Monitoramento das dinâmicas espaciais e temporais dos fluxos sedimentares na Bacia Amazônica a partir de imagens de satélite

Tese (doutorado)—Universidade de Brasília, Instituto de Geociências, 2013.A bacia amazônica é a mais importante do mundo em termos de superfície e de vazão ao oceano, representando uns 15% do volume d’água chegando aos oceanos e proveniente dos continentes. O fluxo de sedimento do Rio Amazonas foi estimado entre 600 e 1200 Milliões de toneladas. Na bacia do Amazonas, por causa de seu tamanho e de difícil acesso, é demasiado complexo e dispendioso o monitoramento das sub-bacias importantes. Para resolver esses problemas serão exigidos instrumentos alternativos, como imagens de satélite. A principal desvantagem da utilização de sensores ópticos nesta região é a grande quantidade de nuvens, mas este problema pode ser solucionado com a utilização de imagens de alta resolução temporal. Este trabalho tem como principal objetivo controlar os fluxos de sedimentos nos grandes rios da Amazônia, e classificar os diferentes tipos de água presente na bacia, a partir de suas características ópticas. O sensor MODIS (Moderate Resolution Imaging Spectroradiometer), a bordo dos satélites TERRA e AQUA, fornecem imagens diárias por cada satélite, fazendo um total de 2 imagens por dia, com resolução espacial de até 250 m. Nesta pesquisa serão usadas imagens compostas de 8 dias com resolução espacial de 250 e 500 m para ambos os satélites, fazendo um total de 4 produtos MODIS (MOD09Q1, MOD09A1, MYD09Q1 e MYD09A1). Estes produtos fornecem dados de reflectância com uma correção atmosférica bastante robusta. A rede de monitoramento ORE-HIBAM vem coletando dados de qualidade de água, a cada dez dias, desde 2003, em diferentes locais da bacia amazônica. Estas amostras são para a medição da concentração de matéria em suspensão (MES) de superfície. Para calibrar estas estações, o projeto HIBAM, em cooperação com entidades regionais, realiza campanhas para a coleta de amostras d’água e medição de diferentes parâmetros. Nessas campanhas foram também realizadas medições de radiometria (reflectância de sensoriamento remoto (Rrs) e coeficiente de atenuação difusa (Kd)) da água. De maneira simultânea às medições de radiometria foram coletadas amostras de água. As medições de Rrs foram relacionados com as concentrações correspondentes de MES, obtendo um coeficiente de correlação (R2 ) de 0,89 para 259 amostras. Da mesma forma foram correlacionados com as medidas de Kd e a concentração de MES, obtendo R2 de 0,93 para 129 amostras. Ambas as medidas com um intervalo de concentrações de 2-621.6 mg/l. As medições de radiometria também foram utilizadas para classificar as águas naturais da Amazônia em 8 classes, dependendo de suas propriedades ópticas. Com as medidas radiométricas de campo foi possível calcular o coeficiente de absorção (a) das águas naturais, estimar a absorção do CDOM (aCDOM) e dos sedimentos (as). Usando estes dados, também foi calculado o coeficiente de espalhamento (b) e retroespalhamento (bb) para diferentes tipos de água, com resultados consistentes com a literatura. A extração da reflectância das imagens MODIS foi realizada de maneira automatizada, mediante a ferramenta computacional MOD3R. Esta ferramenta extrai a reflectância dos pixels correspondentes da água, a partir de uma região previamente designada. Desta forma, pode-se processar e analisar séries históricas a partir de uma grande quantidade de imagens (mais de 500 imagens por estação). Com as imagens MODIS foram criadas 6 estações virtuais ao longo do Rio Madeira. Para esse trabalho foi usada uma razão de bandas (infravermelha / vermelha) e, a partir dos dados de radiometria de campo e de concentração de MES das campanhas, os dados MODIS foram calibrados a partir da relação entre dados de MES e o resultado da razão de bandas. Os dados de MES estimados com as imagens MODIS foram validados com os dados das estações de Fazenda Vista Alegra e Porto Velho, da rede ORE-HIBAM obtendo-se um valor de R2 = 0.78. Assim, foram estimados os valores de MES para cada estação e para um período de 2000 a 2011. Com esses dados, foi calculado um ano médio (12 médias mensais) para as seis estações. Assim, observamos os processos de transporte de sedimentos como diluição e precipitação ao longo do rio Madeira e do comportamento temporal em cada estação e época do ano, e da influência nos sedimentos do remanso hidráulico causado pelo rio Amazonas, em alguns meses do ano. Na confluência dos rios Ucayali e Maranon é formado o rio Amazonas (peruano). Nessa região existem três estações de amostragem de concentração de sedimentos de superfície, da rede ORE-HYBAM, nos três rios (Marañón, Ucayali e Amazonas). A estação do rio Ucayali teve um problema causado pela pluma de um rio afluente, fazendo com que as amostras nesta estação representem as águas do afluente. O projeto HIBAM realiza campanhas de amostragem de sedimentos e medição do caudal sólido e líquido, assim podem se ligar as amostras de sedimentos de superfície com descarga sólida. Os dados de reflectância infravermelha MODIS foram relacionados com as concentrações médias de superfície, medidas durante as campanhas, obtendo-se boas correlações entre estas duas magnitudes. Usando as relações MES- Reflectância, foram estimadas series de concentração de sedimentos e posteriormente foi estimada