M. Amyot et al., EFFECT OF SOLAR-RADIATION ON THE FORMATION OF DISSOLVED GASEOUS MERCURY IN TEMPERATE LAKES, Geochimica et cosmochimica acta, 61(5), 1997, pp. 975-987
We have assessed the effect of solar radiation on the formation of dis
solved gaseous mercury (DGM) in lake water samples incubated in situ.
In temperate forested lakes, solar radiation induced the formation of
DGM, whereas in Lake Erie, light had no effect. Tn lakes where photo-i
nduced DGM production was found, DGM concentrations were higher near t
he surface, whereas in Lake Erie, DGM levels peaked in the metalimnion
. In high DOC lakes, removal of UVB radiation did not affect DGM proje
ction, whereas in a low DOC lake, DGM production rates were significan
tly lower in the absence of UVB radiation, suggesting that DOC compoun
ds are reducing the availability of UVB radiation for photoreduction o
f Hg. The relationship between light intensity and DGM production was
nonlinear in Ranger Lake. Above similar to 3 MJ m(-2) total incident r
adiation, a plateau was reached at about 400 fM during the summer and
about 150 fM during the fall. In this lake, a clear diel pattern of DG
M levels was found which paralleled that for total solar radiation. Sp
iking of samples with Hg(II) prior to incubation in Ranger Lake greatl
y increased the DGM production rate, suggesting that photoreducible Hg
(II) complexes were limiting DGM production. Filtration through GF/F f
ilters or sterilization by heating prior to incubation did not decreas
e DGM production rates, suggesting that agents promoting DGM formation
in Ranger Lake were either dissolved or colloidal. DGM levels in outf
lows of two high DOC drainage lakes were higher than in inflows, confi
rming that the lakes were sites of DGM production. Copyright (C) 1997
Elsevier Science Ltd.