Évaluation spatio-temporelle de la qualité de l’eau du lac de Guiers (Sénégal) par télédétection : dynamique de la chlorophylle-a et des substances jaunes (1995-2025)
Abstract
Cette étude propose une approche intégrée combinant la télédétection spatiale et les systèmes d’information géographique (SIG) pour le suivi et l’évaluation de la qualité des eaux du lac de Guiers. La méthodologie repose sur l’exploitation d’indices multispectraux, notamment le Modified Normalized Difference Water Index (MNDWI), ainsi que sur l’application de modèles empiriques adaptés aux milieux aquatiques sahéliens. Ces outils ont permis d’estimer les concentrations en chlorophylle-a (Chl-a) et en substances jaunes (CDOM). L’analyse spatio-temporelle menée sur la période 1995–2025 révèle une dégradation progressive de la qualité de l’eau, marquée par une transition vers des états trophiques plus élevés et une vulnérabilité accrue aux apports anthropiques. Les cartes produites mettent en évidence une extension des zones à forte productivité phyto-planctonique et à haute charge organique, particulièrement dans les secteurs sud et sud-est du lac. Ces résultats soulignent la pertinence de la télédétection pour le suivi à grande échelle des paramètres de qualité de l’eau et confirment son potentiel en tant qu’outil d’aide à la décision pour la gestion durable des ressources hydriques au Sénégal.
This study presents an integrated approach combining satellite remote sensing and Geographic Information Systems (GIS) to monitor and assess the water quality of Lake Guiers. The methodology relies on the use of multispectral indices, particularly the Modified Normalized Difference Water Index (MNDWI), and on empirical models specifically calibrated for inland water ecosystems. These tools enabled the estimation of chlorophyll-a (Chl-a) and colored dissolved organic matter (CDOM) concentrations. A spatio-temporal analysis covering the period 1995–2025 reveals a progressive degradation of water quality, characterized by a transition from oligotrophic to eutrophic conditions and an increasing vulnerability to anthropogenic inputs. The results highlight a significant expansion of areas with high phytoplankton productivity and elevated organic matter content, mainly in the southern and southeastern parts of the lake. These findings emphasize the potential of remote sensing, coupled with empirical modeling, as an effective and cost-efficient tool for large-scale water quality monitoring and for supporting sustainable water resource management in semi-arid environments.
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