Interdisciplinary research in the fields of ecohydrology and ecogeomorphology is becoming increasingly important as a way to understand how biological and physical processes interact with each other in river systems. The objectives of the current study were 1) to determine changes in invertebrate community due to hydrological stages, 2) to link local physical features [flow configuration, sediment composition and morphological feature) with the ecological structure between and within dissimilar morphological units (meander and confluence), and 3) to determine the existence and the origin of bed hydro‐geomorphic patches, determining their ecological structure. Results were discussed in the frame of prevailing ecological models and concepts. The study site extends over a floodplain area of the large Paraná River (Argentina), including minor and major secondary channels as well as the main channel. Overall results suggested that hydrodynamics was the driving force determining distribution patterns of benthic assemblages in the floodplain. However, while the invertebrates living in minor secondary channels seem to benefit from flooding, this hydrological phase had the opposite effect on organisms from the main and major secondary channels. We also found a clear linkage between physical features and invertebrate ecology, which caused a dissimilar fauna structure between and within the meander and the confluence. Furthermore, several sandy‐patches were recorded in the confluence. These patches were colonized by the particular benthic assemblage recorded in the main channel, supported the view of rivers as patchy discontinua, under uncertain ecological equilibrium.
This study examines the morphological features, suspended sediment inputs and hydraulic conditions within a large river in association with ecological patterns before and after a tributary confluence. In order to examine these effects, the macroinvertebrate distributions from three reaches of the Paraguay and Bermejo Rivers (Paraguay–Argentina) are investigated. The Bermejo River is a tributary that supplies significant quantities of fine sediment to the Paraguay River, primarily in suspension. Two reaches were examined on the Paraguay River, upstream and downstream of the Bermejo River junction, with the third study reach located on the Bermejo River, upstream of the confluence with the Paraguay River. The results provide clear evidence that a significantly increased loading of fine sediment at a river confluence has effects on the distribution and potential movement of benthic invertebrates in the lotic environment by representing physical barriers at affected sites. These effects may be important at both local and regional scales, and such increases in suspended sediment (especially associated with anthropogenic change) may thus pose a major threat to ecosystem integrity that has been historically underestimated. Copyright © 2014 John Wiley & Sons, Ltd.
With the objective of finding fluctuations on fish body condition in the Middle Paraná River floodplain in different hydrological scenarios, this attribute was analyzed in several trophic groups of a secondary floodplain channel and its associated lakes between 2010 and 2012. Standardized residuals generated by length-weight regressions were calculated for each species and the relative weight (Wr) of the most abundant species per group was examined. A two-way factorial ANOVA was carried out (factors: hydrology and habitats) to evaluate the existence of significant spatial-temporal differences by groups and species. Results showed that body condition in detritivorous, herbivorous and omnivorous species fluctuated significantly depending on hydrology and the environment. Optimal body condition was recorded after the largest flood pulse in most species. Body condition decreased during the low-water period and after two disconnection periods, whereas during the second flood pulse it increased in detritivores, herbivores and omnivores. No floods occurred thereafter, but two flow pulses were registered, and body condition increased under these hydrologic scenarios, with similar or higher values to those recorded after the largest pulse. These results indicate that flow pulses, which are supplementary to flood pulses, may have a positive effect on fish body condition.Keywords: Flood/flow pulses, Hydrological fluctuations, Ichthyofauna, Middle Paraná River, Trophic groups.Con el objetivo de conocer la fluctuación de la condición corporal de peces en la planicie de inundación del tramo medio del río Paraná ante diferentes escenarios hidrológicos, se analizó este atributo de diferentes grupos tróficos en un cauce secundario de la planicie y sus lagunas asociadas durante 2010 a 2012. Se calcularon los residuos estandarizados generados por las regresiones longitud-peso para cada especie y se examinó el peso relativo (Wr, por sus siglas en ingles) de las especies más abundantes de cada grupo. Se llevó a cabo un ANOVA factorial de dos vías (factores: hidrología y ambientes) para evaluar la existencia de diferencias significativas espacio-temporales por grupos y por especies. Los resultados mostraron que la condición corporal de las especies detritívoras, herbívoras y omnívoras fluctuó significativamente en función de la hidrología y los ambientes. Óptimas condiciones corporales se registraron en la mayoría de las especies después del mayor pulso de inundación. La condición corporal disminuyó durante el período de aguas bajas y luego de dos períodos de desconexión, mientras que, durante el segundo pulso, aumentó en detritívoros, herbívoros y omnívoros. No hubieron inundaciones luego, pero ocurrieron dos pulsos de flujo y las condiciones corporales se incrementaron bajo estos escenarios hidrológicos, presentando valores similares o incluso mayores a los registrados luego del gran pulso. Esto destaca que los pulsos de flujo complementarios a los pulsos de inundación pueden tener un efecto positivo sobre la condición corporal de ...
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