Genesis of arsenic in groundwater of North Bengal Plain using PCA: A case study of English Bazar Block, Malda District, West Bengal, India
Genesis of arsenic in groundwater of North Bengal Plain using PCA: A case study of English Bazar Block, Malda District, West Bengal, India
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DOI：
10.1002/hyp.6742
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发表时间：
2008-06
影响因子：
3.2
通讯作者：
P. K. Sikdar;S. Chakraborty
中科院分区：
文献类型：
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作者：
P. K. Sikdar;S. Chakraborty
研究区域位于西部Rajmahal山丘和东部Garo山丘之间冲积层填充的间隙的西部。地下水在无压条件下赋存于第四系冲积层中的一个较厚的饱和带中。识别出三种特征明显的水化学相，总体上以碱土和弱酸为主。该地区的主要离子化学受硅酸盐矿物风化、降雨补给、离子交换过程和人为活动（如灌溉回流和无机肥料和农药的应用）控制。化学计量方法表明，矿物溶解和人类活动贡献的79%和21%的总阳离子溶解在地下水中。利用13个化学参数对42个地下水样品进行主成分分析，结果表明，地下水补给过程是降雨、沉积物-水相互作用、地下水流、灌溉回水入渗的综合过程（由于使用含砷杀虫剂、木材防腐剂等，以及为农业目的抽取富含砷的地下水，因此富含砷），天然或人为有机质的氧化以及三价铁和锰氧化物的还原溶解对研究区地下水的演化起着关键作用。因子2的得分，与灌溉回水的渗透和砷浓度的空间分布揭示了城市地区的地下水不会受到砷的影响，在未来，尽管大量的地下水抽取。另一个包含地质、地貌、人为、地球化学和土地利用因素的主成分分析表明，地下水中的砷浓度随着芒果园面积、砂岩相和硝酸盐的增加而增加，随着古河道与监测井的距离和钻井威尔斯深度的增加而减少。硝酸盐的高负荷可能归因于芒果园和农业用地中使用的肥料，杀虫剂等。高负荷的log pCO 2，芒果园（负号）和磷酸盐（正号）表明，芒果园提供的有机废物材料，分解形成有机碳。有机碳在不同的氧化剂作用下发生氧化碳降解，增加了含水层中CO2的浓度。因此，含水层中形成的还原条件有助于溶解吸附在氢氧化铁或羟基氧化物涂层砂边缘、富铁重矿物颗粒边缘、粘土矿物和含水层基质中存在的铁锰结核上的砷。版权所有© 2007约翰威利父子有限公司。
The study area is located on the western part of the alluvium‐filled gap between the Rajmahal hills on the west and the Garo hills on the east. Groundwater occurs under unconfined condition in a thick zone of saturation within the Quaternary alluvial sediments. Three hydrochemical facies with distinct characteristics have been identified which are dominated in general by alkaline earths and weak acids. The major‐ion chemistry of the area is controlled by weathering of silicate minerals, rainfall recharge, ion‐exchange processes and anthropogenic activities such as irrigation return flow and the application of inorganic fertilizers and pesticides. A stoichiometric approach suggests that mineral dissolution and anthropogenic activities contribute 79% and 21% of the total cations dissolved in groundwater. Principal component analysis (PCA) of 42 groundwater samples using 13 chemical parameters indicates that the combined processes of recharge of groundwater from rainfall, sediment water interaction, groundwater flow, infiltration of irrigation return water (which is arsenic rich due to the use of arsenic‐bearing pesticides, wood preservatives, etc. and the pumping of arsenic‐rich groundwater for agriculture purpose), oxidation of natural or anthropogenic organic matter and the reductive dissolution of ferric iron and manganese oxides play a key role in the evolution of groundwater in the study area. Factor 2 scores, associated with the infiltration of irrigation return water and spatial distribution of arsenic concentration reveal that the groundwater of the municipal area will not be affected by arsenic in the future in spite of heavy groundwater abstraction. Another PCA with geologic, geomorphic, anthropogenic, geochemical and landuse factors indicates that arsenic concentration in groundwater increases with increasing area of mango orchards, sand lithofacies and nitrate and decreases with increasing distance of paleochannel from the monitored well and depth of bore wells. High loading on nitrate may be attributed to the use of fertilizer, pesticides, etc. in mango orchards and agricultural land. High loadings on log pCO2, mango orchards (with negative sign) and phosphate (with positive sign) indicate that mango orchards provide the organic waste material which is decomposed to form organic carbon. The organic carbon undergoes oxidative carbon degeneration by different oxidants and increases the concentration of CO2 in the aquifer. The reducing condition thus developed in the aquifer helps to dissolve the arsenic adsorbed on iron hydroxide or oxy‐hydroxide coated margins of sand, iron rich heavy mineral grain margins, clay minerals and Fe–Mn concretions present in the aquifer matrix. Copyright © 2007 John Wiley & Sons, Ltd.