Proliferations of cyanobacteria have detrimental effects on ecosystem functioning, and on the global freshwater food chain. Many studies have focused on the “in situ” dynamics of bloom-forming cyanobacteria, including Cylindrospermopsis raciborskii and Planktothrix agardhii. Few have used experimental assays to explore the fast-growing ability of naturally co-occurring species. Here we investigated the growth of these species when exposed separately (i.e., in monocultures) to a range of light and nutrient conditions, plus their interactive performances in mixed cultures in a short-time experiment (6 days). The use of microplates made it possible to carry out multiple measurements of in-vivo fluorescence (IVF), and to monitor species-dependent biovolumes. No allelopathic effect was significantly observed for any target species, while significantly lower growth rates were obtained in mixed cultures, which may reflect other interference interactions between the species. We showed that Planktothrix grew faster with low light intensity and high nutrient concentrations, and was drastically inhibited by nitrogen deprivation, in contrast to Cylindrospermopsis. However, Cylindrospermopsis outgrew Planktothrix at high NH4+ concentrations, suggesting that this species may be a serious competitor for the native species in many water systems.

Nutrient release from lake sediments may increase concentrations of harmful algal toxins – such as microcystins – by stimulating blooms of toxigenic cyanobacteria. This hypothesis is supported by a series of experiments in which intact cores of sediment were incubated under different environmental conditions, after which the water overlying the sediments was harvested as a culture medium for growing a toxic strain of the common cyanobacterium Microcystis. Both littoral and profundal sediments from Lake Kinneret, the largest freshwater lake in Israel, released substantial amounts of dissolved phosphorus (1.0 and 4.0 mg.m−2.d−1, respectively) and nitrogen (44.2 and 24.3 mg.m−2.d−1, respectively) under simulated summer conditions in the laboratory. In comparison, nutrient fluxes from sediments under simulated winter conditions were considerably smaller or negative. The addition of nutrient-rich overlying water harvested from profundal sediments, and to a lesser extent from littoral sediments, increased both chlorophyll a and microcystin concentrations in Microcystis cultures. In contrast, when Microcystis cells were inoculated in natural surface waters only, the cultures did not grow or produce microcystins, and soon collapsed. This study provides experimental evidence of a link between internal nutrient loading from sediments and microcystin concentrations in freshwaters, and demonstrates how environmental factors may indirectly exert control over toxin concentrations in freshwater lakes.

La dynamique de colonisation par les Macroinvertébrés de substrats artificiels déposés dans un cours d'eau est étudiée dans ce travail. Les différentes techniques mathématiques et statistiques utilisées (indice de diversité, équitabilité, analyse factorielle, etc.) indiquent que cette colonisation peut se diviser en deux périodes. Une première période de colonisation active où les effectifs des espèces colonisatrices fluctuent rapidement d'un jour à l'autre et aussi d'un prélèvement à l'autre ; une deuxième période, environ 15 jours après le début de l'expérience, où les variations observées sont d'amplitude plus faible.

Pour caractériser l'état d'un écosystème aquatique contaminé par des toxiques il est nécessaire de développer des méthodesd'évaluation des impacts écotoxicologiques, basées à la fois sur l'étude de réponses physiologiques et sur la structure des communautésvivant dans cet écosystème. La méthode PICT (Pollution-Induced Community Tolerance) proposée par Blanck et al.(1988), répond à ces deux critères. Elle est fondée sur l'hypothèse qu'une communauté biologique naturelle est constituée dedifférents «composants» ayant des sensibilités variables vis-à-vis d'un toxique donné. Ainsi, suite à une exposition à un toxique,les organismes les plus sensibles ne sont plus concurrentiels et sont remplacés par des organismes plus tolérants. La communautérésultante présente alors une tolérance vis-à-vis du toxique, supérieure à celle observée pour une communauté semblablemais n'ayant pas connu de pression de sélection par ce toxique. Cette différence de réponse peut donner une indication sur l'étatde pollution des milieux dans lesquels ont été échantillonnées différentes communautés. Le choix du test physiologique pourévaluer la tolérance de la communauté est fondamental car la réponse dépend d'une part, du mode d'action du toxique et d'autrepart, des mécanismes à l'origine de la tolérance de la communauté. Il existe peu d'outils de bioévaluation des milieux naturelssoumis à des contaminations toxiques, et cette méthode mérite donc d'être développée. Des travaux appliquant la méthode PICTà des communautés variées et dans divers milieux, permettraient de valider la méthode et de résoudre certains problèmes, quantà la détection de la tolérance. Le développement de méthodologies nouvelles pour caractériser la structure et la tolérance descommunautés étudiées est fondamental pour progresser dans nos connaissances sur le risque écotoxicologique.

