Flooding and hydrologic connectivity modulate community assembly in a dynamic river-floodplain ecosystem

International audienceBraided river floodplains are highly dynamic ecosystems, where aquatic communities are strongly regulated by the hydrologic regime. So far, however, understanding of how flow variation influences assembly mechanisms remains limited. We collected benthic chironomids and oligochaetes over a year across a lateral connectivity gradient in the semi-natural Tagliamento River (Italy). Four bankfull flood events occurred during the study, allowing the assessment of how flooding and hydrologic connectivity mediate the balance between sto-chastic and deterministic community assembly. While invertebrate density and richness were positively correlated with connectivity, diversity patterns showed no significant correlation. Species turnover through time increased with decreasing connectivity. Contrary to expectations, hydrologic connectivity did not influence the response of community metrics (e.g. diversity, density) to floods. Invertebrate composition was weakly related to connectiv-ity, but changed predictably in response to floods. Multivariate ordinations showed that faunal composition diverged across the waterbodies during stable periods, reflecting differential species sorting across the lateral gradient, but converged again after floods. Stable hydrological periods allowed communities to assemble deterministically with prevalence of non-random beta-diversity and co-occurrence patterns and larger proportion of composi-tional variation explained by local abiotic features. These signals of deterministic processes declined after flooding events. This occurred despite no apparent evidence of flood-induced homogenisation of habitat conditions. This study is among the first to examine the annual dynamic of aquatic assemblages across a hydrologic connectivity gradient in a natural flood-plain. Results highlight how biodiversity can exhibit complex relations with hydrologic con-nectivity. However, appraisal of the assembly mechanisms through time indicated that flooding shifted the balance from deterministic species sorting across floodplain habitats, towards stochastic processes related to organisms redistribution and the likely resetting of assembly to earlier stages

Oligochaeta of the Danube River - a faunistical review

The aim of this work is to discuss the distribution of Oligochaeta (Annelida) in the Danube River using the collections made by the Joint Danube Survey 2007 (JDS2) on more than 2800 km of the river. The basic faunistical features of the oligochaete assemblages were analysed with regard to three main sectors of the Danube (upper, middle and lower reaches, the last with the Danube Delta). A total of 52 oligochaete taxa have been recorded. Most of the observed species are typical of the potamon-type rivers in the region, and are well adapted to moderate-to-high organic load. The highest taxa richness and frequency of occurrence were observed among the Tubificidae family. Naididae, Propappidae, Enchytraeidae and Haplotaxidae had also low frequency. The upper reach of the Danube showed the lowest species richness, while the middle reach is characterised by its highest species richness. Construction of dams and regulation of the riverbed have resulted in an increase of limno(rheo)philic taxa which prefer slow-flowing and lentic zones.Ministry of Science and Environmental Protection of the Republic of Serbia [173025 EHS

Oligochaeta of the Danube River - a faunistical review

The aim of this work is to discuss the distribution of Oligochaeta (Annelida) in the Danube River using the collections made by the Joint Danube Survey 2007 (JDS2) on more than 2800 km of the river. The basic faunistical features of the oligochaete assemblages were analysed with regard to three main sectors of the Danube (upper, middle and lower reaches, the last with the Danube Delta). A total of 52 oligochaete taxa have been recorded. Most of the observed species are typical of the potamon-type rivers in the region, and are well adapted to moderate-to-high organic load. The highest taxa richness and frequency of occurrence were observed among the Tubificidae family. Naididae, Propappidae, Enchytraeidae and Haplotaxidae had also low frequency. The upper reach of the Danube showed the lowest species richness, while the middle reach is characterised by its highest species richness. Construction of dams and regulation of the riverbed have resulted in an increase of limno(rheo)philic taxa which prefer slow-flowing and lentic zones.Ministry of Science and Environmental Protection of the Republic of Serbia [173025 EHS

Diversity and distribution patterns of benthic invertebrates along alpine gradients. A study of remote European freshwater lakes

