Natural and Anthropogenic Mercury Sources
39
Table 19. Mercury emissions from forests and its global estimates. (After Lindberg et al. 1996)
Region
High latitude
Mid latitude
Low latitude
All forests"
Soils - non forested"
Soils - forested
Total net emission of
Hg(O)
Forest type
Boreal
Temperate
Tropical
" From Carpi and Lindberg (I998).
Forest area
(in 10 12 m 2 )
1.37
1.04
1.76
4.17
Estimated global emissions
(in t year I)
10-100
300-700
540-1200
850-2000
500-1100
80-160
1400-3200
considers that these estimates do not yet include emISSIOns from either Hgcontaminated or Hg-enriched soils and surface deposits, it becomes clear that an
accurate assessment of air/surface exchange processes on a global scale will be
critical to the refining of global mercury cycling models.
The global wet deposition of mercury to the ocean has been estimated from the
measured concentrations of Hg in precipitation, coupled with estimates of ocean
area and precipitation (Mason et al. I994a). Unfortunately, there are no
comparable regional to global scale estimates of dry deposition, although it is
certainly a highly significant component of the global cycle (Iverfeldt and
Lindberg 1996) The global wet deposition input of mercury to the oceans at
different latitudes has been summarized in Table 20. The mercury fluxes in
individual latitudinal regions were found to range from 0.13 ~lg m- 2 year-I for
Antarctica to 7.7 pg m- 2 year-I for the northern mid latitude region (30-70°).
The fluxes show the influence of anthropogenic activity which is largely confined
to the Northern Hemisphere. It is also evident from the table that the fluxes are at
least a factor of 2 higher in the Northern Hemisphere compared to the
corresponding Southern Hemispheric regions. Because of low particulate
Table 20. Estimated average wet deposition to the oceans and to land for various latitudinal regions.
(Data after Mason and Fitzgerald 1996)
Latitude
Precipit.
Ocean area Global input (t year I)
Flux (pg m 2 y I)
(m/year)
x 10 12 m 2
Ocean
Land
Ocean
Land
70-90° N
0.16
11.7 (47)
8
14
0.68
0.1
30-70° N
0.79
51.4 (50)
400
800
7.7
15.8
10-30° N
0.97
56.6 (69)
540
500
9.5
19.8
lOoN_10° S
1.54
67.9 (77)
320
260
4.7
12.7
10-30° S
1.0
63.2 (77)
260
180
4.1
9.6
30-70° S
0.96
105.1(94)
400
60
3.8
8.5
70-90° S
0.07
3.1 (20)
0.4
2
0.\3
0.32
Total
1928
1816
Note: Values in brackets are % of surface covered by ocean.
39
Table 19. Mercury emissions from forests and its global estimates. (After Lindberg et al. 1996)
Region
High latitude
Mid latitude
Low latitude
All forests"
Soils - non forested"
Soils - forested
Total net emission of
Hg(O)
Forest type
Boreal
Temperate
Tropical
" From Carpi and Lindberg (I998).
Forest area
(in 10 12 m 2 )
1.37
1.04
1.76
4.17
Estimated global emissions
(in t year I)
10-100
300-700
540-1200
850-2000
500-1100
80-160
1400-3200
considers that these estimates do not yet include emISSIOns from either Hgcontaminated or Hg-enriched soils and surface deposits, it becomes clear that an
accurate assessment of air/surface exchange processes on a global scale will be
critical to the refining of global mercury cycling models.
The global wet deposition of mercury to the ocean has been estimated from the
measured concentrations of Hg in precipitation, coupled with estimates of ocean
area and precipitation (Mason et al. I994a). Unfortunately, there are no
comparable regional to global scale estimates of dry deposition, although it is
certainly a highly significant component of the global cycle (Iverfeldt and
Lindberg 1996) The global wet deposition input of mercury to the oceans at
different latitudes has been summarized in Table 20. The mercury fluxes in
individual latitudinal regions were found to range from 0.13 ~lg m- 2 year-I for
Antarctica to 7.7 pg m- 2 year-I for the northern mid latitude region (30-70°).
The fluxes show the influence of anthropogenic activity which is largely confined
to the Northern Hemisphere. It is also evident from the table that the fluxes are at
least a factor of 2 higher in the Northern Hemisphere compared to the
corresponding Southern Hemispheric regions. Because of low particulate
Table 20. Estimated average wet deposition to the oceans and to land for various latitudinal regions.
(Data after Mason and Fitzgerald 1996)
Latitude
Precipit.
Ocean area Global input (t year I)
Flux (pg m 2 y I)
(m/year)
x 10 12 m 2
Ocean
Land
Ocean
Land
70-90° N
0.16
11.7 (47)
8
14
0.68
0.1
30-70° N
0.79
51.4 (50)
400
800
7.7
15.8
10-30° N
0.97
56.6 (69)
540
500
9.5
19.8
lOoN_10° S
1.54
67.9 (77)
320
260
4.7
12.7
10-30° S
1.0
63.2 (77)
260
180
4.1
9.6
30-70° S
0.96
105.1(94)
400
60
3.8
8.5
70-90° S
0.07
3.1 (20)
0.4
2
0.\3
0.32
Total
1928
1816
Note: Values in brackets are % of surface covered by ocean.