Although the data on phosphate obtained in surveys are used to assess the distribution of river biota, the approach is flawed when the organisms use P fractions not included in routine analysis. This is especially important where aquatic phototrophs are partially or largely dependent on aqueous organic phosphate. This paper reports a study where the data are sufficient to assess the quantitative importance of organic phosphate in rivers in eastern UK. Filterable hydrolyzable phosphate-P (FHP) is used as a surrogate for organic phosphate, although FHP sometimes includes other P forms. Eighteen sites were sampled weekly for at least one, but mostly three years (2033 samples). The data are compared for mid- and lower-reach sites. FHP formed at least 20% TFP (total filterable phosphate-P) at 14 sites, with the percentage values higher at the more upstream and more northern sites. FHP exceeded 1000 μg.L−1 P in 32 mid- and 53 lower-reach records. The lower the TFP concentration, the higher the % FHP at both types of site. Five sites had over 25% of their records where FHP is likely to be especially important for growth of algae and bryophytes, based on FHP being >50 μg.L−1 P when TFP ≤200 μg.L−1 P. These include the upper site on River Swale, and other literature for this river indicates that FHP becomes increasingly important further upstream and even more so in tributary streams. FHP should be included in monitoring programmes for upland rivers, especially where the catchment includes peat-rich soils.

The paper presents a description of the hitherto unknown larva of Drusus nigrescens Meyer-Dür, 1875. Information on the morphological and genetic identification of this species is given, and the most important diagnostic features are illustrated. Its systematic position within the genus Drusus is affirmed and some zoogeographical and ecological notes are added.

Raphe-like vestiges have been found regularly in two new taxa which presumably belong to Fragilaria, one of them livingin several lakes of the Kerguelen Islands, the other in the Yellowstone National Park, Wyoming, U.S.A. The latter onepossesses septa-like elements as integrated parts of a girdle band. Other septa-like elements can occur in different speciesof Fragilaria. They represent appendices of the valvocopula, located beneath the transapical costae. Structures like linkingspines on marginal parts of the valve face occur in an Achnanthes species. Most of these characters seem to havebeen unknown in these taxa until recently.

A key to identify the known mature larvae of the South American genera of the family Elmidae is provided. The key includesseven genera presently assigned to the subfamily Larainae and 15 genera assigned to the subfamily Elminae. New distributionaldata for all genera and a checklist of described larvae are also included. The mature larva of Macrelmis saltensis Manzo isdescribed and illustrated for the first time, and compared to other known larvae of the granigera species-group. Distributionalnotes for M. saltensis increase its known range to the north, this being the first citation of the species for Bolivia. Macrelmis isis(Hinton) is also cited for the first time for Bolivia.

The structure and composition of the bacterial community associated with buoyant Microcystis colonies were monitored during the decline of a cyanobacterial bloom (from October 13, 2009 to January 27, 2010). When temperature decreased, the ratio between the colony-associated bacteria and the Microcystis gradually decreased as estimated by a quantitative real-time polymerase chain reaction (qRT-PCR)-based approach. Diversity of bacterial communities was determined through denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments. Cluster analysis of the DGGE profiles showed that most of the bacterial communities associated with Microcystis colonies collected on the nearby dates were clustered together. The bacterial clones from four clone libraries in different months were classified into 5, 12, 6 and 12 operational taxonomic units, most of which were affiliated with Gammaproteobacteria, Alphaproteobacteria and Bacteroidetes. Shift in dominance from pathogenic Aeromonas sp. to Shewanella sp. capable of remineralization of many organic materials was observed, and both species seemed to be associated with Microcystis colonies along with the bloom decline. These results indicated that the potential harmful effects of the Microcystis bloom on the safety of lake water during the decline period should be taken into account.

