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Mortillaro J.M.,University Pierre and Marie Curie | Abril G.,University of Bordeaux 1 | Abril G.,Brazilian Radiological Protection and Dosimetry Institute (IRD) | Moreira-Turcq P.,IRD GET | And 4 more authors.
Organic Geochemistry | Year: 2011

Fatty acid (FA) composition and stable isotope (δ13C, δ15N) signatures of four aquatic plants, plankton, sediment, soil and suspended particulate organic matter (SPOM) collected from open floodplain lakes (Várzea) and rivers of the central Brazilian Amazon basin were gathered during high and low water stages in 2009. SPOM from Várzea had a major contribution of autochthonous material from phytoplankton and C3 aquatic plants. As shown from stable isotope composition of SPOM (δ13C -31.3±3.2‰; δ15N 3.6±1.5‰), the C4 aquatic phanerogam (δ13C -13.1±0.5‰; δ15N 4.1±1.7‰) contribution appeared to be weak, although these plants were the most abundant macrophyte in the Várzea. During low water season, increasing concentration of 18:3ω3 was recorded in the SPOM of lakes. This FA, abundant mainly in the Várzea plants (up to 49% of total FAs), was due to the accumulation of their detritus in the ecosystem. This dry season, when connectivity with the river mainstem was restricted, was also characterized by a high concentration in the SPOM of the cyanobacteria marker 16:1ω7 (up to 21% of total FAs). The FA compositions of SPOM from the Amazon River also exhibited significant seasonal differences, in particular a higher concentration of 16:1ω7 and 18:3ω3 during the dry season. This suggests a seasonal contribution of autochthonous material produced in Várzea to the Amazon River SPOM. © 2011 Elsevier Ltd.

Calmant S.,IRD LEGOS | Da Silva J.S.,UEA CESTU | Moreira D.M.,Federal University of Rio de Janeiro | Seyler F.,IRD Montpellier | And 3 more authors.
Advances in Space Research | Year: 2013

Altimetry is now routinely used to monitor stage variations over rivers, including in the Amazon basin. It is desirable for hydrologic studies to be able to combine altimetry from different satellite missions with other hydrogeodesy datasets such as leveled gauges and watershed topography. One requirement is to accurately determine altimetry bias, which could be different for river studies from the altimetry calibrated for deep ocean or lake applications. In this study, we estimate the bias in the Envisat ranges derived from the ICE-1 waveform retracking, which are nowadays widely used in hydrologic applications. As a reference, we use an extensive dataset of altitudes of gauge zeros measured by GPS collocated at the gauges. The thirty-nine gauges are spread along the major tributaries of the Amazon basin. The methodology consists in jointly modeling the vertical bias and spatial and temporal slope variations between altimetry series located upstream and downstream of each gauge. The resulting bias of the Envisat ICE-1 retracked altimetry over rivers is 1.044 ± 0.212 m, revealing a significant departure from other Envisat calibrations or from the Jason-2 ICE-1 calibration. © 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.

Cordeiro R.C.,Federal University of Fluminense | Turcq B.,IRD Montpellier | Moreira L.S.,Federal University of Fluminense | Rodrigues R.A.R.,Federal University of Fluminense | And 13 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2014