a descarga sólida em 3 estações. Nas estações dos rios Marañon e Amazonas, os dados estimados com as imagens de satélite foram validadso com os dados da rede ORE-HIBAM. Para validar o resultado do rio Ucayali foi realizado um balanço de massa entre as três estações, de modo que a descarga sólida dos rios Maranon e Ucayali seja igual à descarga sólida na estação do rio Amazonas. O equilíbrio foi realizado com dados MODIS estimados, em uma série de imagens entre os anos 2000 e 2009, fechando o equilíbrio entre as estações tanto a montante quanto a jusante. Na presente pesquisa foram estimados dados de MES para um intervalo entre 4 e 1832 mg/l, sem achar saturação na reflectância do canal infravermelho, na razão de bandas e no Kd. As estimações de MES, a partir dos dados MODIS, realizadas na presente pesquisa mostraram um erro médio quadrático entre 30 e 40%. Com a utilização da radiometria de campo, este erro diminui cerca de 23%. ______________________________________________________________________________ RÉSUMÉLe bassin Amazonien est le grand plus réseau hydrographique du monde en termes d’extension géographique et de débit. Il couvre approximativement 5 % des surfaces émergées, représente 15 % des apports continentaux en eau douce aux océans tandis que son débit sédimentaire est de l’ordre de 800 millions de tonnes par an. Le suivi hydro-sédimentaire des fleuves amazoniens est rendu difficile par la taille du bassin et la puissance des flux à mesurer pour lesquels les méthodes traditionnelles de caractérisation sont peu adaptées. Les données de télédétection optique pourraient représenter une alternative intéressante pour le suivi de paramètres de qualité des eaux, notamment pour des grands bassins « sous » instrumentés comme l’Amazonie. Un obstacle important reste cependant le fort ennuagement typique des zones tropicales humides qui ne peut être dépassé que par l’utilisation d’une très haute résolution temporelle. L’objectif de la présente thèse est de caractériser les flux sédimentaires des principaux fleuves amazoniens à partir du suivi par télédétection des propriétés optiques de leurs eaux. Les capteurs MODIS (Moderate Resolution Imaging Spectroradiometer) à bord des satellites Terra et Aqua, fournissent des images journalières sur toute la surface terrestre. Nous considérons les produits continentaux composites à 8 jours et à 250 mètres de résolution spatiale. Ces images présentent l’avantage d’être calibrées, corrigées des effets atmosphériques et géoréférencées de manière robuste permettant un traitement automatisé de longues séries temporelles depuis l’an 2000. La caractérisation des flux sédimentaires in situ se base sur les données de réseaux conventionnels de mesure (ORE-HYBAM) et des campagnes de mesure qui ont permis de mesurer, selon des transects amont-aval, les principales caractéristiques des flux hydrologiques (débit, variations spatiales et saisonnières), des matières en suspension (MES) (concentration, minéralogie, granulométrie) et de leurs propriétés optiques (propriétés optiques apparentes AOP – réflectance télédétectée Rrs et coefficient d’atténuation diffus vertical descendant Kd). Un total de 279 mesures de Rrs et 133 de Kd sont analysées afin de déterminer la variabilité des propriétés optiques des MES au sein du bassin versant de l’Amazone et durant les différentes périodes du cycle hydrologique. Une classification non supervisée de Rrs permet de séparer aisément les eaux des plaines d’inondation et les grands types d’eaux fluviales (eaux noires / claires / blanches). La réflectance est bien corrélée avec la concentration en MES dans l’infrarouge (r² = 0.81 – 840 0.9), sans saturation et pour une large gamme de longueur d’ondes du vert (500 nm) à l’infrarouge (850 nm). Les propriétés optiques inhérentes (IOP) sont aussi étudiées directement (matière organique dissoute colorée – CDOM) ou déduites à partir des mesures des AOP. La moyenne de l'absorption du CDOM à 440 nm varie en fonction des types d’eaux. Pour les eaux noires, aCDOM est de 7.9 m-1, alors qu’il est de l’ordre de 4.8 m-1, pour les eaux blanches. La relation entre aNAP (coefficient d’absorption du matériel particulaire) à 550 nm et la MES est très robuste (r2 =0.91) mais présente une dispersion significative pour les faibles concentrations. L'absorption spécifique des particules non algales (a*NAP), qui est définie comme l'absorption par unité de concentration est évaluée à 0.028 m2/g à 555 nm. La variation de aNAP est modélisée par une exponentielle négative dont l’exposant varie entre 0.006 et 0.015 avec une corrélation négative avec la MES. Le coefficient de diffusion spécifique des particules non algales b*NAP à 555 nm est en moyenne de 0.672 ± 0.18 m2.g-1 et montre une variation spectrale du type λ-0.77 avec la longueur d’onde. Alors que sur l’Amazone et son principal affluent, le Solimões, aucunes variations saisonnières ne sont détectées, on mesure une variation saisonnière de b*NAP au sein du fleuve Madeira qui contribue à hauteur de 50% au débit solide du fleuve Amazone. L’utilisation des données satellitaires de résolution moyenne (hectométrique) est rendu difficile par l’étroitesse des cours d’eau vis-à-vis de la taille des pixels. Le phénomène de mélange spectral peut altérer la réflectance des pixels d’eau en fonction de la proximité d’éléments possédant des signatures spectrales