Environmental and macroinvertebrate dynamics in the Lower Rhône River and a lateral dike field: a study matching two functioning descriptors

Environmental variables and macroinvertebrate communities are studied in two sites of the Lower Rhône River, the main channel and a lateral, occasionally connected dike field. Environmental variables and faunistic communities allow discrimination the two compartments. The environmental and faunistic differences the two sites change over time. The physical and chemical differences are significantly correlated with water discharge of the main channel. The faunistic ones are significantly correlated with the temperature of the dike field water. The connections between the main channel and the dike field could be very important to maintain a high heterogeneity of the habitat, and for recolonization of the main channel after a perturbation.     

Microhabitat diversity and associated macroinvertebrates in aquatic banks of a large European river

Microhabitats and associated macroinvertebrate communities in aquatic banks of the Upper Rhône River (upstream from Lyon, France) were studied during the autumn of 1985, under low flow conditions. Based on a regular sampling design (one site every 500 m) along 70 km of riverbank, 18 microhabitat types were identified. Mineral microhabitats (from boulders to clay) accounted for 70%; the remainder corresponded chiefly to the microhabitats of aerial or semi-aerial submerged vegetation (27%) and aquatic vegetation (less than 2%). Using various methods, 239 faunistic samples of microhabitat types resulted in the collection of nearly 64 000 organisms representing 133 taxa. A correspondence analysis showed that most of the 18 microhabitat types were on average well characterized by a specific macrofauna. Microhabitats of aquatic vegetation (hydrophytes and algae) contained the richest fauna in terms of both mean specific richness (15.0 and 13.2 per sample, respectively) and mean density (73 125 and 59 475 ind. m^?2, respectively). By contrast, mineral microhabitats were faunistically poorer (mean specific richness per sample <6.0, except cobbles; and mean density ≤10405 ind. m^?2). The fewest species and lowest density occurred in clay, silt and sand. Estimated mean density of macroinvertebrates in the aquatic banks of the Upper Rhône River was approximately 16 000 ind. m^?2. This was four times higher than in deeper sections of the channel at the same season. The aquatic banks of this large European river, with its great diversity of microhabitats, must be taken into account in all macroinvertebrate studies of fluvial systems.     

Isolation and characterization of the first eight microsatellite loci in Gammarus fossarum (Crustacea, Amphipoda) and cross-amplification in Gammarus pulex and Gammarus orinos

We characterized the first microsatellite markers for Gammarus fossarum. Eight loci gave satisfactory amplification patterns in two stream populations (Southern France) with number of alleles ranging from 2 to 10 and expected heterozygosity from 0.076 to 0.857. We performed cross-amplification in two closely related gammarid species, Gammarus pulex and Gammarus orinos. Among the eight tested microsatellite loci, four correctly amplified in G. pulex and three in G. orinos.     

Stream continuum and metabolic rate in the larvae of five species of Hydropsyche (Trichoptera)

The effects of temperature on the metabolic rate of five species of Hydropsyche larvae belonging either to the rhithron (Hydropsyche dinarica, H pellucidula and H siltalat) or to the potamon (H contubernalis and H modesta) have been studied The total amplitude of the metabolic rate between 5 and 25°C is higher in the larvae inhabiting the potamon than those of rhithron (particularly in H siltalat and H dinarica) The shapes of the metabolism temperature curves (M/T curves) of H contubernalis and H modesta differ from each other, although they live in the same habitat and are closely related A comparison with some species of Gammarus suggests a relationship between metabolic rate and the variability of environmental conditions     

Oligochaete drift in a large river (French Upper Rhône): the effect of life cycle and discharge

In the framework of a macroinvertebrate drift study, the oligochaete community was analysed over one year (1989) at six sites located in a partly impounded reach of the Upper Rhône River (France). Drift composition between sites was somewhat affected by the environmental conditions. These differences were caused by significant deviations in drift rates (P < 0.05) of endobenthic oligochaetes and non-swimming Naididae. There was no significant difference (P > 0.05) among the swimming Naididae. As the latter strongly dominated, global spatial differences in the drift were weak. Temporal changes constituted the main source of variability in drifting oligochaetes. Life cycles and reproductive ecology of four major swimming Naidid species, Nais elinguis, Stylaria lacustris, Nais christinae, and Nais barbata, explained most of the drift structure over the year. Hydrological fluctuations also affected drift structure, both for swimming and non-swimming species. Taxon richness and relative abundance in the drift were very similar to those obtained in the river benthos from a reference reach previously studied. There was a lack of stygobiont and stygophilous species that are frequent in area of groundwater seepage. Biological and environmental implications of oligochaete drift are stressed. The drift phenomenon is appropriated to provide ecological informations on oligochaete communities in fast flowing and deep, large rivers.     

