Measurements of diffuse fluxes of gaseous elemental mercury (GEM) from the soil of the hydrothermal area of Monterotondo Marittimo (Central Italy), known for the presence of the geosite “Le Biancane”, were performed by the combined use of a static closed chamber (SCC) and a Lumex® RA-915M portable analyzer. At the 89 GEM fluxes measurement points, CO2 fluxes using the accumulation chamber method, as well as temperature at the soil - air interface using a thermocouple, were also measured. The dataset was implemented with CO2/N2 concentration ratios of interstitial gases and soil temperature measured at the depth of interstitial gas sampling. The main aims were to i) investigate the geochemical behaviour of GEM with respect to CO2, soil temperature and soil permeability and ii) estimate the output of GEM and CO2 from the area. The data show that: i) GEM and CO2, despite having a common hydrothermal origin, tend to decouple due to secondary processes (scrubbing) occurring at relatively low depth up to the soil surface; ii) high GEM and low CO2 fluxes were caused by strong soil fracturing favouring air circulation and, consequently, dilution of the major gaseous species (CO2); iii) soil temperatures, although showing a good correlation with the CO2fluxes, seem not to control the GEM fluxes. The gas output estimations suggest that the diffuse degassing from the area (20,000 m2) represents a significant natural source of air contaminants: i) 0.335 tons a day of CO2 and ii) 2.01 × 10-7 tons a day of GEM. The GEM output was in agreement with previous investigations in other active degassing hydrothermal areas (e.g. Solfatara Crater, Southern Italy) and has important implications for air quality at a local scale, despite it only represents a portion of the total output of Monterotondo Marittimo area. Consequently, GEM flux measurements can be of strategic support to monitoring programs aimed to control the impact of this air contaminant, especially in areas where hydrothermal gas emissions are combined with those related to the cultivation and exploitation of geothermal fluids.
Gaseous Elemental Mercury (GEM) fluxes from the soil of the hydrothermal area of Monterotondo Marittimo (Grosseto, Central Italy) / Cabassi J., Di Bennardo F., Venturi S., Tassi F., Nisi B., Magi F., Ricci A., Picchi G., Vaselli O.. - ELETTRONICO. - (2019), pp. 0-0. (Intervento presentato al convegno Il tempo del pianeta Terra e il tempo dell’uomo: le geoscienze tra passato e future. Congresso Nazionale Parma 2019).
Gaseous Elemental Mercury (GEM) fluxes from the soil of the hydrothermal area of Monterotondo Marittimo (Grosseto, Central Italy)
Cabassi J.;Venturi S.;Tassi F.;Magi F.;Vaselli O.
2019
Abstract
Measurements of diffuse fluxes of gaseous elemental mercury (GEM) from the soil of the hydrothermal area of Monterotondo Marittimo (Central Italy), known for the presence of the geosite “Le Biancane”, were performed by the combined use of a static closed chamber (SCC) and a Lumex® RA-915M portable analyzer. At the 89 GEM fluxes measurement points, CO2 fluxes using the accumulation chamber method, as well as temperature at the soil - air interface using a thermocouple, were also measured. The dataset was implemented with CO2/N2 concentration ratios of interstitial gases and soil temperature measured at the depth of interstitial gas sampling. The main aims were to i) investigate the geochemical behaviour of GEM with respect to CO2, soil temperature and soil permeability and ii) estimate the output of GEM and CO2 from the area. The data show that: i) GEM and CO2, despite having a common hydrothermal origin, tend to decouple due to secondary processes (scrubbing) occurring at relatively low depth up to the soil surface; ii) high GEM and low CO2 fluxes were caused by strong soil fracturing favouring air circulation and, consequently, dilution of the major gaseous species (CO2); iii) soil temperatures, although showing a good correlation with the CO2fluxes, seem not to control the GEM fluxes. The gas output estimations suggest that the diffuse degassing from the area (20,000 m2) represents a significant natural source of air contaminants: i) 0.335 tons a day of CO2 and ii) 2.01 × 10-7 tons a day of GEM. The GEM output was in agreement with previous investigations in other active degassing hydrothermal areas (e.g. Solfatara Crater, Southern Italy) and has important implications for air quality at a local scale, despite it only represents a portion of the total output of Monterotondo Marittimo area. Consequently, GEM flux measurements can be of strategic support to monitoring programs aimed to control the impact of this air contaminant, especially in areas where hydrothermal gas emissions are combined with those related to the cultivation and exploitation of geothermal fluids.
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