contrastées (végétation de berge). Un algorithme a été développé afin d’identifier de manière automatique les pixels purs d’eaux au sein des scènes MODIS. La réflectance des eaux fluviales calculées par l’algorithme est validée avec les données radiométriques de terrain décrites précédemment, avec une bonne précision et avec un biais compatible avec les études de CAL/VAL précédemment publiées en milieu tropical humide marquée la présence d’aérosols en grande quantité. L’utilisation de cet algorithme permet un traitement automatisée des séries temporelles MODIS sur toutes les stations du réseau HYBAM en Amazonie et sans connaissance a priori des caractéristiques hydrologiques, météorologiques ou de la géométrie d’acquisition. Au Brésil, le fleuve Madeira est étudiée de manière systématique avec les données MODIS Terra et Aqua à partir de la création d’un réseau de stations virtuelles le long du cours d’eau. L’analyse conjointe des données satellitaires, radiométrique de terrain et des données de MES à deux stations (Porto Velho et Borba) met en évidence une hystérésis dans la relation Rrs – concentration en MES. En effet, il apparait que pour une même concentration en MES, la Rrs est inférieure en période de pic de crue, un comportement cohérent avec celui détecté pour le coefficient de diffusion spécifique de la MES comme décrit précédemment. Cette sensibilité est expliquée par une variation du type de MES qui affecte leur propriétés optique bien qu’il ne soit pas possible de conclure sur l’origine exacte de cette variation (variabilité granulométrique, minéralogique ou de la fraction organique). Cependant, l’utilisation d’un ratio Rrs(Infrarouge) / Rrs(Rouge) permet de s’affranchir de cette sensibilité saisonnière et permet un suivi précis de la concentration en MES comme l’atteste la validation avec les données du réseau HYBAM (r = 0.79 – N = 282) pour une large gamme de MES (4 – 1832 mg/ l). L´étude des comportements moyens de la concentration en MES mesurée par satellite au pas de temps mensuel (estimée par une moyenne interannuelle entre 2000 et 2011), d’amont en aval, permet le suivi fin des processus hydro-sédimentaires qui se développent au cours de la traversée du Madeira au sein de la plaine amazonienne jusqu’à sa confluence avec le fleuve Amazone : dilution, sédimentation et resuspension. En particulier, la zone de sédimentation induite par le barrage hydraulique à la confluence Madeira / Amazone est précisément délimitée lors de la période d’étiage. Au Pérou, nous étudions la zone de confluence Marañon / Ucayali où se forme le fleuve Amazone et où l’ORE HYBAM maintient une station hydro-sédimentaire sur chaque cours d’eau avec le service hydrologique péruvien. La station terrain de l’Ucayali montre des mesures incohérentes pendant plusieurs années du fait de l’influence d’un affluent local à l’amont de la station, rendant impossible l’utilisation de ces données. Pour cette étude, les images MODIS sont calibrées à partir de campagnes de mesures intensives des MES aux trois stations du réseau HYBAM entre 2007 et 2009. La validation est effectuée de manière indépendante de deux manières. D’abord en comparant les MES estimées par satellite et les données du réseau HYBAM (données à 10 jours) aux deux stations montrant des enregistrements valides (fleuves Amazone et Marañon). Ensuite, les données de MES de surface estimées par satellite sont utilisées pour calculer une concentration moyenne sur la colonne d’eau grâce aux données de campagne HYBAM. Les MES moyennes sur la section sont ensuite multipliées par le débit liquide pour calculer un débit sédimentaire à chaque station dans la zone de confluence. La comparaison des débits solides déduit par satellite entre amont (Marañon + Ucayali) et aval (Amazone) montre une excellente robustesse des estimations satellitaires (RMSE de 18 %, biais de 3 % sur 104 mois de données) compatible avec une utilisation opérationnelle des données MODIS pour le suivi des flux sédimentaires au sein du bassin amazonien. La présente thèse démontre pour la première fois que les propriétés optiques des MES au sein d’un grand bassin versant hydrologique sont suffisamment stables spatialement et temporellement afin de permettre un suivi efficace des flux sédimentaires de surface. Nous avons également démontré que les données MODIS, grâce au post-traitement que nous présentons, permettent de suivre robustement la réflectance des eaux de rivières. L’exploitation des images satellitaires permet ainsi de mettre en évidence les processus hydro-sédimentaires sur de larges périodes de temps (> 10 ans) et de mesurer les flux sédimentaires en conjonction avec les réseaux conventionnels de mesure. ______________________________________________________________________________ ABSTRACTThe Amazon basin is the largest hydrographical network in terms of geographical extension and discharge. It covers approximatively 5% of the continental surface, represents 15% of the fresh water continental contribution to the ocean, while its solid discharge is of around the 800 millions of ton per year. The hydro-sedimentary monitoring of the Amazonian rivers is limited by the large extension of the basin and the magnitude of the fluxes to measure, for which the traditionally characterisation methods are not well adapted. The optical remote sensing data could represent an interesting