272 - Modelling the Impact of Amazon Land Use Changes on the Vegetation Sink of Atmospheric Mercury
Information
Vegetation uptake of gaseous elemental mercury (Hg0) is a major removal pathway for atmospheric Hg, with the Amazon rainforest suggested to be an important sink region due to its high productivity. However, deforestation and climate change threaten the role of the Amazon region as a Hg sink, with 20% of the forest area lost since 1970 and an additional 40% at risk by 2050 if current deforestation rates continue. Using the GEOS-Chem atmospheric mercury model and available measurements, we assess the importance of Hg vegetation uptake on the global scale and the impacts of Amazon deforestation on the Hg cycle. To improve the accuracy of the model, we compare simulations with a compiled database of litterfall, throughfall, and flux tower measurements from 93 forested sites globally. 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), yet it underestimates measurements from a flux tower study (0.04 cm/s vs. 0.07 cm/s) and Amazon litterfall (0.05 cm/s vs. 0.17 cm/s). After revising the Hg0 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 and measured Hg concentrations in South America. The simulated Hg0 dry deposition to land is 2276 Mg/yr globally, 29% of which enters the Amazon rainforest. In a worst-case scenario where the Amazon rainforest is completely converted to savannah, an additional 283 Mg Hg/yr would deposit to the ocean instead of the land, where it can bioaccumulate in the marine food chain. Simulations with GEOS-Chem and an erosion model illustrate that business-as-usual practices will lead to the Amazon becoming a net source of Hg by 2050, yet expanded conservation policies could safeguard the Amazon’s role as a net Hg sink.
Authors: Aryeh Feinberg, Martin Jiskra, Thandolwethu Dlamini, Jagannath Biswakarma, Pasquale Borrelli, Viral Shah, Noelle Selin