202 - Investigating Seasonal Patterns of Mercury Uptake across Forest Sites in Slovenia

To better understand mercury (Hg) cycling in forest ecosystems and to further elucidate foliar Hg uptake and assimilation mechanisms, Hg speciation and isotopic fractionation is required in the context of seasonal climatic variations and the proximity to Hg emission sources. Recent studies observe seasonality in the atmospheric Hg concentrations as well as in isotopic signatures mainly driven by vegetation activity and anthropogenic emissions. This is supported by findings that report steady increase in foliar Hg concentration across the season, offsetting Hg re-emission of the Hg bound in the leaf interior. However, it remains to be investigated whether foliar Hg isotopic signatures exhibit similar seasonal pattern at forest sites with contrasting Hg presence. To this end, we investigate seasonal (bi-monthly) changes in relative proportion of foliar Hg species and Hg isotopic signatures across four forest sites in Slovenia with different Hg background: (I) Ljubljana – an urban area, (II) Anhovo – an industrial site near a cement plant, (III) Idrija – a former Hg mine site and (IV) Iskrba - a remote site. Foliage samples, from different locations on the tree crown, were collected from April until November 2021 and analysed. In this contribution, the implications of these results will be discussed to explain how changes in seasonal climate patterns and the origin and levels of Hg in the studied area control foliar Hg uptake and composition.

Authors: Saeed Waqar Ali, Dominik Božič, Marta Jagodic Hudobivnik, David Kocman, Milena Horvat