4. HYBAM: un observatorio para medir el impacto del Cambio Climático sobre la erosión y los flujos de sedimentos en la zona Andino-Amazónica

La cuenca Amazónica es la más grande del mundo. La instalación del observatorio HYBAM con una amplia red de estaciones hidrológicas ubicadas desde el piedemonte andino hasta el océano Atlántico permite, desde el 2003, la generación de registros periódicos y confiables (nivel del agua, caudal, concentración de sedimentos y otros parámetros físico-químicos de la calidad del agua) a lo largo de toda la cuenca. Hoy en día, el desarrollo de técnicas satelitales, como la altimetría, permite completar eficientemente los datos obtenidos por las redes de medición en los ríos. El recrudecimiento de eventos extremos en la Amazonia (Inundaciones, sequias,) por efecto del cambio climático actual asociado a un cambio acelerado de ocupación de los suelos (deforestación, prácticas agrícolas), tiene una incidencia directa sobre la producción sedimentarla. Conocer los flujos de materiales transportados por los ríos es esencial tanto para la navegación fluvial como para guiar la explotación de los recursos naturales (agua, petróleo, minerales), para conocer el transporte de partículas contaminantes o para diseñar infraestructuras.Le bassin de l’Amazone est le plus grand du monde. La mise en œuvre de l’observatoire HYBAM avec un vaste réseau de stations hydrologiques situées sur les contreforts des Andes jusqu’á l’océan Atlantique permet de générer, depuis 2003, des données régulières et fiables tout le long du bassin (hauteur d’eau, débit, concentration de sédiments et d’autres paramètres physico-chimiques de qualité de l’eau). De nos jours, la mise au point des techniques par satellite, tels que l’altimétrie, permet de compléter efficacement les données obtenues par les réseaux de mesure dans les rivières. L’intensification des événements extrêmes dans la région amazonienne (inondations, sécheresses), liés au changement climatique actuel associé á un changement rapide de l’utilisation des terres (déforestation, pratiques agricoles), ont un impact direct sur la production de sédiments. Connaître les flux de matières transportés par les rivières est essentiel pour la navigation fluviale ainsi que pour guider l’exploitation des ressources naturelles (eau, pétrole, minéraux), connaître le trajet de particules polluantes ou concevoir des infrastructures.The Amazon basin is the largest basin in the world. The implementation of the HYBAM observatory, which has installed a large network of hydrological stations located from the Andean foothills down to the Atlantic Ocean, allows since 2003, generate periodical and reliable records (such as water level, flow, sediment concentration and other physicochemical parameters of water quality) along the entire basin. Nowadays, the development of satellite techniques, (such as altimetry), makes it possible to efficiently complete the data obtained by the measurement networks in rivers. The intensification of extreme events in the Amazon region (floods, droughts) occurred as a result of the current Climate Change associated with a more rapid change of land use (deforestation, agricultural practices) have a direct impact on sediment production. It is essential to know the flows of the materials transported by rivers, both for river navigation as well as to guide the exploitation of natural resources (water, oil, minerals), to know the transport of particulate pollutants, or to design infrastructures

Comparaison du nivellement direct, du positionnement GPS bifréquence et de l'altimétrie satellitaire radar pour le nivellement des stations limnimétriques du bassin Amazonien

Three levelling techniques were compared for the levelling of hydrometric stations along Amazonian rivers : spirit levelling, bi-frequency GPS positioning and satellite radar altimetry (Topex/Poseidon T/P. Results show a good agreement between GPS positioning and satellite radar altimetry techniques, the two techniques having been compared on 23 hydrometric stations with an average root mean square error of 0.05 +/- 0.64m. Comparison with spirit levelling allowed the identification of discrepancies in direct geometric land levelling results from Brazilian and Peruvian networks over the Amazon Basin. Levelling hydrometric stations through satellite radar altimetry required a specific methodology : maximum annual water levels (referred to the geoid, using EGM96 geopotential model) are quantified at intersections between the satellite ground tracks and the river network. Maximum annual water levels at hydrometric stations are then derived through longitudinal interpolation. Comparison with maximum annual readings at gauges allows the determination of local orthometric heights at these stations. Altimetric levelling from Topex/Poseidon measurements has been realized for 97 hydrometric stations along 27 740 km of the Amazon hydrographic network. Resulting river surface longitudinal profiles proved to be fully consistent in terms of hydrodynamics

Etablissement d'un référentiel altimétrique sur le bassin amazonien par altimétrie satellitaire radar (Topex Poseidon)

Satellite radar altimetry (Topex/Poseidon T/P) was used to establish a consistent altimetric reference network over the Amazon basin. A methodology was developed to quantify maximum annual water levels (referred to the geoid, using EGM96 geoid model) at intersections between the satellite ground tracks and the river network. Maximum annual water levels (referred to the geoid) at hydrometric stations where then derived using longitudinal interpolation. Comparison with maximum annual readings at gauges allowed the determination of local orthometric heights at these stations. Altimetric leveling from Topex/Poseidon measurements has been realized for 97 hydrometric stations along 27 740 km of the Amazon hydrographic network. Validation has been realized both by checking the overall hydraulic consistency of longitudinal river profiles at low and high river stages and by comparing, for 23 hydrometric stations, orthometric heights obtained from T/P measurements with values obtained from bi-frequency GPS positioning. Results show a good agreement between the two techniques (average root mean square error of 0.05 +/- 0.64m). This levelling method allowed the identification of discrepancies in direct geometric land leveling results from Brazilian and Peruvian networks. These results are of major importance for the study of Amazon river flow dynamics and sediment transport

