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

MARTÍN C. BLETTLER; MARIO L. AMSLER; INÉS EZCURRA DE DRAGO

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2011

0895-9811

Summary.Dunes are ubiquitous bed forms in river channels which interact deeply with the mean and turbulent flow dynamics. These interactions involve the intricate mechanisms governing the entrainment, transport, and deposition of bed sediment which are being studied since long time ago. The links of dunes with the stream ecology such as the benthic fauna distribution, however, was not yet investigated to the authors’ knowledge. This study aims to optimize the benthic samplings on dunes by reducing variance and increasing the accuracy of population estimates. The purpose is reached taking due account of the different hydrauliccharacteristics prevailing on crests and troughs of two dunes surveyed on the main channel of the Middle Paraná River (Argentina). It was also possible to have an insight of the invertebrate distribution living in those bed areas as well as of the influence of dunes location on the channel bed. A significant distinction in the benthic densities on dunes as a consequence of their locations on the bed where hydraulic conditions differ greatly 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. These facts suggest that to discriminate bottom areas, by an appropriate selection of the hydraulicvariables on the associated geometry of dunes, is an effective way to reduce the variance and to increase the accuracy of benthic samplings in large rivers.