alternative for the monitoring of water quality parameters, particularly for large under-instrumented basins like the Amazon. However, a main limitation of this method is the typical nebulosity of the wet tropical regions. This difficulty can only be resolved by using very high temporal resolution of the data. The objective of this thesis is to characterize the sedimentary fluxes of the main amazonian rivers, using the remote sensing monitoring of their water optical properties. The MODIS sensors (Moderate Resolution Imaging Spectroradiometer) on board of Terra and Aqua satellites provide daily images on the whole Earth surface. The continental product composites every 8 days and with 250-m spatial resolution are used. The advantage of those images is that they are calibrated, the atmospheric effects are corrected, and they are robustly georeferenced, which make possible an automatized treatment of large temporal series since 2000. The in-situ sedimentary fluxes characterization is based on a conventional measurement network data (ORE-HYBAM) and field campaigns. Those data provided, via upstream-downstream section, main characteristics of hydrological fluxes (discharge, spatial and seasonal variabilities), suspended sediment (SS) (concentration, mineralogy and granulometry) and their optical properties (apparent optical proprieties AOP – remote sensing reflectance Rrs and downwelling diffuse attenuation coefficient Kd). A total of 279 measurements of Rrs and 133 of Kd are analyzed in order to determinate the variability of optical properties of SS into the Amazon basin and during the distinct periods of the hydrological cycle. With a classification not supervised of Rrs , the flood plains water and the main fluvial water types (black water/clear/white) are separated. The reflectance is well correlated with the SS concentration in the infrared (r² = 0.81 – 840 0.9), without saturation and for a large range of wavelength from green (500 nm) to infrared (850 nm). The inherent optical properties (IOP) are also directly studied (colored dissolved organic matter – CDOM) or deduced from AOP measurements. The mean absorption of the CDOM at 440 nm differs according to water types. For black water, aCDOM is 7.9 m-1, while it is of about 4.8 m-1 for white waters. The relation between aNAP (absorption coefficient of the suspended sediment) at 550 nm and the SS is robust (r2 =0.91) but shows a significative dispersion for weak concentrations. The specific absorption of the non- algal particles (a*NAP), which is defined as the absorption per concentration unity is estimated at 0.028 m2/g à 555 nm. The variation of aNAP is modelized by a negative exponential with an exponent that varies from 0.006 to 0.015, with a negative correlation with the SS. The scattering coefficient specific of the non-algal particles b*NAP at 555 nm is in average of 0.672 ± 0.18 m2.g-1 and shows a spectral variation of the -0.77 type with the wavelength. While for the Amazon and its main tributary, the Solimões, no seasonal variation are detected, a seasonal variation of b*NAP is measured for the Madeira river, which contribute in around 50% to the solid discharge of the Amazon mainstream. The utilization of the medium resolution satellital data (hectometric) is complicated due to the river narrowness by comparison to the pixel size. The mixing spectral phenomenon can degrade the reflectance of the water pixels, in relation to the proximity of the elements having contrasted spectral signatures (riverbank vegetation). An algorithm was developed in order to automatically identify the pure water pixels into the MODIS images. The fluvial water reflectance calculated with the algorithm is validated with the in-situ radiometric data previously described, with a good precision and a compatible bias with the CAL/VAL studies previously published in humid tropical environment characterized by the strong quantity of aerosols. This algorithm is used to automatically treat the MODIS temporal series over all the HYBAM network stations in the Amazon basin, and without an a priori knowledge of hydrological, meteorological or acquisition geometry characteritics. In Brazil, the Madeira River is systematically studied with the MODIS Terra and Aqua data from the creation of a virtual stations network along the river. The parallel analysis of the satellital, in-situ radiometric and SS data at two stations (Porto Velho and Borba) put in evidence an hysterisis in the relation Rrs – SS concentration. Indeed, it seems that for a similar SS concentration, the Rrs is lower during the highflow period, a coherent behavior, with regards to the one detected for the SS specific scattering coefficient, as previously described. This sensibility is explained by a variation of the SS type, which affect their optical properties, while it is not possible to conclude about the extract origin of this variation (granulometrical, mineralogical or organic fraction variability). However, the Rrs(Infrared) / Rrs(Red) ratio is used to avoid the seasonal sensibility and make possible the precise monitoring of the SS concentration, as the validation of HYBAM network data has demonstrated (r = 0.79 – N = 282) for a large SS range (4 – 1832 mg/ l). The study of the mean behaviors of the SS concentration measured by satellite with a monthly time step (estimated with a interannual me

