模擬酸雨對臺灣中部極育土陽離子淋溶的影響

Abstract

酸雨對土壤的影響，主要是造成鹽基陽離子的淋溶及土壤的酸化。台灣地區酸沉降的研究，大多著重於雨水性質的調查，少有對土壤影響的報告。本試驗試選取台灣中部蓮華池森林集水區砂質極育土，以試驗室內的管柱淋溶試驗法，探討不同pH值的模擬酸雨，對於該土壤鹽基陽離子淋溶之影響。 試驗發現模擬酸雨會加速土壤鹽基陽離子的淋溶。pH=2.6的模擬酸雨對於土壤陽離子淋溶的影響比pH=3.6及pH=4.6的模擬酸雨處理來得大，而PH=3.6與PH=4.6的處理之間的差異並不大。此由於pH=2.6的模擬酸雨含有較多的H離子及硫酸根離子，淋溶時會造成有些黏土表面之可交換性鹽基陽離子和鋁離子溶解。可交換性鋁之增加，可能對林木根群造成不良的影響。本試驗也發現表土層淋溶出來的陽離子比其下壤淋溶出更多的。但在pH=2.6處理下，其淋溶液PH值下降的幅度較底土小。這可能由於表土層之富含有機質，導致表土對酸雨的緩衝能力大於底層。 蓮華池森林砂質極育土對酸雨的緩衝作用，主要機制有三：以pH=2.6的模擬酸雨淋溶土壤，土壤對H的緩衝作用，主要機制為黏土的鋁邊緣(Al-site)和鋁氧化物的溶解。pH=3,6的酸雨處理，主要因子為陽離子的交換和硫酸根的吸附，pH=4.6的酸雨處理，則主要機制為陽離子的交換與硫酸根的脫附。 Acid rain enhanced cations leaching and soil acidification, particularly in sandy soils. Most researchers emphasized on the properties of acid rain, and paid less attention to investigate the influence of acid rain on soil properties. This study used column leaching tech nique to investigate the effects of simulated acid rains on cation leaching of an Ultisol of the Lien-hua-chi watershed in the central Taiwan. The results indicated that simulated acid rain increased cations Leaching from soils. The p11=2.6 simulated acid rain solutions had leached substantially more cations from soils than those of p11=3.6 and pH=4.6 simulated acid rains. This was bccause p11=2.6 simulated acid rain solutions contained more protons and sulfate ions , which exchanged with cations and dissolved aluminum from clays. The treatments of pH=3.6 and pH=4.6 acid rain solutions showed no major differences on cation leaching. Simulated acid rain solutions enhanced the leaching of exchangeable and dissolved aluminum from tested soils. The toxicity of aluminum might produce the ecological problems. The results also indicated that the top soils leached more cations than the deeper soils. However, when treated with pH=2.6 simulated acid rain, the pH of the leachate solution in surface soils decreased not stongly as those of underlying soils. This might result from relatively higher organic content in the soils. Three mechanisms were proposed to govern proton buffering capacity of the stud ied soils. The major mechanism of soils leaching with pH=2.6 simulated acid rain solutions, was the dissolution of aluminum oxides or Al in the clay complexes. Cation exchange and sulfate adsorption were the key factors governing the buffering of soils treated with pH=3.6 simulated acid rains. Exchangeable cations were the major factor for proton buffering capacity for soils treated with p11=4.6 simulated acid rains.