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Deanne D. Grant Jose D. Fuentes Stephen Chan William R. Stockwell Daniel Wang Seydi A. Ndiaye 《Journal of Atmospheric Chemistry》2008,60(1):19-35
The objectives of this study were to identify species and levels of volatile organic compounds (VOCs), and determine their
oxidation capacity in the rural atmosphere of western Senegal. A field study was conducted to obtain air samples during September
14 and September 15, 2006 for analyses of VOCs. Methanol, acetone, and acetaldehyde were the most abundant detected chemical
species and their maximum mixing ratios reached 6 parts per billion on a volume basis (ppbv). Local emission sources such
as firewood and charcoal burning strongly influenced VOC concentrations. The VOC concentrations exhibited little temporal
variations due to the low reactivity with hydroxyl radicals, with reactivity values ranging from 0.001 to 2.6 s−1. The conditions in this rural site were rather clean. Low ambient NO
x
levels limited ozone production. Nitrogen oxide (NO
x
) levels reached values less than 2 ppbv and maximum VOC/NO
x
ratios reached 60 ppbvC/ppbv, with an overall average of 2.4 ± 4.5 ppbvC/ppbv. This indicates that the rural western Senegal
region is NO
x
limited in terms of oxidant formation potential. Therefore, during the study period photochemical ozone production became
limited due to low ambient NO
x
levels. The estimated ozone formation reactivity for VOCs was low and ranged between −5.5 mol of ozone/mol of benzaldehyde
to 0.6 mol/mol of anthropogenic dienes. 相似文献
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Alodah Abdullah Seidou Ousmane 《Stochastic Environmental Research and Risk Assessment (SERRA)》2020,34(7):993-1021
Stochastic Environmental Research and Risk Assessment - While Stochastic Weather Generators (SWGs) are used intensively in climate and hydrological applications to simulate hydroclimatic time... 相似文献
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Aurèle Vuillemin Mapathe Ndiaye Rossana Martini Eric Davaud 《Swiss Journal of Geoscience》2011,104(1):55-66
Cement stratigraphy of carbonates aims to establish the chronology of processes involved in the rock diagenesis. Regional
cement stratigraphy allows correlations and understanding of the petrological heterogeneities in reservoirs and aquifers,
but is a long and rigorous approach. This article exposes a methodology of image analysis that facilitates the spatial correlation
of diagenetic events in carbonate rocks. Based on the statistical comparison of signals extracted from the red spectrum emission
of cathodoluminescence digital images, it gives via crosscorrelation a measure of similarity (values scaled from minimum −1
to maximum 1) between two cathodoluminescence facies. Cementation events and diagenetic chronologies can thus be quickly correlated
without the support of a full chronology, the model normally established on cement morphologies, petrological analyses and
cathodoluminescence zonation sequences. A case study from two Upper Kimmeridgian Mount Salève outcrops (France) illustrates
this methodology. Their diagenetic sequences recorded in cathodoluminescent cements are presented and being compared. The
final statistical similarity between the two outcrops reaches an index of R = 0.78. This result is sustained by petrological and geochemical analyses such as alizarine–ferricyanure stained thin sections,
X microfluorescence mapping of elements, and microthermometry of fluid inclusions. 相似文献
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RÉSUMÉL’objectif de cet article est d’analyser à l’échelle du bassin du fleuve Sénégal l’évolution de quatre classes de précipitations journalières, le nombre de jours de pluie et la durée de la saison des pluies. La méthode consiste à appliquer des tests statistiques d’homogénéité aux séries de pluies annuelles sur la période 1950–1998 pour détecter des ruptures et caractériser l’évolution de ces six variables de part et d’autre des dates de rupture. Les séries de pluie annuelle présentent une rupture entre 1966 et 1970. Les déficits de jours pluvieux de la période après rupture par rapport à celle d’avant varient entre 6,2% à Kédougou et 38,6% à Saint Louis. La classe de pluie de plus de 50 mm (P4) présente les déficits les plus importants qui varient entre 14,8% à la station de Mamou et 66,6% à la station de Nioro du Sahel. 相似文献
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Ketvara Sittichok Ousmane Seidou Abdouramane Gado Djibo Neeranat Kaewprasert Rakangthong 《水文科学杂志》2018,63(4):630-645
Two methods for generating streamflow forecasts in a Sahelian watershed, the Sirba basin, were compared. The direct method used a linear relationship to relate sea-surface temperature to annual streamflow, and then disaggregated on a monthly time scale. The indirect method used a linear relationship to generate annual precipitation forecasts, a temporal disaggregation to generate daily precipitation and the SWAT (Soil and Water Assessment Tool) model to generate monthly streamflow. The accuracy of the forecasts was assessed using the coefficient of determination, the Nash-Sutcliffe coefficient and the Hit score, and their economic value was evaluated using the cost/loss ratio method. The results revealed that the indirect method was slightly more effective than the direct method. However, the direct method achieved higher economic value in the majority of cost/loss situations, allowed for predictions with longer lead times and required less information. 相似文献
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K. Diouf F. Guilhaumon C. Aliaume P. Ndiaye T. Do Chi J. Panfili 《Estuarine, Coastal and Shelf Science》2009
