Diffuse emission and transport of gaseous elemental mercury (GEM) in the Mapamyum geothermal system, Western Tibet (China)

Abstract

Mercury (Hg) is a widely spread pollutant, owing to its high mobility in the nature. The rising input of Hg into the atmosphere has resulted in enhanced Hg pollution in both terrestrial and aquatic ecosystems. The Tibetan plateau, which is known as the roof of the world, is considered as a Hg-sensitive ecosystem. The Himalayan-Tibetan geothermal belt, which is formed due to the collision between India and Eurasia, is an important potential source of Hg to the atmosphere. However, previous studies to the emission and transport of geological Hg in the Tibetan Plateau are still rare. Understanding emission and transport of Hg in the Tibetan Plateau can provide important constraints on global Hg budget and its pollution transport. Diffuse emission and transport of gaseous elemental mercury (GEM or Hg0) in the Mapamyum geothermal system (MGF) of western Tibet was investigated and simulated by the closed-chamber method and the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) dispersion model. The estimated annual output of GEM in the MGF, calculated over an area of 41,615 m2, was in the order of 6.1 × 10−4 ton. He-C isotope ratios of the geothermal samples were all within the range of typical crustal domain. Combing with the hydrothermal analysis, it could deduce the Hg0 in the MGF might derive from both deep lithosphere and the upper crust. The GEM diffused from the source region was mainly dispersed to the NW direction. The maximum concentration of GEM is mainly distributed around the MGF, which is also the region with the largest deposition rate. The simulated results of the HYSPLIT dispersion model suggest that the GEM emitted from the MGF would not significantly enhance the atmospheric Hg concentration, whereas the deposition and accumulation of GEM around the source region is not negligible.