Spatial distribution and mobility of sedimentary phosphorus in a hydroelectric reservoir
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.