Longitudinal patterns of sedimentation in a deep, monomictic subtropical reservoir (Itaipu, Brazil- Paraguay)
Pagioro, Thomaz A.; Thomaz, Sidinei M.
Archiv für Hydrobiologie Volume 154 Number 3 (2002), p. 515 - 528
published: Jul 1, 2002
ArtNo. ESP141015403008, Price: 29.00 €
The sedimentation of seston has important ecological roles in aquatic ecosystems, especially in reservoirs where it leads to prominent longitudinal zonation in the main axis. We investigated the patterns of settling fluxes of total organic and inorganic seston, phosphorus and nitrogen in the main body of a large (1,350 km2), deep (170 m close to the dam), monomictic, subtropical reservoir (Itaipu Reservoir). The method of sediment traps, left for one week at different depths in the water column, was used. Higher amounts of settled material were registered in the deeper traps, indicating the presence of resuspended material, focused and longitudinal transported particles in the water column. The settling fluxes of total organic and inorganic seston as well as nitrogen and phosphorus were high when compared to other reservoirs in the Paraná River basin and an exponential decrease of their values along the head waterdam gradient was observed. The peak in settling fluxes was observed together with the peak in the Paraná River discharge, indicating the importance of this river as source of seston for the reservoir. This importance was also indicated by the similarities in organic matter of the settled material collected at all 5 sampling stations. Together with the predominance of inorganic material (81.2-89.6 % of the settled material), it shows that most of the seston in the main body of Itaipu has an allochthonous origin. This is in accordance with the oligo-mesotrophic features of this reservoir, as has been shown by phosphorus, chlorophyll-a and primary production measurements.