7 research outputs found
Distribution and Uptake Dynamics of Mercury in Leaves of Common Deciduous Tree Species in Minnesota, U.S.A.
A sequential extraction technique
for compartmentalizing mercury
(Hg) in leaves was developed based on a water extraction of Hg from
the leaf surface followed by a solvent extraction of the cuticle.
The bulk of leaf Hg was found in the tissue compartment (90–96%)
with lesser amounts in the surface and cuticle compartments. Total
leaf concentrations of Hg varied among species and was most closely
correlated with the number of stomates per sample, supporting the
hypothesis that stomatal uptake of atmospheric Hg (most likely Hg<sup>0</sup>) is a potential uptake pathway. Mercury concentrations in
leaves were monitored from emergence to senescence and showed a strong
positive correlation with leaf age. Leaves accumulated Hg throughout
the growing season; the highest uptake rates coincided with periods
of high photosynthetic activity. Concentrations of Hg in leaf tissue
increased steadily throughout the season, but no such trends were
observed for surficial or cuticular accumulation. Factors affecting
the variability of Hg in leaves were analyzed to improve protocols
for the potential use of leaves as passive monitors of atmospheric
Hg. Results show that total leaf Hg concentrations are affected by
leaf age and leaf placement in the crown
A vegetation control on seasonal variations in global atmospheric mercury concentrations
International audienceAnthropogenic mercury emissions are transported through the atmosphere as gaseous elemental mercury (Hg(0)) before they are deposited to Earth’s surface. Strong seasonality in atmospheric Hg(0) concentrations in the Northern Hemisphere has been explained by two factors: anthropogenic Hg(0) emissions are thought to peak in winter due to higher energy consumption, and atmospheric oxidation rates of Hg(0) are faster in summer. Oxidation-driven Hg(0) seasonality should be equally pronounced in the Southern Hemisphere, which is inconsistent with observations of constant year-round Hg(0) levels. Here, we assess the role of Hg(0) uptake by vegetation as an alternative mechanism for driving Hg(0) seasonality. We find that at terrestrial sites in the Northern Hemisphere, Hg(0) co-varies with CO, which is known to exhibit a minimum in summer when CO is assimilated by vegetation. The amplitude of seasonal oscillations in the atmospheric Hg(0) concentration increases with latitude and is larger at inland terrestrial sites than coastal sites. Using satellite data, we find that the photosynthetic activity of vegetation correlates with Hg(0) levels at individual sites and across continents. We suggest that terrestrial vegetation acts as a global Hg(0) pump, which can contribute to seasonal variations of atmospheric Hg(0), and that decreasing Hg(0) levels in the Northern Hemisphere over the past 20 years can be partly attributed to increased terrestrial net primary production