Aquatic macroinvertebrate response along a gradient of lateral connectivity in river floodplain channels

Abstract

Large river floodplains potentially include the full range of freshwater ecosystems from permanently flowing channels to temporary pools and springs. Attempts to restore such complex systems require tools adapted to assess restoration success. In an analysis of invertebrate assemblages in the Rhoˆne River floodplain (France), taxonomic-based indices (rarefied richness and assemblage composition) were compared with functional metrics using trait-based ratios as surrogates of ecosystem processes. Their ability to respond to a gradient of hydrological connectivity was assessed in 7 cut-off channels. The sampling design included 2 sites/channel (upstream and downstream), 4 randomly chosen sampling points (0.530.5- m quadrats)/site, and 2 sampling seasons (spring and summer). Water physicochemical and habitat variables were recorded when invertebrates were sampled. Environmental variables, including water conductance, [NH3-N], submerged vegetation cover, diversity of sediment grain size, and organic matter content of the sediment, were used to construct a synthetic variable describing the hydrological connectivity of each site with the main river channel. A quadratic regression of rarefied taxonomic richness and the connectivity gradient was not quite significant, but assemblage composition was strongly related to the gradient. Four of 8 trait-based metrics were correlated with the connectivity gradient. Values of metrics that are surrogates for top-down control of assemblage structure and habitat stability (based on functional feeding groups) declined along the gradient from disconnected sites to more connected sites. Values of metrics that are surrogates for voltinism and food supply for water-column-feeding fish increased with connectivity. Top-down control and voltinism surrogates suggested a decline in predator–prey relationships and lower habitat stability, respectively, in the more connected sites. Assemblage composition and some of the trait-based metrics were sensitive to a flood that occurred before one of the sampling dates. Some of the trait-based metrics showed potential for explaining floodplain invertebrate assemblages and for monitoring postrestoration conditions in floodplain water bodies. However, the metrics were developed initially for studies of lotic systems and their use in heterogeneous floodplain water bodies will require further investigation, e.g., delineation of reference conditions for trait-based metrics

Reconstructing riverine paleo-flow regimes using subfossil insects (Coleoptera and Trichoptera): the application of the LIFE methodology to paleochannel sediments

“…The paleochannel in the current study therefore reflects the evolution of one channel section with a period of active flow and a second representing isolation and eventual terrestrialisation. The temporal pattern reflected in the sequences is characteristic of the spatial pattern recorded on contemporary floodplain water bodies (Castella et al 1984;Paillex et al 2007), where active channels, cut-offs and isolated backwaters may all exist in close proximity, and highlights the biological value of diverse floodplain water bodies, and paleochannels in the study of river channel evolution.…”

A floodplain-scale lake classification based on characteristics of macroinvertebrate assemblages and corresponding environmental properties

“…Table 2). Previous research (Paillex et al, 2007;Gallardo et al, 2008) showed that diversity and abundance of macroinvertebrates would increase with the increase of hydrological connectivity. In the river-disconnected lakes, macroinvertebrate assemblages in the lakes at low level of eutrophication were characterized by dominance of epiphytic animals, and those in other lakes at high level of eutrophication were characterized by dominance of pollution-tolerant animals (Pan et al, 2012).…”

Lateral and longitudinal patterns of water physico-chemistry and trace metal distribution and partitioning in a large river floodplain

“…Although these sites have all a permanent connection, the influence of the main river can still vary. These variations in connection with the main channel have been quantified by a synthetic index of lateral connectivity that includes several site characteristics (Paillex et al, 2007). In the rest of the paper, we refer to this index as lateral connectivity.…”

“…Mixture of HNO 3 and H 2 O 2 (4:1 v/v) (Suprapur reagents, Merck, Darmstadt, Germany) was added to the biological material and left overnight. The digestion was performed at 80°C during 1 h. Table 1 The four site types with their locations and connectivity index (CI), calculated as in (Paillex et al, 2007), 0 meaning no lateral connection to the river, and 1 full permanent connection with the river.…”

“…Studies looking for main drivers of community changes in floodplains invariably found hydrological variables describing the connection, respectively the isolation from the main channel to be the most important factors (e.g., bacteria (Lew et al, 2016), phytoplankton (Grabowska et al, 2014), macrophytes (Keruzoré et al, 2013), macroinvertebrates (Castella et al, 2015;Paillex et al, 2007), and fish (Daufresne et al, 2015)). However, hydrological connections were often modified by anthropogenic interventions affecting floodplains and large rivers (e.g., Olivier et al, 2009a;Tockner and Stanford, 2002).…”