污水灌溉对林地土壤中磷的数量与形态影响

为避免城市生活污水携带的N、P进入水体,新西兰罗托鲁阿市处理后的污水直接喷灌至Whakarewarewa森林,同时建立污水灌溉林地处理系统长期定位试验地,以评价林地生态系统对污水携带营养物质的同化能力。为了解长期污水灌溉对土壤中P的数量、形态、环境的影响,对该灌溉系统中的土壤进行了剖面采样分析。结果表明:土壤TP(全磷)、Olsen P、M3P(Mehlich-3 P)在所有灌溉区的表层土壤(0～10 cm)均有显著(p<0.05)增加,部分指标的显著增加达深层土壤。随灌溉进入土壤的P大多被保存在上层土壤(0～40 cm)中。土壤中各形态的磷所占比例因长期污水灌溉而改变,灌溉前占优势的NaOH Po(以NaOH浸提得到的有机磷)经长期灌溉后被NaOH Pi(以NaOH浸提得到的无机磷)所取代,上层土壤WSP(水溶性磷,Wa-ter-soluble P)变化明显。以Olsen P 60 mg kg-1和M3P 150 mg kg-1为环境临界值可预测土壤剖面中P的淋失危机,WSP可望成为适用更广的土壤P淋失环境危机预测指标。

Effect of long term effluent irrigation on content and movement of phosphorus in soil of forest land

In New Zealand,to avoid the risk of urban sewage bringing N and P into Lake Rotorua,Rotorua city sprays treated sewage direct into Whakarewarewa Forest as irrigation and to evaluate capacity of the forest ecosystem of assimilating the nutrients brought in with the irrigation,a long term field experiment on sewage irrigation of forest land has been established and carried out.To understand effects of long term sewage irrigation on content and form of soil P,and on the environment,soil samples were collected from the system for analysis.Results show that soil TP(total phosphorus),Olsen P,M3P(Mehlich-3 P) all increased significantly(p<0.05) in the top soil(0~10 cm) in all the effluent treated plots as compared with the control plots and some even in the 20~40 cm or deeper soil layer.Most of the P brought in with the irrigation accumulated in the top 40 cm soil.Fractionation of soil P changed due to long term effluent irrigation.NaOH Po(organic P extracted by NaOH) was replaced by NaOH Pi(inorganic P extracted by NaOH) in dominancy.Significant change in WSP(water soluble P) was observed in top soil.To set measurement value 60 mg kg-1 Olsen P(measured value) and 150 mg kg-1 for M3P as environment thresholds enables prediction of the risk of P leaching,and WPS may be a better indicator of environmental crisis of P leaching and applicable to more soils.