Climatic and anthropogenic changes in Eastern Amazonia may promote significant alterations in hydrologic and sedimentary dynamics of fluvial systems and threaten aquatic and flooding forest ecosystems. As such, this study aimed at the reconstruction of precipitation and vegetation changes in Eastern Amazonia during the late Holocene in order to understand the response of this system to climatic variations of the last millennia. Since changes promoted by the construction of hydropower plants have been generating abrupt and severe environmental transformations in Amazonian rivers, the present study also tried to improve the current knowledge about carbon dynamics in the Xingu River, which is one of the largest rivers in Eastern Amazonia and was recently affected by the Belo Monte dam. Sediment cores and bottom and suspended sediment samples were investigated through isotope analysis of specific organic compounds and inorganic geochemistry. Changes in precipitation, vegetation and sediment influx were compared to global climatic events and variations in the South American Monsoon System obtained from other climatic archives. With the purpose of investigating the climatic and anthropogenic impacts on carbon dynamics, potential shifts in organic matter retention and methane and carbon dioxide emissions in the Xingu River were also evaluated. The obtained results allowed the identification of variations in the water discharge of the Amazon and Xingu rivers associated with temperature anomalies in extratropical regions during the late Holocene. They also demonstrated that natural and anthropogenic alterations affect carbon balances in Amazonian aquatic environments.

Unconventional biogenic shale gas systems may represent an important energy resource and significantly contribute to geological greenhouse gases emissions. In order to better understand the controls on biogenic methane (CH 4) and carbon dioxide (CO 2) generation in organic-rich shales, the present study evaluated the generation potential and the pore structure of shales from Taubaté and Paraná basins, located in southeastern Brazil. The Ponta Grossa (Devonian, Paraná basin), Irati (Permian, Paraná basin) and Tremembé Formations were analyzed in order to quantify production rates of biogenic CH 4 and CO 2 under distinct experimental conditions. Twenty four shale samples were used for batch incubations under dry, wet and acetic acid solution conditions during time periods reaching up to 1 year. The organic carbon content and nitrogen adsorption analysis for determining specific surface area and porosity were also performed to evaluate their role on biogenic gas generation.The biogenic gas production rates in samples under dry conditions reached up to 3.17 ml/t.d (CH 4) and 2.45x10³ ml/t.d (CO 2) during the first 30 days of incubation. Samples under wet conditions demonstrated production rates 54% higher for CH 4 and 151% higher for CO 2 in comparison with dry tests. Acetic acid addition restarted or increased CH 4 and CO 2 production in most cases. The Irati Formation showed the highest potential for biogenic methane production, which could be linked to the biodegradation of heavy liquid hydrocarbons occurring in this unit. Total pore volume and specific surface does not appear to significantly affect the biogenic production of CH 4 and CO 2. However, water content and substrate availability would exert predominant control over the biogenic gas generation within organic rich shales.