Interpreting the geological record of Amazon biomass combustion requires comparing charcoal accumulation rates in various biomes at different time scales. Charcoal accumulation rates, a proxy for palaeofire records, were obtained in sediment cores from Amazon lakes surrounded by several vegetation types and from a reservoirs in an intense land use change region. The records presented in this study were obtained in the following areas i) a reservoirs in Alta Floresta region (northern Mato Grosso State); ii) Lago do Saci (southern Pará State), a lake close to Alta Floresta and located at the southern border of Pará State; iii) a bog in an ecotone area in the Humaitá region (southern Amazonas State); iv) lakes in lateritic iron crust of the Carajás Hills (southeastern Pará State); v) Lago Comprido, a floodplain lake close to the Amazon River and surrounded by tropical rain forest (Monte Alegre, Pará State; vi) Lagoa da Pata in the Morro dos Seis Lagos alkaline complex (São Gabriel da Cachoeira, Amazonas State) and vii) Lago Caracaranã, a secluded lake in the northern Amazon cerrado (Roraima State). The highest charcoal accumulation rates were observed for modern records related to an intense change in land use at Alta Floresta, which had no precedent during the Holocene history of the Amazon. High charcoal accumulation rates that were observed in the Carajás region during low lake level phases in the Amazon in the mid-Holocene were comparable to those at the onset of the human settlement in Alta Floresta region. An increase in charcoal accumulation rate was observed in the late Holocene when the lake level was high, suggesting an interaction between climates and human presence. Low charcoal accumulation rates are typical of modern high rainfall environments, as observed in Lagoa da Pata where the environment is not susceptible to occurrences of wildfires even during relatively drier climatic phases. Low charcoal accumulation rates also exist in the relatively dry cerrado (savanna type) biome even during relatively dry phases in the Caracaranã region where the savanna-type vegetation biomass is lower and thus generates less charcoal particles than forest ecosystems. © 2014 Elsevier B.V. All rights reserved.

Ramarohetra J.,IPSL | Sultan B.,IPSL | Baron C.,CIRAD - Agricultural Research for Development | Gaiser T.,University of Bonn | Gosset M.,IRD GET
Agricultural and Forest Meteorology | Year: 2013

Rainfall monitoring via satellite sensors is particularly relevant for the agricultural sector of West Africa. Indeed, food shortages in this region are often caused by rainfall deficits and an early access to data available for the entire region can help to provide credible and timely information for better decision making. This study assesses the accuracy of state-of-the-art satellite rainfall retrievals for agriculture applications in two sites in Niger and Benin. Although these satellite data are widely used instead of rain gauge data for such applications, we found that, in a crop-modelling framework, their use can introduce large biases in crop yield simulations. Biases differ strongly among the four cultivars considered in both sites and are not simple extrapolation of each satellite product cumulative rainfall amount biases. In particular, we found that if an accurate estimation of the annual cumulative rainfall amount is important for yield simulations of pearl millet 'Souna 3' and 'Somno' cultivars in Niger, a realistic distribution of rainfall is also very important for predicting pearl millet 'Somno' and 'HK' yields in Niger as well as maize yields in Benin. Overall the satellite products tested, 3B42v6 appears to be the most suitable satellite product for our specific agricultural application since it minimizes both biases in rainfall distribution and in annual cumulative rainfall amount. For each crop and in both regions, biases in crop yield prediction are the highest when using non-calibrated satellite rainfall products (PERSIANN, 3B42RT, CMORPH and GSMAP). © 2013 Elsevier B.V.

Mansanarez V.,IRSTEA | Le Coz J.,IRSTEA | Renard B.,IRSTEA | Lang M.,IRSTEA | And 2 more authors.
Water Resources Research | Year: 2016

Stage-fall-discharge (SFD) rating curves are traditionally used to compute streamflow records at sites where the energy slope of the flow is variable due to variable backwater effects. We introduce a model with hydraulically interpretable parameters for estimating SFD rating curves and their uncertainties. Conventional power functions for channel and section controls are used. The transition to a backwater-affected channel control is computed based on a continuity condition, solved either analytically or numerically. The practical use of the method is demonstrated with two real twin-gauge stations, the Rhône River at Valence, France, and the Guthusbekken stream at station 0003⋅0033, Norway. Those stations are typical of a channel control and a section control, respectively, when backwater-unaffected conditions apply. The performance of the method is investigated through sensitivity analysis to prior information on controls and to observations (i.e., available gaugings) for the station of Valence. These analyses suggest that precisely identifying SFD rating curves requires adapted gauging strategy and/or informative priors. The Madeira River, one of the largest tributaries of the Amazon, provides a challenging case typical of large, flat, tropical river networks where bed roughness can also be variable in addition to slope. In this case, the difference in staff gauge reference levels must be estimated as another uncertain parameter of the SFD model. The proposed Bayesian method is a valuable alternative solution to the graphical and empirical techniques still proposed in hydrometry guidance and standards. © 2016. American Geophysical Union. All Rights Reserved.

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