Carla Semiramis Silveira

Dinâmicas de regeneração, degeneração e desmatamento da vegetação provocadas por fatores climáticos e geomorfológicos: uma análise geoecológica através de SIG

The purpose of this paper was to evaluate the influence of climate (insolation and annual precipitation) and relief (slope) on the land use and forest changes in a mountainous watershed (Paquequer / RJ) representative of the Atlantic Forest. Land use thematic maps for different dates (1976 and 1996) were derived from aerial photographs and SPOT-3 XS/PAN image. Land use and natural regeneration changes in 20 years were classified as initial natural regeneration, late natural regeneration, degeneration and deforestation. GIS spatial informations were dealt with ArcGIS 9.0. While initial regeneration occurs indistinctly of the climatic and relief parameters, it is suggested that advanced regeneration is a more selective process. That is, advanced regeneration occurs mainly in areas with less insolation and higher humidity. On the other hand, the deforestation for human use tends to be more intense in lower and greater insolation slopes (toward north).

Mismatch Between Sediment Metal Distribution and Pollution Source Gradient: A Case Study of a Small-Size Drainage Basin (Southeastern Brazil)

Metal contamination in aquatic environments may occur when the anthropogenic emission exceeds the natural contribution although other factors might influence the metal distribution. In the small-size Macaé river basin, most of the metal emission was originated from anthropogenic sources suggesting a contamination status. Total and exchangeable metal concentrations were determined in sediments from the pristine upstream to the urban estuary and compared to the metal content in rocks to establish contamination and background concentrations. The enrichment of Pb in sediments compared to the regional background and high exchangeable concentrations suggest the influence of anthropogenic sources on Pb distribution. Al, Fe Mn, Zn, Ba, Cu, Cr, Ni concentrations in sediments were similar to the rock content and the values were considered regional background. Spatial distribution did not follow the whole-basin emission source gradient suggesting that despite actual anthropogenic sources, the sediment mineralogy and basin geomorphology might influence the sediment metal distribution.

Emissões de óxido nitroso em águas fluviais não poluídas e poluídas da Bacia do Rio Paquequer (Teresópolis, Rio de Janeiro)

As concentracoes de N2O dissolvido e os fluxos de N2O na interface agua-ar (utilizando câmaras estaticas) foram determinados ao longo do Rio Paquequer e em alguns de seus tributarios. As concentracoes de N2O variaram de 0,32 a 4,7 μgN.L-1, e os fluxos de N2O, de <0,56 a 141 μgN.m-2 .h-1 . As menores concentracoes e fluxos de N2O ocorreram nas cabeceiras do Rio Paquequer e do Corrego Principe, e a maiores, nos trechos urbanos e no Corrego Fischer. As concentracoes de N2O dissolvido e os fluxos de N2O na interface agua-ar foram positivamente correlacionados com a alta variabilidade nas concentracoes de NH4+. Espera-se que a taxa de emissao de N2O, em massa de N, no trecho poluido do Rio Paquequer seja maior do que o valor estimado de 0,62 kgN.dia-1, uma vez que a transferencia pela purga em razao da turbulencia provocada por cascatas, cachoeiras e corredeiras nao foi determinada.

Comportamento Hidrológico da Região Serrana do Rio de Janeiro: Bacia do Rio Piabanha

A regiao serrana do Rio de Janeiro apresenta um historico de desastres naturais. Com o objetivo de entender o comportamento hidrologico da regiao foram analisados dados de chuva (4 estacoes) e de vazao (3 estacoes) na bacia do rio Piabanha (2065 km2) com series historicas de ate 70 anos. O total anual medio de pluviosidade variou de 2900 mm (na cabeceira) a 1250 mm na regiao central da bacia. Os resultados demonstraram boa correlacao entre as estacoes e a existencia de sazonalidade com inverno seco (valores medios mensais entre 15 e 90 mm de chuva) e vazao media na foz de 16 m3/s e verao chuvoso (valores medios mensais entre 150 e 450 mm de chuva) e vazao media na foz de 80 m3/s. As series historicas de chuva e vazao apresentaram uma ciclicidade, de aproximadamente 15 anos, marcada por anos mais secos. Os dados apontam que os registros existentes de eventos catastroficos regionais foram em anos proximos aos apices dos ciclos de pluviosidade e vazao propostos. O ultimo ciclo identificado iniciou-se em 1999 e o periodo atual (2015- 2016) representa o fim deste ciclo, representado pela fase mais seca. Entretanto, neste ultimo ciclo o comportamento da chuva e, principalmente, da vazao e muito variavel. Isto, em conjunto com o aumento recente da frequencia de desastres naturais de grande magnitude, pode ser um indicativo de efeito antropico.

