Hydrological budget of Lake Chad : assessment of lake-groundwater interaction by coupling Bayesian approach and chemical budget

International audienceEstimation of lake-groundwater interactions is a crucial step to constrain water balance of lacustrine and aquifersystems. Located in the Sahel, the Lake Chad is at the center of an endorheic basin of 2,5.106 km2. One of themost remarkable features of this terminal lake is that, despite the semi-arid context and high evaporation rates of thearea, its waters are fresh. It is proposed in the literature that the solutes are evacuated in the underlying quaternaryaquifer bearing witness to the importance of surface water and groundwater exchanges for the chemical regulationof the lake. The water balance of this system is still not fully understood. The respective roles of evaporation versusinfiltration into the quaternary aquifer are particularly under constrained.To assess lake-groundwater flows, we used the previous conceptual hydrological model of the lake Chad proposedby Bader et al. (Hydrological Sciences Journal, 2011). This model involves six parameters including infiltrationrate. A probabilistic inversion of parameters, based on an exploration of the parameters space through a Metropolisalgorithm (a Monte Carlo Markov Chain method), allows the construction of an a posteriori Probability DensityFunction of each parameter yielding to the best fits between observed lake levels and simulated. Then, a chemicalbudget of a conservative element, such as chloride, is introduced in the water balance model using the optimalparameters resulting from the Bayesian inverse approach.The model simulates lake level and chloride concentration variations of lake Chad from 1956 up to 2008. Simulated lake levels are in overall agreement with the observations, with a Nash-Sutcliffe efficiency coefficient above0.94 for all sets of parameters retained. The infiltration value, obtained by such probabilistic inversion approach,accounts for 120±20 mm/yr, representing 5% of the total outputs of the lake. However, simulated chloride concentrations are overestimated in comparison to the scarce measurements available over that period. As an example,the mean chloride concentration measured in the southern pool on a basis of our synthesis of existing chemicaldata since the 1970’s is approximately three time lower than the computed mean concentration. This may be dueto either the non-representativeness of our chemical dataset or overestimation of the evaporation rate that is fixedto 2000 mm/yr in our model.This study tackles the quantification of the lake water flows to the quaternary aquifer system and the associateduncertainties from a probabilistic point of view. This is an essential step to improve predictions of groundwaterresources in the Lake Chad Basin under climate change

Women, ethnicity and nationalisms in Latin America

Gutierrez Chong, Natividad (ed. lit.) "Women, ethnicity and nationalisms in Latin America". Aldershot : Ashgate, 2007. 235 p. ISBN 978-075-464-925-0Nationalism is a multifaceted phenomenon that has recently become a focus of redefinition through new multidisciplinary and multi-method approaches. The complex links among gender, ethnicity and nationalism, neglected for a long time in academic research, are increasingly receiving coverage in the scholarly literature. The book "Women, Ethnicity and Nationalisms in Latin America”, edited by Natividad Gutiérrez Chong, systematically explores these links in the context of Latin America, with case studies covering Argentina, Ecuador, Bolivia and Mexico. Contributions are by leading Latin American scholars from diverse academic fields who share the aim of overcoming the limitations of the Eurocentric and androcentric framework that characterizes the main approaches to nationalism

Reef response to sea-level and environmental changes during the last deglaciation: Integrated Ocean Drilling Program Expedition 310, Tahiti Sea Level

The last deglaciation is characterized by a rapid sea-level rise and coeval abrupt environmental changes. The Barbados coral reef record suggests that this period has been punctuated by two brief intervals of accelerated melting (meltwater pulses, MWP), occurring at 14.08-13.61 ka and 11.4-11.1 ka (calendar years before present), that are superimposed on a smooth and continuous rise of sea level. Although their timing, magnitude, and even existence have been debated, those catastrophic sea-level rises are thought to have induced distinct reef drowning events. The reef response to sea-level and environmental changes during the last deglacial sea-level rise at Tahiti is reconstructed based on a chronological, sedimentological, and paleobiological study of cores drilled through the relict reef features on the modern forereef slopes during the Integrated Ocean Drilling Program Expedition 310, complemented by results on previous cores drilled through the Papeete reef. Reefs accreted continuously between 16 and 10 ka, mostly through aggradational processes, at growth rates averaging 10 mm yr-1. No cessation of reef growth, even temporary, has been evidenced during this period at Tahiti. Changes in the composition of coralgal assemblages coincide with abrupt variations in reef growth rates and characterize the response of the upward-growing reef pile to nonmonotonous sea-level rise and coeval environmental changes. The sea-level jump during MWP 1A, 16 ± 2 m of magnitude in ~350 yr, induced the retrogradation of shallow-water coral assemblages, gradual deepening, and incipient reef drowning. The Tahiti reef record does not support the occurrence of an abrupt reef drowning event coinciding with a sea-level pulse of ~15 m, and implies an apparent rise of 40 mm yr-1 during the time interval corresponding to MWP 1B at Barbados. © 2012 Geological Society of America

11th Applied isotope geochemistery conference AIG-11

36Cl measurements in groundwaters of the deep confined aquifer of the Lake Chad Basin (LCB) were performed in order to constrain groundwater geochemical ages and residence times. Twenty-seven wells were sampled in Nigeria, Niger and Chad in the southern parts of the large (700 000 km2) multilayered aquifer of the LCB. 36Cl/Cl values range between 11±1.10-15 to 148±8.10-15 at/at. The highest ratios are observed near the recharge zone of the Nigerian part of the Continental Terminal aquifer, while the lowest ones are found in wells located near the southern fringe of the present-day lake Chad. Chloride concentrations are low (below 100 mg/l) and not correlated to the 36Cl/Cl values, indicating negligible dissolution of evaporites in most samples. Reliable 36Cl ages can be calculated along the different flow paths investigated, suggesting residence times of the deep groundwaters larger than 300 000 years. These results are consistent with new AMS-14C data below the detection limit but are in contradiction with previous 14C data obtained in the area

Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV

A search for pair-production of supersymmetric particles under the assumption that R-parity is violated via a dominant LQDbar coupling has been performed using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV. The observed candidate events in the data are in agreement with the Standard Model expectation. This result is translated into lower limits on the masses of charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81 GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the 95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure

Search for the glueball candidates f0(1500) and fJ(1710) in gamma gamma collisions

Data taken with the ALEPH detector at LEP1 have been used to search for gamma gamma production of the glueball candidates f0(1500) and fJ(1710) via their decay to pi+pi-. No signal is observed and upper limits to the product of gamma gamma width and pi+pi- branching ratio of the f0(1500) and the fJ(1710) have been measured to be Gamma_(gamma gamma -> f0(1500)). BR(f0(1500)->pi+pi-) < 0.31 keV and Gamma_(gamma gamma -> fJ(1710)). BR(fJ(1710)->pi+pi-) < 0.55 keV at 95% confidence level.Comment: 10 pages, 3 figure

A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007

We present the results of the first search for gravitational wave bursts associated with high energy neutrinos. Together, these messengers could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy. Our search uses neutrinos detected by the underwater neutrino telescope ANTARES in its 5 line configuration during the period January - September 2007, which coincided with the fifth and first science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed for candidate gravitational-wave signals coincident in time and direction with the neutrino events. No significant coincident events were observed. We place limits on the density of joint high energy neutrino - gravitational wave emission events in the local universe, and compare them with densities of merger and core-collapse events.Comment: 19 pages, 8 figures, science summary page at http://www.ligo.org/science/Publication-S5LV_ANTARES/index.php. Public access area to figures, tables at https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p120000