Empirical models were established, which link the biomasses or productions of the successive planktonic trophic levels in lakes of different depth and trophic status. Published data on 56 lakes were analysed, using both least-square and reduced-major-axis regressions. Reduced-major-axes regression technique was used in order to take into account variability due to both bottom-up and top-down forces. In shallow lakes, the energy transfer efficiency between phytoplankton and zooplankton decreases with increasing trophy. An inverse tendency appears in deep lakes. However, when considering only the oligo- and mesotrophic temperate lakes, the mean primary and secondary productivities per unit of area are about the same in shallow and in deep sites. On the other hand, shallow water bodies are characterized by a smaller mean size of the crustacean species, a lower mean biomass of zooplankton and a higher P zoo/B zoo ratio than deep lakes, probably as a response to the predation by fish. While the consumers seem to have a strong influence on the size structure and biomass of plankton, the energy flows between the trophic levels could be largely controlled by bottom-up forces.

Blooms of toxic cyanobacteria became a common feature of temperate lakes and ponds owing to human induced eutrophication. Occurrence of cyanobacterial blooms in an urban context may pose serious health concerns. This necessitates the development of tools for assessment of the risk of noxious bloom occurrence. A five year study of 42 Brussels ponds showed that cyanobacteria have threshold rather than linear relationships with environmental variables controlling them. Hence, linear relationships have limited predictive capacity for cyanobacterial blooms. A probabilistic approach to prediction of bloom occurrence using environmental thresholds as conditions in conditional probability calculation proved to be more useful. It permitted the risk of cyanobacterial bloom occurrence to be quantified and thus the conditions and thence the ponds the most prone to cyanobacterial bloom development to be singled out. This approach can be applied for the assessment of the risk of cyanobacterial bloom occurrence in urban ponds and thus can facilitate monitoring planning, remediation efforts and setting restoration priorities.

Species richness of macrophytes of artificial and natural water bodies covering rivers, streams, canals and habitats with standing water was studied in two Central European biogeographical regions, Pannonian and Carpathian, represented by two model areas (the Borská nížina Lowland and the Turčianska Kotlina Basin). We found that: (i) the total number of macrophytes was higher in artificial water bodies compared to natural aquatic habitats in both regions and differences were statistically significant (P<0.05); and (ii) species richness of macrophytes is relatively low in both regions; slightly higher mean number was found in the Pannonian region (3.53) compared with the Carpathian region (3.06). Effects of environmental characteristics on species richness studied by generalized linear model (GLM) showed that explained variances of GLM were similar in both regions. The main drivers of the diversity pattern were those connected with the hydrology of water bodies, such as substrate characteristics and turbidity, less frequent were chemical characteristics, such as water conductivity and N-contents, whereas landscape characteristics manifested the smallest impact.

One of the agro-environmental characteristics of Brittany is the extensive use of pesticides, which leads to high concentrations of atrazine in continental water systems. Periphytic algae play a basic part in aquatic ecosystems and some of them, diatoms, are highly sensitive to environmental changes. Analyses of diatoms can thus indicate the impact of a herbicide on aquatic systems. We compared the effects of two herbicides (atrazine and nicosulfuron) on an aquatic ecosystem in 1998. This study was conducted in 15 identical ponds, each containing a holder for installing artificial substrates. The periphytic diatoms were analysed for cell density, biomass, species diversity and morphology. The general specific diversity was poor, and the diatom community was essentially dominated by Achnanthidium minutissimum. The first results showed a strong similarity between the different categories of mesocosms. Chlorophyll a concentration only seems to be affected by high herbicide concentrations.

