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Keywords: Ciclo do Hg;  Mata Atlântica;  Bioacumulação de metais traço;  Hg Cycle;  Atlantic Forest;  Trace metal bioaccumulation
Issue Date: 30-May-2012
Abstract: The tropical forest soils have been shown mercury concentration 10 times higher than temperate and boreal zones soils (more industrialized), this disparity have been found if compared to the Hg litterfall values. The litterfall besides being produced more in these forests has more foliar Hg bioaccumulated. The main entrance way is by photosynthetic gas exchanging and by foliar surface adsortion. The quantitative approach, from Hg ecological pools and the fluxes between compartments, is crucial to understand the cycle of this metal. The Hg stocked into tropical soils along thousands of years, may have two fates: 1. Immobilization inside the forestsoil, into lower layers e 2. Re-emission on gaseous form to atmosphere occurred during forest burn or erosion/leaching when pastures and/or another soil use suppress the forests. Therefore, this potentially toxic metal, once free to soils can reach the watercourses; suffer methylation and biomagnification, along trophic web. At Itatiaia National Park (PNI), inside a native forested watershed, was assessed the total Hg from litter, the litter and Hg litter fluxes. During two years the litter baskets collected the litterfall at 3 different stages from ecological succession. The tree density form each successional type was evaluated. Fifteen tree species were chosen for Hg concentration tests, likewise, were analysed in situ the photosynthetic maximum rate, transpiration and stomatal conductance from these trees. The transference from Hg trough the litterfall carried by the river was quantified. The mean litterfall flux was 6,1±0,15 t.ha-1.ano-1, while the mean Hg concentration was 59±7,6 ng.g-1, and the litter Hg flux was 34,6±1,2 μg.m-2ano-1. These values are in agreement with others found at tropical areas like Amazon, but they were higher than the means assessed at Temperate and Boreal biomes, the major Hg capture by tropical species and the high transference to soil, can be explained by the highest gaseous change done by these forests. The different successional forest stages, due the species physiological fitness, capture more Hg when are composed by species with more photosynthesis assimilation and a short time life span. Therefore pioneers species with fast growing are more able to capture Hg. Brazilian Tropical forests maybe capture 200 tons of mercury from the atmosphere. This transference must be considered on the Hg global balance.
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