Hydraulic factors controlling the benthic invertebrate distribution within and among dunes of the Middle Paraná River (Argentina) and sampling techniques.

Abstract

Dunes are ubiquitous bed forms in river channels which deeply interact with the mean and turbulent flow dynamic. These interactions involve the intricate mechanisms governing the entrainment, transport, and deposition of bed sediment which are being studied since long time ago. However, the links between dunes and stream ecology, such as the benthic fauna distribution, was not yet investigated to the authors knowledge. This study aims to optimize the benthic sampling techniques on bed forms, and links the different hydraulic characteristics prevailing on crests and troughs of dunes and the invertebrate distribution on the Middle Paraná River (Argentina). It was also possible to have an insight of the invertebrate distribution living in these bed areas (i.e. crests and troughs) as well as the influence of dunes location on the channel bed. A significant distinction of benthic distribution (densities) on dunes, as a consequence of their location on the bed and hydraulic conditions, was found. The overall results showed a clear preference by invertebrates for the dune with lower bed shear stresses. The study concluded that dunes could be considered as biotopes hydraulically differentiated and, consequently, with a stratified benthic distribution. Consequently, to discriminate bottom areas, by an appropriate selection of the hydraulic variables over the associated geometry of dunes, is an effective way to reduce the variance and to increase the accuracy of benthic samplings in large rivers.