ror.org/02cp04407
Abstracts
Résumé
Malgré la réduction des rejets de phosphore (P) dans l’environnement, les efflorescences phytoplanctoniques sont toujours observées dans un grand nombre de masses d’eau. C’est notamment le cas dans les retenues de barrage où la perturbation de la continuité sédimentaire peut conduire à une accumulation importante de phosphore au sein du compartiment sédimentaire. Ainsi, pour lutter contre l’eutrophisation, une meilleure connaissance de la distribution, de la réactivité et de la mobilité du P sédimentaire s’avère indispensable. Dans ce contexte, les sédiments de surface de la retenue de Champsanglard (Creuse, France) ont été prélevés en différents points selon un gradient amont/aval. Une caractérisation physico-chimique (granulométrie; teneurs en P, Fe, Al, matière organique; fractionnement chimique du P suivant le protocole de RYDIN et WELCH [1998]) a été effectuée afin d’évaluer le potentiel de relargage de P de ces sédiments. Les résultats montrent une évolution de la concentration et de la distribution du P dans les sédiments de surface dans la retenue de l’amont vers l’aval (de 1,5 à 2,3 mg P∙gsec‑1), qui semble corrélée avec l’évolution de la granulométrie. L’analyse du fractionnement chimique a montré que le P était majoritairement lié aux oxyhydroxydes de Fe et Mn amorphes (66 %), ces concentrations augmentant également à l’approche du barrage. Ces résultats indiquent que les conditions d’oxydoréduction sont l’un des paramètres clés du contrôle de la remobilisation du P sédimentaire vers la colonne d’eau. À l’opposé, le P associé aux fractions de la matière organique et de l’aluminium ne semble quant à lui ne pas évoluer spatialement de façon significative.
Mots-clés :
- Eutrophisation,
- retenue de barrage,
- sédiment,
- phosphore,
- fractionnement chimique
Abstract
Despite the reduction of phosphorus (P) discharged into the environment, phytoplankton blooms are still observed in many water bodies, especially in dam reservoirs where the disturbance of sediment continuity could lead to a significant accumulation of sedimentary phosphorus. Thus, a better understanding of the distribution, reactivity and mobility of sedimentary P is essential in the control of eutrophication. In this context, the surface sediments of Champsanglard reservoir (Creuse, France) were sampled at different points along an upstream/downstream gradient. A physicochemical characterization (particle size; P, Fe, Al and organic matter content; P fractionation following the modified protocol of RYDIN and WELCH [1998]) was conducted to assess the potential leaching of P from the sediment. Results show an evolution of the concentration and distribution of P within the dam reservoir from upstream to downstream (from 1.5 to 2.3 mg P∙gdw‑1), potentially correlated with the particle size. Chemical fractionation results show that P was predominantly associated with amorphous Fe and Mn oxyhydroxides (66%) and concentrations increased with distance down-reservoir. This result suggests that the redox conditions are one of the key parameters controlling the remobilization of sedimentary P into the water column. In contrast, P bound to the organic matter and Al fractions did not show any significant variations in spatial distribution.
Keywords:
- Eutrophication,
- dam reservoir,
- sediment,
- phosphorus,
- chemical fractionation
Appendices
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