A future higher risk of severe flooding of streams and rivers has been projected to change riparian plant community composition and species richness, but the extent and direction of the expected change remain uncertain. We conducted a meta-analysis to synthesize globally available experimental evidence and assess the effects of increased flooding on (1) riparian adult plant and seedling survival, (2) riparian plant biomass and (3) riparian plant species composition and richness. We evaluated which plant traits are of key importance for the response of riparian plant species to flooding. We identified and analysed 53 papers from ISI Web of Knowledge which presented quantitative experimental results on flooding treatments and corresponding control situations. Our meta-analysis demonstrated how longer duration of flooding, greater depth of flooding and, particularly, their combination reduce seedling survival of most riparian species. Plant height above water level, ability to elongate shoots and plasticity in root porosity were decisive for adult plant survival and growth during longer periods of flooding. Both 'quiescence' and 'escape' proved to be successful strategies promoting riparian plant survival, which was reflected in the wide variation in survival (full range between 0 and 100%) under fully submerged conditions, while plants that protrude above the water level (>20 cm) almost all survive. Our survey confirmed that the projected increase in the duration and depth of flooding periods is sufficient to result in species shifts. These shifts may lead to increased or decreased riparian species richness depending on the nutrient, climatic and hydrological status of the catchment. Species richness was generally reduced at flooded sites in nutrient-rich catchments and sites that previously experienced relatively stable hydrographs (e.g. rain-fed lowland streams). Species richness usually increased at sites in desert and semi-arid climate regions (e.g. intermittent streams).

Several studies have demonstrated a latitudinal gradient in the proportion of omnivorous fish species (that is, consumers of both vegetal and animal material) in marine ecosystems. To establish if this global macroecological pattern also exists in fresh and brackish waters, we compared the relative richness of omnivorous fish in freshwater, estuarine, and marine ecosystems at contrasting latitudes. Furthermore, we sought to determine the main environmental correlates of change in fish omnivory. We conducted a meta-analysis of published data focusing on change in the relative richness of omnivorous fishes in native fish communities along a broad global latitudinal gradient, ranging from 41°S to 81.5 N°including all continents except for Antarctica. Data from streams, rivers, lakes, reservoirs, estuaries, and open marine waters (ca. 90 papers covering 269 systems) were analyzed. Additionally, the relationship between the observed richness in omnivory and key factors influencing trophic structure were explored. For all ecosystems, we found a consistent increasing trend in the relative richness of omnivores with decreasing latitude. Furthermore, omnivore richness was higher in freshwaters than in marine ecosystems. Our results suggest that the observed latitudinal gradient in fish omnivory is a global ecological pattern occurring in both freshwater and marine ecosystems. We hypothesize that this macroecological pattern in fish trophic structure is, in part, explained by the higher total fish diversity at lower latitudes and by the effect of temperature on individual food intake rates; both factors ultimately increasing animal food limitation as the systems get warmer.

1. The objective of the present study was to examine how the physical stream environment in regulated and unregulated lowland streams affects the diversity and distribution of macrophyte communities. We analysed the abundance, distribution and composition of macrophytes, together with physical parameters, in seven regulated and seven unregulated unshaded Danish stream reaches. 2. Total macrophyte coverage was similar in the regulated and unregulated streams, but species richness and Shannon diversity were higher in the unregulated streams. Overall, we found fifty‐two different species in the regulated stream reaches and sixty‐two in the unregulated stream reaches. The spatial distribution of macrophytes on the stream bottom was more heterogeneous in the unregulated streams. 3. We found positive correlations between the coverage and diversity of macrophytes and the coverage of coarse‐textured substratum types on the stream bottom, as well as between macrophyte coverage and diversity and substratum heterogeneity. We also found that the macrophytes were more heterogeneously distributed where substratum heterogeneity was greater. 4. The species growing both submerged and emergent were more abundant in the regulated streams, whereas species growing only submerged were more abundant in the unregulated streams. Species growing submerged, species growing both submerged and emergent, and species only growing emergent segregated differently in a canonical correspondence analysis ordination. The submerged species were primarily associated with coarser‐textured substrata, whereas species growing both submerged and emergent, and species growing only emergent were associated with finer‐textured substrata. 5. The most abundant species in the regulated streams, Sparganium emersum, accounting for almost one‐third of the total macrophyte coverage, was primarily associated with clay and sandy bottom substrata, whereas the most abundant species in the unregulated streams, Batrachium peltatum, was primarily associated with gravel and stony substrata.

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1. We evaluated restoration success on macrophyte species diversity and composition in lowland streams using communities in 30 naturally meandering stream reaches in the western part of Jutland, Denmark, as reference target communities. Fuzzy set clustering was used to examine the floristic and environmental similarity among reaches, whereas fuzzy set ordination was used to relate floristic patterns to environmental variables. 2. Two major groups of streams were identified based on their floristic composition. One group consisted of reference and restored reaches and the other of the majority of channelised reaches. We found that management exerted a strong influence on the macrophyte communities and that the identified groups were related to differences in management intensity. 3. Our results also indicate that bank morphology and bed level affected macrophyte communities in the streams, particularly the richness and abundance of terrestrial species. The analyses performed suggest that shallow and wide banks allow for a larger migration of species from the stream banks into the streams, thereby enhancing species diversity within the stream channel. 4. The results of this study suggest that macrophyte communities in channelised lowland streams can recover following restorative interventions given that stream management (i.e. weed cutting and dredging) is minimised and that stream banks are reprofiled to improve the lateral connectivity between the stream and its valley.

We surveyed macrophyte community structure and measured community metabolism and nutrient uptake along a temperature gradient (9.7-17.4°C) in four Icelandic streams influenced by geothermal heating. The study streams are part of the geothermal area in Hengill that is uniquely characterised by streams with comparable water chemistry despite the geothermal influence. Stream metabolism was studied applying the diurnal upstream-downstream dissolved oxygen change technique. Nutrient uptake was studied by adding solutions of nitrogen and phosphorus together with a conservative tracer. Rates of primary production (GPP) and uptake of nitrate-N and phosphate-P increased with increasing stream temperature. GPP was 20 times higher (up to 12.99 g O 2 m -2 day -1 ) and rates of nutrient uptake were up to 30-times higher (up to 22.99, 13.31 and 7.94 mg m -2 h -1 for ammonium, nitrate and phosphate, respectively) in the warmest streams compared with the coldest. Furthermore, macrophytes, when present, were strongly controlling ecosystem processes. Our study implies that temperature may affect stream ecosystem processes both directly (i.e. physiologically) and indirectly (i.e. by changing other structural parameters).

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