34
R. Ebinghaus et al.
polluted wetlands, namely East Fork Poplar Creek (EFPC) in Tennessee, USA
(Lindberg et al. 1995), and the river Elbe in Germany (Wallschlager et al. 1997a).
The former is a small waterbody that was contaminated directly from a single
large industrial point source, while the latter is the third largest river in Germany
and comprises a much larger area that became contaminated by much larger
absolute amounts of Hg discharges from the entire industrial area along its
course. However, both study areas are relatively similar in that they are
floodplain ecosystems which show similar degrees of Hg contamination.
Therefore, it seems appropriate to compare the results of investigations on airsoil exchange of Hg at both sites.
The EFPC floodplains has an area of 250 ha and is estimated to contain a total
Hg pool of 80 t. Soil Hg concentrations range from 4 to 60 pg g-I in less
contaminated and 50-200 pg g -I in more contaminated areas (Lindberg et al.
1995). Solid-phase speciation experiments seem to reveal that most of the
deposited Hg is present in the forms of HgS (cinnabar and meta-cinnabar) with
minor amounts of elemental Hg( 0) (Barnett et al. 1995). Mercury volatilization
from these floodplain soils was studied by the first micrometeorological
approach to be developed for Hg, the modified Bowen-ratio method (MBR)
(Lindberg et al. 1995). Naturally, a net Hg emission from these soils was observed,
and fluxes were found to be between 10 and 200 ng m- 2 h- I over the study site
containing an average of 4.3 ± 0.3 pg g-I Hg. Since the applied technique has a
fairly large "footprint area" (i.e., is representative of a large area surrounding the
actual measurement site), these fluxes are partially influenced by air masses
passing over more contaminated areas of the floodplain. Higher fluxes were
correlated with wind directions coming from the more contaminated parts of the
floodplains, and lower fluxes came from the less contaminated regions. The total
annual emission from the EFPC floodplains to the atmosphere was estimated to
be between 1 and 10 kg.
The Elbe floodplains have an estimated area of 1100 km 2 and total deposited
Hg amount Of1500 t (Wallschlager and Wilken 1997). Average Hg concentrations
in the soils range from 1 to 10 pg g-I and most of the Hg is bound by high
molecular weight organic matter (Wallschlager et al. 1997a). In these studies, flux
chamber measurements were employed to estimate Hg volatilization, but they
were also compared to the MBR method by measuring the concentration gradient
of atmospheric Hg in the soil atmosphere boundary layer and adopting the
micro meteorological parameters from the EFPC floodplains (Lindberg et al.
1995). Additionally, Hg volatilization was estimated from soil air concentration
data assuming laminar diffusion. Results for Hg emissions from soils containing
10 ~lg g-I range from 28 to 260 ng m -2 h -I and are thus comparable to the fluxes
measured at EFPC. However, it was noted that the individual applied techniques
did not agree very well due to their inherent methodological differences, and that
there is a need for intercomparison studies (Wallschlager et al. 1997C). The
overall annual emission of Hg from the Elbe floodplains to the atmosphere was
estimated to be on the order of 1 t year-I, thereby representing a significant, but
not dominant Hg source on the regional scale.
Micrometeorological studies over background forest soils at Walker Branch
Watershed (WBW), Tennessee, USA, led to the conclusion that these soils can act
R. Ebinghaus et al.
polluted wetlands, namely East Fork Poplar Creek (EFPC) in Tennessee, USA
(Lindberg et al. 1995), and the river Elbe in Germany (Wallschlager et al. 1997a).
The former is a small waterbody that was contaminated directly from a single
large industrial point source, while the latter is the third largest river in Germany
and comprises a much larger area that became contaminated by much larger
absolute amounts of Hg discharges from the entire industrial area along its
course. However, both study areas are relatively similar in that they are
floodplain ecosystems which show similar degrees of Hg contamination.
Therefore, it seems appropriate to compare the results of investigations on airsoil exchange of Hg at both sites.
The EFPC floodplains has an area of 250 ha and is estimated to contain a total
Hg pool of 80 t. Soil Hg concentrations range from 4 to 60 pg g-I in less
contaminated and 50-200 pg g -I in more contaminated areas (Lindberg et al.
1995). Solid-phase speciation experiments seem to reveal that most of the
deposited Hg is present in the forms of HgS (cinnabar and meta-cinnabar) with
minor amounts of elemental Hg( 0) (Barnett et al. 1995). Mercury volatilization
from these floodplain soils was studied by the first micrometeorological
approach to be developed for Hg, the modified Bowen-ratio method (MBR)
(Lindberg et al. 1995). Naturally, a net Hg emission from these soils was observed,
and fluxes were found to be between 10 and 200 ng m- 2 h- I over the study site
containing an average of 4.3 ± 0.3 pg g-I Hg. Since the applied technique has a
fairly large "footprint area" (i.e., is representative of a large area surrounding the
actual measurement site), these fluxes are partially influenced by air masses
passing over more contaminated areas of the floodplain. Higher fluxes were
correlated with wind directions coming from the more contaminated parts of the
floodplains, and lower fluxes came from the less contaminated regions. The total
annual emission from the EFPC floodplains to the atmosphere was estimated to
be between 1 and 10 kg.
The Elbe floodplains have an estimated area of 1100 km 2 and total deposited
Hg amount Of1500 t (Wallschlager and Wilken 1997). Average Hg concentrations
in the soils range from 1 to 10 pg g-I and most of the Hg is bound by high
molecular weight organic matter (Wallschlager et al. 1997a). In these studies, flux
chamber measurements were employed to estimate Hg volatilization, but they
were also compared to the MBR method by measuring the concentration gradient
of atmospheric Hg in the soil atmosphere boundary layer and adopting the
micro meteorological parameters from the EFPC floodplains (Lindberg et al.
1995). Additionally, Hg volatilization was estimated from soil air concentration
data assuming laminar diffusion. Results for Hg emissions from soils containing
10 ~lg g-I range from 28 to 260 ng m -2 h -I and are thus comparable to the fluxes
measured at EFPC. However, it was noted that the individual applied techniques
did not agree very well due to their inherent methodological differences, and that
there is a need for intercomparison studies (Wallschlager et al. 1997C). The
overall annual emission of Hg from the Elbe floodplains to the atmosphere was
estimated to be on the order of 1 t year-I, thereby representing a significant, but
not dominant Hg source on the regional scale.
Micrometeorological studies over background forest soils at Walker Branch
Watershed (WBW), Tennessee, USA, led to the conclusion that these soils can act