Land Use and Soil Texture Effects on Organic Carbon Change in Dryland Soils, Senegal

Soil organic carbon (SOC) losses due to poor soil management in dryland are now well documented. However, the influence of soil properties on organic carbon change is not well known. The groundnut plant (Arachis hypogaea L.), and the dominant crop system in the Senegal’s Soudanian zone, have been compared with semi-natural savanna. Leaves, stems and roots biomass were measured, and soil characteristics were analysed. The total leaves and stems biomass was 1.7 and 2.7 Mg ha-1 dry matter in groundnut fields and savanna respectively. Total SOC stocks were low (8 to 20 Mg C·ha-1 within upper 0.2 m depth, 20 to 64 Mg C·ha-1 within upper 1 m depth) and were significantly lower (P δ13C values show that SOC quality is transformed from the savanna plants (C4/C3 mixed-pools) to C3-pools in groundnut cultivated zone, with the organic matter signature more preserved in the clayey soils. This study confirms that converting woodland to groundnut fields provokes texture transformation and SOC loss. The results call for the extreme necessity to regenerate the wooded zone or encourage practices that favour SOC restitution.

Multidisciplinary Approach for a Solution to Floods in SampathéDistrict (Thiès-Est, Senegal)

In recent years (2003), Senegal has been confronted with many urban flooding problems that have become recurrent due to the configuration of its settlement. This is due to galloping population growth, climate change and a lack of planning and rainwater drainage networks. To fix these phenomena, Senegalese government has initiated rainwater drainage programs. In the city of Thiès, particularly in Sampathé district, flooding problem is a reality that is observed during every winter period. It is within this framework that we have proposed a project for the design and dimensioning of a rainwater evacuation network in Sampathé. The network will be integrated into a Geographic Information System for efficient management of project. This study involved identifying flood zones, determining geotechnical characteristics of the soil, and exploiting rainfall data in order to propose a storm water drainage network that will be integrated into a database management system. Thus, we carried out topographical and geotechnical studies, then designed and dimensioned the drainage network, and finally set up a geographic information system. At the end of this project, we designed a sewerage network consisting of two primary pipelines, four secondary pipelines, one tertiary pipeline, ninety-two manholes and a retention basin. To manage the network, we set up a geographic information system to geolocate various elements for rapid intervention in the field in event of a problem, make requests, generate thematic maps, and perform spatial analyses for good decision-making.

Complementarity of Sentinel-1 and Sentinel-2 Data for Mapping Agricultural Areas in Senegal

The small size of agricultural plots is the main difficulty for crops mapping with remote sensing data in the Sahelian region of Africa. The study aims to combine Sentinel-1 (radar) and Sentinel-2 (Optic) data to discriminate millet, maize and peanut crops. Training plots were used in order to analyse temporal variation of the three crops’ signals. The NDVI (Normalized Difference Vegetation Index) was able to differentiate crops only at the end of the rainy season (October). The optical data as well as the radar ones could not easily discriminate the three crops during the growing season, because in that period vegetation cover is low, and soil contribution to the signals (due to roughness and moisture) was more important than that of real vegetation. However, the ratio of VH/VV (VH: incident signal in vertical polarization and reflected signal in horizontal polarization;VV: incident signal in vertical polarization and reflected signal in horizontal polarization) gave a difference between millet and the two other crops at the beginning cultural season (July 11). Difference appears from the second third of September when the harvest of cereals crops (millet and maize) began. From middle of October, the peanut signal dropped sharply thus facilitating the differentiation of peanut from the two other crops. This analysis led to the identification of data that have could be used to discriminate these crops (useful data). Classification of the combined useful data gave an overall high accuracy of 82%, with 96%, 61% and 65% for peanut, maize and millet, respectively. The non-agricultural areas (water, natural vegetation, habit, bare soil) were well classified with an accuracy greater than 90%.

Coastline Dynamics Analysis in Dakar Region, Senegal from 1990 to 2040

In the context of climate change, the study of shoreline dynamics is a critical issue concerning economic losses in coastal countries. Therefore, since it is an important parameter to study the impacts of climate change in coastal areas, scientists are more interested in littoral studies seeking deep existential knowledge. This study aims to depict separately the coastal dynamics from 1990 to 2020 in Dakar region. The difference in terms of geologic, geomorphologic and hydrodynamic conditions within the three different coasts of Dakar and the prediction until 2040 have been taken into account in comparison to the previous studies. To achieve this purpose, the Geographic Information System (GIS) approach which is among the most current methods to determine the coastline dynamics is used. Historical Landsat images from the USGS, QGIS 3.12.0, Arc GIS 10.4 and DSAS software have been used for the Landsat images pre-processing and coastline dynamic computation. After obtaining the coastline velocity rate, some predictions of future coastline position have been estimated using the formula of velocity. The results showed that the Dakar region is characterized by an average rate of retreat about −0.44 m/year on the northern coast. The western and southern coasts record respectively a rate of about 0.21 and −0.11 m/year. In 2030, the average rates of retreat of −4.4, 2.1 and −1.1 m/year were estimated respectively in the northern, western and southern coasts.

