Disentangling multiple pressures on fish assemblages in large rivers

Abstract

European large rivers are exposed to multiple human pressures and maintained as waterways for inland navigation. However, little is known on the dominance and interactions of multiple pressures in large rivers and in particular inland navigation has been ignored in multi-pressure analyzes so far. We determined the response of ten fish population metrics (FPM, related to densities of diagnostic guilds and biodiversity) to 11 prevailing pressures including navigation intensity at 76 sites in eight European large rivers. Thereby, we aimed to derive indicative FPM for the most influential pressures that can serve for fish-based assessments. Pressures' influences, impacts and interactions were determined for each FPM using bootstrapped regression tree models. Increased flow velocity, navigation intensity and the loss of floodplains had the highest influences on guild densities and biodiversity. Interactions between navigation intensity and loss of floodplains and between navigation intensity and increased flow velocity were most frequent, each affecting 80% of the FPM. Further, increased sedimentation, channelization, organic siltation, the presence of artificial embankments and the presence of barriers had strong influences on at least one FPM. Thereby, each FPM was influenced by up to five pressures. However, some diagnostic FPM could be derived: Species richness, Shannon and Simpson Indices, the Fish Region Index and lithophilic and psammophilic guilds specifically indicate rhithralisation of the potamal region of large rivers. Lithophilic, phytophilic and psammophilic guilds indicate disturbance of shoreline habitats through both (i) wave action induced by passing vessels and (ii) hydromorphological degradation of the river channel that comes along with inland navigation. In European large rivers, inland navigation constitutes a highly influential pressure that adds on top of the prevailing hydromorphological degradation. Therefore, river management has to consider river hydromorphology and inland navigation to efficiently rehabilitate the potamal region of large rives.

Poleward shift in large‐river fish communities detected with a novel meta‐analysis framework

“…Daufresne & Boët, 2007;Souchon & Tissot, 2012;Teletchea et al, 2009). However, other environmental changes are likely to have occurred locally over the same period and may also have contributed to the observed biological changes (Malmqvist & Rundle, 2002;Zajicek et al, 2018). However, other environmental changes are likely to have occurred locally over the same period and may also have contributed to the observed biological changes (Malmqvist & Rundle, 2002;Zajicek et al, 2018).…”

“…For all sites except for Civaux on the Vienne River, the number of newcomer species exceeded the number of species no longer present.4 | D ISCUSS I ON4.1 | General long-term changes and comparison with previously identified trendsLarge rivers have been undergoing multiple and profound environmental changes with direct and indirect, and possibly interacting effects on their biodiversity(Vörösmarty et al, 2010;Zajicek, Radinger, & Wolter, 2018). 18 in the 2010s;Figure 6a); over the same period, average cumulative abundance increased approximately four-fold (from an average 100 individuals per 20 min fishing in the 1980s to >400 in the 2010s;Figure 6b).…”

“…Large rivers have been undergoing multiple and profound environmental changes with direct and indirect, and possibly interacting effects on their biodiversity(Vörösmarty et al, 2010;Zajicek, Radinger, & Wolter, 2018). Long-term data provide valuable opportunities to better understand the effects of cumulative stressors(Counihan et al, 2018) or large-scale restoration measures(Daufresne et al, 2015; on aquatic biodiversity at spatial and temporal scales relevant to the effective management of these complex river ecosystems.The present study identified concomitant large-scale trends in environmental features (i.e.…”

A systematic review of assessment and conservation management in large floodplain rivers – Actions postponed

“…Accordingly, examples of in-depth assessment of pressure effects, rehabilitation measures in or rehabilitation guidance for LFRs are rather scarce (e.g. Zajicek et al, 2018). Correspondingly, in Germany an analysis of the first river basin management plans implementing the European Water Framework Directive (WFD, 2000/60/EEC) revealed that huge knowledge gaps were evident (especially for large rivers), and mostly conceptual measures were planned (Kail and Wolter, 2011).…”

Overcoming the dichotomy of implementing societal flood risk management while conserving instream fish habitat – A long-term study from a highly modified urban river

“…Conventional FRM also involves construction of extensive flood defence structures, such as in Rotterdam in the Netherlands, New Orleans in the United States and the Huai River in China, where main river channels have been isolated from their floodplains (Sayers et al 2013). This isolation profoundly affects fluvial processes and ecosystem functioning, and also eliminates or degrades the habitats required by many aquatic animals for foraging, refuge and reproduction (Bernhardt & Palmer 2007;Weber & Wolter 2016;Zajicek et al 2018).…”