Performance of the prescribed gear of the European Standard (i.e. 1.5 m deep Nordic gillnet) was compared with gillnets deep enough to cover the whole water column (WWCG) for characterizing fish assemblages in a large and shallow lake (Lake Balaton, Hungary). Differences in species number, relative abundance and biomass, and length distribution of fish were examined in both inshore and offshore habitats of the lake. Nordic gillnet samples provided comparable information to that of WWCG for both species richness and abundance and biomass of benthic species. However, substantial differences were found between the two net types in the representation of pelagic fish species (i.e. bleak, razor fish and asp). Overall, the WWCG provided different information with more precise (less variable) data on fish assemblage structure than the Nordic gillnet. Results suggest that identification of neither horizontal nor vertical gradients in within lake fish assemblage structure can be guaranteed with the Nordic gillnet alone even in such shallow lakes, like Lake Balaton. It was concluded that benthic Nordic gillnet samples should be complemented with information on fish occurring in the upper water layers (i.e. pelagic species) even in very shallow lakes either by using pelagic or floating gillnets or by whole water column gillnetting.

Cet inventaire des diatomées d'eau douce des îles Kerguelen (Grande Terre) a été réalisé à partir de prélèvements effectués sur 31 stations représentant divers milieux : ruisseaux, rivières, lacs, rochers suintants. Dans la présente note, 279 taxons ont été déterminés, dont 3 sont considérés nouveaux pour la science. La plupart des espèces et variétés recensées ont une large répartition géographique ; l'endémisme est restreint. De nombreuses espèces sont représentées seulement par quelques individus. Si les Pennales présentent une large gamme de genres et d'espèces, il n'en est pas de même pourles Centrales, non seulement du point de vue diversité, mais également du point de vue abondance (à l'exception de Melosira distans).

En raison de la nature particulière des cours d'eau de son bassin, l'Agence de l'Eau Artois-Picardie a adopté en 1988 les diatomées et les indices diatomiques pour l'estimation de la qualité biologique de l'eau. Six indices ont été testés. Les résultats montrent que l'IPS ou Indice de Polluosensibilité Spécifique (Coste in CEMAGREF 1982) est le seul à donner une évaluation réaliste de la qualité des eaux. Cet indice intègre en effet des phénomènes tels que la pollution organique exprimée par la DBO5, la DCO ou l'ammonium, la salinité exprimée par la conductivité et les chlorures ou encore l'eutrophisation qu'elle soit réelle et exprimée par la chlorophylle ou potentielle et exprimée par les phosphates. Ces trois phénomènes sont les principaux facteurs responsables de la variation de la qualité des eaux dans le bassin. Par ailleurs, les conditions physicochimiques étant particulièrement stables tout au long de l'année, les indices diatomiques calculés en septembre sont représentatifs de la qualité estivale des eaux. Différentes simulations ont été effectuées, à l'aide du logiciel OMNIDIA, en vue de la mise au point d'un indice pratique fiable applicable en routine. Les résultats montrent que la meilleure approche consisterait à travailler au niveau générique avec parfois des déterminations à l'espèce.

The biomass and composition of the phytoplankton was studied at seven sampling stations located at different water bodies (open water, inner pond and canal) of a large, shallow turbid lake (Lake Fertő, Neusiedlersee). The open water was characterized by picocyanobacteria and meroplanktonic diatoms, the artificial canal by epiphytic diatoms, cryptophytes and chlorophytes. The inner ponds, based on the phytoplankton composition, were positioned between these water bodies. High picoplankton abundance (>106 cells.mL−1) and predominance (up to 80% contribution to the total phytoplankton biomass) were detected in the open water and the inner ponds, which was hypothesized to be the result of the turbid environment by the suppression of the top down control and by light-limitation. Information on the diversity of the picoplankton in the open water of the lake has been presented first time in this study. Based on molecular analysis (16S rRNA gene and cpcBA-IGS region) the dominant group of picocyanobacteria belonged to the Cyanobium gracile cluster (group A) of the picophytoplankton clade in April. Members of two other picocyanobacterial groups (group B and C) were also detected.