Contrasting iron isotopic compositions in river suspended particulate matter : the Negro and the Amazon annual river cycles

Iron isotopic compositions (delta Fe-56(IRMM-14)) of suspended particulate matter (SPM) from two major rivers in the Amazon Basin, the Amazon River itself (at the Obidos Station) and the Negro River (at the Serrinha Station), were investigated in the present study. The main objective was to search for temporal variations during their annual river cycles. delta Fe-56(IRMM-14) values for the Amazon River at Obidos range between 0.00 and +0.15 parts per thousand, indistinguishable from the average continental crust value. In contrast, the iron isotopic compositions of the Negro River (Serrinha Station) SPM vary between -0.34 and -0.82 parts per thousand, whereas the dissolved matter is isotopically heavier in this river. The lack of significant isotopic variations in the Amazon River indicates that one individual SPM subsurface sample is representative of the river during the whole annual river cycle, in opposition to results obtained for the Negro River. The data suggest that in organic-poor white water rivers, such as the Amazon, iron isotopic signatures of the suspended fraction reflect a detrital crustal component with little isotopic fractionation. On the other hand, in the organic-rich Negro River, which has tropical podzols as the main iron source, the iron redox cycling at the water-soil interface influences the iron isotopic composition

Sediment budget in the Ucayali River basin, an Andean tributary of the Amazon River

Formation of mountain ranges results from complex coupling between lithospheric deformation, mechanisms linked to subduction and surface processes: weathering, erosion, and climate. Today, erosion of the eastern Andean cordillera and sub-Andean foothills supplies over 99% of the sediment load passing through the Amazon Basin. Denudation rates in the upper Ucayali basin are rapid, favoured by a marked seasonality in this region and extreme precipitation cells above sedimentary strata, uplifted during Neogene times by a still active sub-Andean tectonic thrust. Around 40% of those sediments are trapped in the Ucayali retro-foreland basin system. Recent advances in remote sensing for Amazonian large rivers now allow us to complete the ground hydrological data. In this work, we propose a first estimation of the erosion and sedimentation budget of the Ucayali River catchment, based on spatial and conventional HYBAM Observatory network

Source area and seasonal Sr-87/Sr-86 variations in rivers of the Amazon basin

We report the results of a detailed study of dissolved Sr isotopes in the Solimoes and Beni-Madeira Rivers of the Amazon basin. This study developed data collected over 8years indicating large spatial and temporal variations in dissolved Sr isotopes among the rivers of the Amazon basin. The large Sr-87/Sr-86 variations were found to be correlated with the geology of the source areas of the suspended sediments. The Beni-Madeira River displays a high average Sr-87/Sr-86 ratio and large Sr-87/Sr-86 fluctuations during the hydrological cycle. This large average value and fluctuations were related to the presence of Precambrian rocks and Ordovician sediments in the source area of the suspended sediment of the river. In contrast, the Solimoes River displays a narrow range of Sr isotope ratio variations and an average value close to 0.709. This river drains mostly Phanerozoic rocks of northern Peru and Ecuador that are characterized by low Sr isotope ratios. The isotopic fluctuations in the Beni-Madeira River were observed to propagate downstream at least as far as bidos. This signal is characterized by an inverse relationship between the concentration of elemental Sr and its isotopic ratios. We further demonstrate that the Sr isotopic composition and content in the Beni-Madeira River is controlled by suspended sediments derived from the Andes. Despite draining areas underlain by Precambrian rocks and having high Sr-87/Sr-86 ratios, such rivers as the Negro and Tapajos play a minor role in the total Sr budget of the Amazon basin

Evolución regional de los caudales en el conjunto de la cuenca del Amazonas para el periodo 1974-2004 y su relación con factores climáticos

Previos estudios describen de manera general la variabilidad anual de los caudales en el curso principal del Amazonas en Brasil, el cual sólo representa el estado general del sistema hidrológico de la cuenca. Por ello, este estudio utiliza una nueva serie de datos que incluye la descarga diaria de 18 subcuencas, con la finalidad de analizar la variabilidad de los extremos regionales en la cuenca del Amazonas. Luego de describir la diversidad de los ciclos hidrológicos anuales, diferentes pruebas estadísticas son aplicadas para detectar tendencias y rupturas de las series temporales. Este estudio muestra que durante el período 1974-2004, la estabilidad de caudales del río principal en Óbidos, se explica por cambios regionales opuestos que involucran principalmente a ríos Andinos: una disminución de la escorrentía en el periodo de estiage, particularmente importante en las regiones del sur, y un incremento de la escorrentía durante aguas altas en las regiones del noroeste. Ambas características se observan desde comienzos de los años noventa. Se observa también este comportamiento en las subcuencas más pequeñas del sur de Perú y Bolivia. Los cambios en los caudales extremos se relacionan con la variabilidad regional de las lluvias, la circulación atmosférica asociada e índices océanos atmosféricos de gran escala

Epidemiology and spatio- temporal analysis of cancer in Peru

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