Linking hydro‐morphology with invertebrate ecology in diverse morphological units of a large river‐floodplain system

Abstract

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.

Hydraulic complexity at a large river confluence in the Amazon basin

“…The macroinvertebrate decline downstream of the confluence was attributed to the input of fine sediment from the Bermejo River, creating a physical barrier to the migration of macroinvertebrate (Blettler et al, ). In the channel and floodplain of Argentina's large Paranà River, Blettler et al () used surveys to map physical features, for example, local flow configuration, hydrological stage, sediment composition and morphological characteristic, and ecological structure, such as, invertebrate density, diversity, evenness and number of species, and established a physical–ecological link between and within floodplain and channel morphological units. In summary, these findings support the view of a river as a patchy “discontinuum” (Poole, ), where the river responds to local ecomorphodynamics and highlight the role of food abundance, energy expenditure for fish, differences in water characteristics (e.g., white waters vs. black waters) and in sediment grain size in providing a suitable environment for ecological richness.…”

Ecological relevance of anabranch confluences: Hydrological and morphological effects

“…Despite the speculative nature of the previous reasoning, it has a solid hydraulic foundation as stated before. Moreover, the explanations are empirically supported by Blettler et al (2016), who have linked sandy patches to benthic colonization patterns in anabranching confluences located in the same study area and with dissimilar momentum ratios.…”

“…Finally, very low densities of the active bed assemblage were recorded in s-s5 in 1992/1993 (during and after the ENSO; Figure 1c) in spite of the existence of a sandy substratum suitable for those species (Figure 4; Table 2). We speculated that s-s5 was sampled during the so-called colonization in progress (Blettler et al, 2016). This phenomenon could be attributed to a short time lag or brief delayed response of organisms to environmental changes (Gunn, O'Hare, Maitland, & May, 2012;Sukhodolov, Blettler, Zhang, Sukhodolova, & Nützmann, 2015); that is, a short period is required to guarantee invertebrate colonization after the sandy-patches settling.…”

Fish Structure in Channel Networks of a Large Anabranching Floodplain: Effect of Isolation/Connection Processes

“…Black line = cross section where the discharge rating curve was measured. Hydrometric level = 3.5 m (Santa Fe port gauge; modified from Blettler et al, ).…”

“…Hence, the larger abundance of Siluriformes would be explained by the typical high water turbidity of lotic habitats in the Paraná River (Figure ) together with low flow velocities and backwater sectors allowing particulate organic matter to deposit. Moreover, bank erosion in scour holes (Blettler et al, ) prevents the settlement of rooted macrophytes and, thus, the existence of refuges for preys. To this is associated the presence of large predators, for example, catfishes ( A. inermis , A. militaris , and L. pati ) and piranhas ( P. nattereri ).…”