15 February 2024

Deforestation fosters mercury emissions into the atmosphere

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La foresta amazzonica conserva circa il 30% del mercurio sequestrato nel suolo a livello globale. Foto: Neil Palmer/CIAT CC BY-SA 2.0 DEED Attribution-ShareAlike 2.0 Generic

Forests perform an essential ecosystem service by storing mercury and preventing its spread into waterways. That’s why deforestation poses a threat in terms of pollution, a MIT study finds

by Matteo Cavallito

 

About 10 percent of human-caused mercury emissions into the atmosphere are the result of global deforestation, a Massachusetts Institute of Technology (MIT) study says. The element, the researchers explain, is absorbed by global vegetation. But current rates of deforestation, they add, could lead to an increase in net emissions, that is, the balance between the amount absorbed of the element and the amount released.

The mercury cycle

Vegetation, the researchers explain, absorbs the element from the atmosphere no differently from what they do with CO2. Anyway, mercury does not perform an essential biological function for plants. The element sits largely within the leaves until it falls out and is absorbed into the soil.

When it ends up in watersheds or streams instead, however, mercury becomes a problem for human health as well. Especially when, after being absorbed by fish, it enters the food chain.

In soils, notes Ari Feinberg, researcher and co-author of the study, in a memo released by MIT, “mercury is much more tightly bound than it would be if it were deposited in the ocean.” Forests, in short, “are doing a sort of ecosystem service, in that they are sequestering mercury for longer timescales.”

The investigation

MIT scientists divided areas of the Planet into eight regions and ran several simulations for each of them to calculate emission factors. “Deforestation reduces the capacity of the terrestrial biosphere to take up toxic pollutant mercury (Hg) and enhances the release of secondary Hg from soils,” the study states.

Further, “Using global Hg modeling constrained by field observations, we estimate that net Hg fluxes to the atmosphere due to deforestation are 217 Mg year–1 for 2015, approximately 10% of global primary anthropogenic emissions.”

If deforestation were a nation, “it would be the second highest emitting country, after China, which emits around 500 tons of mercury a year.”, says Feinberg. Today, however, the consequences of deforestation on the mercury cycle are not currently included in the calculation of anthropogenic emissions, nor are they given specific attention.

The role of the Amazon

The model built in the research reveals how the Amazon rainforest plays a key role as a reservoir of mercury, storing about 30 percent of the amount of the element sequestered globally. Curbing deforestation in the region would significantly reduce pollution.

In contrast, “IIf deforestation of the Amazon rainforest continues at business-as-usual rates, net Hg emissions from the region will increase by 153 Mg year–1 by 2050, enhancing the transport and subsequent deposition of Hg to aquatic ecosystems.”

Finally, the researchers estimate that global reforestation efforts could increase annual mercury uptake by about 5 percent. In any case, however, forest regeneration efforts are not enough to solve the problem and therefore cannot replace pollution control actions.