Summary 1. The application of environmental policy and legislation across large‐scale administrative units creates a growing need for standard tools to assess and monitor the ‘ecological health’ of rivers, a requirement that can be achieved through the description of ecological functions of lotic invertebrate species in river communities. 2. To assess alternative metrics, we tested how the functional structure (described by 14 biological traits) of invertebrate communities in 190 large river reaches differed with respect to differences in taxonomic resolution (species, genus, family), taxa weighting of traits (raw abundance, ln‐transformed abundance, presence–absence data) and consideration of alien species (inclusion or exclusion), and how these differences influenced the potential of functional descriptions to discriminate river reaches across a gradient of multiple human impacts. 3. Functional descriptions derived at the level of species, genera and families were very similar, whereas functional descriptions derived from raw abundances differed significantly from those derived from both ln‐transformed abundances and presence–absence data. Functional descriptions after the exclusion of alien species differed considerably from those including alien species. 4. Generally, the functional descriptions significantly discriminated river reaches according to the level of human impact. Taxonomic resolution scarcely influenced the discrimination of impact levels, whereas the use of raw abundances decreased impact discrimination in comparison with ln‐transformed abundances and presence–absence data. Exclusion of alien species also decreased discrimination of impact levels. 5. When considered separately, individual biological traits describing maximal size, number of descendants per reproductive cycle, number of reproductive cycles per individual, life duration of adults, reproductive method, parental care, body form and feeding habits had the highest potential to discriminate the level of human impact. 6. Our findings indicate that genus or perhaps family identifications are sufficient for large‐river biomonitoring using invertebrate traits. Although raw abundances could provide a better discrimination of low levels of human impact, presence–absence data should be sufficient to discriminate functional community changes caused by elevated levels of human impact across Europe.

No abstract

1. Studies on biodiversity and ecosystem function require considering metrics for accurately describing the functional diversity of communities. The number of taxa (richness) is commonly used to characterise biological diversity. The disadvantage of richness as a measure of biological diversity is that all taxa are taken into account on an equal basis regardless of their abundance, their biological characteristics or their function in the ecosystem. 2. To circumvent this problem, we applied a recently described measure of biological diversity that incorporates dissimilarities among taxa. Dissimilarities were defined from biological traits (e.g. life history, morphology, physiology and behaviour) of stream invertebrate taxa and the resulting biological diversity index was considered as a surrogate for functional diversity. 3. As sampling effort is known to affect the number of taxa collected within a reach, we investigated how change in functional diversity is affected by sampling effort. We used stream invertebrate community data from three large European rivers to model accumulation curves and to assess the number of samples required to estimate (i.e. closeness to the maximal value) functional diversity and genera richness. We further evaluated the precision of estimates (i.e. similarity of temporal or spatial replicates) of the total functional diversity. 4. As expected, richness estimates were strongly dependent on sampling effort, and 10 replicate samples were found to underestimate actual richness. Moreover, richness estimates showed much variation with season and location. In contrast, functional diversity had greater accuracy with less sampling effort and the precision of the estimates was higher than richness both across sampling occasions and sampling reaches. These results are further arguments towards conducting research on the design of a biomonitoring tool based on biological traits.

The interstitial space of bed-sediments is a major component of the stream system as it influences both physical and biological processes and patterns, such as exchanges between surface water and groundwater or the assemblage of invertebrates. To investigate the influence of grain-size distribution and vertical bed-packing on the interstitial habitat, we used 99 frozen cores collected from 15 French streams. On our data, overall invertebrate density, density of Chironomidae and taxon richness were more strongly related to effective porosity than to other physical variables describing bed-sediments. We built two models to quantify the influence of grain-size distribution and vertical bed-packing on effective porosity. The effective porosity decreased with increasing grain-size heterogeneity and was strongly related to grain-size distribution. These relationships differed with vertical bed-packing, but were consistent across three geologic types of sediments that varied in particle shape and particle texture. These general relationships suggest that effective porosity could be helpful to better understand the distribution patterns of invertebrates in bed-sediments.

