A floristic survey of angiosperm species occurring at three landscapes of the Central Amazon várzea, Brazil

The Amazonian floodplains harbor highly diverse wetland forests, with angiosperms adapted to survive extreme floods and droughts. About 14% of the Amazon Basin is covered by floodplains, which are fundamental to river productivity, biogeochemical cycling and trophic flow, and have been subject to human occupation since Pre-Colombian times. The botanical knowledge about these forests is still incomplete, and current forest degradation rates are much higher than the rate of new botanical surveys. Herein we report the results of three years of botanical surveys in floodplain forests of the Central Amazon. This checklist contains 432 tree species comprising 193 genera and 57 families. The most represented families are Fabaceae, Myrtaceae, Lauraceae, Sapotaceae, Annonaceae, and Moraceae representing 53% of the identified species. This checklist also documents the occurrence of approximately 236 species that have been rarely recorded as occurring in white-water floodplain forests

Aplicação do modelo de mistura na decomposição do espectro de reflectância da água em espectros de seus componentes opticamente ativos: uma avaliação

The linear mixing models have been applied successfully to determine the fractional abundance of pure endmembers contributing to the radiance of a mixed pixel. The resulting abundances are then reassembled spatially to provide subpixel information. In the present paper, the linear mixing model is being applied to determine in which proportion the reflectance of each optically active component contributes to the water reflectance. Spectral reflectance factors measured at the Tucurui reservoir during April 1992 were used to carry our this study. To select the endmembers the following criteria were used; 1- ­the pure endmember of a given water component was represented by the spectrum of the sample station where that component has thehighest concentration; 2- the pure endemember selected were: chlorophyll, dissolved organic matter and total of suspended solids. As the final objective of the unmixing process is to generate pure endmember spectra to help the interpretation of Airborne Visible/Infrared Imaging Spectrometric (AVIRIS) data, all the spectral were resampled to its resolution. The following analyses were performed to assess the suitability of the model: 1- computation of the correlation coefficients between the fractional abundance of given endmember and the component concentration for the unmixed spectra in the range between 400nm and 800nm; 2- the determination of the residuals; 3- computation of the correlation coefficient between the water component concentration and the fractional abundance of a given endmember resulting from application of the mixing model to various spectral windows selected according to the residuals. The results showed that the correlation coefficient between the fractional abundances of the selected endmembers and the concentration of optically active components are different in the different spectral regions. The results showed that it is possible to unmix the chlorophyll signal in the red region, and that the best region to unmix the TSS is the green region. RESUMO: Os modelos lineares de mistura têm sido aplicados com bastante sucesso na determinação das proporções de componentes puros que contribuem para a radiância de um pixel e na transformação destas proporções em imagens com a distribuição espacial dos mesmos. Neste trabalho, o modelo linear de mistura esta sendo aplicado para determinar a proporção com que a reflectância de cada componente opticamente ativo contribui para a reflectância total da água. Para a realização do trabalho foram utilizados dados espectrais coletados em abril de 1992 no reservatório da UHE Tucuruí. Para a seleção de três estações amostrais representativas dos componentes puros adotou-se o seguinte critério: o espectro puro de um dado componente opticamente ativo seria representado pela estação amostral com máxima concentração daquele componente e mínima concentração dos demais componentes. Os componentes puros selecionados foram: clorofila, matéria orgânica dissolvida e totais de sólidos em suspensão. Como o objetivo final deste estudo era gerar espectro de componentes puros da água para integrar uma biblioteca de espectros que auxilie a interpretação de dados do Airborne Visible and Infrared Imaging Spectrometer (AVIRIS), os dados espectrais foram reamostrados para a resolução espectral daquele sensor. Para avaliar o desempenho do modelo de mistura as seguintes análises foram feitas: 1- cálculo da correlação entre a fração de um dado endmember e a concentração do componente opticamente ativo que representa na região espectral compreendida entre 400 e 800nm; 2- cálculo do resíduo; 3­cálculo do coeficiente de correlação entre a fração de um dado endmember e a concentração do componente ativo representado por ele, quando o modelo de mistura foi aplicado a diferentes janelas espectrais selecionadas a partir da análise dos resíduos. Os resultados mostraram que os coeficientes de correlação entre os componentes opticamente ativos e as frações de espectros puros variam nas diferentes janelas espectrais. Os resultados também permitiram verificar que o signal produzido pela clorofila pode ser separado daquele produzido pelos demais componentes na região vermelha do espectro.Pages: 96-10

