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Atmospheric and catchment mercury concentrations and fluxes in Fennoscandia

image of Atmospheric and catchment mercury concentrations and fluxes in Fennoscandia

Measurements in Southern Fennoscandia show a weak declining trend in mercury deposition which can be attributed to reduction controls in EU countries. Deposition of mercury in Arctic areas is likely to be governed by the amount of mercury in background air and therefore largely dependent on mercury emissions from mercury sources in the entire northern hemisphere. Hence, further reduction in anthropogenic emissions of mercury will require control measures in the entire northern hemisphere. The so called atmospheric mercury depletion events (AMDEs) are occurring during polar spring. How much of the deposited mercury that remains contra is re-emitted to the atmosphere is, however, crucial for assessing the importance of AMDE in the Arctic environment. Forest soils are an important sink for mercury deposited from the atmosphere. However, this sink can be affected by perturbations in conjunction to common forestry practices and lead to mobilization of the stored mercury and enhanced methyl mercury formation. Similar effects can be expected in areas where climate change results in large increases in precipitation amounts. The processes governing these changes in mercury mobilization are to some extent unknown and general predictions of the magnitude of the changes are thus associated with a large degree of uncertainty

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Discussion

Deposition of mercury is regulated by precipitation amounts and mercury concentration in deposition. The variation of the latter is to some degree due to the proximity to major mercury sources as well as to meteorology, e.g. wind transport patterns. The former East Countries still constitute a source area for airborne mercury. In Southern Poland, for example, the mercury deposition may during winter be more than 10 times higher then in Southern Sweden (Zielonka et al., 2005). Mercury deposition appears to decrease at many of the investigated sites, but at a slower rate than during the 1990-ties. The decreasing trend is likely to be an effect of reduced anthropogenic emissions in Europe. This started already in the beginning of the 1990-ties as a consequence of the economical breakdown in the former east block (Munthe et al., 2001) when many coal power plants and other industries were closed. As a result sulphur and also mercury emissions were strongly reduced. Today the deposition of mercury at for example Råö is 2-3 times lower than before 1990 (Wängberg et al., 2007). Nowadays the reduction in mercury emission in Europe is due to reduction controls in EU countries. That is control measures in coal power plants that are mainly intended for reduction of emissions of SO2 and particles also have a reducing effect on mercury emissions.

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