On the relationship between suspended sediment concentration, rainfall variability and groundwater: An empirical and probabilistic analysis for the Andean Beni River, Bolivia (2003-2016)

Fluvial sediment dynamics plays a key role in the Amazonian environment, with most of the sediments originating in the Andes. The Madeira River, the second largest tributary of the Amazon River, contributes up to 50% of its sediment discharge to the Atlantic Ocean, most of it provided by the Andean part of the Madeira basin, in particular the Beni River. In this study, we assessed the rainfall (R)-surface suspended sediment concentration (SSSC) and discharge (Q)-SSSC relationship at the Rurrenabaque station (200 m a.s.l.) in the Beni Andean piedmont (Bolivia). We started by showing how the R and Q relationship varies throughout the hydrological year (September to August), describing a counter-clockwise hysteresis, and went on to evaluate the R-SSSC and Q-SSSC relationships. Although no marked hysteresis is observed in the first case, a clockwise hysteresis is described in the second. In spite of this, the rating curve normally used (SSSC = aQb) shows a satisfactory R2 = 0.73 (p < 0.05). With regard to water discharge components, a linear function relates the direct surface flow Qs-SSSC, and a hysteresis is observed in the relationship between the base flow Qb and SSSC. A higher base flow index (Qb/Q) is related to lower SSSC and vice versa. This article highlights the role of base flow on sediment dynamics and provides a method to analyze it through a seasonal empirical model combining the influence of both Qb and Qs, which could be employed in other watersheds. A probabilistic method to examine the SSSC relationship with R and Q is also proposed. © 2019 by the authors

