长江中游河湖平原浅层地下水中砷空间异质性的同位素指示

近年来陆续有报道发现长江中游河湖平原广泛分布着高砷地下水，鄱阳湖平原与江北平原（古彭蠡泽）作为长江中游南北两岸典型的河湖平原，其地下水资源丰富，但砷的空间分布规律尚不清楚，区域供水安全存在风险.本研究在两个区域系统采集98个浅层地下水（< 40 m）样品和8个地表水样品，通过水化学、氢氧稳定同位素分析，查明地下水中砷的空间分布异质性及其影响因素.研究发现江北平原浅层地下水砷含量为0.65~956.72 μg/L（平均值210.78 μg/L），高砷地下水集中分布于长江古河道；鄱阳湖平原浅层地下水砷含量为0.09~267.45 μg/L（平均值11.85 μg/L），高砷地下水仅分布于赣江三角洲局部地区.江北平原地下水δD与δ18O值相对鄱阳湖平原更偏负，且与地表水的差异更大.地下水化学及主成分分析结果表明物源和含水层结构差异是影响鄱阳湖平原和江北平原砷空间分布异质性的关键因素，来自长江物源的古彭蠡泽区域沉积物为高砷含水层的形成提供了物质来源，湖相含水层中含砷铁氧化物的还原性溶解是地下水砷富集的主要过程.地下水氢氧稳定同位素指示江北平原较鄱阳湖平原地下水赋存环境更封闭，地下水循环交替速度缓慢，有利于砷的富集. 

Isotopic Indication of Spatial Heterogeneity of Arsenic in Shallow Groundwater of Middle Yangtze River Lacustrine Plain

In recent years, it has been reported that high arsenic groundwater is widely distributed in the the middle Yangtze River lacustrine plain. The Poyang Lake plain (PYP) and the Jiangbei plain (ancient Pengli Lake, JBP) are typical lacustrine plains rich in groundwater resources on the northern and southern sides of the middle reach of the Yangtze River. However, the spatial distribution of groundwater arsenic in these regions has not been clearly studied, which posed potential risks to regional water supply security. In this study, 98 shallow groundwater samples and 8 surface water samples were collected in these two regions. The spatial heterogeneity of arsenic in groundwater and its controlling factors were identified by hydrochemistry and stable isotope analysis. The arsenic contents of shallow groundwater in JBP range from 0.65 to 956.72 μg/L (average 210.78 μg/L), and the high arsenic groundwater is mainly distributed in the ancient Yangtze River channel. The arsenic contents of shallow groundwater in PYP range from 0.09 to 267.45 μg/L (average 11.85 μg/L), and the high arsenic groundwater is only distributed in parts of Ganjiang River delta. Stable water isotope composition (δD and δ18O) of groundwater samples from the JBP is more negative and significantly different from surface water relative to the PYP. Multivariate statistical results of groundwater chemistry data indicate that the differences of provenance and aquifer structure are the key factors affecting arsenic spatial heterogeneity in shallow groundwater in PYP and JBP, the microbially mediated reductive dissolution of arsenic-bearing iron minerals leads to arsenic release in groundwater. Groundwater arsenic in the Jiangbei plain is supposed to be originated from the sediments from ancient Pengli area of Yangtze River provenance. The stable isotopic signatures of hydrogen and oxygen in groundwater indicate that the aquifer environment in JBP is closer and the groundwater circulation and alternation speed is slower compared with the PYP, which is more conducive to arsenic release and enrichment in the groundwater.