The benthic macroinvertebrate community and substratum characteristics were assessed at 17 study sites diffe ring in the amount of interstitial space in the sub surface interstitial zone (O-IScm deep). The invertebrate community was described in terms of density, taxonomic richness, Shannon diversity and morphological traits (size, flexibility and body shape of the invertebrates). The amount of interstitial space in the subsurface zone that is described by porosity was significantly and negatively related to percentage of fine sediment, but not to stream slope, particle heterogeneity and par ticle size. Invertebrate density was significantly and positively re lated to the amount of interstitial space whereas taxonomic richness was slightly and negatively related to fine particulate organic matter content. Relative abundance of intermediate body size (S -lOmm), intermediate body flexibility (10-300°), and flattened or streamlined shape were significantly and positively re lated to the amount of interstitial space, contrasting with relative abundance of small body size «S mm), and cylindrical or spherical shape that were significantly and negatively re lated to this variable. These results high light the importance of interstitial space, both as a factor partly controlling community structure and as an evolutionary factor acting on macroinvertebrate ability to penetrate the substratum. In addition to fl ow, the substratum selects the invertebrates through their different abilities to use the interstitial habitat.

No abstract

RÉSUMÉLe développement des activités humaines a conduit dans de nombreuses régions à une augmentation du transfert de sédiments fins vers les cours d'eau, multipliant les phénomènes de colmatage. Le colmatage fait référence au dépôt de sédiments organiques ou minéraux et à leur infiltration dans le benthos et l'hyporhéos. Dans cet article de synthèse, le colmatage par les sédiments minéraux est présenté du point de vue de ses mécanismes et de sa variabilité spatio-temporelle dans un schéma d'organisation global du cours d'eau. Le colmatage entraîne une modification des habitats benthique et interstitiel, ainsi que des échanges d'eau et de matières entre la surface et l'hyporhéos. Il affecte la structure du peuplement d'invertébrés en modifiant la structure et la stabilité du substrat, la disponibilité des ressources trophiques et de l'oxygène, ainsi que de la pression de prédation. Les conséquences à court terme sont une augmentation de la dérive et une réduction de l'abondance totale des organismes. Sur le long terme le colmatage affecte la survie, le développement et la croissance des invertébrés ainsi que la biomasse et la productivité du peuplement. Les espèces sensibles adaptées aux substrats grossiers disparaissent au profit des espèces adaptées aux sédiments fins. Les conséquences sur la faune hyporhéique sont peu connues mais l'importance de l'hyporhéos dans le fonctionnement du cours d'eau suggère que son altération pourrait avoir des conséquences importantes en terme de capacité de résilience du peuplement face aux perturbations. Mots-clés : substrat, hyporhéos, sédiment, invertébrés, matières en suspension (MES).Bull. Fr. Pêche Piscic. (2002) THE CLOGGING OF STREAM BEDS: A REVIEW OF MECHANISMS AND CONSEQUENCES ON HABITATS AND MACROINVERTEBRATE COMMUNITIES. ABSTRACTThe clogging refers to deposition and infiltration of fine organic and inorganic sediments downward within the hyporheic zone. In this review, we presented clogging mechanisms and their spatio-temporal variability in the context of a global stream functioning. Clogging modifies stream bottom and interstitial habitats characteristics and reduces the exchange of water and dissolved substances between the stream surface and the hyporheic zone. Modifications of substrate structure, substrate stability, oxygen and trophic resources and predator influence lead to changes in community structure. In a first step, drift increases whereas the invertebrate abundance drops. In a second step, likelihood to survive, growing, standing crop and productivity are affected. Coarse substrate adapted assemblages are progressively replaced by invertebrates adapted to fine sediments. The studies about consequences of clogging on the hyporheos are scarce, but the major role of the hyporheos on the dynamic of streams suggests that its alteration would strongly decrease the stream resilience capacity after disturbances.

No abstract