Alterações da paisagem de várzea do Baixo Amazonas entre 1970 e 2008

Remote sensing data coupled with landscape ecology metrics were used to investigate the landscape evolution of the Lower Amazon floodplain over ~30 years. 1970 and 2008 vegetation cover maps were used to calculate landscape ecology metrics for forest patches. Results showed a fragmented landscape in both periods, especially at 2008, with increasing forest degradation throughout the study period. The number of forest patches increased, along with a decrease in mean patch size, denotes fragmentation and reduction of forest area in the region. The remaining metrics were also indicative of forest degradation, such as increasing edge area and reduction of core area for forest patches. The clear differences in the amount remaining and its spatial distribution must be considered when planning for biodiversity conservation, as well as information about the fauna, flora and local human populations.Pages: 7778-778

Correção geométrica da máscara de áreas alagáveis da bacia amazônica

Wetlands are important sources of carbon emissions. Accurate mapping of these environments is essential to produce precise estimates of this greenhouse gas. Since mid-2000 a map of wetlands for the entire Amazon basin is available. This map, called wetlands mask, has been used in some regional studies. However, geometric distortions have prevented its use for local-scale studies, where precise positioning is required. In this paper, we present the methodology to reduce these geometric distortions using SRTM-DEM as reference. To achieve this goal, a computer program was developed. In order to rectify local distortions, the wetlands mask was vectorized and overlaid on SRTM-DEM. From a control point set collected in both mask and SRTM-DEM, the whole area was decomposed into small triangles. A mathematical transformation was determined using the vertices of each pair of triangles (correct and warped) and was applied over all polygons enclosed by the triangles. The geometric correction of the distortions caused no significant changes in the estimate of the total flooded area. Furthermore, the displacements needed for correction rarely exceeded 1 km. The geometric correction substantially improved the consistency between the wetlands mask and the SRTM-DEM data.Pages: 5507-551

Dinâmica temporal da cobertura de macrófitas nos lagos de Mamirauá

The aim of this paper is to analyze the macrophyte coverage dynamics during two hydrograph phases (flood and drought) in different types of lakes at Mamirauá Sustainable Development Reserve. 20 Landsat TM images were selected, corresponding to the drought and flood hydrograph phases for each year from 1999 to 2009, except 2003. The images were classified using the maximum likelihood algorithm using bands 3, 4 and 5 being mapped the following classes: 1) Water, 2) macrophytes, 3) Clouds and 4) Exposed soil. Lakes were visually classified based on satellite imagery as circular, elongated (direct and simple) and complexes. Results showed that macrophyte coverage extent varied over the hydrograph phases, between years and lakes. The elongated lakes showed the greatest variation in macrophyte cover between hydrograph phases and the circular lakes had the smallest variation between phases. We observed an inverse correlation between macrophyte cover and water level in different types of lakes. The direct elongated lakes (with direct connection to the main channel) showed the highest inverse correlation with the water level. These lakes are subject to seasonal bank exposure favoring macrophyte colonization. Therefore, these lakes are more susceptible to large variations in water level, and hence to climate change.Pages: 6387-639

Modelos para estimativa da concentração de sedimentos em suspensão em rios amazônicos de águas brancas via sensoriamento remoto

This paper presents empirical models for suspended sediment concentration (SSC) retrieval from Landsat 5 images in several Amazon Rivers. In view of great gaps in the time series of in situ SSC database in Amazon Rivers, estimates based on historical orbital data may be an option to open new research possibilities. The models are based on a database composed of 504 in situ samples and near-simultaneously Landsat images. Two approaches are tested: i) using the entire database and ii) regionalizing the data according to environmental features of the watersheds they belong. The results show that the use of the whole database does not provide accurate SSC estimates. The regional modeling provides better estimates by fragmenting the data into five clusters. All these models display p-values ≈ 1*10-6 , R² values ranging from 0,83 to 0,91. The cross validation LOOCV and relative error values also showed their robustness. The models are very accurate, mainly for low SSC levels, between 0 to 200 mg/l. As the concentration increases, the absolute error increases too, but relative errors remain low (up to 7%).Pages: 5848-585

Backscattering response of different land cover types in the Lago Grande de Curuai floodplain (Amazon, Brazil) determined from Radarsat-2 and TerraSAR-X data

