奥林匹克森林公园典型人工林地非点源污染输出特征分析

The characteristics of non-point source pollution in typical artificial forest lands in Beijing Olympic Forest Park

选取北京奥林匹克森林公园的典型人工林地为研究对象,通过对天然降雨径流过程及泥沙、氮、磷等污染物浓度随径流变化过程的监测,研究公园典型密草林地覆盖下,不同坡形及人工沟渠汇流条件下的径流及污染物浓度、形态和负荷的输出特征.结果表明,相同降雨条件下,林地1的坡长/坡宽比小,径流深度大,林地1坡度较大的草皮型汇流沟渠对径流的削减作用弱于林地2坡度较小的植草型汇流沟渠.两林地的泥沙浓度随径流量变化明显,总氮、总磷浓度在径流过程中的变化幅度较小.氮、磷的流失以可溶性为主,可溶性氮、磷在总氮、总磷中的比例分别为60%～80%和60%～64%.降雨量为6.8mm时,林地1的径流深度为0.16mm,总氮、总磷单位面积的流失负荷分别为0.74mg.m-2和0.09mg.m-2,林地2无径流;当降雨量为45mm时,林地1的径流深度为7.77mm,泥沙、总氮和总磷单位面积的流失负荷分别为1662.82mg.m-2、35.58mg.m-2和3.24mg.m-2,林地2的径流深度为0.41mm,泥沙、总氮和总磷单位面积的流失负荷分别为86.48mg.m-2、2.49mg.m-2和0.31mg.m-2.径流深度对泥沙、总氮、总磷单位面积的流失负荷影响较大.因此,要减少公园林地非点源污染负荷,应重点控制地表径流总量.

In order to discover the characteristics of non-point source pollution in Beijing Olympic Forest Park,two typical artificial forest lands with different topography and vegetation covers were selected to study the rainfall-runoff process and pollutant concentrations combined with natural rainfall events. The results showed that the runoff depth of site 1 with smaller length/width ratio was deeper than site 2 with larger length/width ratio. The planted grass swales in site 2 had a better performance in runoff reduction than the artificial turf swales in site 1. A high variability of sediment concentration range and a lower variability of total nitrogen （TN） and total phosphorus （TP） concentration range were obtained during the runoff process. The majority of TN and TP lost were in dissolved form,in which,the TDN/TN and TDP/TP ratios were from 60%-80% and 60%-64%,respectively in the two sites. In a 6.8 mm rainfall event,the observed runoff depth was 0.16 mm,and the losses of TN and TP were 0.74 mg·m^-2and 0.09 mg·m^-2respectively in site 1; while there was no runoff yield in site 2. In a 45 mm rainfall event,the runoff depth was 7.77 mm,and the losses of sediment,TN and TP were 1662.82 mg·m^-235.58 mg·m^-2and 3.24 mg·m^-2respectively in site 1; while in site 2,the runoff depth was 0.41 mm,and the losses of sediment,TN and TP were 86.48 mg·m^-22.49 mg·m^-2and 0.31 mg·m^-2respectively. It was shown that the runoff depth could reflect the significant impact on pollutant loss. Thus reducing the runoff yield is critical to non-point source pollution control in the park.