培地茅與狼尾草應用於關渡平原砷污染地之植生復育

Abstract

近年來的調查發現北投關渡平原地區土壤砷含量超過國家標準 (60ppm)的農地達128公頃，本試驗希望利用植生萃取的方式，透過植物根系吸收土壤中的砷汙染物運移到地上部組織，再透過採收地上部組織將土壤的汙染物移除，以達到植生復育的目的。本研究選用培地茅及狼尾草這兩種多年生大型禾草，以三種種植密度及施用兩種不同肥料量進行植生復育效果評估，以取得最佳復育條件。於關渡地區砷污染農地歷經建立初期及一次割刈與生長累積共計種植318日，估算出培地茅於高密度高肥田區獲得的21.26公噸/公頃的植株地上部乾物中，能累積11.71公克的砷，具有最佳的移除效果；狼尾草最佳表現在於低密度高肥田區，所獲得24.46公噸/公頃的植株地上部乾物中能累積6.3公克/公頃的砷。培地茅與狼尾草於此試驗對砷的吸收量皆不高，其可能的原因是因為植株仍在初期建立階段，尚未達到成熟穩定狀態，但因兩種植物在此段研究期間呈現穩定健康的生長，因此仍預期具有深厚的潛力，另一方面造成吸收量較少的原因，可能來自砷的來源是母岩，因此其生物有效性遠低於工業性外來汙染源，在此同時培地茅的龐大根系具有極佳的植生穩定潛力，可以考慮作為關渡地區砷污染的植生穩定作物。

Recently, the arsenic concentration of soil exceeding the national standard (60mg kg-1) were found in Guandu, Beitou, Taipei, up to 128 hectares of contaminated area. This study hoped to use phytoextration to absorb arsenic from soil by plant root system, and then to transport to shoot tissues, finally, to remove arsenic by harvesting shoot. In order to evaluate the best condition of phytoremediation, napiergrass (Pennisetum purpureum Schum.) and vetiver (Vetiveria zizanioides L.) were grown by three levels of planting densities and applied two different nitrogen rates to arsenic-contaminated farmland. After the establishment, mowing, and accumulated growth of 318 days, The best performance was found in vetiver in high density - high nitrogen plot, harvested 21.26 ton/ha of shoot dry biomass containing 11.71g of arsenic. The best result of napiergrass was found in low density - high nitrogen plot, harvested 24.46 ton/ha of shoot dry biomass containing 6.3g of arsenic. In this experiment, the absorptive ability of arsenic in napiergrass and vetiver were both not well. Because of the origin of arsenic from parent rocks, the bioavailability of arsenic in the study was lower than industrial pollution.The other reason was the plants still in the early establishment stage, and showed healthy and stable growing during the experiment. Their biomass production and phytoremediation potential were expected to be increased as the plants reach maturation. Furthermore, the dense root system of vetiver may have good potential of phytostabilization for arsenic-contaminated soil in Guandu.