Environmental Engineering Reference
In-Depth Information
table 10.6
Numerical Model and Mass Balance Results for Cycling of Total Mercury in the Ocean
Increase in Hg
since preindustrial
times (Mmol)
Current rate
of increase
in Hg (Mmol yr
1
)
Past rate
of increase
in Hg (Mmol yr
1
)
a
Study
Surface Waters
Mason et al., 1994 (MFM)
36 (200%)
b
0.5 (
0.9% yr
1
)
b
0.24 (1.3% yr
1
)
b
Lamborg et al., 2002a (GRIMM)
25 (86%)
b
0.8 (1.5% yr
1
)
b
0.17 (0.57% yr
1
)
b
Mason and Sheu, 2002
15 (
5%)
d,e
0.1 (
0.03% yr
1
)
d
0.1 (
0.03% yr
1
)
d,e
Strode et al., 2007
NA
0
f
NA
Sunderland and Mason, 2007
Entire Ocean
129 (25%)
g
7.7 (1.2% yr
1
)
g
0.86 (0.17% yr
1
)
g
Atlantic
(58%)
g
NA
(0.39% yr
1
)
g
Pacifi c/Indian
(56%)
g
NA
(0.37% yr
1
)
g
Selin et al., 2008
22 (1800%)
f
0
f
0.15 (12% yr
1
)
f
Deep Waters
Mason et al., 1994 (MFM)
NA
0.7 (0.07% yr
1
)
c
NA
Lamborg et al., 2002a (GRIMM)
178 (20%)
4.0 (0.40% yr
1
)
1.2 (0.13% yr
1
)
Mason and Sheu, 2002
120 (11%)
e
2.4 (0.22% yr
1
)
0.8 (0.07% yr
1
)
e
Strode et al., 2007
NA
7.7 (0.70% yr
1
)
NA
Sunderland and Mason, 2007
Entire Ocean
124 (11%)
1.5 (0.14% yr
1
)
0.83 (0.07% yr
1
)
Atlantic
(32%)
NA
(0.21% yr
1
)
Pacifi c/Indian
(
1%)
NA
(<0.01% yr
1
)
Selin et al., 2008
249 (17%)
8.5 (0.49% yr
1
)
1.7 (0.11% yr
1
)
note: Total Hg amounts are reported in Mmol, with percent change given in parentheses. Fluxes are reported as Mmol yr
1
,
with percent change per year given in parentheses. NA
not available.
a. Averaged over the past 150 years, assuming simple linear increase.
b.
100 m.
c. Assumes subthermocline total Hg pool of 1000 Mmol.
d.
500 m.
e. Assumes past increases in oceanic Hg were primarily limited to the deep ocean, consistent with the mass balance described
for the present day.
f. Variable mixed layer depth, mean of 53 m, g.
1500 m.
increases are not predicted to occur quickly, with the sys-
tem requiring decades to millennia to reach steady state,
but time scales will vary as a function of both depth and
location in the ocean (Selin et al., 2008; Sunderland and
Mason, 2007). Such differences refl ect the spatial hetero-
geneity of total Hg inputs to the ocean, which occur pri-
marily to surface waters via atmospheric deposition, and
to a lesser extent to coastal waters via runoff. Spatial dif-
ferences and increases in Hg atmospheric deposition are
displayed in Figures 10.5 and 10.6. Figure 10.5 shows the
mean annual atmospheric deposition of Hg globally by spe-
cies and fl ux during preindustrial times, while Figure 10.6
shows the increase in net Hg atmospheric deposition in
the present-day relative to preindustrial times, both as esti-
mated by Selin et al. (2008).
Mercury models have also been created for local and
regional scales. Macleod et al. (2005) developed a mul-
tispecies model describing the distribution of mercury
in the San Francisco Bay Area, a region contaminated by
both historic mining and contemporary industrial activ-
ities. Riverine inputs and resuspension of contaminated
sediment dominate the mercury cycle in that estuary.
Their model suggests that the response time of mercury
concentrations to changes in mercury loads is on the
