A spatial assessment of current and future foliar Hg uptake fluxes
across European forests
Atmospheric mercury (Hg) is deposited to land surfaces mainly through
vegetation uptake. Foliage stomatal gas exchange plays an important role
for net vegetation Hg uptake, because foliage assimilates Hg via the
stomata. Here, we use empirical relationships of foliar Hg uptake by
forest tree species to produce a spatially highly resolved (1 km2) map
of foliar Hg fluxes to European forests over one growing season. The
modelled forest foliar Hg uptake flux is 23 ± 12 Mg Hg season−1, which
agrees with previous estimates from literature.
We spatially compare forest Hg fluxes with modelled fluxes of the
chemistry-transport model GEOS-Chem and find a good overall agreement.
For European pine forests, stomatal Hg uptake was shown to be sensitive
to prevailing conditions of relatively high ambient water vapor pressure
deficit (VPD). We tested a stomatal uptake model for the total pine
needle Hg uptake flux during four previous growing seasons (1994, 2003,
2015/2017, 2018) and two climate change scenarios (RCP 4.5 and RCP 8.5).
The resulting modelled total European pine needle Hg uptake fluxes are
in a range of 8.0 - 9.3 Mg Hg season−1 (min - max). The lowest pine
forest needle Hg uptake flux to Europe (8 Mg Hg season−1) among all
investigated growing seasons is associated with unusually hot and dry
ambient conditions in the European summer 2018, highlighting the
sensitivity of the investigated flux to prolonged high VPD. We conclude,
that stomatal modelling is particularly useful to investigate changes in
Hg deposition in the context of extreme climate events.