| 天鹅洲长江故道湿地地下水砷的时空分布特征及控制机理 |
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| 引用本文： | 金戈,邓娅敏,杜尧,陶艳秋,范红晨.天鹅洲长江故道湿地地下水砷的时空分布特征及控制机理[J].地球科学,2022,47(11):4161-4175. |
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| 作者姓名： | 金戈 邓娅敏 杜尧 陶艳秋 范红晨 |
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| 作者单位： | 1.中国地质大学地质调查研究院, 湖北武汉 430074 |
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| 基金项目： | 国家自然科学基金面上项目41977174 |
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| 摘 要： | 高砷地下水不仅直接危害供水安全，还可通过与湿地之间的交互作用，影响湿地水质进而威胁湿地生态安全.长江中游河湖平原已被报道广泛分布有高砷地下水，而位于长江中游故道区域的天鹅洲湿地地下水中砷的空间分布特征尚不明确，湿地与地下水的交互作用对地下水中砷季节性动态的控制机理尚不明确.本研究在天鹅洲湿地采集2个水文地质钻孔的35件沉积物样品、12个分层监测井不同季节的共72组地下水样和18组地表水样，通过水位-水化学监测、沉积物地球化学组成分析和砷、铁形态表征探究天鹅洲湿地地下水中砷的时空分布规律及控制机理.研究发现天鹅洲湿地地下水砷含量为1.08~147 μg/L，牛轭湖外侧浅井（10 m）地下水砷含量普遍高于深井（25 m）和牛轭湖内侧浅井（10 m）、深井（25 m）地下水，枯水期和平水期的砷含量高于丰水期.牛轭湖外侧浅层地下水系统具有更厚的粘土、亚粘土沉积，沉积物中总砷、强吸附态砷和易还原的铁氧化物的含量更多，吸附砷的水铁矿等无定形铁氧化物还原性溶解导致砷释放进入地下水中.枯水期天鹅洲湿地底部向牛轭湖外侧浅层含水层输送不稳定的有机质，使天鹅洲湿地地下水-地表水界面成为砷释放的热点区域.丰水期时牛轭湖外侧含水层受长江补给的影响，还原环境发生改变使地下水中的砷和铁被氧化固定从而不利于砷向地下水释放.
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| 关 键 词： | 天鹅洲湿地 高砷地下水 时空分布特征 沉积物砷、铁形态 地下水-地表水界面 控制机理 |
| 收稿时间： | 2022-08-21 |
Spatial-Temporal Distribution of Arsenic in Groundwater System in Tian-E-Zhou Wetland of the Yangtze River and Its Controlling Mechanism |
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| Abstract: | High arsenic groundwater not only directly endangers water supply safety, but also affects the water quality of wetlands and thus threatens the ecological safety of wetlands through the long-term interactions between groundwater and surface water. The spatial distribution of arsenic in groundwater in the Tian-E-Zhou wetland in the middle reach of the Yangtze River has been reported to be wide, but the spatial distribution characteristics of arsenic in groundwater in the Tian-E-Zhou wetland in the middle reach of the Yangtze River are still not clear, and the control mechanism of the interaction between the wetland and groundwater on the seasonal dynamics of arsenic in groundwater is not clear. In this study, 35 sediment samples from 2 hydrogeological boreholes, a total of 72 sets of groundwater samples and 18 sets of surface water samples from 12 stratified monitoring wells in different seasons were collected in the Tian-E-Zhou wetland, and the spatial-temporal distribution patterns and control mechanisms of arsenic in groundwater in the Tian-E-Zhou wetland were investigated by water level-water chemistry monitoring, sediment geochemical composition analysis and arsenic-iron morphological characterization. It was found that the arsenic content of groundwater in the Tian-E-Zhou wetland ranged from 1.08 to 147.00 μg/L. The arsenic content of groundwater in shallow wells (10 m) under the outer side of the Oxbow Lake was generally higher than that in deep wells (25 m) and groundwater under the inner side of Oxbow Lake, and the arsenic content in the non-monsoon was higher than that in the monsoon. The shallow groundwater system under the outer side of the Oxbow Lake has thicker clayey and sub-clayey deposits with higher total arsenic, strongly adsorbed state arsenic and easily reduced iron oxides in the sediments, and reductive dissolution of amorphous iron oxides such as ferrihydrite minerals that adsorb arsenic leads to the release of arsenic into the groundwater. The transport of reactive organic matters from the bottom of the Tian-E-Zhou wetland to the shallow aquifer outside the Oxbow Lake during the non-monsoon makes the groundwater-surface water interface of the Tian-E-Zhou wetland a hot spot area for arsenic release. During the monsoon, the aquifer on the outer side of the Oxbow Lake is influenced by the recharge of the Yangtze River, and the reduction environment is changed so that the arsenic and iron in the groundwater are fixed by oxidation, which is detrimental to the release of arsenic to the groundwater. |
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