Prevalence of diarrhoea and risk factors among children under five years old in Mbour,Senegal:a cross-sectional study

Background:Diarrhoeal diseases remain an important cause of mortality and morbidity among children,particularly in low-and middle-income countries.In Senegal,diarrhoea is responsible for 15%of all deaths in children under the age of five and is the third leading cause of childhood deaths.For targeted planning and implementation of prevention strategies,a context-specific understanding of the determinants of diarrhoeal diseases is needed.The aim of this study was to identify risk factors of diarrhoeal diseases in children under the age of five in Mbour,Senegal.Methods:Between February and March 2014,a cross-sectional survey was conducted in four zones of Mbour to estimate the burden of diarrhoeal diseases(i.e.diarrhoea episodes in the 2 weeks preceding the survey)and associated risk factors.The zones covered urban central,peri-central,north peripheral and south peripheral areas.Overall,596 households were surveyed by a questionnaire,yielding information on sociodemographic,environmental and hygiene behavioural factors.Univariable and multivariable logistic regression analyses were used to identify risk factors associated with the occurrence of diarrhoea.Results:The reported prevalence of diarrhoea among children under the age of five during the 2 weeks preceding the survey was 26%.Without adjustment,the highest diarrhoea prevalence rates were observed in the peri-central(44.8%)and urban central zones(36.3%).Multivariable regression revealed significant associations between diarrhoeal diseases and unemployment of mothers(adjusted odds ratio[aOR]=1.62,95%confidence interval[CI]:1.18-2.23),use of open bags for storing household waste(aOR=1.75,95%CI:1.00-3.02),evacuation of household waste in public streets(aOR=2.07,95%CI:1.20-3.55),no treatment of stored drinking water(aOR=1.69,95%CI:1.11-2.56)and use of shared toilets(aOR=1.69,95%CI:1.11-2.56).Conclusion:We found a high prevalence of diarrhoea in children under the age of five in Mbour,with the highest prevalence occurring in the central and peri-central areas.These findings underscore the need for public health interventions to alleviate the burden of diarrhoea among vulnerable groups.Promotion of solid waste disposal and reduction of wastewater exposure should be implemented without delay.

Risk factors for schistosomiasis in an urban area in northern Cote d’Ivoire

Background:Schistosomiasis is a water-based disease transmitted by trematodes belonging to the genus Schistosoma.The aim of this study was to assess the relationship between the prevalence of schistosomiasis and access to water,sanitation and hygiene(WASH)and environmental and socioeconomic factors in the city of Korhogo,northern Côte d'Ivoire.Methods:A cross-sectional study including 728 randomly selected households was conducted in Korhogo in March 2015.The heads of the households were interviewed about access to WASH and environmental and socioeconomic factors.All children abed between 5 and 15 years living in the households were selected to provide stool and urine samples for parasitological diagnosis of Schistosoma mansoni and Schistosoma haematobium infection.The relationship between infection with S.mansoni and potential risk factors was analysed by a mixed logistic regression model with‘household’as a random factor.Likelihood ratio tests were used to identify factors that were significantly associated with a Schistosoma spp.infection.Results:The overall prevalence of schistosomiasis among school-aged children in Korhogo was 1.9%(45/2341)composed of 0.3%(3/1248)S.haematobium and 3.5%(42/1202)S.mansoni.Due to the low prevalence of S.haematobium infection,risk factor analysis was limited to S.mansoni.Boys were 7.8 times more likely to be infected with S.mansoni than girls.Children between 10 and 15 years of age were 3.8 times more likely to be infected than their younger counterparts aged 5-10 years.Moreover,living in a house further away from a water access point(odds ratio[OR]=0.29,95%confidence interval[CI]:0.13-0.70)and abstaining from swimming in open freshwater bodies(OR=0.16,95%CI:0.04-0.56)were significantly associated with decreased odds of S.mansoni infection.The socioeconomic status did not appear to influence the prevalence of S.mansoni.Conclusions:A strategy to reduce the incidence of schistosomiasis should focus on health education to change the behaviour of populations at risk and encourage communities to improve sanitation and infrastructure in order to reduce contact with surface water.