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| Titel |
Hg0 evasion from boreal mires determined with chamber methods and a novel REA design |
| VerfasserIn |
Stefan Osterwalder, Johannes Fritsche, Staffan Åkerblom, Mats B. Nilsson, Christine Alewell, Kevin Bishop |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105951
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| Publikation (Nr.) |
 EGU/EGU2015-5546.pdf |
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| Zusammenfassung |
| Anthropogenic mercury has accumulated in superficial organic soils of boreal mires, hotspots
of methylmercury production. We hypothesize that emission from the peat surface is an
important factor in regulating the pool of mercury in mires and ultimately the loading of
methylmercury to surface waters. To test this hypothesis, we used both dynamic flux
chambers (DFCs) and a dual-intake, single analyzer Relaxed Eddy Accumulation (REA)
system to quantify the land-atmosphere exchange of elemental mercury (Hg0) from a mixed
acid mire system situated near Vindeln in the county of Västerbotten, Sweden. Teflon and
polycarbonate DFCs were used to (i) investigate the effect of sulfur and nitrogen
addition as well as warming and changed moisture regimes on Hg0 flux and (ii) to
quantify typical all-day summertime fluxes. The novel REA design was developed
for long-term, all-year flux monitoring and uses twin inlets at the same level for
simultaneous accumulation of up and downdrafts on a pair of gold traps which are
then analyzed sequentially on the same detector while another pair of gold traps
takes over the accumulation. The exchange of Hg0 from the peatland surface was
measured continuously with DFC during cloudless conditions in July 2014 and
averaged 0.62 ± 1.3 ng m-2 h-1. The flux revealed a significant diurnal pattern and a
strong linear relationship with air temperature inside (R2= 0.65, p < 0.001) and
outside (R2= 0.58, p < 0.001) the DFC. Hg0 exchange was significantly lower on
experimental plots exposed to elevated sulfur deposition. This indicated either earlier
Hg evasion or Hg binding to sulfur in organic matter, making Hg less susceptible
to volatilization and more prone to transport in runoff. The REA measurements
revealed a seasonal pattern of Hg0 fluxes over the year with net evasion during
growing season and dominating deposition from autumn to spring. We managed to
perform the first conditional sampling of Hg0 flux over a boreal mire using REA and
were able to determine drivers and inhibitors of Hg0 evasion during short-term
DFC measurements. Hg removal via volatilization resembled the annual export of
Hg in streamwater hence indicating that the estimated time-span for reduced Hg
emissions to translate into lower Hg levels in the soil are too long because up to
now the emission of Hg from the mire surface to the atmosphere has been ignored. |
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