5种水生植物对模拟菜地径流中总氮和硝氮净化效果

Purification effect of five kinds of hydrophytes on total nitrogen and nitrate in simulated vegetable field runoff water

近年来,太湖地区蔬菜大棚种植面积日益增加,高施肥量造成菜地土壤硝氮(NO-3-N)积累严重,夏季揭棚期菜地在降雨初期会产生高浓度NO-3-N(富硝)的地表径流。为净化菜地富硝地表径流,选取苦草、伊乐藻、黄花水龙、狐尾藻和铜钱草5种常见水生植物,开展了模拟富硝地表径流的箱内净化试验。结果表明:在模拟径流总氮(TN)浓度为6.32~6.80 mg/L、NO3^--N浓度为4.76~5.09 mg/L时,5种水生植物在试验初期(第1周)均表现出较好的氮去除效果,TN和NO3^--N去除率分别超过80%和90%,试验后期(第3、4周)苦草、伊乐藻和铜钱草对TN、NO3^--N的去除率明显下降,而黄花水龙和狐尾藻仍保持较高的NO-3-N去除率(90%以上);在模拟径流TN浓度为15.62~18.00 mg/L,NO3^--N浓度为13.19~13.96 mg/L时,5种水生植物的生长均受到不同程度的胁迫,但黄花水龙和狐尾藻对氮去除能力显著高于其他植物;黄花水龙和狐尾藻具有较大的生物量,使其具有良好的氮去除能力,2种植物通过反硝化等途径去除的氮在不同处理间无显著差异,黄花水龙和狐尾藻较适宜净化富硝地表径流。

In recent years,the planting area of vegetable greenhouse in Taihu Lake region had been increasing,and the high amount of fertilization had resulted in serious nitrate(NO-3-N)accumulation in vegetable soils.Nitrate was abundant in surface runoff at the beginning of rainfall during the opening of greenhouse in summer.In order to purify the surface runoff of vegetable field rich in NO3^--N,a static simulated experiment with five common kinds of hydrophyte of Vallisneria natans,Elodea nuttallii,Ludwigia peploides,Myriophyllum verticillatum L.and Hydrocotyle chinensis in a tank containing simulated nitrate-rich runoff water was carried out.Results showed that at low NO3^--N concentration with TN of 6.32-6.80 mg/L and NO3^--N of 4.76-5.09 mg/L,all the five hydrophytes showed good removal effects in the early stage(the first week)with the removal rates of TN and NO3^--N over 80%and 90%,respectively.But in the late stage(the third and fourth week),the removal rate of TN and NO-3-N by Vallisneria natans,Elodea nuttallii and Hydrocotyle chinensis decreased obviously,while Ludwigia peploides and Myriophyllum verticillatum L.still maintained high NO3^--N removal rate(over 90%).At high NO3^--N concentration with TN of 15.62-18.00 mg/L and NO3^--N of 13.19-13.96 mg/L,the growth of five hydrophytes all showed different degrees of stress.However,Ludwigia peploides and Myriophyllum verticillatum L.still maintained higher nitrogen removal capacity,which was mainly attributed to the large biomass and nitrogen uptake.There was no significant difference in nitrogen removal by denitrification between different treatments,therefore,Ludwigia peploides and Myriophyllum verticillatum L.were more suitable to purify the runoff water with high nitrate concentration.