Modifications faunistiques engendrées par une faible variation de débit dans une grande rivière

Artificial substrates suspended in the water column and benthic dredging were employed to study the drift of macrofauna and the macrobenthic populations respectively, in a cross section of the Rhône River upstream of Lyon, France. The samples were collected in autumn 1979: first in September under a low flow egime around 400 m³·s^–1, then in October during a discharge increase up to 630 m³·s^–1.The first factor of correspondence analysis showed a clear cleavage between the two periods, especially for drift communities. The differences are most important in the centre of the stream channel. In October, the water column was invaded by unusual and abundant fauna. This dynamics is due to the increase in number of Crustacea (Gammarus fossarum, Asellus aquaticus), the decrease of some insect larvae (Leuctra fusca, Simuliidae, Baetis fuscatus, stages 1 and 2 of Hydropsyche) and the appearance of typical wetland taxa (some limnophilous Coleoptera and Trichoptera). For some other dominant invertebrates, a modification may occur only in their distribution (stages 3 to 5 of Hydropsyche, Heptagenia sulphurea) while the distribution of Psychomyia pusilla remains the same.These results are discussed with respect to the effects of species biology and the unusual consequences caused by a minor increase in discharge.

Structure et fonctionnement des écosystèmes du Haut Rhône français n° 46.     

Flood drift and propagule bank of aquatic macrophytes in a riverine wetland

Abstract. Drift of aquatic macrophyte propagules was investigated in a wetland along the River Rhône, during the first flood after the growing season (i.e. in the winter of 1995–1996). Input and output drift were studied at the beginning, around the top, and at the end of the river overflow in the upper reach of a cut-off channel. The soil propagule bank was sampled along the study area before and after the flood. The amount and composition of viable propagule drift and bank were determined, analysed and compared. Drift densities and richness were on average higher at the outlet of the channel than at the inlet (respectively: 23.2 vs 13.1 viable propagules/100 m³ of water and 8.7 vs 2.6 taxa per sample). Immigrating taxa were mostly in the form of helophyte seeds, whereas numerous resident hydrophyte species left the disturbed area rather as vegetative propagules. Temporal variability in propagule bank structure was weak, and mean bank densities did not change before and after the flood (respectively: 33 047 ± 10 510 vs 35 653 ± 15 070 viable propagules/m² of ground, including Chara). However, the density of Elodea canadensis significantly increased after the flood while that of Eleocharis acicularis decreased. This contrast suggests that flood responses vary among species. Despite a broad overlap in the taxa (18 out of 25 were common both to drift and bank collections), no significant relationship occurred in composition or structural changes between flood drift and propagule bank. Flood acted as a means of distribution of existing propagules and also as a provider of new vegetative dispersal units.     

Infectious Events Prior to Chemotherapy Initiation in Children with Acute Myeloid Leukemia

Background

The primary objective was to describe infectious complications in children with acute myeloid leukemia from presentation to the healthcare system to initiation of chemotherapy and to describe how these infections differ depending on neutropenia.

Methods

We conducted a retrospective, population-based cohort study that included children and adolescents with acute myeloid leukemia diagnosed and treated at 15 Canadian centers. We evaluated infections that occurred between presentation to the healthcare system (for symptoms that led to the diagnosis of acute myeloid leukemia) until initiation of chemotherapy.

Results

Among 328 children, 92 (28.0%) were neutropenic at presentation. Eleven (3.4%) had sterile-site microbiologically documented infection and four had bacteremia (only one Gram negative). Infection rate was not influenced by neutropenia. No child died from an infectious cause prior to chemotherapy initiation.

Conclusion

It may be reasonable to withhold empiric antibiotics in febrile non-neutropenic children with newly diagnosed acute myeloid leukemia until initiation of chemotherapy as long as they appear well without a clinical focus of infection. Future work could examine biomarkers or a clinical score to identify children presenting with leukemia and fever who are more likely to have an invasive infection.