长期污水灌溉后林地土壤中磷的含量与移动

为尽可能地削减污水携带的N、P进入湖泊,处理后的城市生活污水被直接喷灌到新西兰罗托鲁阿市的Whakarewarewa森林,并建立了污水灌溉林地处理系统的长期定位试验地以评价生态系统对污水携带营养物质的同化能力.为查清长期污水灌溉土壤中P的数量、迁移淋失及其环境危机,对11a污水灌溉后火山灰土壤中磷的积累、再分布进行剖面分层采样测定.结果表明,土壤pH、TP、Olsen P、M3P、M3Ca和M3Mg在所有灌溉处理区的表层土壤(0～10 cm)均有显著(p0.05)增加,部分增加的显著性达到20～40 cm土层或更深层次土壤.大多数随灌溉而进入土壤的P被保存在上层土壤(0～40 cm)中.土壤Olsen P和M3P的浓度在中、高水平处理区的20 cm以上土层中超过了环境临界值(Olsen P为60 mg.kg-1;M3P为150mg.kg-1),磷饱和率(M3PSR)数值同时显示表层土壤对P的吸持已近饱和,预示土壤磷素有随下渗水向下移动的潜在可能.常规土壤采样以60 mg.kg-1 Olsen P测定值为环境临界值,可解决土壤剖面中磷的下移监测难题.以M3P与M3Al、M3Fe的摩尔比计算的磷饱和率(M3PSR)作为长期污水灌溉林地处理系统中土壤磷向下移动的环境危机临界值参数指标已不是很理想,对新的磷饱和参数的研究是今后的主要工作之一.

Contents and Movement of Phosphorus in Soil of Long Term Effluent Irrigated Land Forest

Treated sewage effluent from Rotorua City, New Zealand, has been spray-irrigated into Whakarewarewa Forest to minimize effluent-derived nitrogen (N) and phosphorus (P) entering Lake Rotorua. To assess the capacity of the ecosystem to assimilate the effluent derived nutrients, a long term field trial was established within the Rotorua land treatment system. The objective of this study was to determine the accumulation, redistribution and movement of P in the volcanic soil after 11year effluent irrigation. The soil samples were analyzed. Soil pH, total phosphorus (TP), Olsen P, Mehlich-3 P(M3P), M3Ca and M3Mg had increased significantly (p<0.05) in the top soil (0-10cm) in all effluent treated plots compared with the control plots. Some significant increase had extended deeper soil layer (20-40cm) or much deeper soil layer. Most effluent-derived P had accumulated in top 40cm. Concentrations of soil Olsen P and M3P in the medium and high effluent treatments were over environmental threshold levels(Olsen P, 60 mg·kg^-1; M3P, 150 mg·kg^-1) in the top 20cm. The values of soil saturation ratio (M3PSR) show that it was nearly saturated of soil P sorption in top soil. It was suggested that there was a potential environment crisis for soil P to move downward with drainage water. Regular soil sampling and Olsen P measurement using 60 mg·kg^-1 as an environment threshold could provide a solution for monitoring the movement of P down the soil profile. Phosphorus saturation ratio index (M3PSR) calculated as the molar ratio of M3P to (M3Al + M3Fe) appeared to be inadequate as an indicator for downward movement of soil P in such land treatment system. A new Phosphorus saturation ratio index for this system will be one of future study work.