Controlling Mechanism of Paleoclimate Change on Iodine Enrichment in Alluvial Aquifers of Middle Reach of Yangtze River since Late Pleistocene
The presence of geogenic high iodine groundwater in alluvial aquifers in the middle reach of the Yangtze River poses a serious threat to regional water supply security.Iron minerals and organic matter in aquifer sediments are the main carriers of iodine,and revealing the control mechanism of climate change on iodine enrichment in aquifers since the Late Pleistocene from the perspective of regional-geological background and sedimentary evolution is a prerequisite for scientific understanding of the causes of high iodine groundwater and ensuring water supply security.In this study,Quaternary sediments in the distribution area of high iodine groundwater in the middle reach of the Yangtze River were collected,and sediment geochemistry was systematically characterized to identify the main carriers of iodine enrichment in aquifer sediments and to reveal the controlling mechanisms of iodine enrichment in aquifers by weathering and deposition pocesses driven by paleoclimatic changes.The results show that the main iodine speciation in sediments are iron oxide-bounded(IFe-ox)and organic matter bounded(Iorg),and the chemical weathering index CIA and K/Na ratio of sediments are significantly positively correlated with IFe-ox and Iorg.Amorphous iron oxides(Feox1),clay minerals and organic matter are the main carriers of iodine.Climate changed from cold and arid to warm and humid since the Late Pleistocene and Holocene,enhanced chemical weathering,which contributed to the formation of more amorphous iron oxides,and the expansion of lakes after the Holocene led to the co-burial of iodine,organic matter and iron oxides in the lacustrine sediments.Paleoclimatic changes play an important role in controlling iodine enrichment in the middle Yangtze River aquifer.
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