Temporal and spatial trends in the sedimentation process in a canyon-type reservoir (El Gergal, Seville, Spain)

The seasonal and spatial (vertical and horizontal) variations in the magnitude of sestonic fluxes and the chemical composition (C, N, P and organic matter concentrations) of entrapped material have been studied over a year on a monthly basis in El Gergal, a mesotrophic canyon-type reservoir in the south of Spain. The chemical composition of settled particles and of surficial sediment was compared in trying to elucidate the role of some relevant processes like mineralization and resuspension of unconsolidated sediment. A very clear increasing tendency in the magnitude of settling fluxes from the down-reservoir to the up-reservoir zone as a consequence of the prevailing wind direction and of water level fluctuations has been found. Vertical gradients in sestonic rates can mainly be explained by the different contribution of resuspension processes that can be ultimately related to the thermal and hydrologic regime. A comparison of the chemical composition of the total settled matter and of the surficial sediment revealed a predominantly inorganic matrix, which reflects the dominating role of inorganic allochthonous material input.