Unique migration-distribution processes and pollution risks of typical elements from geothermal spring discharge: A systematic assessment on Gudui geothermal field (southern Tibet)

Abstract

The Gudui geothermal field in southern Tibet, China's second-largest non-volcanic high-temperature geothermal system, exhibits vigorous hydrothermal activity, with widespread geothermal springs discharging harmful elements that threaten around environment. However, the enrichment and migration mechanisms of hazardous elements during geothermal spring discharge remain unclear, in particular, the unusual enriched and highly hazardous elements like Tl has not been drawn attention by previous researches. This study focuses on a high-temperature geothermal spring discharge area in Karugou watershed in Gudui and systematically track the distribution and partition law of As, Tl, and B in geothermal deposits, river water, sediments, and around farmland soils. Results indicate that concentrations of As, Tl, and B progressively increase along the river, with corresponding trends observed in sediments. Concentration of these elements exceed basic permission limits by 302.22, 1326.61 and 15.16 times, respectively. In farmland soils irrigated with river water, As and Tl levels at 40 cm depth exceed natural soil by 1.2 times, while surface B concentrations are over 4.2 times. Harmful elements from geothermal discharge exhibit systematic migration-distribution-partition patterns in geothermal deposits, river sediments, and soils, where elements first accumulate in geothermal deposits, with partial partitioning into travertine or sinter. With respect to As and B that enrich more in general travertine, Tl prefers to be enriched in sinter. Irrigation has distinctly introduced these elements into downstream farmland soils (0–40 cm). Such high enrichment poses significant potential environmental risks. Future geological events like tectonic activities, floods, or large-scale development could trigger massive release of these harmful elements from geothermal fluids or remobilization from river sediments, potentially endangering downstream populated areas. This study firstly highlights the uncommon natural hazardous elements like Tl enriched in geothermal spring and provides a reference for environmental impact assessments of geothermal exploitation in Tibet as well as worldwide.