|
(T/MF144) Importance of photoinduced formation of Dissolved Gaseous Mercury and air-exchange in the Mediterranean basin. Lanzillotta, Enrica1, Ferrara, Romano1, Ceccarini, Claudia1, 1 ABSTRACT- The mercury exchange from aquatic surface to the atmosphere is the result of the formation of volatile forms of mercury in natural waters and their subsequent evasion. Dissolved Gaseous Mercury (DGM) is mainly constituted of elemental mercury (about 90%), with low contribution of organic mercury species. The formation of elemental mercury depends on the abiotic and biotic reduction of reactive mercury which is partially removed from the water column , where it could otherwise be methylated. From the global point of view mercury evasion from surface water accounts for about 30% of the current total annual flux to the atmosphere. The DGM production is photoinduced throughout photochemical and/or photobiological processes. The air-sea exchange of mercury plays an important role in the Mediterranean basin which is characterised by an intense solar radiation, high environmental temperatures and large cinnabar deposits (HgS). We have determined the DGM concentrations and mercury flux levels in coastal and open seawater. A pronounced seasonal behaviour has been observed, with values about for times higher in summer than those measured in winter. A daily trend of DGM concentration in shallow coastal water has been measured: a value up to 47 pg/l (spring season) was determined during the hours of highest insulation. In deep waters of the same basin only low and almost constant values have been measured. Also the evasional flux shows a daily trend, with the highest values for mercury emission rate ranging from 4-12 ng/m2h (summer season). The values of emission rate suggest that the evasional flux is the major natural source of mercury released annually into the Mediterranean atmosphere. Key words: mercury, speciation, photoreduction, mediterranean basin |