We analyzed the radiometric responses of main vegetation groups and other classes of interest at the Lago Grande de Curuai floodplain, in the Brazilian Amazon, to determine the influence of several radar imaging parameters (incidence angle, wavelength, spatial resolution and polarization) on the backscattering. Overall, images from the Radarsat-2 sensor, from the S1 imaging mode were the most effective to differentiate the analyzed cover types, mainly due to its greater target penetration capability in relation to TerraSAR-X images. Images with higher spatial resolution showed good potential to characterize local variations in target structure, while HH, VV and HV polarizations had smaller differences in their response variability, with HH polarization showing the largest responses magnitudes. Changes in incidence angle did not significantly affect target differentiation, except in the case of open water surfaces. We also noticed larger variation in target responses related to the time of imaging along the flooding season, evidencing the importance of multitemporal imagery for proper target identification. Overall, Radarsat-2 S1 and TerraSAR-X Stripmap or Spotlight modes offer the most promising capabilities for target discrimination and structure detection in the Amazon floodplain.Pages: 8475-848

Ajuste de bandas de modelos empíricos de estimativa de clorofila aplicados à região da planície de inundação do Lago Grande Curuai - PA

Empirical Models to estimate chlorophyll-a concentrations are among the most used in the remote sensing community. Historically, those models were applied to ocean monitoring, but in the last decade they were tested for Case II water types studies. In particular, in tropical water bodies characterized by highly complex mixture of optically active components. This complexity, based on high concentration of colored dissolved Organic Matter (CDOM), Total of Suspended Sediments (TSS) and Chlorophyll- (Chlo-a) that varies independently, one from each other, makes it necessary the search for a set of spectral bands able to improve the accuracy of chlorophyll estimates. This work uses a computational search method to find the best band set, for 295 samples distributed in 4 periods in a hydrological cycle. The samples are from the Curuai floodplain located in the Pará State in the Amazon Region. Results show good agreement to literature, but also shows some discrepancies, mostly because of tropical waters complexity. The new bands show better adjustments compared to standard bands intervals, found in literature. Models of Two and three band are adequate only for two periods with high degree of confidence. A discussion about the behavior of each period, and its empirical model best fit is also made.Pages: 8924-893

Aplicação de um índice de estado trófico (IETR TM4/TM3) para monitorar a degradação da água do reservatório da UHE Ibitinga

This paper describes the application of a remote sensing Trophic State Index (TSI) to assess changes in eutrophication suffered by Ibitinga hydroelectric reservoir from 1985 to 2008. The TSI, from now on referred as TSIRTM4/TM3, was calibrated with images acquired in 2005. Its application to a Landsat/TM time series was based on the following assumptions: i) the conversion from digital numbers to water surface reflectance would normalize the data set reducing the need for further calibration; ii) images with Sun elevation larger then 40o would minimize surface effects on underwater signal ; ii) images acquired under similar hydraulic residence time would guarantee uniform limnological environment. A set of 15 images were selected, calibrated, atmospheric corrected and geo-referenced. A water mask was built using band TM5 to create a comparable reference among the dates and applied to all scenes. A series of filters were tested and applied to images in order to reduce stripe. After noise removal TM4/TM3 ratio was computed and the TSIRTM4/TM3 look up table developed for the 2005 image was applied to all dates. The area occupied for each trophic state class was then computed. The results showed that the Ibitinga reservoir since 1985 can be classified as super-hypereutrophic. These findings are corroborated by data available in the literature showing that the TSIRTM4/TM3 can be used as a semi-quantitative tool for assessing the degree of water eutrophication.Pages: 6556-656

Atualização e correção do delineamento de áreas alagáveis para a bacia Amazônica

Delineation and characterization of areas subject to periodical inundation remains a challenge in the study of Amazonian wetlands, considering the geographical complexity of these environments. Hess et al. (2003) performed the only existing wetland habitat map for the mainstem Amazon floodplain, using synthetic aperture radar images from the Japanese Earth Resources Satellite 1 (JERS-1). These authors have produced a wetlands mask product for the entire basin, which has been used extensively by researchers. Recent studies have shown evidence of geometric distortion and mapping inconsistencies in this product, resulting from the process of automatic delimitation. The present paper analyzes a procedure for revision and correction of the original mask product, identifying the main types of distortion and comparing area differences between original and edited products. The revision procedure was based on visual interpretation and manual digitization of the original mask product, based on three main image sources: the original JERS-1 high water mosaic, the Shuttle Radar Topography Mission global elevation dataset, and a mosaic of orthorectified LandsatTM + images from the GeoCover dataset. The use of two additional sources was invaluable to resolve ambiguities and inconsistencies in areas where JERS-1 images did not allow clear distinction of wetlands. Considering the first 40 1\ub0 x 1\ub0 grid cells edited to date, the results show that the difference in area between the original and corrected masks was of approximately 3500 km² (3% of the total corrected area). Grid cells with the largest variation had a decreasing trend in area, reaching up to 16%. Most grid cells, however, had up to 10% reduction over the originally mapped area, suggesting a slight overestimation of the wetlands by Hess et al. 2003 research.Pages: 5864-587