We assessed the effects of land use on the structure of stream fish assemblages in Northwest Patagonia, Argentina. To this end, a total of 18 sites distributed in 15 streams were sampled during the low water period. At each site, 26 regional and local scale variables were used to describe the environmental conditions. The macroinvertebrate density, and the composition and abundance of fish were then recorded. Statistical associations between local assemblage structures and environmental variables were quantified by canonical correspondence analyses. The results revealed that, at a regional scale, the fish assemblages were primarily determined by watershed features like altitude and catchment area, and by land use effects (exotic forest and pasture). Assemblage compositions were also related to some local-scale features such as water velocity, food availability (density of benthic macroinvertebrates), instream characteristic and riparian features. Also, the observed fish species richness was low. Overall, exotic salmonids largely dominated in the samples both in numbers of individuals (98.9%) and in biomass (99.9%), whereas native fish (Hatcheria macraei and Odontesthes hatcheri) were scarcely represented. Rainbow trout (Oncorhynchus mykiss) was the most abundant fish, and was present in all streams. Native species were restricted to five streams located in the ecotone between the Andes and the steppe, where salmonids were also present. Salmonids were the only fish at Andean streams which suggest the existence of a strong geographic segregation between native and exotic species. Some aspects related to the incidence of the introduced species in the structure of fish assemblages are discussed.

Les étangs centraux de la Camargue (Vaccarès et Etangs inférieurs), couvrent une grande surface (environ 110 km2) mais sont peu profonds (un mètre en moyenne). Ils constituent une unité hydraulique à niveaux et à salinités variables dans l'espace et dans le temps. Niveaux et salinités évoluent en fonction de paramètres climatiques, de l'action de la mer et, surtout, des activités humaines.Au cours des cinquante dernières années, le système d'étangs a connu plusieurs bouleversements aux conséquences importantes sur le plan écologique :

- avant 1950, le bilan hydrique dépend essentiellement des pluies et de l'évaporation. L'amplitude saisonnière des salinités (en moyenne élevées) et des niveaux (en moyenne bas) est très forte ;

- de 1950 à 1978, l'apport massif d'eau douce estival (riziculture) renforçant l'action d'années pluvieuses, provoque l'élévation des niveaux moyens, le dessalement du système (4 g/l à la mi-1978) et le tassement de l'amplitude des variables sel et eau ;

- de 1979 à 1985, l'apport massif d'eau de mer (vétusté de la digue littorale, "valorisation" des pêcheries en étangs) et la diminution des apports d'eau douce (années sèches, déclin de la riziculture) provoquent le maintien de hauts niveaux et une forte augmentation de la salinité du système (35 g/l à la mi-1984). L'amplitude des variables sel et eau reste faible.

- en 1986, 1987 et 1988, de fortes pluies provoquent la crue hivernale et le dessalement des étangs. Le dessalement se poursuit en 1991.

A l'échelle pluridécennale, les changements de salinité sont induits par des variations du stock de sels dissous dans le système d'étangs. Le présent travail se propose d'analyser la dynamique et de quantifier ce stock au cours des cinquante dernières années. Le stock tombe de quelque 3 millions de tonnes avant la riziculture à 600 000 tonnes en 1978, puis il s'accroît de plus de 3 millions de tonnes de 1979 à 1985, et baisse de 2 millions de tonnes de 1986 à 1991. Les variations en moins sont provoquées par les hémorragies de sels qui accompagnent la vidange à la mer du trop-plein des étangs en crue par les vannages de la digue littorale. Les variations en plus sont le fait d'apports d'eau de mer ou d'eaux souterraines salées.

The assemblage patterns of pelagic Cladocera species were investigated in a meso-eutrophic reservoir from January 2000 to December 2002. Trends of environmental factors (water temperature, conductivity, pH, and nutrient concentrations), as well as of biotic factors (availability of potentially edible phytoplankton and densities of herbivorous and carnivorous copepods) were assessed. Zooplankton community was dominated by Cladocera and Copepoda. Assemblage patterns for Cladocera were identified by performing a cluster analysis on abundance data of the dominant species: Daphnia longispina, Ceriodaphnia pulchella, Bosmina longirostris and Diaphanosoma brachyurum. In winter and spring, Daphnia was dominant. In early summer and end of autumn, Ceriodaphnia and Daphnia coexisted. During summer, Ceriodaphnia was dominant and coexisted with Diaphanosoma. Bosmina was present in low densities during the whole study period. Cladoceran populations exhibited non-synchronous peaks of abundance, evidencing different ecological optima. Temperature seemed to be the main structuring factor of this assemblage. The way biotic interactions influenced pelagic cladoceran assemblage in this reservoir was not clear and needs further research.

