ReviewMercury sequestration by rainforests: The influence of microclimate and different successional stages

- Global climate change could increase mobilization of mercury to the atmosphere.
- Litterfall transfers mercury from the atmosphere to forest soils.
- Mercury in tropical forest soils and litter is 10 times higher than in temperate zones.
- Scenarios affecting the global mercury cycle must consider the role of tropical rainforests.

Mercury (Hg) concentrations in tropical forest soils and litter are up to 10 times higher than those from temperate and boreal forests. The majority of Hg that has been stored in tropical soils, as the forest is left intact, could be trapped in deeper layers of soil and only small quantities are exported to water bodies. The quantitative approach to the Hg cycle in tropical forests is uncommon; the South America Atlantic Forest indeed is a hotspot for species conservation and also seems to be for the Hg's cycle. This study reports on a biannual dynamics of Hg through different species assemblage of different successional stages in this biome, based on 24 litter traps used to collect litterfall from 3 different successional stages under a rainforest located at Brazilian Southeast. The mean Hg litterfall flux obtained was 6.1 ± 0.15 μg ha−1 yr−1, while the mean Hg concentration in litter was 57 ± 16 ng g−1 and the accumulation of Hg via litterfall flux was 34.6 ± 1.2 μg m−2 yr−1. These inventories are close to those found for tropical areas in the Amazon, but they were lower than those assessed for Atlantic Forest biome studies. These low concentrations are related to the remoteness of the area from pollution sources and probably to the climatic limitation, due to the altitude effects over the forest's eco-physiology. The mercury fluxes found in each different successional stage, correlated with time variations of global radiation, suggesting a mandatory role of the forest primary production over Hg deposition to the soil.