Issue 9, 2022

Evaluating atmospheric mercury (Hg) uptake by vegetation in a chemistry-transport model


Mercury (Hg), a neurotoxic heavy metal, is transferred to marine and terrestrial ecosystems through atmospheric transport. Recent studies have highlighted the role of vegetation uptake as a sink for atmospheric elemental mercury (Hg0) and a source of Hg to soils. However, the global magnitude of the Hg0 vegetation uptake flux is highly uncertain, with estimates ranging 1000–4000 Mg per year. To constrain this sink, we compare simulations in the chemical transport model GEOS-Chem with a compiled database of litterfall, throughfall, and flux tower measurements from 93 forested sites. The prior version of GEOS-Chem predicts median Hg0 dry deposition velocities similar to litterfall measurements from Northern hemisphere temperate and boreal forests (∼0.03 cm s−1), yet it underestimates measurements from a flux tower study (0.04 cm s−1vs. 0.07 cm s−1) and Amazon litterfall (0.05 cm s−1vs. 0.17 cm s−1). After revising the Hg0 reactivity within the dry deposition parametrization to match flux tower and Amazon measurements, GEOS-Chem displays improved agreement with the seasonality of atmospheric Hg0 observations in the Northern midlatitudes. Additionally, the modelled bias in Hg0 concentrations in South America decreases from +0.21 ng m−3 to +0.05 ng m−3. We calculate a global flux of Hg0 dry deposition to land of 2276 Mg per year, approximately double previous model estimates. The Amazon rainforest contributes 29% of the total Hg0 land sink, yet continued deforestation and climate change threatens the rainforest's stability and thus its role as an important Hg sink. In an illustrative worst-case scenario where the Amazon is completely converted to savannah, GEOS-Chem predicts that an additional 283 Mg Hg per year would deposit to the ocean, where it can bioaccumulate in the marine food chain. Biosphere–atmosphere interactions thus play a crucial role in global Hg cycling and should be considered in assessments of future Hg pollution.

Graphical abstract: Evaluating atmospheric mercury (Hg) uptake by vegetation in a chemistry-transport model

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Article information

Article type
27 Jan 2022
21 Apr 2022
First published
22 Apr 2022
This article is Open Access
Creative Commons BY license

Environ. Sci.: Processes Impacts, 2022,24, 1303-1318

Evaluating atmospheric mercury (Hg) uptake by vegetation in a chemistry-transport model

A. Feinberg, T. Dlamini, M. Jiskra, V. Shah and N. E. Selin, Environ. Sci.: Processes Impacts, 2022, 24, 1303 DOI: 10.1039/D2EM00032F

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