We studied the Cladocera in four shallow brackish lakes at El Hondo and Salinas de Santa Pola in Mediterranean Spain fromFebruary 1999 to June 2000, sampling each month. We recorded five species : Daphnia magna, D. pulex, D. longispina,Simocephalus exspinosus and Moina brachiata. D. magna was the most abundant species and the only one present all yearround. Total abundance of Cladocera varied significantly between wetlands and months, and was highest in the largest, deepest,least saline wetlands. For a given wetland and month, abundance increased at points of greater depth or lower salinity. Speciesrichness of Cladocera was highest in those seasons and lakes where salinity was lowest, and in those seasons and lakes wherecladoceran abundance was highest. These wetlands hold a particularly high number of waterbird species, but a very low numberof Cladocera species. Ready dispersal via waterbirds does not appear to promote cladoceran diversity in this system, owingto local conditions such as high salinity. We suggest that the conservation value of wetlands for birds is not a good predictor ofvalue for Cladocera.

Corbicula fluminea, is one of the most successful invasive species in fresh and brackish waters. Dispersal is one of the most determinant steps in the invasive process, and the full understanding of the mechanisms involved in this step is critical for adequate pest management both in the wild and in industries affected by this species’ biofouling activity. A mucous drogue line produced by mucocytes packed along the inner demibranchs of the clams’ gills seem to play an important role in assisting drifting and hence dispersal. Two Asian clam populations geographically separated (one in the USA and the other in Portugal), investigated at different times of the year, were reported to differ in terms of mucous drogue line production and floating. In this study, genetics and seasonality effects were hypothesized to explain the difference between the populations. To test these hypotheses, the two populations were genetically compared, and the Portuguese one was followed for 14 months to record the animals’ mucous drogue line production and flotation capabilities and locate the population reproductive periods. Our results signal a possible scenario of microevolution with consequences on the production of the clams’ mucilaginous drogue line. Although some authors advocate a link between mucous threads formation and reproduction events, such a relationship was not observed in this study. By contributing to the understanding of a physiological trait of the Asian clam that is important for dispersal, this study may be of practical relevance for pest monitoring and control.

The river Nile is the main source of drinking water in Egypt. Nutrient loading coupled with year-round warm weather favor the growth of cyanobacteria, several of which can produce cyanotoxins, especially the potent liver toxins called microcystins. Most microcystin resides inside or closely attached to cyanobacteria cells, and are released into the water column as cells lyse from senescence or chemical treatment. The present study evaluated microcystin levels, as measured by immunoassay (ELISA), in both raw and finished drinking water of the river Nile, during the warm season (May-October), near the drinking water intake for Sohag City, Egypt. The results showed that microcystin content within the cells correlated better with type of microcystin-producing cyanobacteria (Gomphosphaeria, Microcystis, Oscillatoria) rather than chlorophyll a. Microcystin concentration in cell-free water correlated significantly with that measured within the cells, with maximum values being recorded in September (0.4-0.78 µg l-1). Microcystin levels in the finished drinking water were low (56.1- 87.1 ng l-1) and were detected only in May and June. The study indicates that microcystin is present in the raw and finished drinking water at Sohag City but that levels did not exceed the World Health Organization (WHO) drinking water guideline level of 1µg l-1 during May-October 1999.

In Morocco, poisoning events of fish, aquatic birds and livestock have been observed in some reservoirs and shallow lakes. In all cases, the reasons for animal mortality reasons have not been confirmed and the toxic cyanobacteria strains that were abundant in these water bodies have been suggested as their cause. Since 1994, the authors started taxonomic, ecological and toxicological studies by collecting samples from various lakes reservoirs and ponds. The results show that more than 18 out of 26 lakes reservoirs used for human water supply contained at least one species of planktonic cyanobacteria, where the genus Microcystis was dominant (Microcystis aeruginosa f. aeruginosa, M. aeruginosa f. flos-aquae, M. ichthyoblabe, M. pulverea f.delicatissima) and was associated with Oscillatoria, Planktothrix, Anabaena, Aphanizomenon, Phormidium and other genera. Taxonomic studies shows that among more than 150 cyanobacteria taxa identified in Moroccan freshwater ecosystems, 35 are potentially toxic. For several species, the toxicity of both natural blooms and isolated strains lyophilized material was confirmed by mouse bioassay and the microcystins content evaluated by the Enzyme-linked immunosorbent assay (ELISA). A map of geographicdistribution of Microcystis strains inventoried in moroccan water bodies is presented.

