The meanders and floodplains of the Kushiro River were restored in March 2011. A 1.6-km stretch of the straightened main channel was remeandered by reconnecting the cutoff former channel and backfilling the straightened reach, and a 2.4-km meander channel was restored. Additionally, flood levees were removed to promote river-floodplain interactions. There were four objectives of this restoration project: to restore the in-stream habitat for native fish and invertebrates; to restore floodplain vegetation by increasing flooding frequency and raising the groundwater table; to reduce sediment and nutrient loads in the core wetland areas; to restore a river-floodplain landscape typical to naturally meandering rivers. In this project, not only the natural landscape of a meandering river but also its function was successfully restored. The monitoring results indicated that these goals were likely achieved in the short term after the restoration. The abundance and species richness of fish and invertebrate species increased, most likely because the lentic species that formerly inhabited the cutoff channel remained in the backwater and deep pools created in the restored reach. In addition, lotic species immigrated from neighboring reaches. The removal of flood levees and backfilling of the formerly straightened reach were very effective in increasing the frequency of flooding over the floodplains and raising the water table. The wetland vegetation recovered rapidly 1 year after the completion of the meander restoration. Sediment-laden floodwater spread over the floodplain, and approximately 80-90% of the fine sediment carried by the water was filtered out by the wetland vegetation.

1. Flow refugia, characterised by low hydraulic stress during a flood, are key habitats that contribute to the persistence of benthic invertebrate. We investigated the use of different refugium types distributed across stream and floodplains and clarified which refugia contributed most to the persistence of assemblage and population during a seasonal snowmelt flood. 2. We sampled invertebrates and measured physical variables from six or nine types of channel units ('riffle', 'run ', 'lateral pool', 'backwater', 'abandoned pool' and 'tributary' at base flow, plus 'fast inundated area', 'slow inundated area' and 'side channel' at high flow) at four times (before, during, immediately after and after a flood). We analysed the use of refugia by assemblages, species with different ecological 'lifestyles' (a classification into different modes of mobility: burrower, climber, sprawler, clinger and swimmer) and populations. 3. Total density and species richness decreased significantly with flooding in riffles, runs and lateral pools. In contrast, total density and species richness did not change significantly in the other six types of channel units; therefore, these were distinguished as refugia. Among the six refugia, backwaters, tributaries and slow inundated areas had higher total densities than other refugia. The densities of the five lifestyles also decreased with flooding in riffles, runs and lateral pools. During flooding, high densities in backwaters and slow inundated areas were common for all lifestyles, whereas densities in other refugia varied with lifestyle. 4. The results for five common species showed that refugium use is species-dependent. The mayfly Paraleptophlebia japonica (Leptophlebiidae) and the cased caddisfly Neophylax ussuriensis (Uenoidae) were more numerous in refugia during flooding and recovered rapidly after flooding. In contrast, the mayfly Epeorus latifolium (Heptageniidae) and the net-spinning caddisfly Hydropsyche orientalis (Hydropsychidae) were rare in all types of channel units during and immediately after flooding. The cased caddisfly Allomyia delicatula (Apataniidae) was specific to tributaries and persisted throughout the research period. 5. Although some species did not use refugia effectively, various species with different mobility and ecological traits did persist and were found in refugia. Specifically, habitats with slowly flowing water that were spatially close to the main channel favoured the persistence of benthic invertebrates.

Rivers suffer from multiple stressors acting simultaneously on their biota, but the consequences are poorly quantified at the global scale. We evaluated the biological condition of rivers globally, including the largest proportion of countries from the Global South published to date. We gathered macroinvertebrate‐ and fish‐based assessments from 72,275 and 37,676 sites, respectively, from 64 study regions across six continents and 45 nations. Because assessments were based on differing methods, different systems were consolidated into a 3‐class system: Good, Impaired, or Severely Impaired, following common guidelines. The proportion of sites in each class by study area was calculated and each region was assigned a Köppen‐Geiger climate type, Human Footprint score (addressing landscape alterations), Human Development Index (HDI) score (addressing social welfare), % rivers with good ambient water quality, % protected freshwater key biodiversity areas; and % of forest area net change rate. We found that 50% of macroinvertebrate sites and 42% of fish sites were in Good condition, whereas 21% and 29% were Severely Impaired, respectively. The poorest biological conditions occurred in Arid and Equatorial climates and the best conditions occurred in Snow climates. Severely Impaired conditions were associated (Pearson correlation coefficient) with higher HDI scores, poorer physico‐chemical water quality, and lower proportions of protected freshwater areas. Good biological conditions were associated with good water quality and increased forested areas. It is essential to implement statutory bioassessment programs in Asian, African, and South American countries, and continue them in Oceania, Europe, and North America. There is a need to invest in assessments based on fish, as there is less information globally and fish were strong indicators of degradation. Our study highlights a need to increase the extent and number of protected river catchments, preserve and restore natural forested areas in the catchments, treat wastewater discharges, and improve river connectivity.

Summary Degradation of floodplains continues with an increasing number of floodplain lakes disconnected from the fluvial dynamics of rivers. Limited understanding is available as to how historical geomorphic formation processes (i.e. geomorphic legacy) determine contemporary ecosystem structure and function. We tested the hypothesis that geomorphic legacy mediates morphometry and results in heterogeneity of macrophyte distributions in disconnected floodplain lakes. The distribution of macrophyte cover was examined in relation to environmental factors, including water nutrient level, morphometry of lakes and patch shelter level across and among three types of lakes along the Ishikari River, Japan. Artificial lakes (isolated by channelisation), natural oxbow lakes and marsh lakes have been disconnected for more than 40 years from natural flood pulses because of dyke construction. The presence of macrophytes (in 5 × 5 m areas) was predicted well by a combination of local water depth and bed slope. Lake average depth, higher values indicating lakes that are more deeply incised with a steeper‐sloped littoral zone, had the strongest and most negative influence on total macrophyte cover across lakes. Cover was least in artificial lakes because of greater average depth. Predicted area of macrophyte cover was significantly less than occupied by actual cover in artificial lakes compared with other lake types. Macrophyte cover in artificial lakes was particularly vulnerable to external factors such as waves and wind. This study underscored the significance of geomorphic legacy in explaining a large proportion of heterogeneity of total macrophyte cover in the study lakes. Artificial lakes did not have the macrophyte habitat quality of natural lakes. When lake morphometry needs to be altered, local conditions as well as patch‐scale properties should be carefully examined in the light of the geomorphic legacy left by dynamic river–floodplain interactions.

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