To investigate denudation rates in the southern part of the Espinhaço Range (central-eastern Brazil) and to understand how this important resistant and residual relief has evolved in the past 1.38 My, cosmogenic 10 Be concentrations produced in situ were measured in alluvial sediments from the three main regional basins, whose substratum is composed primarily of quartzites. The long-term denudation rates (up to 1.38 My) estimated from these measurements were compared with those that affect the western (São Francisco River) and eastern (Doce and Jequitinhonha Rivers) basins, which face the West San Francisco craton and the Atlantic, respectively. Denudation rates were measured in 27 samples collected in catchments of different sizes (6-970 km 2) and were compared with geomorphic parameters. The mean denudation rates determined in the northern part are low and similar to those determined in the southern part, despite slightly different geomorphic parameter values (catchment relief and mean slope). For the southern catchments, the values are 4.91 ± 1.01 m My −1 and 3.65 ± 1.26 m My − 1 for the Doce and São Francisco River basins, respectively; for the northern catchments, they are 4.40 ± 1.06 m My − 1 and 3.96 ± 0.91 m My − 1 for the Jequitinhonha and São Francisco River basins, respectively. These low values of denudation rates suggest no direct correlation if plotted against geomorphic parameters such as the catchment area, maximum elevation, catchment relief, average relief and mean slope gradients. These values show that the regional landscape evolves slowly and is strongly controlled by resistant lithology, with similar erosional rates in the three studied basins.

The Serra do Mar escarpment, located along the southeastern coast of Brazil, is a high-elevation passive margin escarpment. This escarpment evolved from the denudation of granites, migmatites and gneisses. The granites outcrop in the form of a ridge along the escarpment crest, due to its differential erosion ('sugarloaf' hills) from the surrounding lithologies. Several studies suggest that the passive margin escarpments are actively retreating toward the interior of the continent. However, no prior study has calculated the long-term denudation rates of Serra do Mar to test this hypothesis. In this study, we measured the in situ-produced 10 Be concentration in fluvial sediments to quantify the catchment-wide long-term denudation rates of the Serra do Mar escarpment in southern Brazil. We sampled the fluvial sediments from ten watersheds that drain both sides of the escarpment. The average long-term denudation rate of the oceanic side is between 2.1-and 2.6-fold higher than the rate of the continental side: 26.04 ± 1.88 mm ka -1 (integrating over between 15.8 ka -1 and 46.6 ka -1 ) and 11.10 ± 0.37 mm ka -1 (integrating over between 52.9 ka -1 and 85.4 ka -1 ), respectively. These rates indicate that the coastal base level is controlling the escarpment retreat toward the continental high lands, which is consistent with observations made at other high-elevation passive margins around the globe. The results also demonstrate the differential erosion along the Serra do Mar escarpment in southern Brazil during the Quaternary, where drainages over granites had lower average denudation rates in comparison with those over migmatites and gneisses.Moreover, the results demonstrate that the ocean-facing catchments have been eroded more intensely than those facing the continent. The results also reveal that drainage over the granites decreases the average denudation rates of the ocean-facing catchments and the 'sugarloaf' hills therefore are natural barriers that slowly retreat once they are exhumed.

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Resumo:A Chapada das Mesas, Maranhão/Tocantins, possui uma das paisagens mais fi dedignas às unidades de chapadas no Brasil. Entretanto, esta região foi pouco estudada, principalmente em termos de gênese de sua paisagem. Neste contexto, insere-se o presente trabalho que analisou os processos que infl uenciaram na morfogênese da Chapada das Mesas através da correlação entre a litologia, morfoestrutura e o sistema de drenagem regional. Para tanto, os métodos de análise utilizados, foram: (a) parâmetros morfométricos, (b) mensuração de processos denudacionais de longo termo ( 10 Be) e, (c) trabalhos de campo. Com base nas análises realizadas concluiu-se que a estrutura regional infl uenciou diretamente a confi guração da drenagem pretérita e atual, potencializando a morfogênese dessa paisagem devido a processos internos associados a um antigo sistema de drenagem subterrânea típico de paisagens cársticas. Assim, torna-se possível afi rmar que a morfogênese regional é mais complexa do que sugerem os modelos de evolução de longo termo para paisagens do tipo Chapada e, sendo assim, é necessário rever os conceitos teóricos acerca dos processos que envolvem a gênese e evolução dessas formas de relevo.

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O presente trabalho avalia a qualidade da água em duas microbacias urbanas (rios Urucutiua e Claro) situadas na Ilha do Maranhão, visando comparar os efeitos da urbanização e os impactos ambientais. Para isso, realizou-se  análise laboratorial de parâmetros físico-químicos e microbiológicos de amostras de água superficial coletadas bimestralmente (2013-2014) em quatro pontos e; o mapeamento do uso e ocupação do solo das microbacias por meio do SIG ArcGIS, em recorte temporal (2007-2014) de imagens de satélite Quickbird. Os resultados indicaram, a contaminação em níveis elevados por microrganismos patogênicos em todas as amostras: Escherichia coli, na bacia do rio Urucutiua e; Escherichia coli, Proteus mirabilis, Proteus penneri, e Chromobacterium violaceum, na bacia do rio Claro. Os parâmetros físico-químicos mostraram acidez elevada em todas as amostras; Oxigênio Dissolvido abaixo do recomendado em 75% das amostras do rio Claro e 33% do rio Urucutiua; e Nitrogênio total acima do permitido em 91,7% das amostras. O uso do solo mostrou que a microbacia do rio Urucutiua sofreu as maiores alterações, com expressiva supressão da vegetação (71,6%, em 2007 e; 34,1% em 2014) e aumento das áreas de solo exposto, enquanto a bacia do rio Claro apresentou consolidação do processo de urbanização.

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