The knowledge of juvenile fish growth in extreme environmental conditions is a key to the understanding of adaptive responses and to the relevant management of natural populations. The juvenile growth of an extreme euryhaline tilapia species, Sarotherodon melanotheron (Cichlidae), was examined across a salinity gradient (20–118) in several West African estuarine ecosystems. Juveniles were collected during the reproduction period of two consecutive years (2003 and 2004) in six locations in the Saloum (Senegal) and Gambia estuaries. Age and growth were estimated using daily otolith microincrements. For each individual, otolith growth rates showed three different stages (slow, fast, decreasing): around 4 ± 0.5 μm d−1 during the first five days, 9 ± 0.5 μm d−1 during the next 15 days and 4 ± 0.50 μm d−1 at 60 days. Growth modelling and model comparisons were objectively made within an information theory framework using the multi-model inference from five growth models (linear, power, Gompertz, von Bertalanffy, and logistic). The combination of both the model adjustment inspection and the information theory model selection procedure allowed identification of the final set of models, including the less parameterised ones. The estimated growth rates were variable across spatial scales but not across temporal scales (except for one location), following exactly the salinity gradient with growth decrease towards the hypersaline conditions. The salinity gradient was closely related to all measured variables (condition factor, mean age, multi-model absolute growth rate) demonstrating the strong effect of hypersaline environmental conditions—induced by climate changes—on fish populations at an early stage. 相似文献
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Continuous prediction of clay‐bed stream erosion in response to climate model output for a small urban watershed 
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下载免费PDF全文 Colin P. Brennan Parna Parsapour‐Moghaddam Colin D. Rennie Ousmane Seidou 《水文研究》2018,32(8):1104-1119
The response of the semi‐alluvial clay‐bed Watts Creek is assessed subject to climate change. Climate impacts are expected to have regional variability, and few studies have assessed the impacts of future climate in a small urban watershed. The 21‐km2 watershed located in Ottawa, Ontario, Canada, is highly urbanized (68%) and agricultural (20%) with limited forest cover (12%). Continuous simulations were performed using the SWMHYMO lumped hydrologic modelling platform for the open water year, excluding spring freshet (April 1 to October 31). A shear stress exceedance and stream power erosion routine was added to the platform to calculate erosion potential. To account for uncertainty in the collected data, 9 different field datasets were used to calibrate the model, each leading to a distinct set of calibrated parameter values. The difference between the datasets lies in the choice of the rating curves and calibration period. The 2041–2080 precipitation outputs of the 4th version of the Canadian Regional Climate Model (CanRCM4) ran under representative concentration pathways (RCPs) 4.5 and 8.5 at the MacDonald Cartier International Airport were downscaled using quantile matching and then used as input to the continuous hydrologic model. For each set of calibrated parameters, a cumulative effective work index based on the reach‐averaged shear stress was calculated for Watts Creek using both the historic (1967–2007) and projected future (2041–2080) flows, using a bed material critical shear stress for entrainment of 3.7 Pa. These results suggest an increase of 75% (respectively 139%) under RCP4.5 (respectively RCP8.5) in cumulative effective work index compared with historic conditions for the average measured bed strength. The work index increase is driven by an increased occurrence of above‐threshold events and, more importantly, by the increased frequency of large events. The predicted flow regime under climate change would significantly alter the erosion potential and stability of Watts Creek. 相似文献
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Allometric relationships and peak-season community biomass stocks of native shrubs in Senegal's Peanut Basin 总被引：1，自引：0，他引：1
A. Lufafa I. Diédhiou N.A.S. Ndiaye M. Séné F. Kizito R.P. Dick J.S. Noller 《Journal of Arid Environments》2009,73(3):260-266
Allometric equations and community biomass stocks are presented for Guiera senegalensis J.F. Gmel (Gs) and Piliostigma reticulatum (DC.) Hochst (Pr) – two native shrub species in the Sahel. These shrubs are of interest because they dominate semi-arid sub-Sahalien Africa but have been largely overlooked as a key biomass component and regulator of ecosystem composition and function in this landscape. In Year 1, best predictors of aboveground biomass were height and number of stems (Gs) and crown diameter (Pr); and for belowground biomass were height and basal diameter (Gs) and basal diameter (Pr). In Year 2, height and crown diameter were the best predictors of aboveground biomass (R2 = 0.90 for Gs and 0.87 for Pr), whereas basal diameter and number of stems (Gs) and basal diameter (Pr) were best predictors of belowground biomass. Peak-season biomass estimates ranged from 0.44 to 4.58 ton ha?1 (mean = 2.38 ton ha?1) in the Gs sites and from 0.33 to 7.38 ton ha?1 (mean = 3.71 ton ha?1) in the Pr communities. Both species exhibited unusually large root:shoot ratios (4.5:1 for Gs and 10.2:1 for Pr). Although models differ between years, allometric relationships provide reasonable biomass estimates for Gs and Pr. 相似文献