地表灌溉对沉积含水层中碘迁移释放过程的影响

Influence of Surface Irrigation Practices on Iodine Mobilization in Sedimentary Aquifers

灌溉等人为活动会造成外源物质的输入,如硝酸盐、有机质等,从而引起浅层地下水环境发生周期性波动。为研究农业灌溉对沉积含水层中碘迁移富集过程的影响,选取代表性富碘沉积物,通过室内实验模拟了灌溉活动外源物质输入条件下,盆地地下水系统中碘迁移释放的(生物)地球化学过程。实验结果表明:厌氧条件下,外源有机质输入可促使微生物利用有机质作为电子供体,还原固相铁矿物相,进而造成搭载于铁氧化物/氢氧化物表面的碘释放,以碘离子形式在地下水中富集;而在NO_3^-输入情况下,微生物会优先利用NO_3^-为电子受体,至硝酸盐被全部消耗后,Fe(Ⅲ)可进一步被还原为Fe(Ⅱ)。研究结果表明,人为活动造成浅表环境外源物质的输入可直接影响浅层地下水中碘的迁移释放过程。伊利石黏土矿物吸附的铁氧化物矿物相可能为浅层环境中碘的主要搭载介质,微生物作用下,铁氧化物/氢氧化物的还原溶解是高碘地下水形成的主控因素。

Surface irrigation and other agricultural activities cause the input of exogenous materials,such as nitrate,organic matter and so on,which will lead to seasonal fluctuations in the shallow sedimentary aquifers.In this study,the iodine-rich sediments were selected to explore the influence of irrigation practice on iodine mobilization and accumulation in shallow groundwater system.The results show that under the anaerobic conditions,the reduction of iron mineral phase will be promoted by microbes using organic matter as electron donor because of the input of exogenous organic matter.This process can lead to iodine release into the liquid phase from iron oxide/hydroxide surface,mainly in the form of iodine ion in groundwater.With extra NO 3-input,Fe(III)will be reduced to Fe(II)until nitrate is consumed completely by microbes using NO 3-as electron acceptor.The input of exogenous substances by human activities is favorable for the iodine release from solid into shallow groundwater.Iron phase adsorbed by Illite may be the main carrier of solid iodine in shallow aquifers.Under the action of microorganisms,the reductive dissolution of solid Fe is the main controlling factor for release of solid iodine,thereby forming high iodine groundwater in shallow aquifers.