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International audience; Plankton are a major component of food web structure in aquatic ecosystems. Their distribution and community structure are driven by the combination and interactions between physical, chemical, and biological factors within the environment. In the present study, water quality and the community structure of phytoplankton and zooplankton were monthly investigated from January to December 2015 at 11 sampling sites along the gradient course of the Day River (Red River Delta, northern Vietnam). The study demonstrated that the Day River was eutrophic with the average values of total phosphorus concentration 0.17 mg/L, total nitrogen concentration 1.98 mg/L, and Chl a 54 mu g/L. Microscopic plankton analysis showed that phytoplankton comprised 87 species belonging to seven groups in which Chlorophyceae, Bacillariophyceae, and Cyanobacteria accounted for the most important constituents of the river's phytoplankton assemblage. A total 53 zooplankton species belonging to three main groups including Copepoda, Cladocera, and Rotatoria were identified. Plankton biomass values were greatest in rainy season (3002.10-3 cell/L for phytoplankton and 12.573 individuals/m(3) for zooplankton). Using principal correspondence and Pearson correlation analyses, it was found that the Day River was divided into three main site groups based on water quality and characteristics of plankton community. Temperature and nutrients (total phosphorus and total nitrogen) are key factors regulating plankton abundance and distribution in the Day River.

The equilibrium of inland hydrosystems is presently a cause for concern, with species extinction rates there estimated to be 5 times higher than for terrestrial fauna in the 21st century. Urgent measures must be taken to conserve these ecosystems particularly with regard to fishes, which represent an especially rich and diverse evolutionary heritage. Fishes were long unaffected by human activity on the African continent, but anthropogenic pressure has increased in recent decades. Good management of African continental waters is thus of paramount importance in terms of heritage and economics, as fishes are a vital natural resource for the people in sub-Saharan Africa. In view of biodiversity conservation, African fishes are investigated here as a biological model owing to their enormous ecological and genetic diversity. It is essential to know the ecology and structure of various communities, and to understand the impact of human activity. This book discusses the diversity of environments, the origin and evolution of species, survival and adaptive strategies, the structure of fish communities, and the impact of human activity. It also devotes a section to fisheries and fish culture. This ambitious project summarizes the current state of knowledge on African fishes and their populations, highlighting the mechanisms regulating their equilibrium and the causes contributing to their erosion. It is a reference not just for readers involved in African aquatic environments, but for anyone interested in biodiversity conservation in general.

The authors present an ecophysiological model of the bivalve Cerastoderma edule that simulates individual growth and reproduction under ambient conditions in temperature and food availability in the Oosterschelde estuary, SW Netherlands. The model contains feedback loops in the uptake and metabolism of food and in the partitioning of carbon to the internal state variables: somatic tissue, storage, organic shell matrix and gametes. The model was calibrated for 24 parameters, based on random distributions of parameter values. This procedure includes an estimate of confidence intervals of the output variables. The simulated growth of shell length and animal wet and dry weight reflected the observed values of growth in the field for the period 1993–1997. The model is a tool for the integration of ecophysiological knowledge of this species and also for carrying-capacity studies of shellfish culture and for environmental management of populations in estuarine and coastal areasWe present an ecophysiological model of the bivalve Cerastoderma edule that Simulates individual growth and reproduction under ambient conditions in temperature and food availability in the Oosterschelde estuary, SW Netherlands. The model contains feedback loops in the uptake and metabolism of food and in the partitioning of carbon to the internal state variables: somatic tissue, storage, organic shell matrix and gametes. The model was calibrated for 24 parameters, based on random distributions of parameter values. This procedure includes an estimate of confidence intervals of the output variables. The simulated growth of shell length and animal wet and dry weight reflected the observed values of growth in the field for the period 1993-1997, The model is a tool for the integration of ecophysiological knowledge of this species and also for carrying-capacity studies of shellfish Culture and for environmental management of populations in estuarine and coastal areas. (c) 2005 Elsevier B.V. All rights reserved.

UItleg over een nieuw ecologisch beoordelingssysteem voor brakke binnenwateren, aansluitend bij de al bestaande STOWA-beoordelingssystemen voor andere watertypen. Op grond van het ecologisch functioneren en een geformuleerd ecologisch streefbeeld worden beïnvloedingsfactoren, karakteristieken en maatstaven onderscheiden, waarmee voor verschillende hoofdtypen en subtypen brakke binnenwateren een ecologisch profiel kan worden opgesteld. Zowel het zoutgehalte als de dynamiek blijken belangrijke differentiërende factoren tussen brakwatersystemen; morfologie en voedselrijkdom spelen een ondergeschikte rol

