In north-east Abidjan, a lagoon has gone from being a natural environment to a drinking water reserve for the city for less than fifteen years. This transformation has prompted the production of a significant amount of expertise on its vulnerability. Based on an ethnography of the sciences and scientists brought together by this lagoon, this text aims to report on the production of these diagnoses and their articulation with public action "driven" by the drinking water infrastructure. In a post-conflict context, where the reconstruction of scientific and drinking water production capacities is taking place in a fragile ecological environment, it shows in particular how this articulation leads to the selection of a type of vulnerability based on the "state" of the environment justifying its exploitation, at the expense of another type emphasising the "processes" of its degradation. In doing so, it also offers an example of how the infrastructuring of environments operates at the junction of "metrological zones" and the control capacities of administrations in countries "under aid regimes".
The quality of aquatic ecosystems is strongly influenced by inputs of nutrients and trace elements. Identifying their sources and bioavailability is critical for understanding elemental cycling and assessing environmental risks in lakes exposed to increasing anthropogenic pressures, such as Lake Paranoá, a man-made reservoir in Brasília, Brazil. This study investigates the spatial distribution and geochemical partitioning of sedimentary nutrients and metals in Lake Paranoá to elucidate their origins and behavior. Sediment distribution patterns reflect the lake’s hydrodynamics and proximity to input sources. Human-induced erosion from expanding urban areas contributes to the influx of both lithogenic and anthropogenic materials. Our results indicate that Ca, Mg, P, and Zn are predominantly derived from anthropogenic sources, notably domestic sewage discharges and leaching of construction-related materials. Sediments near the wastewater treatment plant (WWTP) exhibit particularly elevated concentrations of P, Ca, Mg, and Zn, identifying the WWTP as a key source of these elements. Moreover, the enrichment of P, Mn, and Zn in labile geochemical phases suggests that these elements may be readily mobilized from sediments into the water column during early diagenetic processes. Given that urban lakes provide critical ecosystem services—such as water supply, recreation, and biodiversity habitats—for a growing proportion of the world’s urban population, and considering their increasing number globally, understanding sediment dynamics in these systems is essential for sustainable management. These findings offer valuable insights for assessing the potential impacts of the planned sediment dredging project in Lake Paranoá and for informing future management strategies.
Cet article présente une partie de nos solutions aux défis et questions réels rencontrés lors d’un projet pilote industriel. Pour surmonter la complexité de la configuration de la chaîne de traitement des effluents industriels en raison de la variété des contaminants et des diverses technologies de traitement disponibles, un arbre de décision a été développé sur la base de la meilleure technologie disponible adaptée aux types de polluants. Un inventaire paramétrique du cycle de vie a été développé pour la phase d’exploitation de quinze modules de technologies de traitement conventionnelles et avancées afin de faciliter une évaluation comparative de l’impact environnemental, y compris une analyse paramétrique de la sensibilité et de l’incertitude. L’évaluation comparative du cycle de vie modulaire a révélé les points chauds et les contributions de quinze modules de traitement aux impacts environnementaux du traitement d’un effluent de 1 m³, la nanofiltration, l’osmose inverse et l’échange d’ions ayant les impacts globaux les plus élevés. La configuration de traitement modulaire intégrée dans un arbre de décision promet plus de flexibilité dans la mise en place de scénarios de traitement adaptés et dans la réalisation d’évaluations modulaires du cycle de vie pour l’évaluation de la durabilité des scénarios de traitement dérivés des arbres de décision.
