channels network with various sizes. Based on that, an innovative subsurface structure modification method of constructed wetlands, named as constructed root channel technology (CRCT), was developed. This technology utilized artificially buried straws as substrate media, aiming to emulate the structure and functions of natural root channel systems. Self-renewal of wetland substrates were effectively achieved by the transition between constructed root channels and natural root channels and the continual renewal of wetlands root channels. This mechanism overcame the shortcoming that the substrates of common subsurface flow constructed wetlands tended to be clogged with a period of operation. Constructed root channels would fill the gap before a great number of natural root channels were developed during the initial operation period of constructed wetlands. The CRCT had been successfully applied in the pilot constructed wetlands. Corn straws and Kochia straws were used as the subsurface media in this pilot study, whose volumetric amount accounted for 2%~4% of the soil mass. The experimental cells with constructed root channels could stimulate hydraulic conductivity and nutrient removal efficiency with comparison to the matrix soil cells without buried straws. Results showed that the lateral hydraulic infiltration rates of the constructed root channels formed by decayed straws were about 20 times that of matrix soil. Under the low to moderate inflow nutrient loads, the cells with buried straws could increase the removal efficiency of dissolved total nitrogen (DTN) and dissolved total phosphorus (DTP) by 4.5%~27.1% and 7.0%~20.4% in average, respectively.