自然沟渠控制村镇降雨径流中氮磷污染的主要作用机制

Primary mechanisms of nitrogen and phosphorus removal from stormwater runoff by a natural ditch in a rural township

以四川盆地紫色丘陵区林山村镇为例,分析降雨径流过程中氮磷在自然沟渠内的空间变化特征和不同控制机制的净化能力,研究了自然沟渠控制村镇降雨径流中氮磷的主要作用机制.研究结果表明,除NO3--N浓度在沿程上呈先减后增而后再减的趋势外,其它氮磷污染物(TN、PN、NH4+-N、TP、PP和PO34--P)均为沿程递减趋势.溶解态氮是降雨径流氮素在空间沿程上的主要迁移形态,溶解态磷是流量限制型事件降雨径流磷素空间沿程的主要迁移形态,而颗粒态磷是物质限制型事件降雨径流磷素空间沿程的主要迁移形态.泥沙截控固持是自然沟渠控制降雨径流氮磷污染的主要作用机制,有效降低径流中颗粒物浓度和拦截泥沙是控制降雨径流氮磷污染的关键.沉降段和沉沙凼具有明显的泥沙及颗粒态氮磷截控固持作用,可较好地去除村镇降雨径流中的氮磷颗粒态污染物,平均氮磷去除量分别为144·51、65.20g·m-2(平均雨量37·85mm).植物吸收是植被段氮磷去除的重要途径,在雨季共吸收氮磷分别可达82.69、12.52g·m-2.跌落曝氧也是降雨径流氮磷污染控制的重要作用机制,跌落段对NH4+-N的平均去除负荷为15.05g·m-2.

To reveal the main nitrogen and phosphorus removal mechanisms of a natural ditch in a rural township, experiments were conducted in Linshan Township （area of 2.32 hm^2 ） in the hilly area of Siehuan basin, China. The spatial variance of nitrogen and phosphorus in stormwater runoff, and the purification capacity of nitrogen and phosphorus at different control sections of the natural ditch were examined from June 2006 to July 2007. The results showed that concentrations of NO3^- -N （Nitrate） tended to decrease first before a flush, then decrease with increasing distance downstream, while concentrations of other pollutants, such as TN （Total Nitrogen） , PN （ Particulate nitrogen）, NH4^＋ -N （ Ammonia nitrogen） , TP （Total phosphorus） , PP （Particulate phosphorus）, and PO3^- -P （Phosphate） reduced with increasing distance downstream. DN （Dissolved nitrogen） was the primary transport form of nitrogen with increasing distance downstream in all events. DP （ Dissolved phosphorus ） was the primary transport form of phosphorus with increasing distance downstream during flow-limited events, while PP was the primary form during mass-limited events. Sediment retention and immobilization was the most important mechanism for removing nitrogen and phosphorus from stormwater runoff in the natural ditch. The key to remove nitrogen and phosphorus pollution in stormwater runoff was to reduce the concentrations of particulate forms effectively. For each event with an average of 37.85 mm of precipitation, the nitrogen and phosphorus removal capacities averaged 144.51 g·m^-2 and 65.20 g·m^-2 by sediment retention and immobilization in the GS （Grit removal segment） and the GT （Grit removal tank）. Plant assimilation was the other pivotal mechanism for removing nitrogen and phosphorus in stormwater runoff. In the natural segment （NS）, the total assimilated nitrogen and phosphorus amounts were 82.69 g·m^-2 and 12.52 g·m^-2 during the rainy season in the natural ditch. Aeration in a waterfall was another pivotal mechanism. However, the nitrification ability in the falling segment was low as the average removal load for NH4^＋ -N was 15.05 g·m^-2