Sédiments superficiels du système lacustre Déganobo (San-Pédro, Côte d’Ivoire), source ou puits de phosphore ?

Abstract

Surface sediments of the Déganobo lacustrine system (San-Pédro, Côte d'Ivoire), source or sink of phosphorus? This study focused on evaluating the seasonal self-purification potential of phosphorus at the water-sediment interface in the Deganobo lake system. To this end, samples of free water at the water-sediment interface and surface sediments of this aquatic ecosystem were collected over a one-year period (from August 2021 to July 2022). The concentrations of orthophosphates in these free waters and interstitial waters were determined in accordance with the NF ISO 6878 standard. The seasonal diffusive fluxes of this nutrient at the water-sediment interface of this lake site were evaluated using a chemical method based on Fick’s first law. The average seasonal diffusive fluxes ranged between 5±4 and 3±5 µmol/(day.m²), with an annual average of 4±2 µmol/(day.m²). They were relatively more significant during the small rainy and dry seasons than during the larger rainy and dry seasons. These results indicate that the surface sediments of this aquatic ecosystem constituted an additional source of phosphorus in the free waters, contributing to their hypereutrophication during the study period.