Zooplankton samples collected at low and high water in 14 and 21 stations respectively along some 900 km of the Orinoco and its Delta, revealed the presence of 100 rotifer and 48 cladoceran taxa. Of these, only 13 rotifer and 8 cladoceran species were frequent and numerically important, mainly Keratella americana, Lecane proiecta, Ploesoma lenticulare, Polyarthra vulgaris, Bosmina tubicen, Bosminopsis deitersi, Diaphanosoma birgei and Moina minuta. Nauplii were dominant among the copepods. At low water, rotifers were by far the most abundant group (mean 49 org./l ) followed by cladocerans (mean 2.8 org/l) and copepods (1.5 org/l). At high water, rotifer densities declined to a mean of 3,5 org/l, followed by copepods (mean 3.4 org/l) and cladocerans (1.2 org/l). Mean zooplankton densities at low water were eight times higher than at high water. At low water, longitudinal zooplankton densities seemed to be influenced by tributary river waters. At high water, densities were generally low up to the Delta where a longitudinal increase was observed. A high proportion of egg carrying cladocerans, particularly B. tubicen, B. deitersi and M. minuta, were observed at low water along the sampling sites, suggesting an ability of the species for growth and reproduction in the river.

We studied the effect of point-source and non-point-source pollution on the retention capacity of the stream and its link with the metabolic state (primary production and respiration) and invertebrates assemblages in a third order Mediterranean stream. Two experimental sites were chosen: one in the upper part of the catchment (Montégut site) characterized by low concentrations in nitrate and phosphate and one in the lower part of the catchment (Lézat site) characterized by high nitrate and phosphorus concentrations. Both experimental sites were located on reaches that included a Waste Water Treatment Plant (WWTP) point nutrient source allowing discussion of the relative effects of point-source and non-point-source nutrients loads on ecosystem function (respiration and uptake rates) and aquatic organism assemblages. NH4 +-N, and PO4 3 −-P uptake rates were determined using solute additions conducted at constant rates (short-term nutrient addition procedure) and NO3 −-N uptake rates were determined using instantaneous solute addition (slug addition procedure). Rates of gross primary production (GPP) and ecosystem respiration were determined using the open system, two-stations diurnal oxygen change method. Benthic invertebrate communities were investigated for species and functional feeding groups diversities measurements. Results show that autotrophy in the river results from nutrients of two distinct origins: point sources for phosphorus (urban area and WWTP) and non-point sources for nitrogen (agricultural zones) with local additions from WWTP inputs. Comparison between the two sites shows that the WWTP did not affect uptake rates, respiration or primary production of the ecosystem in the low-nutrient Montégut reach despite increase of invertebrates communities biomass density. Inputs from the WWTP, in the high nitrate and phosphate Lézat reach, increased respiration, lower benthic biomass and led to changes in the species composition and did not affect uptake rates.