Amazon hydrology from space : scientific advances and future challenges

As the largest river basin on Earth, the Amazon is of major importance to the world's climate and water resources. Over the past decades, advances in satellite-based remote sensing (RS) have brought our understanding of its terrestrial water cycle and the associated hydrological processes to a new era. Here, we review major studies and the various techniques using satellite RS in the Amazon. We show how RS played a major role in supporting new research and key findings regarding the Amazon water cycle, and how the region became a laboratory for groundbreaking investigations of new satellite retrievals and analyses. At the basin-scale, the understanding of several hydrological processes was only possible with the advent of RS observations, such as the characterization of "rainfall hotspots" in the Andes-Amazon transition, evapotranspiration rates, and variations of surface waters and groundwater storage. These results strongly contribute to the recent advances of hydrological models and to our new understanding of the Amazon water budget and aquatic environments. In the context of upcoming hydrology-oriented satellite missions, which will offer the opportunity for new synergies and new observations with finer space-time resolution, this review aims to guide future research agenda toward integrated monitoring and understanding of the Amazon water from space. Integrated multidisciplinary studies, fostered by international collaborations, set up future directions to tackle the great challenges the Amazon is currently facing, from climate change to increased anthropogenic pressure

The optical properties of river and floodplain waters in the Amazon River Basin: Implications for satellite-based measurements of suspended particulate matter

Satellite images can now be used to assess river sediment discharge, and systematic studies over rivers and lakes are required to support such applications and document the variability of inland water optical properties at the watershed scale. The optical properties of the Amazon Basin waters were analyzed from in situ measurements of the remote sensing reflectance (Rrs) at 279 stations and downwelling diffuse attenuation coefficients (Kd) at 133 stations. Measurements of the apparent optical properties, suspended particulate matter (SPM) contents, and characteristics and colored dissolved organic matter (CDOM) absorption spectra were performed during 16 cruises along the main Amazonian Rivers draining the Andes and for some tributaries. Surface-suspended sediment granulometry and mineralogy showed a stable distribution at the catchment scale, even over large distances and between tributaries. The particle number-size distribution was best described using a segmented distribution with a slope of 2.2 for the fine range (1-15μm), and the CDOM absorption coefficient at 440nm varied from 1.8 to 7.9m-1. Overall, both Rrs and Kd were strongly correlated with SPM, although strong CDOM absorption limited the use of the blue spectrum. Reflectance saturation from blue to red was observed at approximately 100gm-3, whereas the near-infrared (NIR) wavelength enabled the monitoring of the full SPM range (5-620gm-3). In contrast, Kd showed no saturation for SPM from green to NIR, and a linear model was calculated. The use of the reflectance ratio was investigated and shown to improve the suspended sediment concentration retrieval performance. ©2015. American Geophysical Union. All Rights Reserved

