Doctor of Philosophy / Department of Geography / John A. Harrington Jr / The Senegal River valley and delta (SRVD) are affected by long term climate variability. Indicators of these climatic shifts include a rainfall deficit, warmer temperatures, sea level rise, floods, and drought. These shifts have led to environmental degradation, water deficits, and profound effects on human life and activities in the area. Geographic Information Science (GIScience), including satellite-based remote sensing methods offer several advantages over conventional ground-based methods used to map and monitor salt-affected soil (SAS) features. This study was designed to assess the accuracy of information on soil salinization extracted from Landsat satellite imagery. Would available imagery and GIScience data analysis enable an ability to discriminate natural soil salinization from soil sodication and provide an ability to characterize the SAS trend and pattern over 30 years? A set of Landsat MSS (June 1973 and September 1979), Landsat TM (November 1987, April 1994 and November 1999) and ETM+ (May 2001 and March 2003) images have been used to map and monitor salt impacted soil distribution. Supervised classification, unsupervised classification and post-classification change detection methods were used. Supervised classifications of May 2001 and March 2003 images were made in conjunction field data characterizing soil surface chemical characteristics that included exchange sodium percentage (ESP), cation exchange capacity (CEC) and the electrical conductivity (EC). With this supervised information extraction method, the distribution of three different types of SAS (saline, saline-sodic, and sodic) was mapped with an accuracy of 91.07% for 2001 image and 73.21% for 2003 image. Change detection results confirmed a decreasing trend in non-saline and saline soil and an increase in saline-sodic and sodic soil. All seven Landsat images were subjected to the unsupervised classification method which resulted in maps that separate SAS according to their degree of salinity. The spatial distribution of sodic and saline-sodic soils has a strong relationship with the area of irrigated rice crop management. This study documented that human-induced salinization is progressively replacing natural salinization in the SRVD. These pedologic parameters obtained using GIScience remote sensing techniques can be used as a scientific tool for sustainable management and to assist with the implementation of environmental policy.

Dans un contexte d’aménagement de la vallée du fleuve Sénégal et de développement de l’agriculture irriguée, les populations d’éleveurs mettent en avant un ensemble de stratégies afin de renforcer leurs exploitations familiales. En effet, depuis les crises de sécheresse des années 1970-1980, la situation de l’élevage transhumant dans la vallée ne cesse de se détériorer et sa pérennisation remise en cause, en raison de la réduction des parcours pastoraux. L’objectif de ce travail est de faire comprendre les stratégies de survie mises en application par les éleveurs pour maintenir leurs exploitations viables. Un travail d’enquête chez 41 chefs d’exploitations a permis d’analyser les logiques de diversification agricole et de capitalisation foncière chez les Peul Walwalbé. Pour face faire à l’expansion des Périmètres Irrigués Villageois, les éleveurs ont choisi de renforcer leur pratique de l’agriculture irriguée afin de varier leurs sources de revenus et d’avoir un meilleur accès aux parcours post-culturaux. Dans les communautés rurales de Gamadji et de Guédé village situées dans la moyenne vallée, les éleveurs sont très présents dans les systèmes de production irriguée. Plusieurs modes de tenures foncières leur permettent, en plus des cultures céréalières de décrues ou pluviales, de développer les spéculations maraîchères (tomate et oignon) plus rentables. L’agriculture irriguée offre aussi aux agro-éleveurs un accès privilégié aux parcours post-culturaux. Leur présence dans les terroirs du Waalo est aussi un moyen de garantir leur droit foncier traditionnel sur ces terres. Ainsi la pratique de l’agriculture irriguée répond à des logiques financières et foncières. Alors que la pratique d’élevage ne permet pas aux éleveurs Peul d’avoir accès à la terre, l’agriculture irriguée apparaît comme une stratégie détournée de capitalisation foncière. La pratique conjointe de l’agriculture irriguée et de l’élevage transhumant a permis l’émergence d’un territoire agropastoral autour du département de Podor composé: de parcours de décrue, de parcours post-culturaux, de points d’abreuvement sur fleuve, de piste de transhumance…. Pour autant, les mouvements de transhumance restent la pratique centrale chez les éleveurs Peul de la moyenne vallée et les déplacements de longues durées encore de mises. / In the development of the Senegal River Valley and more precisely irrigated agriculture, pastoralist populations put forward a set of strategies to strengthen family farms. Since the 1970-1980 drought crises the situation of nomadic livestock as well as sustainability challenges in the valley continues to deteriorate, due to the reduction of rangeland. This work aims to understand the survival strategies adopted by farmers to keep their farms viable. Survey work in 41 farm managers was used to analyze the logic of agricultural diversification and land capitalization among Fulani Walwalbé. To face to the expansion of Irrigated Village Perimeters, ranchers have chosen to strengthen their practice of irrigated agriculture to vary their sources of income and have better access to postharvest lands. Farmers in rural communities of Gamadji and Guede towns located in the middle valley are very present in irrigated production systems. In addition to the rain fed cereal production, the several modes of land tenure permit them to speculate on profitable horticulture, such as vegetable crops (tomato and onion). Irrigated agriculture also provides breeders the privilege to access to post- harvest lands. Their presence in the Waalo land is also a means of ensuring their traditional land rights on these lands. Thus the practice of irrigated agriculture meets financial and property logic. While farming practice does not allow Fulani herders have access to land, irrigated agriculture appears as a strategy to move away from land capitalization. The joint practice of irrigated agriculture and livestock transhumance has encouraged the emergence of an agro-pastoral area around Podor made of: golf recession, post-crop lands, water points, transhumance pathways.... However, transhumance movements remain the central practice among Fulani herders of the middle valley and long displacement periods still possible.