Rubber tree plantations may improve the soil's physical and chemical properties, and they may sequester atmospheric carbon in the biomass or the soil. However, the potential role of these plantations in sequestering carbon in the soil and plant biomass has not been fully evaluated. This study evaluated rubber tree plantations at Paranapoema, which is located in the northwestern region of the Paraná state of Brazil, to measure the biomass in plantations of different ages and to determine the organic carbon content and  13 C in the soils. Biomass accumulation was evaluated using the destructive method in plantations of different ages. The total carbon stock in the top 60 cm of the soil was 63.4 Mg C ha -1 for the pasture adjacent to the plantations and 66.8 and 79.3 Mg C ha -1 for the 4-and 15-year-old rubber tree plantations, respectively. These values are equivalent to an annual increase in soil carbon stocks of 0.85 and 1.06 Mg ha -1 , respectively, and they do not include the accumulation of carbon as tree woody biomass. The soil  13 C indicated a relatively fast conversion from the previous C4-C (pasture; Brachiaria-Urochloa brizantha) to C3-C (rubber tree). The results from this study suggest that rubber tree plantations have untapped potential to sequester carbon over a relatively short time period.Potencial de sequestro de carbono em seringais no noroeste do Paraná, Brasil RESUMO. O plantio de seringueiras é uma opção para melhorar as propriedades físicas e químicas do solo e promover o sequestro de carbono atmosférico, seja na biomassa ou no solo. Apesar das vantagens, o potencial de sequestro de carbono dos seringais no solo e na biomassa não foi ainda avaliado. Um estudo foi conduzido em seringais localizados em Paranapoema, na região noroeste do Paraná, com os objetivos de medir a biomassa em seringais de diferentes idades, e determinar o conteúdo de carbono e o  13 C do solo. O acúmulo de biomassa foi avaliado pelo método destrutivo em seringais de diferentes idades. O estoque total de carbono até 60 cm do solo foi de 63,4 Mg C ha -1 na pastagem adjacente aos seringais, 66,8 e 79,3 Mg C ha -1 nos seringais de 4 e 15 anos de idade, respectivamente, equivalendo a uma taxa anual de aumento de carbono no solo de 0,85 e 1,06 Mg ha -1 , sem considerar o acúmulo de carbono pela biomassa da planta. Os valores de  13 C do solo indicaram uma conversão relativamente rápida do carbono proveniente de plantas C4 (pastagem, Brachiaria-Urochloa brizantha) para carbono de plantas C3 (seringal). Os resultados deste estudo indicam o grande potencial de seringais em sequestrar carbono em um período relativamente curto.Palavras-chave: seringueira, Hevea brasiliensis,  13 C do solo, razão isotópica, estoque de carbono no solo.

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The impact of the Itaipu Lake on the climate and local circulation is investigated here using the meteorological information available in the area. The Itaipu Lake is an artificial water reservoir of 1460 km 2 (approximately 170 km by 7.5 km), formed in 1982 as part of the Itaipu Power Plant. It is situated on the Brazil-Paraguay frontier, in the central portion of Parana River Valley. The analysis of the available meteorological data (air and water temperatures, air relative humidity, precipitation and radiosonde soundings) provides observational evidences supporting the hypothesis that the Itaipu Lake presence has an important impact in the local circulation, inducing a local circulation with lake breeze characteristics showing horizontal wind divergence over the lake during daytime and convergence during nighttime. From the regional point of view, the Itaipu Lake formation has reduced the thermal amplitude of the diurnal air temperature cycle. The precipitation data, investigated here, has not indicated any systematic effect associated to the lake formation. The reason for the apparent inconsistency is that others phenomena (e.g., valley-mountain circulation and El Niño events) could be masking the impact of the lake formation on the rain deficit in the region.

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