Recent significant decline of strong carbon peat accumulation rates in tropical Andes related to climate change and glacier retreat

Climate change has altered precipitation and temperature patterns in the tropical Andes. As a result, tropical glaciers have retreated significantly over the past 50 years and have even disappeared in some areas. Andean peatlands, one of the most important Andean carbon reservoirs, also seem to be affected by these climate changes, since glaciers have been recognized as one of their vital water sources. Here, we point out the important role of Andean peatlands on carbon accumulation rates (CAR), one of the highest in the world, and the impact of climate on carbon storage over the last 65 years, using four peat cores. The peat cores were radiocarbon-dated and ages were post-bomb calibrated and chronological models indicated basal ages (30 cm depth) ranging from 1957 to 1972 CE, where accumulation rates reached up 1.7 cm yr?1. For both peatlands, carbon accumulation rates are high (mean of 470 and 220 g C m?2 yr?1 at APA 1 and APA 2 sites, respectively) and can reach up to 1010 g C m?2 yr?1. Distichia muscoides is the dominant species in the Peruvian Central Andes peatlands and the high CAR, among other factors, is a characteristic of this species. Our results point out that a marked decrease of CAR after the early 1980s at both peatlands is likely related to an increase in annual temperature, which is responsible for the retreat of glaciers. We use a new high-resolution proxy (Skrzypek et al., 2011) based on the ?13C of Distichia along the cores to evaluate the temperature variability at the site. We observed a general trend of increase in the reconstructed temperature from both studied peatlands from 1.9 to 2 ºC for the period 1970-2015 CE. Comparison with air temperature data from the NCEP-NCAR reanalysis for the higher resolution cores shows a good relationship and an increase of 2.15 °C for the same period. Temperature increase may directly affect CAR by an increase in organic matter degradation rates. The decrease in CAR during the period of study may also be due to a decrease in melt water inflow generated by the retreat of glaciers that have almost disappeared today in the catchments as a consequence of regional warming. Our findings emphasize that marked changes in carbon accumulation rates demonstrate the high ecological sensitivity of tropical high-Andean peatlands, endangering their outstanding role in the regional (and even global) C cycle as large C sinks that contribute to the mitigation of global climate change

Decline of Fine Suspended Sediments in the Madeira River Basin (2003–2017)

The Madeira River is the second largest Amazon tributary, contributing up to 50% of the Amazon River&rsquo;s sediment load. The Madeira has significant hydropower potential, which has started to be used by the Madeira Hydroelectric Complex (MHC), with two large dams along the middle stretch of the river. In this study, fine suspended sediment concentration (FSC) data were assessed downstream of the MHC at the Porto Velho gauging station and at the outlet of each tributary (Beni and Mamor&eacute; Rivers, upstream from the MHC), from 2003 to 2017. When comparing the pre-MHC (2003&ndash;2008) and post-MHC (2015&ndash;2017) periods, a 36% decrease in FSC was observed in the Beni River during the peak months of sediment load (December&ndash;March). At Porto Velho, a reduction of 30% was found, which responds to the Upper Madeira Basin and hydroelectric regulation. Concerning water discharge, no significant change occurred, indicating that a lower peak FSC cannot be explained by changes in the peak discharge months. However, lower FSCs are associated with a downward break in the overall time series registered at the outlet of the major sediment supplier&mdash;the Beni River&mdash;during 2010