Geochemistry of river suspended sediments in tropical watersheds: anthropogenic and granite-gneiss sources, SE Brazil

ABSTRACT Mineralogy and geochemistry of the total suspended sediment (TSS) from a granite-gneiss watershed in southeast Brazil brought light to geogenic and anthropogenic sources. TSS was sampled in 15 points along the Piabanha watershed in summer (February 2013) and winter (August 2013). The Piabanha watershed (2 × 103 km2) is located in the mountainous region of Rio de Janeiro, and it is an affluent of the Paraiba do Sul River, the most important river from the Brazilian southeastern coast. TSS mineralogical analyses were performed with X-ray powder diffraction. Geochemical analysis was done with energy dispersive X-ray fluorescence. Quartz, kaolinite and gibbsite were dominant in the TSS mineralogy, followed by feldspar and mica. Granite and gneiss rocks contribution in the TSS have a common mineralogical and geochemical source. But the alluvial deposits from river banks might have been responsible for the differences between summer and winter samples. The major features in TSS from geogenic sources were SiO2, Al2O3, MgO, Ga2O3, Nb2O5, Rb2O, K2O, SrO, ZrO2 and TiO2. The good correlation on the Si:Al molar ratio suggested that the source area is intensely weathered. Pollution features (sewage source) were given by significant TSS concentration of Fe2O3, MnO, ZnO, CuO, As2O3, CaO, Na2O, P2O5 and SO3.

Hidrogeoquímica de Metais em Água Fluvial: Fontes Geológicas Graníticas e Gnáissicas - Bacia do Rio Paquequer, Teresópolis, Estado do Rio de Janeiro

The Paquequer watershed (269 km ²) belongs to Paraiba do Sul river drainage basin and is located in the municipal area of Teresopolis, Rio de Janeiro state. Its geology is typical of southeastern Brazil granites and gneisses. The aim of this work was to evaluate the weathering process of these rocks and the mobilities of the chemical elements through a hydrogeochemical approach. 15 river points were sampled. River discharge and physico-chemical parameters were measured. Nine points were located in the main channel and six in the major tributaries. The samples were analyzed by ICP-MS for Si, Fe, Mn, Al, Cu, Ni, Cr, Zn, Ba, Rb, Sr, Pb, Cd and Co and by ion chromatography for Na+, K+, Mg2 + and Ca2 +. Literature data concerning the geochemistry of these rocks was used. The fluvial hydrogeochemistry is dominated by Na, Ca and Si. In contrast, Pb, Cd, Co and Cr showed very low values reflecting negligible abundance in rock composition and the absence of anthropogenic industrial sources. Ni, Zn, and Cu concentrations were low and associated with the urban area. Multivariate statistical analysis showed four main groups. Group 2 (medium and low course of the mainstream) was used for weathering estimation. Rio Negro Unit (migmatite) geochemistry affected the hydrogeochemistry through a higher Mg /Fe ratio in the tributary that drains this geological unit. The elemental load showed that the rock are the main sources for Si, Mg, Na, K, Ca, Sr, Ba and Rb. The estimated weathering rate indicated three behaviors for the elements: i) the ones with high mobility (Ca and Sr); ii) the ones with low mobility (Mg, K, Mn, Rb, Ba and Si); iii) the ones that are not mobile (Fe and Al). Thus it was suggested that plagioclase (with Ca and Sr in its crystal structure) is the first mineral to be leached and dissolved in water from the weathering profile, followed by K- feldspar and biotite. Part of the Si is retained in the formation of the secondary minerals such as clay minerals. Fe and Al tend to form oxides and hydroxides that remain in the weathering profile, explaining their low mobility.