The Zenne River in Brussels (Belgium) and effluents of the two wastewater treatment plants (WWTPs) of Brussels were chosen to assess the impact of disturbance on bacterial community composition (BCC) of an urban river. Organic matters, nutrients load and oxygen concentration fluctuated highly along the river and over time because of WWTPs discharge. Tag pyrosequencing of bacterial 16S rRNA genes revealed the significant effect of seasonality on the richness, the bacterial diversity (Shannon index) and BCC. The major grouping: -winter/fall samples versus spring/summer samples- could be associated with fluctuations of in situ bacterial activities (dissolved and particulate organic carbon biodegradation associated with oxygen consumption and N transformation). BCC of the samples collected upstream from the WWTPs discharge were significantly different from BCC of downstream samples and WWTPs effluents, while no significant difference was found between BCC of WWTPs effluents and the downstream samples as revealed by ANOSIM. Analysis per season showed that allochthonous bacteria brought by WWTPs effluents triggered the changes in community composition, eventually followed by rapid post-disturbance return to the original composition as observed in April (resilience), whereas community composition remained altered after the perturbation by WWTPs effluents in the other seasons., Journal Article, Research Support, Non-U.S. Gov't, SCOPUS: ar.j, info:eu-repo/semantics/published

International audience; The cyanobacterium Microcystis aeruginosa is known to proliferate in freshwater ecosystems and to produce microcystins. It is now well established that much of the variability of bloom toxicity is due to differences in the relative proportions of microcystin-producing and non-microcystin-producing cells in cyanobacterial populations. In an attempt to elucidate changes in their relative proportions during cyanobacterial blooms, we compared the fitness of the microcystin-producing M. aeruginosa PCC 7806 strain (WT) to that of its non-microcystin-producing mutant (MT). We investigated the effects of two light intensities and of limiting and non-limiting nitrate concentrations on the growth of these strains in monoculture and co-culture experiments. We also monitored various physiological parameters, and microcystin production by the WT strain. In monoculture experiments, no significant difference was found between the growth rates or physiological characteristics of the two strains during the exponential growth phase. In contrast, the MT strain was found to dominate the WT strain in co-culture experiments under favorable growth conditions. Moreover, we also found an increase in the growth rate of the MT strain and in the cellular MC content of the WT strain. Our findings suggest that differences in the fitness of these two strains under optimum growth conditions were attributable to the cost to microcystin-producing cells of producing microcystins, and to the putative existence of cooperation processes involving direct interactions between these strains.

Changes in abundances of 0+, 1+ and 2+ age classes of the two most important piscivorous species - asp (Aspius aspius) and pikeperch (Sander lucioperca) in a deep canyon-shaped reservoir were investigated. A long-term fish sampling in the reservoir including fry trawling, fry and adult beach seining and gillneting was used to determine the factors affecting the recruitment. All data were used in a single linear model and the results obtained using different sampling methods were discussed.

The transport and cycling of nutrients through the various pools in water, soil and sediment is controlling the long term and short term productivity of water bodies. An understanding of the size of these pools and the fluxes between them is essential for the assessment of the usefulness of management measures resulting in reduced external input and the anticipated resilience of the system towards changes in trophic character. Large pools, such as phosphorus in surficial sediments and nitrate in groundwater have a potential for prolonged stimulation of productivity. Diffuse sources, fluxes towards sinks, competition between biota and adsorbents for sparse nutrients, feedback mechanisms, non-linearities and shifts among prevailing processes are discussed.

Canonical community ordination comprises a collection of methods that relate species assemblages to their environment, in both observational studies and designed experiments. Canonical ordination differs from ordination sensu stricto in that species and environment data are analyzed simultaneously. Part I reviews the theory in a non-mathematical way with emphasis on new insights for the interpretation of ordination diagrams. The interpretation depends on the ordination method used to create the diagram. After the basic theory, Part I is focused on the ordination diagrams in linear methods of canonical community ordination, in particular principal component analysis, redundancy analysis and canonical correlation analysis. Special attention is devoted to the display of qualitative environmental variables.

International audience; The cyanobacterium, Microcystis aeruginosa, is able to proliferate in a wide range of freshwater ecosystems and to produce many secondary metabolites that are a threat to human and animal health. The dynamic of this production and more globally the metabolism of this species is still poorly known. A DNA microarray based on the genome of M. aeruginosa PCC 7806 was constructed and used to study the dynamics of gene expression in this cyanobacterium during the light/dark cycle, because light is a critical factor for this species, like for other photosynthetic microorganisms. This first application of transcriptomics to a Microcystis species has revealed that more than 25% of the genes displayed significant changes in their transcript abundance during the light/dark cycle and in particular during the dark/light transition. The metabolism of M. aeruginosa is compartmentalized between the light period, during which carbon uptake, photosynthesis and the reductive pentose phosphate pathway lead to the synthesis of glycogen, and the dark period, during which glycogen degradation, the oxidative pentose phosphate pathway, the TCA branched pathway and ammonium uptake promote amino acid biosynthesis. We also show that the biosynthesis of secondary metabolites, such as microcystins, aeruginosin and cyanopeptolin, occur essentially during the light period, suggesting that these metabolites may interact with the diurnal part of the central metabolism.

