Effects of iodine content on the hydrochemical characteristics and microbial community structure of groundwater in coastal zone: A case study of Bailang River Basin.

Iodine is an important component of the thyroid gland, producing hormones. Excess iodine can trigger autoimmune thyroid disease. The salt-freshwater interaction zone of the coastal aquifer is affected by seawater intrusion, and the physical and chemical environment is constantly changing. Exploring the characteristics and influencing factors of high-iodine groundwater in coastal areas play an important role in the prevention and control of groundwater pollution. In this study, the hydrochemical characteristics of high-iodine groundwater were analyzed. The interrelationship between the water's chemical components was revealed, and the microbial community composition under different iodine concentration gradients in the groundwater was examined using 16sRNA high-throughput sequencing. The influence of water quality on microbial distribution was also explored. The results showed that the iodine content in the Bailang River Basin ranged from 31 to 1776 μg/L, and the high-iodine groundwater samples accounted for 67.7%, with uneven spatial distribution. Groundwater samples with different iodine concentrations were grouped and compared, and there was no significant difference in the diversity and richness of microbial communities. At the genus level, iodine concentrations were significantly correlated with Sediminibacterium and Thauera. In addition to iodine, nitrates and sulfates also have a significant effect on microbial communities. PRACTITIONER POINTS: Groundwater in the south bank of Laizhou Bay is predominantly alkaline, with uneven spatial distribution of iodine content. As the concentration of iodide increases, the groundwater chemical type tends towards Na-Cl type. The concentration of iodine has little effect on the richness and diversity of microbial communities. The concentrations of sulfate, nitrate, and nitrite also affect the microbial structure and species diversity of groundwater.