The mid Tafna wadi (N-W Algeria) is exposed to several man induced disturbances including urban, industrial, and agricultural effluents, and alteration of the natural flow regime. The recent installation of a reservoir upstream of the study area has strongly modified the flow regime by extending the period of low water level, and this stream section is only occasionally fed by water releases. Investigations on the hyporheos and benthos of this stream have allowed the comparison of densities, taxa richness and diversity, during three hydrological periods (natural high water, low flow and reservoir water releases), with the aim to highlight effects of the reservoir management on downstream hydrosystems. Species richness and abundance of stygobite crustaceans were low in the hyporheos. Surface water Crustaceans represented 53% of the overall fauna, with Cyclopoidae composing 50% of the Crustaceans. The dominance of the Cyclopoidae was also observed in the hyporheos. Daphniidae were more abundant (37%) in the benthic habitat than in the hyporheic zone. The alternation of high and low discharges appeared to affect the hyporheos more than the benthic communities. The stability concept of the hyporheic habitat does not fit with our results showing a great range of spatial (mosaic habitat) and temporal changes according to the flow regime.

A method for measuring NH3 colorimetrically by Nesslerization without distillation is proposed. Precipitation of CaCO3 is prevented by adding Na salicylate, which chelates the Ca2+, but not the Hg2+ of Nessler's reagent. NO3 - can be measured in the same way after reduction with TiCl3. Precision and accuracy are those of a colorimetric method ; the sensitivity is somewhat lower than with the indophenol-blue method using phenol, but about the same as when using salicylate.

A scale of sensitivity of mollusc species to biodegradable pollution was proposed in a previous paper (Mouthon 1996). Using these results as a basis, and introducing supplementary elements in a correspondence analysis, we have been able to formulate a scale of sensitivity of mollusc genera and families. A quantification of information lost when using genus or family-level rather than species-level identification was carried out by calculating the Euclidean distances between each species and the gravity centre of the genus and family to which it belongs. The results obtained showed that the genus-level identification can constitute an acceptable compromise for using molluscs as water quality indicators in biomonitoring.

Les deux espèces Gammarus pulex et G. fossarum montrent des différences spécifiques d'ordre physiologique. Des animaux d'une même station placés dans des conditions expérimentales strictement identiques présentent des courbes métabolisme/température différentes. G. pulex serait « adapté » à des températures moyennes (15-20° C) avec des possibilités d'ajustement aux températures extrêmes (5 et 25° C). G. fossarum serait « adapté » à des températures plus basses (5-10° C) avec des possibilités d'ajustement limitées dès 20° C. Ces particularités physiologiques permettent d'expliquer la cohabitation fréquente de ces espèces dans des conditions écologiques moyennes, leur répartition géographique actuelle, et peut-être même les conditions de leur formation.

Chironomid assemblages collected from seven different streams in South Korea were investigated. The subfamily composition of chironomids was clearly differentiated accross different levels of organic pollution. Species abundance distributions (SADs) of chironomid communities were compared with the total macroinvertebrate communities across different levels of pollution. The number of species with minimal range of abundance was lower in SADs for chironomid communities compared with total communities. The log normal distribution was accepted for both total and chironomid communities, while the geometric series was relatively more suitable for chironomids and the log series were more fitted to total communities. The a values in the log normal distribution increased in chironomid communities across different levels of pollution, while γ values increased at the polluted sites for both chironomid and total communities. In the Power law analysis, the parameter decreased in chironomid communities. The dominance decay model was more fitted to chironomid communities in clean conditions while random fraction and assortment models were more suitable for the polluted sites.