Degassing and Cycling of Mercury at Nisyros Volcano (Greece)

Abstract

Nisyros Island (Greece) is an active volcano hosting a high-enthalpy geothermal system. During June 2013, an extensive survey on Hg concentrations in different matrices (fumarolic fluids, atmosphere, soils, and plants) was carried out at the Lakki Plain, an intracaldera area affected by widespread soil and fumarolic degassing. Concentrations of gaseous elemental mercury (GEM), together with H2S and CO2, were simultaneously measured in both the fumarolic emissions and the atmosphere around them. At the same time, 130 samples of top soils and 31 samples of plants (Cistus creticus and salvifolius and Erica arborea and manipuliflora) were collected for Hg analysis. Mercury concentrations in fumarolic gases ranged from 10,500 to 46,300 ng/m3, while Hg concentrations in the air ranged from high background values in the Lakki Plain caldera (10-36 ng/m3) up to 7100 ng/m3 in the fumarolic areas. Outside the caldera, the concentrations were relatively low (2-5 ng/m3). The positive correlation with both CO2 and H2S in air highlighted the importance of hydrothermal gases as carrier for GEM. On the other hand, soil Hg concentrations (0.023-13.7 μg/g) showed no significant correlations with CO2 and H2S in the soil gases, whereas it showed a positive correlation with total S content and an inverse one with the soil pH, evidencing the complexity of the processes involving Hg carried by hydrothermal gases while passing through the soil. Total Hg concentrations in plant leaves (0.010-0.112 μg/g) had no direct correlation with soil Hg, with Cistus leaves containing higher values of Hg with respect to Erica. Even though GEM concentrations in the air within the caldera are sometimes orders of magnitude above the global background, they should not be considered dangerous to human health. Values exceeding the WHO guideline value of 1000 ng/m3 are very rare (<0.1%) and only found very close to the main fumarolic vents, where the access to tourists is prohibited.

Quantification of volcanic degassing and analysis of uncertainties using numerical modelling: the case of Stephanos crater (Nisyros Island, Greece)

“…3 indicate that there is no hazard posed by CO 2 and H 2 S outside the crater, as well as no serious conditions are expected to occur within it, considering the present-day volcanic degassing. Our simulated averaged concentrations result to be lower than those reported in the literature for the same investigated area (see Gagliano et al, 2019), and are in very good agreement with the instantaneous concentrations acquired during the April-June 2023 (Fig. 2b; Table 2) and the CO 2 concentration time-series measured by the gas sensors during the gas survey (Supplementary Information).…”

Measurement of Atmospheric Mercury over Volcanic and Fumarolic Regions on the North Island of New Zealand Using Passive Air Samplers

“…Most previous estimations of Hg flux from volcanic systems have been obtained through the monitoring of SO 2 fluxes and the Hg/SO 2 ratio measured in the volcanic plume. ,, Hg flux from fumaroles has more often been estimated based on the Hg/CO 2 ratio and monitored CO 2 fluxes in the fumarole plume. , Some studies directly measured the Hg flux using field flux chambers . Compared to previously reported Hg emissions from geothermal sources, the estimated emission flux from Karapiti is higher than Hg fluxes measured at La Fossa crater of Vulcano, Italy (4.4–7.1 kg year –1 ), and Nisyros, Greece (0.7 kg year –1 ), similar to Hg fluxes at Tatun volcanic field, Taiwan (5–50 kg year –1 ), and Yellowstone caldera (15–56 kg year –1 ), while much smaller than Hg fluxes at Mount Etna (5.4 t year –1 ) and Masaya volcano, Nicaragua (7.2 t year –1 ) . The large range reflects the complexity in determining the Hg fluxes from geothermal sources, which is affected by many factors such as the physical nature of degassing (i.e., temporal and spatial variability), the temperature of the geothermal activities, and the mineralogical composition of the underlying area.…”

“…Mercury is emitted into the atmosphere from both natural and anthropogenic sources, though the exact proportion of each continues to be debated. , Natural sources include the contribution from primary natural sources (e.g., volcanoes) and re-emissions of previously deposited Hg over land and sea surfaces . Degassing volcanoes, fumaroles, and geothermal fields can emit significant amounts of Hg − and are perhaps the most important natural Hg sources as they represent a geological input of Hg into the active biogeochemical cycle of Hg at or above the Earth’s surface. Mercury fluxes from volcanoes and geothermal sources, which are predominantly in the form of GEM (>98%), , are estimated to contribute substantially to the total natural Hg flux to the atmosphere both on a global and a regional scale. ,, Two recent reviews estimated a global Hg emission flux from volcanoes to be 90 and 700 t year –1 , another study reported a global Hg flux from degassing volcanoes of 76 ± 30 t year –1 , and a global GEM flux from hydrothermal fields was estimated to be 8.5 t year –1 .…”

Mercury in the terrestrial environment: a review

“…The important factor for Hg concentrations in forest soils is the time since standreplacing fires have occurred, and high soil burn severity has the potential to reduce the concentrations of Hg in burned soils for tens to hundreds of years [53,54]. In a specific emission source in Nisyros Island (Greece), Hg concentrations in fumarolic gases in Nisyros Island (Greece) ranged from 10,500 to 46,300 ng/m 3 , while Hg concentrations in the air ranged from high background values in the Lakki Plain caldera (10-36 ng/m 3 ) up to 7100 ng/m 3 in the fumarolic areas [55].…”