Influence of hydrodynamic bottom conditions on the benthic fauna in the Paraná River basin. Preliminary results

BLETTLER, MARTIN; AMSLER, MARIO; EZCURRA DE DRAGO, INÉS; MARCHESE, MERCEDES

Santa Fe, Argentina

Workshop; Workshop on Morphodynamic Processes in Large Lowland Rivers; 2007

Facultad de Ingeniería y Ciencias Hídricas (UNL) - National Center of Earth-Surface Dynamics (Universidad de Minnesota/USA) - Universidad de Illinois (USA)

ABSTRACT. This study deals with the incidence of the near-bottom hydraulic conditions and alluvial bed forms on the bethic fauna distribution in sandy bed rivers of diverse hierarchy of the Paraná River basin. A significant role played by these physical characteristics on the benthic community studied herein, was found. The highest correlations in N. bonettoi (the studied benthic species) population data, were obtained with hydraulic variables such as the friction Reynolds number and the bed shear stress, the substratum type (sand, silt, clay), and the sediment organic matter quantity. N. bonettoi would be related with the hydraulic variables following a "bell shaped" tendency, i.e. there would be an optimum range of these variables where the densities are the highest. For lower or larger values out of that range the densities tend to decrease. Another investigated topic, do not reported in literature, was the relationship between hydraulic variables measured along dune profiles and macroinvertebrates density. To this end, two dunes were sampled in the Paraná River. The PCA and CCA results showed different hydraulic conditions on each dune and a clear macroinvertebrates preference for places (biotopes) where the hydraulic conditions are less intense such as on the dune 1. The highest densities occurred on this dune, i.e. the hydraulic biotope with the smaller values of t0 and t*. The highest intensity of bed flow conditions on dune 2 may sweep the benthic organisms putting them into suspension. This study deals with the incidence of the near-bottom hydraulic conditions and alluvial bed forms on the bethic fauna distribution in sandy bed rivers of diverse hierarchy of the Paraná River basin. A significant role played by these physical characteristics on the benthic community studied herein, was found. The highest correlations in N. bonettoi (the studied benthic species) population data, were obtained with hydraulic variables such as the friction Reynolds number and the bed shear stress, the substratum type (sand, silt, clay), and the sediment organic matter quantity. N. bonettoi would be related with the hydraulic variables following a "bell shaped" tendency, i.e. there would be an optimum range of these variables where the densities are the highest. For lower or larger values out of that range the densities tend to decrease. Another investigated topic, do not reported in literature, was the relationship between hydraulic variables measured along dune profiles and macroinvertebrates density. To this end, two dunes were sampled in the Paraná River. The PCA and CCA results showed different hydraulic conditions on each dune and a clear macroinvertebrates preference for places (biotopes) where the hydraulic conditions are less intense such as on the dune 1. The highest densities occurred on this dune, i.e. the hydraulic biotope with the smaller values of t0 and t*. The highest intensity of bed flow conditions on dune 2 may sweep the benthic organisms putting them into suspension.