Complex hydromorphology of meanders can support benthic invertebrate diversity in rivers

Abstract

In freshwater environments, high biodiversity is commonly associated with habitat heterogeneity. River bends and meanders are particularly complex morphodynamic elements of watercourses. However, the specific spatio-temporal interactions between hydromorphology and the resident biota have scarcely been studied. This article reviews the relationships between hydraulic processes, and morphological units that are typical for meanders, and analyzes the concomitant spatial and temporal dynamics of habitats suitable for aquatic invertebrates. Flow in river bends is characterized by significant crossstream velocities, which modify primary flow patterns, and create helical flow trajectories. Consequently, boundary shear stresses at the river-bed are altered, so that complex erosion, transport, and accumulation processes characteristically shape bed and bank morphology. The diversity of substrate types and complex bathymetry in meanders provide a large variety of habitat conditions for benthic invertebrates within a relatively small spatial domain, which are connected via hydraulic pathways. Periodic reversal of hydromorphological processes between low and high flow, and seasonal growth of aquatic macrophytes creates spatio-temporal dynamics at the meso-and microhabitat scales. Such habitat dynamics increases benthic invertebrate diversity to the extent it is consistent with spatio-temporal scales of invertebrate mobility and life cycle. Furthermore, the presence of flow refugia, and hydraulic dead zones in meanders is essential to sustain species richness. This study concludes that meanders are highly complex morphodynamic elements that exhibit several self-regulating principles supporting invertebrate diversity and resilience in fluvial ecosystems.

Characterization of hydraulic habitat and retention across different channel types; introducing a new field-based technique

“…The rationale underpinning this theory is that physical heterogeneity provides more niches for species to occupy, a wider range of habitats for breeding and foraging and more refugia in highly variable flow environments (Townsend et al, 1997;Ward et al, 1999;Ward & Tockner, 2001). Many studies have noted this relationship at multiple hierarchical spatial scales (Garcia et al, 2012). At large scales, Brown (1997) reported the morphological diversity of wooded alluvial floodplains on the Lee River in south-west Ireland, increased benthic invertebrates within the river corridor.…”

“…Characteristic combinations of depth, mean velocity, bed shear stresses and substrate typify these features (Harrison et al, 2011). Riffles and runs for example, typically have high velocities, high bed shear stresses and coarse substrate, but vary in flow attributes as runs show three-dimensional flows (Garcia et al, 2012). Pools have lower velocities, finer sediments, deeper depths and often have recirculation zones (Brierley & Fryirs, 2005;Gordon et al, 2008).…”

Effects of flow regulation on river bed dynamics and invertebrate communities in a Mediterranean river

“…Such involuntary or catastrophic drift is an important reset mechanism in fluvial ecosystems and the persistence of certain species may depend on the occurrence of these events (e.g. Picket & White, 1985;Grimm & Fisher, 1989;Garcia et al, 2012). In the downstream section, the reduced flood magnitude and frequency (i.e.…”

Native submerged macrophyte distribution in seasonally-flowing, south-western Australian streams in relation to stream condition

“…Excessive growth is perhaps prevented by seasonal drying (Deegan et al 2012), which restricts dispersal and vegetative growth required for widespread colonisation (Barrat-Segretain 1996). In addition, self-regulation of patch size may result from the diversion of flow around plant stands, created by resistance within the stands that in turn creates adjacent areas of high velocity and coarser, less stable substrate that are unsuitable for macrophyte colonisation (Sand-Jensen and Mebus 1996;Garcia et al 2012).…”