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Abstract Title: An assessment of current and future foliar Hg uptake fluxes to European pine forests
Presenter Name: Lena Wohlgemuth
Session: Predicting the Impacts of Climate Change on Hg Cycling
Co-Authors: Lena Wohlgemuth

Abstract Information :

Uptake of gaseous elemental mercury (Hg(0)) by vegetation represents the largest atmospheric source of Hg to global soils (60 % ? 90 %). Forests in particular are a sink for Hg(0). Under global warming forest ecosystems are anticipated to undergo substantial changes, which possibly results in a shift of the forest Hg(0) deposition flux depending on local conditions like land-use change, drought and transformation of tree species. Around 40% of European forested area is covered by pine trees. Pine is an isohydric tree species, which counters water loss under conditions of elevated atmospheric evaporative demand (high vapor pressure deficit (VPD)) by closing needle stomata, thus restraining stomatal Hg(0) uptake. Here we use an empirical bottom-up model to simulate changes in foliar stomatal Hg(0) uptake fluxes to European pine forests under two climate change scenarios (RCP 4.5, RCP 8.5) for the years 2068 ? 2072 in comparison to modelled fluxes during 4 past growing seasons (1994, 2003, 2015/17, 2018). Flux simulations were based on stomatal controls of Hg(0) uptake by pine needles related to VPD and on the projected distribution of pine in Europe. We find, that the total modelled foliar Hg(0) uptake flux to European pine forests over the growing seasons 1994, 2003 and 2015/17 (9.2 Mg Hg season-1) is nearly identical to the corresponding projected flux over the years 2068 ? 2072 under RCP 4.5. Respective total fluxes are similar between the projection under RCP 8.5 (7.7 Mg Hg season-1) and the growing season 2018 (8.0 Mg Hg season-1), during which a record summer drought was recorded in Central and Northern Europe, where most European pine forests are located. We conclude, that summer droughts have the potential to reduce the stomatal Hg(0) uptake flux to pine forests, and thus this process should be incorporated into global Hg Earth system models like GEOS-Chem.

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