Les Ciliés sont une composante importante du nano- et du micro-plancton des eaux stagnantes, mais peu d'attention a été portésur la part qu'ils pouvaient prendre dans les eaux courantes. Nous avons réalisé, de juin à octobre 1996, une étude bimensuelledes Ciliés du potamoplancton de la Loire moyenne, comparativement à l'examen des algues et des Rotifères qui abondent certainesannées en étiage, dans cette partie du fleuve. Deux sites, situés en ordre 8, respectivement à 550 km et à 640 km de la sourcedu fleuve, ont été échantillonnées.Les augmentations de la teneur en oxygène dissous, des matières en suspension, de la DBO5 et des teneurs en chlorophylle a,associées à la baisse de la teneur en éléments nutritifs, sont typiques des eaux eutrophes. La communauté algale, dominée par lesChlorophytes et les Bacillariophytes, atteint son maximum de développement fin juillet (avec respectivement 40.106 cell.l-1 et70.106 cell.l-1 du site amont au site aval). Les Ciliés, dominés par les Oligotriches et les Péritriches ont leur maximum de densitédeux semaines plus tard (respectivement 6.200 cell.l-1 et 14.340 cell.l-1). La densité maximale des Rotifères dominés par lesBrachionidés et les Trichocercidés, est observée simultanément à celle des Ciliés (respectivement 3610 ind.l-1 et 1780 ind.l-1) ;contrairement aux années antérieures, elle est plus faible en aval, ces organismes ayant réagi aux perturbations induites par lestravaux réalisés sur le site aval.Comme dans les milieux stagnants, dans cette partie eutrophe de fleuve, la matière organique disponible favorise le développementde Ciliés et de Rotifères consommateurs d'algues et de bactéries. Le rapport hétérotrophes / autotrophes, exprimé en carbone,passe de 0,34 en amont à 0,17 en aval ; il illustre le rôle régulateur des Rotifères filtreurs, dont la régression en aval attribuéeaux travaux de terrassement et amplifiée par la prédation invertébrée, a favorisé le développement des Chlorophycées. Labiomasse en carbone des Rotifères est supérieure à celle des Ciliés, mais, en fin d'été, ces derniers jouent un rôle important dansles transferts d'énergie au sein de cet écosystème fluvial.

We assessed the effect of small dams on stream habitats and on the structure and function of benthic macroinvertebrate communities in mountain streams of Córdoba, Argentina. Two streams with small dams (impacted streams) and two streams without dams (control streams) from the Carcarañá River upper sub-basin were selected. Dominant hydraulic units were identified and benthic samples were collected in each of these units during high and low water periods. According to this study small dams may have impact on the function and structure of the invertebrate community, though hydraulic habitats would not be affected. Fourteen hydraulic units were found and changes due to dams were not observed as assessed by the detrended correspondence analysis. The canonical correspondence analysis grouped samples mainly in relation to hydraulic habitats whereas TWINSPAN grouped samples according to the presence of dams. Nested ANOVAs showed changes in richness and diversity, in the abundance of filterers and shredders and in the abundance of certain species. Small dams generate quite small reservoirs and their permeability may be greater than those of large dams. The behaviour of macroinvertebrate populations in drift and colonization processes, the continuity of the riparian structure and the discharge of planktonic algae downstream the dams may be some factors determining the ecological changes produced by small impoundments.

A meeting held in Toulouse, France, from 23rd to 25th February 2006 and co-organised by the University Paul Sabatier ToulouseIII & CNRS (France), Pôle Relais Mares et Mouillères de France (France), University of Applied Sciences of WesternSwitzerland (Switzerland), University of Geneva (Switzerland), Pond Conservation (UK), University of Leuven (Belgium).

The biomass and the biochemical composition of periphyton were studied during one year in three streams of Réunion Island. The results revealed that nutritional conditions for fish development were most favourable during the dry season. The nutritive value of periphyton was highest in the Marsouins and Mât streams and remained the lowest in the Roches stream. Food availability was strongly affected by high flow, particularly during the exceptional hydrological events of February 1998 (cyclonic high flows). Study of seasonal variations of morphophysiological characteristics and biochemical composition (lipids, proteins) of the grazer gobiidae Sicyopterus lagocephalus showed that inspite of unfavourable nutritional conditions caused by hydrological disturbances, fish continue their reproduction which coincides with the summer high flow period. The significant depletion of lipid reserves which express a deterioration in animal condition is influenced by flooding period. At this time of gonad development involving an additional energy investment, fish were not able to recover a stable nutritional state after the complete achievement of the reproduction cycle. Except during this period, there is a weak participation of the reproductive physiological processes in the seasonal changes of somatic composition of this fish.

