Seasonal Variation of Arsenic Speciation in Shallow Groundwater from Endemic Arsenicosis Area in Jianghan Plain
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摘要: 查明地下水中砷的时间变异性规律及机理是高砷地下水研究的难点和热点, 也是防控地下水砷污染的根本.选择在雨季前后对浅层潜水和孔隙承压水进行了动态监测.研究表明地下水砷含量和形态与地下水位波动存在明显的响应关系: 雨季开始后随着地下水位抬升, 地下水还原环境增强, As(Ⅴ)和Asp转化成As(Ⅲ), 颗粒态铁大幅降低, 导致水中溶解的砷和铁大幅增加, 地下水砷含量在雨季达到最高且As(Ⅲ)所占比例达到90%;雨季结束后随着水位逐渐降低, 地下水中As(Ⅲ)所占比例和溶解的砷含量下降.农业活动对浅层潜水砷形态季节性变化有明显的影响.孔隙承压水的砷形态分布变化较浅层潜水幅度大, 其变化与水位波动存在滞后效应.自然或人为活动引起的地下水位季节性变化改变了含水层的氧化还原环境, 补给水源与地下水之间的混合过程带来新的物质输入促进地下水系统中砷的迁移转化.Abstract: Understanding the seasonal variation of arsenic occurrence in shallow groundwater system is one of the challenges and hot spots concerning the research on high arsenic groundwater, which plays an important role in evaluation of safe groundwater availability and remediation of arsenic-affected aquifer. To investigate the seasonal variation of arsenic speciation in the shallow aquifer from the endemic arsenicosis area in the Jianghan plain, groundwater from shallow phreatic aquifer and unconfined aquifer were monitored for arsenic speciation (As(Ⅲ), As(Ⅴ) and acid-leacheable particulate As) and water level during pre-monsoon (May), monsoon (July-August) and post-monsoon (November-December) seasons. Arsenic concentration and speciation in groundwater varied temporally: the concentration of As(Ⅴ) and particulate As were higher, together with higher particulate Fe in most samples during the pre-monsoon seasons; As(Ⅴ) and particulate As decreased significantly during monsoon seasons, while dissovled As and Fe increased dramatically. Higher As concentrations were associated with an increasing percentage of As(Ⅲ) in rainy season and a decrease towards the end of dry season, indicating a reductive moblization responding to groundwater level fluctuation.
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Key words:
- arsenic speciation /
- seasonal variation /
- water level fluctuation /
- redox /
- Jianghan plain /
- groundwater /
- geochemistry.
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图 5 监测场浅层潜水与孔隙承压水不同季节砷形态分布
图例同图 4
Fig. 5. Comparison of arsenic speciation distribution in shallow phreatic aquifer and confined aquifer in different months at field monitoring site
表 1 江汉平原高砷地下水监测场剖面不同深度含水层水位季节性变化统计
Table 1. Seasonal variations of water level at different depths at monitoring field site (SY01-SY05)
监测点编号 全新统浅层孔隙潜水水位(m) 下中更新统孔隙承压水水位(m) 丰水期 枯水期 水位变幅 丰水期 枯水期 水位变幅 SY01 22.12 21.38 0.74 22.26 21.00 1.26 SY02 22.24 20.77 1.47 22.06 20.84 1.22 SY03 22.17 21.67 0.50 21.94 20.87 1.07 SY04 22.04 21.66 0.38 21.67 20.64 1.03 SY05 22.18 21.53 0.65 21.56 20.58 0.98 表 2 地下水砷形态分析的HPLC-HG-AFS条件
Table 2. Experimental condition for determination of arsenic speciation with HPLC-HG-AFS
HPLC HG-AFS 色谱柱 保护柱 流动相 进样体积 还原剂 负高压 载气 Hamilton PRP-X100(250 mm×4.1 mm i.d., 10 μm) Hamilton PRP-X100(25 mm×2.3 mm i.d., 12~20 μm) 15 mmol/L(NH4)2HPO4,pH=6.00,流速1.0 mL/min 20 μL 1.5% NaBH4+0.5% NaOH 300 V 450 mL/min 载流7% HCl 灯电流50 mA 屏蔽气/min 表 3 监测场内不同深度监测井中溶解性有机碳的季节性变化
Table 3. Seasonal variation of dissolved organic matter in different aquifers from Jianghan plain
监测点编号 A井DOC含量(mg/L) B井DOC含量(mg/L) 2013-05 2013-08 2013-11 2013-05 2013-08 2013-11 SY03 12.34 18.25 6.54 3.75 13.84 3.27 SY05 11.01 13.98 13.54 8.11 13.49 3.03 SY07 8.08 17.64 4.47 3.84 4.67 3.44 -
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