Invertebrates inhabiting alpine water bodies are sensitive to environmental variability and lake faunal communities can therefore be important indicators of long-range airborne pollution, climate change and other human impacts. Information about the trophic structure and species composition of alpine lake ecosystems over space and time should therefore give important insights into environmental change effects. To explore the sensitivity of the faunal communities to environmental variability at local and regional scales we sampled biological and environmental variables from alpine lakes in seven different alpine lake districts in six European mountain regions. The fauna of the lakes was mainly composed of oligotrophic/ultraoligotrophic species, predominantly chironomids which made up more than 60% of all individuals. Species accumulation curves were used to explore patterns of species turnover and distribution, and the results indicated strong patterns in species diversity and also environmentally driven patterns in species distributions among lake districts. We used ordination analyses to explore these patterns in more detail. The results showed that the over-riding patterns in faunal assemblages were found between the lake districts. Lake-water chemistry appeared to be the major driver of the faunal assemblages at this scale, but altitude and geography could also account for significant fractions of the variability. In addition to these broad-scale patterns, repeatable trends in the faunal assemblages could be found in the faunal assemblages within lake districts. At this scale, the strongest compositional trends were found along the altitudinal gradient, but the faunal communities also responded to within-district variability in lake-water chemistry. Lake size or maximum depth did not appear to have any statistically significant effect on the littoral faunal assemblages at either scale.Gli invertebrati che colonizzano gli ambienti acquatici d\u27alta quota sono sensibili alle variazioni ambientali e le loro comunit? possono essere utili indicatori di trasporto di inquinanti, cambiamenti climatici e altri impatti antropici. Informazioni relative alla struttura trofica e alla composizione in specie degli ambienti lacustri possono fornire utili informazioni sugli effetti dei cambiamenti climatici. Per definire la sensibilit? delle comunit? lacustri alle variabilit? ambientali su scala regionale e locale abbiamo campionato laghi in 7 diversi distretti alpini appartenenti a 6 regioni montane europee. Le curve di accumulo utilizzate hanno fornito informazioni relative al turn-over di specie ed alla loro distribuzione. L\u27idrochimica lacustre sembra essere uno dei principali fattori determinanti la struttura di comunit? fra i diversi distretti, l\u27altitudine e la distribuzione geografica hanno anche un ruolo importante

The STAR project: context, objectives and approaches

STAR is a European Commission Framework V project (EVK1-CT-2001-00089). The project aim is to provide practical advice and solutions with regard to many of the issues associated with the Water Framework Directive. This paper provides a context for the STAR research programme through a review of the requirements of the directive and the Common Implementation Strategy responsible for guiding its implementation. The scientific and strategic objectives of STAR are set out in the form of a series of research questions and the reader is referred to the papers in this volume that address those objectives, which include: (a) Which methods or biological quality elements are best able to indicate certain stressors? (b) Which method can be used on which scale? (c) Which method is suited for early and late warnings? (d) How are different assessment methods affected by errors and uncertainty? (e) How can data from different assessment methods be intercalibrated? (f) How can the cost-effectiveness of field and laboratory protocols be optimised? (g) How can boundaries of the five classes of Ecological Status be best set? (h) What contribution can STAR make to the development of European standards? The methodological approaches adopted to meet these objectives are described. These include the selection of the 22 stream-types and 263 sites sampled in 11 countries, the sampling protocols used to sample and survey phytobenthos, macrophytes, macroinvertebrates, fish and hydromorphology, the quality control and uncertainty analyses that were applied, including training, replicate sampling and audit of performance, the development of bespoke software and the project outputs. This paper provides the detailed background information to be referred to in conjunction with most of the other papers in this volume. These papers are divided into seven sections: (1) typology, (2) organism groups, (3) macrophytes and diatoms, (4) hydromorphology, (5) tools for assessing European streams with macroinvertebrates, (6) intercalibration and comparison and (7) errors and uncertainty. The principal findings of the papers in each section and their relevance to the Water Framework Directive are synthesised in short summary papers at the beginning of each section. Additional outputs, including all sampling and laboratory protocols and project deliverables, together with a range of freely downloadable software are available from the project website at www.eu_star.a