CONICET | Buscador de Institutos y Recursos Humanos

Peatlands are important wetlands accounting for nearly 60% of the global wetlands area or 5% of the Earth´s land surface. They play an important environmental role due to their relatively high capacity to stock fresh water and their ability to sequester and fix carbon from the atmosphere. The mismanagement and ensuing damage to the environment have been affecting most peatlands and this is driving special efforts to better understand and disseminate their real ecological value. From the climate research point of view, undisturbed peat is a unique archive of atmospheric deposits, and a great archive of atmospheric pollutants such as metals and organic contaminants. In the same way, peatlands can accumulate radioactive elements. Along the Serra do Espinhaço Meridional, Minas Gerais, Brazil, there are quite a few peatlands currently in formation that are of great interest for several environmental and economical meaning. To help understand their properties and their genesis we have studied the activity of natural (226Ra, 232Th and 40K) and anthropogenic (137Cs) gamma-ray emitters and characterized the Fe compounds by Mössbauer spectroscopy of three peatlands of the Serra do Espinhaço Meridional: São João da Chapada, Pinheiro and Pau de Fruta. We studied samples collected at each 5 cm down from the top to a maximum depth of 45 cm. For the Pinheiro and Chapada sampling sites, the 232Th activity increases with depth, while it remains constant for the Pau de Fruta. In Pinheiro, the 226Ra activity values are significantly higher than in the other peatlands (maximum value of 775 Bq/kg), showing a Gauss-type distribution with depth, as also observed in Pau de Fruta but with a maximum activity value of 119 Bq/kg. In Chapada, the 226Ra activity, in general, decreases with depth; the maximum observed activity value is 53 Bq/kg. The 40K activity in Pau de Fruta is relatively higher, with about 100 Bq/kg at the surface and decreasing to about 50 Bq/kg in the deeper soil layer. In Chapada, the 40K concentration also decreases with depth but from 35 to 17 Bq/kg. In Pinheiro, the 40K activity fluctuates between 20 and 53 Bq/kg. These natural activity values make evident the special characteristics of the systems, which are quite different from the values and behaviors found in other South American soils. The activity values yield a significant correlation only for 232Th-226Ra, with a Pearson correlation coefficient of -0.5, also different to the correlations determined in other soil types. The only anthropogenic radionuclide found in the peatlands is 137Cs. The activity profiles were fitted by the convection-diffusion model, although the Pinheiro profile seems to be affected by other soil mechanisms as well. The differences of the radionuclides behaviors in the three peatlands can be due to the different locations, the different sediment compositions that are deposited in each peatland and the different age of the organic matter. Mössbauer spectra reveal Fe3+ in two environments and the occurrence of hematite in the superficial samples of Chapada. The Fe concentration was determined by the methodology proposed by Montes et al., 2016, finding that it decreases with depth. Significant correlations were obtained between Fe phases and natural radioactivity, like in other soil types. The striking differences displayed by the results presented here between the different peatlands and with the radioactive profile of other South American soils demands a soil formation model to explain the diversity and also to correlate with all the already collected information gathered by some of us working at the UFVJM.ReferenceMontes ML, Rivas PC, Taylor MA, Mercader RC. Approximate total Fe content determined by Mössbauer spectrometry: Application to determine the correlation between gamma-ray-emitter activities and total content of Fe phases in soils of the Province of Buenos Aires, Argentina. Journal of Environmental Radioactivity 162-163 (2016) 113-117.

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