Impact of local recharge on arsenic concentrations in shallow aquifers inferred from the electromagnetic conductivity of soils in Araihazar, Bangladesh
Impact of local recharge on arsenic concentrations in shallow aquifers inferred from the electromagnetic conductivity of soils in Araihazar, Bangladesh
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DOI：
10.1029/2007wr006000
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发表时间：
2008-07-26
影响因子：
5.4
通讯作者：
Ahmed, K. M.
中科院分区：
文献类型：
--
作者：
Aziz, Z.;van Geen, A.;Ahmed, K. M.
孟加拉盆地浅层含水层中溶解砷水平的高度空间变异性已有很好的记载，但其根本机制仍然知之甚少。我们在这里比较了从孟加拉国25公里(2)地区4700口井和22米(75英尺)深的地下水中测得的地下水浓度与从18,500个频域电磁感应测量得出的表层土壤性质的变化。从同一地区发现的一组14个手动螺旋钻芯表明，颗粒大小和土壤水的导电性共同决定了电磁信号。在距离50m的范围内，成对的电磁电导率和溶解AS之间的关系是显著的，但高度分散(r(2)=0.12；n=614)。在砂质土壤下面的浅层含水层中，As的浓度往往较低，而在细粒和高电导率土壤下，As的浓度往往较高。然而，当数据在50m的平均距离上(r(2)=0.50；n=145)时，电导率的变化几乎解释了As浓度随深度增加速率的变化的一半。这种关联被解释为地下水通过渗透砂质土壤的补给防止了浅层地下水中砷浓度上升的迹象。
The high-degree of spatial variability of dissolved As levels in shallow aquifers of the Bengal Basin has been well documented but the underlying mechanisms remain poorly understood. We compare here As concentrations measured in groundwater pumped from 4700 wells < 22 m (75 ft) deep across a 25 km(2) area of Bangladesh with variations in the nature of surface soils inferred from 18,500 measurements of frequency domain electromagnetic induction. A set of 14 hand auger cores recovered from the same area indicate that a combination of grain size and the conductivity of soil water dominate the electromagnetic signal. The relationship between pairs of individual EM conductivity and dissolved As measurements within a distance of 50 m is significant but highly scattered (r(2) = 0.12; n = 614). Concentrations of As tend to be lower in shallow aquifers underlying sandy soils and higher below finer-grained and high conductivity soils. Variations in EM conductivity account for nearly half the variance of the rate of increase of As concentration with depth, however, when the data are averaged over a distance of 50 m (r(2) = 0.50; n = 145). The association is interpreted as an indication that groundwater recharge through permeable sandy soils prevents As concentrations from rising in shallow reducing groundwater.