Influence of deforestation on soil mercury emissions in the Alta Floresta region (MT)

Abstract

In forest ecosystems, intact soils and tree cover buffer the movement of mercury (Hg) in the forest, and thus mediate its impact on the human food chain. In the Amazonian region, deforestation by biomass burning can lead to the remobilization of this element at local and regional scale, thus increasing the concentrations of mercury to which local populations are exposed. Hg can be remobilized to the atmosphere and aquatic system through various processes: 1) volatilization of large amounts of mercury in biomass that is almost completely emitted into the atmosphere during biomass burning, 2) atmospheric emission by thermal desorption of mercury from soil, 3) atmospheric emission of Hg following the burn event, as emissions from exposed soils, 4) direct transfer of Hg from soil to aquatic system by lixiviation. In this context, Prof. Anne H. Fostier is currently coordinating the project "Impact of deforestation on mercury emissions in tropical forest from the Amazonian region" (Proposal submitted to FAPESP - No 2010/19040-4, period from 01/03/2011 to 28/02/2013), which aims to examine the impact of deforestation on mercury emissions originating both from biomass burning and from emissions at the soil-atmosphere interface during and after biomass burning. To perform this project, field experiments (planned burning of 4 ha areas) are planned in the region of Alta Floresta, MT (2011) and in the Alto Juruá (AC) (2012) in collaboration with the FAPESP project (projeto temático 2008/04490-4) "Combustion of biomass in the Amazonian forest", coordinated by Prof. João Andrade Carvalho Jr. (Unesp/INPE). Beyond Prof. Anne H. Fostier, the project will count on the participation of the Invited Researcher Prof. Anthony Carpi, an expert in mercury flux quantification at the soil-atmosphere interface and in risk assessments, and also on the participation of Prof. Claudia Windmöller from the Universidade Federal de Minas Gerais (UFGM), expert in Hg speciation in soil by thermal desorption. In this project, the collaboration of Prof. Carpi will be particularly important in the study of Hg emissions from soil in response to deforestation and in the risk assessment of mercury released by deforestation. He will participate in the field works planned in September 2011, on a farm where Prof. Fostier already performed studies on the impact on forest fires on Hg emissions in 2004 and 2005. Prof. Carpi will be in charge of the quantification of Hg fluxes at the soil-atmosphere interface, which will be performed by using equipment (Tekran® continuous mercury analyzer and Teflon soil flux chambers) that he will bring with him from the United States. Measurements will be performed in pristine areas and in areas that were previously burned and that are currently in the regeneration phase or have been converted to pasture. In parallel to Hg fluxe quantification, various parameters able to influence Hg emissions such as air moisture and temperature, soil moisture and temperature, and UV radiation will also be measured. Once field research is completed, the researchers will work collaboratively to examine the local and regional impacts of mercury emitted from soils and biomass burning. Local transport phenomenon, pathways of mercury methylation, accumulation in the human food chain, and exposure scenarios will be evaluated to quantify the additional risk to local populations from mercury released by deforested soils. Prof. Anthony Carpi will stay in Brazil from August 2011 to January 2012. Beyond his research activities he will offer graduate lectures at Unicamp's Instituto de Química and a series of public seminars on the consequences of mercury in the Amazon, and on other areas of his research expertise: forensic chemistry and science education. Upon return at his home institution, he will also offer a series of public seminars to further broaden the audience reached by this project. (AU)