Showing papers by "John Munthe published in 1995"

Mechanisms of deposition of methylmercury and mercury to coniferous forests

Abstract: Deposition of methylmercury (MeHg) and mercury (Hg) to a coniferous forest have been investigated using field measurements. Samples of open field (OF) wet deposition, throughfall (TF) and litterfall (LF) have been collected and analyzed for MeHg and Hg during the period November 1991 to April 1994. Average concentrations in TF were 22.8 and 0.38 ng L-1, for Hg and MeHg, respectively. Concentrations in OF precipitation were 11.9 and 0.37 ng L-1, for Hg and MeHg, respectively, during the same period. Considerable differences were found for Hg in TF and OF which was attributed to a dry deposition of Hg. Hg in LF contributes a deposition of equal size as in TF. The relations between OF, TF and total Hg deposition were approximately 1:1.5:3. A decrease in OF Hg was found over the three year period studied. MeHg deposition in OF was also found to decrease during the same period whereas the TF MeHg showed a slight increase. Dry deposition of MeHg is also an important process in a coniferous forest although the flux to the forest floor is not via TF but rather as MeHg in LF.

Long-Term Changes in Concentration and Deposition of Atmospheric Mercury Over Scandinavia

Abstract: Samples for measurements of total gaseous mercury (Hg) in air have been collected since 1980 in south-western part of Scandinavia. A collection program for precipitation samples used to determine changes in depositional fluxes of total Hg has been in operation since 1987. A comparison of today’s total gaseous Hg levels in air and the total Hg concentrations in precipitation with the ones found earlier, shows a clear decrease with time. At the Swedish west-coast, yearly average air concentrations and median levels of 3.3 and 3.1 (1980–1984), 3.2 and 2.8 (1985–1989), and 2.7 and 2.6 ng Hg/m3 (1990–1992), respectively, were found. Increased average and median winter concentrations were always found, with levels at 3.7 and 3.4, 3.7 and 3.3, and 3.0 and 2.7 ng Hg/m3 for the respective time period. Higher winter values were expected due to increased anthropogenic emissions and changes in the mixing height of the atmosphere. The corresponding total wet deposition rates decreased from 27 (1987–1989) to 10 µg Hg/m2 yr. (1990–1992). A finding of special interest was the decreased number of episodic events of high total gaseous Hg levels in air, from 1990 and further on. In addition, the frequency distribution of the concentrations of Hg in air seems to be different for these years compared to the other two time periods. A frequency distribution of air concentrations of Hg more resembling a normal distribution was found for the years 1990 to 1992. The decrease of the atmospheric burden of total gaseous Hg and deposition of total Hg are most probably connected to lower emissions in source areas on the European continent. It seems logical to state that the problem of high Hg depositional fluxes to Scandinavia, is best solved by abatement strategies on the regional scale.

Cycling of Methyl Mercury and Mercury — Responses in the Forest Roof Catchment to Three Years of Decreased Atmospheric Deposition

Abstract: Studies of the biogeochemistry of total mercury (Hg) and methyl mercury (MeHg) in the Lake Gardsjon watershed have shown that the atmosphere is the most important source of Hg and MeHg in the ecosystem. Soils are accumulating most of the deposited Hg and MeHg, but transport of Hg and MeHg from the forested catchments into the lake ecosystems is enough to explain elevated concentrations of MeHg in fish in more than 10 000 Swedish lakes. An experimental roof was constructed to study effects of decreased atmospheric input on an entire forested catchment. The experiment started in April 1991, and decreases in the output of both MeHg and Hg occurred during 1991, 1992 and 1993. Runoff fluxes from the control catchment during the pre-treatment period were related to the experimental catchment using regression analyses. Since April 1991, after three year experiment, predicted compared to measured fluxes showed that Hg output decreased by 32% and MeHg by 28%. The decrease in Hg was most obvious during high water flows in winter/spring while MeHg decreased during all seasons of the year. The decreased input of Hg and MeHg to the Forest Roof Catchment is the most probable explanation to the rapid decrease in output of Hg and MeHg by runoff from the catchment basin.

Modeling the atmospheric chemistry of mercury: the importance of a detailed description of the chemistry of cloud water

Abstract: A model describing the aqueous chemistry and mass transfer processes of atmospheric mercury (Hg) has been used for analyzing the influence of various chemical and physical parameters on aqueous Hg concentrations. The model involves 39 gas phase species in 79 reactions and 32 aqueous species in 93 reactions. Modeled concentrations are in the range 2 to 5 and 5 to 10 ng L -1 for dissolved and total Hg respectively. Accurate descriptions of gas phase as well as aqueous phase chemistry of oxidants, acidifying substances and chlorine chemistry are necessary since there is a complex relationship between a number of species and the aqueous Hg concentrations. Of the physical parameters studied the influence of the assumed fog liquid water content was also found to be of great importance.

Modeling the Atmospheric Chemistry of Mercury

Abstract: A model describing the aqueous chemistry and mass transfer processes of atmospheric mercury (Hg) has been used for analyzing the influence of various chemical and physical parameters on aqueous Hg concentrations. The model involves 39 gas phase species in 79 reactions and 32 aqueous species in 93 reactions. Modeled concentrations are in the range 2 to 5 and 5 to 10 ng L-1 for dissolved and total Hg, respectively. Accurate descriptions of gas phase as well as aqueous phase chemistry of oxidants, acidifying substances and chlorine chemistry are necessary since there is a complex relationship between a number of species and the aqueous Hg concentrations. Of the physical parameters studied the influence of the assumed fog liquid water content was also found to be of great importance.

Trends of mercury and methylmercury in deposition, run-off water and sediments in relation to experimental manipulations and acidification

Abstract: In the covered catchment at Lake Gardsjon, the reversibility of acidification and the effects on Hg output of a decreased deposition of Hg and MeHg have been investigated since 1991. A first indication of a decreased from the covered catchment, caused by the artificial removal of Hg and MeHg input, has been observed. This has occurred in parallel with an overall decrease in Hg deposition fluxes in SW Sweden during 1990 to 1993. In the sediments of two acidified lakes, Lake Gardsjon (limed) and Lake Harsevatten (acid), Hg concentrations decrease by 60% in the top cm, from the maximum around 1000 ng g−1 at 5 cm depth indicating a decreasing deposition during the last 10 years. This decrease has occurred in parallel with decreasing atmospheric S-levels and is most likely caused by decreasing European Hg emissions. Decreasing trends of MeHg in run-off from two catchments has also been observed while the Hg output has remained somewhat more stable.