Distribution and Hydrogeochemical Characteristic of High Iodine Groundwater in Oasis Zone in the Tarim Basin in Xinjiang, China

Groundwater is the main water supply source in the Tarim Basin in China. Endemic disease caused by high iodine(I) groundwater in the Tarim Basin was reported previously. Therefore, it is crucial to systematically identify the distribution and genesis of groundwater I. Based on hydrochemical analysis of 717 groundwater samples collected in 2015 – 2018, spatial distribution and hydrogeochemistry characteristic of high I groundwater in different aquifers were analyzed. Results showed that groundwater I ranged between < 10.00 and 4 000.00 μg/L(mean of 53.71 μg/L).High I groundwater(I > 100.00 μg/L) accounted for 7.25% of the total samples. Horizontally,groundwater I significantly increased from recharge zone(RZ) to transition zone(TZ) and to evaporation zone(EZ). Vertically, groundwater in shallow confined aquifer(SCA) had the greatest I concentration, followed by single-structure phreatic aquifer(SSPA), phreatic aquifer in confined groundwater area(PACGA), while groundwater in deep confined aquifer(DCA) generally had low I concentration. Groundwater I enrichment in SSPA was mainly affected by organic matter(OM) decomposition and that in SCA was mainly affected by evaporite mineral dissolution, OM decomposition under alkaline environment. While I enrichment in groundwater of PACGA was restrained under neutral environment. Lacustrine sedimentary environment was crucial for I enrichment in groundwater. Besides, fine-grained lithology of aquifer, smooth topographic slope, shallow buried depth of groundwater, weak alkaline and reducing environment, reductive dissolution of iron oxide/hydroxide minerals and OM decomposition were advantageous to I enrichment in groundwater.