Seasonal variation of mercury concentration of ancient olive groves of Lebanon
Résumé
This study investigates the seasonality of the mer- cury (Hg) concentration of olive tree foliage, an iconic tree of the Mediterranean basin. Hg concentrations of foliage, stems, soil surface, and litter were analyzed on a monthly ba- sis in ancient olive trees growing in two groves in Lebanon, Bchaaleh and Kawkaba (1300 and 672 m a.s.l. respectively). A significantly lower concentration was registered in stems ( ∼ 7–9 ng g−1) in comparison to foliage (∼ 35–48 ng g−1) in both sites, with the highest foliage Hg concentration in late winter–early spring and the lowest in summer. It is noteworthy that olive fruits also have low Hg concentra- tions (∼ 7–11 ng g−1). The soil has the highest Hg content (∼ 62–129 ng g−1) likely inherited through the cumulated lit- ter biomass (∼ 63–76 ng g−1). A good covariation observed between our foliage Hg time series analysis and those of at- mospheric Hg concentrations available for southern Italy in the western Mediterranean basin confirms that mercury pol- lution can be studied through olive trees. Spring sampling is recommended if the objective is to assess the trees’ sus- ceptibility to Hg uptake. Our study draws an adequate base- line for the eastern Mediterranean and the region with similar climatic inventories on Hg vegetation uptake, in addition to being a baseline to new studies on olive trees in the Mediter-
ranean to reconstruct regional Hg pollution concentrations in the past and present.
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