雨水花园对不同赋存形态氮磷的去除效果及土壤中优先流的影响

雨水花园作为一种生物滞留系统,能够有效降低城市化进程对城市水文和水质带来的负面影响,但其效果与雨水径流中污染物的赋存形态以及花园内部的水力特性等因素有关。通过一项在黄土地区开展的雨水花园对路面雨水径流水文过程及污染物降解的试验研究,分析了雨水花园对不同赋存形态氮磷污染物的去除效果;同时根据雨水花园入流和出流的水文过程监测数据,分析了土壤优先流的存在及其对污染物去除效果的影响。结果显示,雨水花园入流中颗粒态磷和溶解态磷的浓度比例约为4∶1,颗粒态氮和溶解态氮的浓度比例接近1∶1;颗粒态总磷的浓度去除率和负荷去除率分别为40.1%和69.9%,颗粒态总氮的浓度去除率和负荷去除率分别为44.8%和73.8%;系统对于溶解态的氮、磷几乎没有去除能力。雨水花园土壤中存在的优先流现象导致出流速度较快,雨水径流在花园内的水力停留时间较短,结果表明:系统能够拦截颗粒态污染物,但对溶解态污染物去除效果较差;雨水花园对入流中总磷和总氮的浓度去除率很低,平均值仅为6.3%和-2.7%,但因截留了很大比例的入流(平均为51.5%),其对氮、磷污染物总负荷的削减分别达到52.5%和51.5%。所以,利用城市雨水花园来滞留雨水径流,净化雨水水质在研究区具有良好的应用前景。

An experimental study on N and P reductions in a rain garden and the influence of preferential flow

As bioretention systems,rain gardens can mitigate the adverse impact of urbanization on hydrolo-gy and water quality ; but its performance is affected by many factors including the existing forms of pol-lutants and the internal hydraulic characteristics of rain gardens. This paper presents an experimental study on hydrological processes and the water quality improvement of retaining road surface runoff with a rain gar-den in loess region of China. We analyzed the variation of dissolved and particulate nitrogen and phospho-rus measured at the inlet and outlet of the rain garden, and the potential effect of preferential flow on hydrology and pollutant removal efficiency in the rain garden. The results show that the ratio of particulate phosphorus to dissolved phosphorus concentration in inflow is 4:1, but the ratio of particulate nitrogen to dissolved nitrogen concentration in inflow is close to 1:1. For total phosphorus of particle forms, the con-centration reduction is 40.1% and load removal rate is 69.9%; for total particle nitrogen, the concentra-tion reduction is 44.8%, and the load removal rate is 73.8%. The system has little removal capability for dissolved nitrogen and phosphorus. The existence of preferential flow in rain garden soil leads to faster out-flow and shorter hydraulic retention time, resulting in poor reduction of the dissolved N and P, while the particle forms of N and P are effectively intercepted by the rain garden; the concentration reduction of the total phosphorus and the total nitrogen was only 6.3% and -2.7%, respectively. However, the effective flow retention in the rain garden (51.5% in average) results in the significant load reduction rate of 52.5% for phosphorus and 51.5% for nitrogen. Therefore, rain gardens can be used for effective retention of storm water runoff and improving water quality in the study area and the similar regions.