Spatio-temporal monitoring of suspended sediments in the Solimões River (2000–2014)

The Amazon River sediment discharge has been estimated at between 600 and 1200 Mt/year, of which more than 50% comes from the Solimões River. Because of the area's inaccessibility, few studies have examined the sediment discharge spatial and temporal pattern in the upper Solimões region. In this study, we use MODIS satellite images to retrieve and understand the spatial and temporal behaviour of suspended sediments in the Solimões River from Peru to Brazil. Six virtual suspended sediment gauging stations were created along the Solimões River on a 2050-km-long transect. At each station, field-derived river discharge estimates were available and field-sampling trips were conducted for validation of remote-sensing estimates during different periods of the annual hydrological cycle between 2007 and 2014. At two stations, 10-day surface suspended sediment data were available from the SO-HYBAM monitoring program (881 field SSS samples). MODIS-derived sediment discharge closely matched the field observations, showing a relative RMSE value of 27.3% (0.48 Mtday) overall. Satellite-retrieved annual sediment discharge at the Tamshiyacu (Peru) and Manacapuru (Brazil) stations is estimated at 521 and 825 Mt/year, respectively. While upstream the river presents one main sediment discharge peak during the hydrological cycle, a secondary sediment discharge peak is detected downstream during the declining water levels, which is induced by sediment resuspension from the floodplain, causing a 72% increase on average from June to September. © 2017 Académie des science

From drought to flooding: understanding the abrupt 2010-11 hydrological annual cycle in the Amazonas River and tributaries

International audienceIn this work we document and analyze the hydrological annual cycles characterized by a rapid transition between low and high flows in the Amazonas River (Peruvian Amazon) and we show how these events, which may impact vulnerable riverside residents, are related to regional climate variability. Our analysis is based on comprehensive discharge, rainfall and average suspended sediment data sets. Particular attention is paid to the 2010-11 hydrological year, when an unprecedented abrupt transition from the extreme September 2010 drought (8300 m3 s-1) to one of the four highest discharges in April 2011 (49 500 m3 s-1) was recorded at Tamshiyacu (Amazonas River). This unusual transition is also observed in average suspended sediments. Years with a rapid increase in discharge are characterized by negative sea surface temperature anomalies in the central equatorial Pacific during austral summer, corresponding to a La Niña-like mode. It originates a geopotential height wave train over the subtropical South Pacific and southeastern South America, with a negative anomaly along the southern Amazon and the southeastern South Atlantic convergence zone region. As a consequence, the monsoon flux is retained over the Amazon and a strong convergence of humidity occurs in the Peruvian Amazon basin, favoring high rainfall and discharge. These features are also reported during the 2010-11 austral summer, when an intense La Niña event characterized the equatorial Pacific

Reconstrução de uma serie histórica de descarga de sedimentos usando imagens de satélite MODIS nos rios da Amazônia peruana

The use of satellite imagery to assess river sediment discharge is discussed in the context of poorly gauged basins. The HYBAM program completed the Peruvian Meteorological and Hydrological Service (SENAMHI) network increasing water quality, allowing assessment of both river discharge and surface suspended sediment (SSS) concentration. We analyze the case of the three stations near the Marañon and Ucayali rivers confluence that form the Amazon River. Two stations present complete time series of 10-day SSS samples. The third station, along the Ucayali River, failed to provide valid estimates of SSS concentration at the river. The objective is to use the satellite data 1) to substitute the missing records in order to assess the Ucayali river sediment discharge that has never been assessed directly before; 2) to extend the river sediment discharge records over the two other stations. Water reflectance assessed from time series of MODIS images is calibrated using field sampling campaigns to provide SSS estimates from satellite. Validation is achieved on an independent dataset that is the 10-day SSS samples derived from the network. Over the 2004-2008 period, we demonstrate that there is a good agreement, better than 10%, for two stations for which we have complete field records. Making use of satellite-derived SSS estimate assessed from 2000-2009, we show that the river sediment balance is closed between upstream and downstream stations.Pages: 5356-536