Le peuplement des Harpacticides du milieu hyporhéique du ruisseau de Lachein (Pyrénées) a été étudié pendant un an sur un site de 75 m2. 21 espèces dont 9 stygobies ont été recensées. Ce peuplement est caractérisé par sa stabilité dans le temps puisqu'aucune variation saisonnière importante n'a pu être mise en évidence entre les sept séries de prélèvements réalisées. En revanche, ce peuplement présente une forte hétérogénéité spatiale : quatre groupements ont été reconnus dont la répartition se superpose aux différentes unités physiographiques définies par les écoulements de surface : bancs de graviers, chenal, zone d'eau morte. Les bancs de graviers constituent le milieu de vie préférentiel des Harpacticides: à cet endroit, les formes hypogées dominent les espèces épigées qui sont repoussées à la périphérie des bancs. Les conditions hydrodynamiques au sein du milieu hyporhéique permettent d'expliquer ce type de distribution. En effet, ce sont les zones où la perméabilité est la plus élevée qui abritent les populations les plus abondantes et les plus riches en espèces. Toutefois, ces zones ont une diversité spécifique plus faible en raison des phénomènes de compétition inter-spécifique.

Nitrogen dynamics were investigated in the top centimeters of bottom sediment in three different geomorphologic units(riffles, sand bars, pools) and along two contrasted reaches (nitrogen-rich, nitrogen-poor) of a rural stream. Some predictionsof links between geomorphology and processes were verified: (i) hydrological exchanges and nitrification were lower in poolsthan in riffles and bars, whereas (ii) ammonification and denitrification were higher in pools. Studies of denitrification potentialin six other reaches of three N-rich streams support these conclusions and demonstrate that pools are spots of high microbialactivity in streams.

The aim of this work was to evaluate the potential of aquatic macrophytes as biological indicators of the environmental conditionsof rivers in north-eastern Spain. To this end, twenty five river basins were studied to assess the species composition andabundance of macrophytes, and to examine their relation with different geographic, morphometric, mineralization, and trophicstatus parameters. Of the twenty six macrophyte species found, five appeared to be useful as biological indicators of the environmentalconditions of the rivers. L. minor was a good indicator of high mineralization (i.e., conductivity and Cl-) and high trophicstate (especially, N-NO2 -). C. stagnalis was a good indicator of high P-PO4 3- concentrations. P. crispus, P. polygonifolius,and R. penicillatus seemed to be useful indicators of high N-NO3 - concentration. We conclude that, in our study area, aquaticmacrophytes can indeed be used as biological indicators of the environmental conditions of rivers.

We studied assemblages of littoral chironomids from three alpine lakes in the High Tatra Mountains (Slovakia) along an altitude range of 1725–2157 m. The study sites were selected in order to emphasize differences in their thermal regimes. Littoral samples were taken quantitatively in the ice-free seasons of 2000 and 2001. In total, 3468 chironomid larvae and pupae were collected and 32 taxa were identified. Some parameters of the littoral chironomid assemblages showed clear patterns along the altitude gradient. The number of taxa and Shannon diversity increased markedly with decreasing altitude. Density, however, did not show any correlation with altitude. Even though gatherers highly dominated in all sites, their relative abundance decreased with decreasing altitude. The ratio of scrapers and predators correlated negatively with altitude. According to the results of a Detrended Correspondence Analysis, Pseudodiamesa arctica and Micropsectra radialis were chosen as indicator species for alpine lakes >2000 m a.s.l. Typical subalpine lake inhabitants are Zavrelimyia sp., Prodiamesa olivacea, Corynoneura scutellata group, Cricotopus polaris, Micropsectra bavarica and Paratanytarsus austriacus. A single species, Micropsectra junci, seemed to be characteristic of alpine lakes <2000 m a.s.l. This “gradient lake concept” could be used to predict changes in mountain lake fauna under expected climate change scenarios. Generally, an upward shift of subalpine species would be expected. The thermal regime of lakes, however, also depends on several local factors. Consequently, the schemes outlined here would not be valid for the entire Tatra lake district.