含砷地下水灌溉後砷在農田土壤中的空間分佈

臺灣嘉南平原地區由於地質背景因素，地下水中含有較高濃度的砷，本論文目的為闡明地下水來源的砷與土壤性質的關係，並運用地理資訊系統(geographic information system, GIS)空間套疊之功能呈現。不同深度土壤之總砷總砷與游離鐵、錳、無定型鐵錳、陽離子交換容量、黏粒含量等均呈現顯著(p<0.05)正相關。從由序列萃取法可看出砷主要是被固定於無定型鐵鋁氧化物及結晶型鐵鋁氧化物。利用此地下水灌溉後，會影響土壤中之鐵鋁氧化物之氧化還原狀態，進一步導致砷的溶出。乾濕交替作用亦會釋放此兩型態之砷。由於本論文為一砂質壤土，又因水流及重力因素影響，導致總砷在空間分佈上是以入水口位置向下呈扇形擴散。砷被固定在淺層土壤，使深層土壤之總砷濃度較淺層土壤低，主要是含砷地下水灌溉後因淺層土壤之鐵錳氧化物較高，將砷固定並累積於淺層土壤，並因pH值在深層土壤較高，使砷不易被土壤固定，故深層土壤之總砷濃度較淺層土壤低。

關鍵字

土壤；嘉南平原；砷；空間分佈；序列萃取

並列摘要

The groundwater has higher concentration of arsenic due to geological background of Chianan Plain. Here we aim to understand the relation between geological conditions and As contribution through the investigation of soil properties, and further visualize the spatial distribution of As in a paddy field along with irrigation through the approach of geographic information system (GIS). This study found that total As concentration positivelyand significantly (p<0.05) correlated with the soil properties including Fed, Mnd, Feo, Mno, cation capacity exchange, and clay content. The sequential extraction of soil As showed that As was mainly fixed by both amorphous and crystalline Fe/Mn oxides, which may be ascribable to that As has a high affinity for Fe/Mn oxides under reduction regime of groundwater. As a consequence, As probably would become soluble due to the usage of groundwater and the change of redox regime. Besides, alternating wet and dry could also solubilize As bound to Fe/Mn oxides. Because of the coarse texture of study soil, the flow way of irrigation water, and the gravity impact, the soil arsenic was concentrated on the surface soil, gradually decreased with soil depth, and showed a fan-shaped spatial distribution since the inlet as fan top. . Therefore, total As in subsoils was lower than topsoil because As was adsorbed and accumulated by abundant Fe/Mn oxides in surface soil after irrigation. High pH of subsoils may lead to the dissolution and leaching of As from soil particles so that the concentration of As in subsoils was lower in comparison with topsoils.

並列關鍵字

soil ； Chianan Plain ； Arsenic ； spatial distribution ； sequential extraction procedure

參考文獻

歐東坤，2005，嘉南地區地下水砷濃度之研究，碩士論文，國立臺灣大學，地質科學研究所，臺北。

Appelo, C. A. J., Weiden, M. J. J., Tournassat, C., Charlet, L., 2002, “Surface complexation of ferrous iron and carbonate on ferrihydrite and the mobilization of arsenic,” Environ Sci Technol, vol. 36, pp. 3096-3103.

Belzile, N., and Tessier, A., 1990, “Interactions between arsenic and iron oxyhydroxides in natural sediments,” Geochimica et Cosmochimica Acta, vol. 54, pp. 103-109.

Bolan, N. S., Adriano, D. C., and Duraisamy, P., 2003, “Immobilization and phytoavailability of cadmium in variable charge soils,” Plant and Soil, vol. 251, pp. 187-198.

Bottrell, S. H., Newton, R. J., 2006, “Reconstruction of changes in global sulfur cycling from marine sulfate isotopes,” Earth Science Review , vol. 75, pp. 59-83.

國際替代計量

含砷地下水灌溉後砷在農田土壤中的空間分佈

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