Seasonnality and variability in rainfall is the principal attribute of Mediterranean-type climate. As a consequence, Mediterranean-type streams exhibit strong seasonnal variability which can lead to extreme conditions of flooding and drying. Large areas of karst geology occur in the Mediterranean region, consequently large amounts of water may be stored in subterranean aquifers ; so, many karstic streams occur in Mediterranean-climate areas. Karstic streams are lotic habitats supplied from underground water in contrast to surface run-off, and this gives them some characteristics quite different from those of other true Mediterranean streams ; mainly, water conditions are more regular and uniform. Karstic streams, vary little in flow volume and temperature all year round (the temperature fluctuates by only a few degrees, even in areas with cold winters and warm summers ; summer temperatures seldom exceed 20 °C). Moreover, water issuing from sedimentary rocks, such as limestones, contains large amount of dissolved salts, notably calcium bicarbonate ; these streams are liable to deposit calcium carbonate (tufa concretions). The present paper concerns four karstic watercourses in Provence (South-East France) ; it relates the influence of the ground water supplying on hydrology, ecology and hydrobiology of streams issuing from limestone formations. The peculiarities of these streams and the specificities of their animal community, analized through the knowledge of their macroinvertebrate fauna, are pointed out. In the studied karstic streams, the invertebrate community is dominated in numbers by taxa (Crustacea Gammarus, Coleoptera Elmidae, Gasteropod) regularly found in strongly mineralized water-courses with high Ca contents ; these taxa have always been found associated. In addition to that, two species of Diptera Simuliids, Simulium xanthinum and S. galloprovinciale, occur on tufa (from Spain to Libanon). One of the most noteworthy faunal peculiarity, common to karstic hydrologic regime watercourses, is the occcurence of a lot of coldstenothermous invertebrates which usually live at higher altitudes in mountain streams and in springs. Their occurrence in Mediterranean streams at middle and low altitudes is atypic. This peculiarity is correlated with thermal regime of the karstic streams which appear as cold enclaves in the Mediterranean region. The ecology of 11 cold-stenothermous species (1 Planarian, 3 Ephemeroptera, 2 Plecoptera, 4 Trichoptera, 1 Blepharicerid) which are both inhabitants of karstic and of non-karstic streams in the same mediterranean region (South-East France) is compared. The invertebrate community of karstic streams also contains some endemic species. The most worthy of note is Rhyacophila vallisclausae, a caddisfly (Trichoptera) which lives in the upper reach of the river Sorgue. This species, belonging to the European group of R. vulgaris, is clearly distinguished from all species in this group by the strongly marked brachyptery of specimens ; it appears to be a relic remnant of an ice age fauna which could survive in an aquatic environment characterized by its remarquable cold stenothermy., Les cours d’eau à régime karstique sont alimentés par des aquifères souterrains. Leurs caractéristiques physico-chimiques sont : – la faible variabilité des débits, car les apports d’eau souterraine assurent des débits réguliers avec des étiages peu marqués et des crues modérées ; – la température de l’eau, basse et constante sur la totalité ou sur une partie importante du cours ; – la minéralisation élevée des eaux de surface, avec de fortes teneurs en calcium. Ces caractéristiques confèrent aux cours d’eau karstiques des spécificités écologiques et faunistiques originales, atypiques dans le contexte régional méditerranéen. Le présent article porte sur quatre cours d’eau à régime karstique : l’Argens (Var), la Siagne et le Loup (Alpes-Maritimes), les Sorgues (Vaucluse). Il met en évidence leur originalité hydroécologique et surtout les particularités de leur peuplement analysées à travers la faune de macroinvertébrés. La communauté des invertébrés de ces cours d’eau karstiques est dominée en effectifs par des taxons qui nécessitent une concentration importante en calcium (Crustacés Gammaridae, Coléoptères Elmidae, Gastéropodes). Une des particularités faunistiques les plus remarquables, commune à ces cours d’eau, est la présence d’espèces sténothermes d’eau froide qui vivent habituellement dans le crénal et le rhithral des cours d’eau de montagne, à des altitudes bien supérieures à celles où elles ont été récoltées dans les cours d’eau karstiques. Une analyse comparative du statut écologique de 11 espèces sténothermes, que l’on trouve à la fois dans les cours d’eau de régime karstique et dans les cours d’eau de type méditerranéen, a été réalisée. De plus, les cours d’eau recevant les apports des systèmes karstiques hébergent des populations qui, du fait de leur caractère sténotherme, se sont trouvées isolées par rapport aux cours d’eau méditerranéens adjacents. Ceci explique la présence d’espèces endémiques. En définitive, les cours d’eau de régime karstique, bien qu’ils soient assez nombreux, sont atypiques dans la région méditerranéenne. On y trouve des conditions hydrologiques, thermiques et des peuplements (ripisylves, biocénoses, populations) qui sont habituellement présents dans des cours d’eau de montagne et dans des cours d’eau médio-européens., Giudicelli Jean, Olivari Georges. Les cours d’eau méditerranéens à régime de soutien karstique. Spécificités écologiques et hydrobiologiques. In: Ecologia mediterranea, tome 36 n°1, 2010. pp. 25-44.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE; Metapopulation theory has recently been stirred by the development of a metapopulation persistence criterion (Rm) quantifying the "lifetime dispersal success" of a newly colonized deme in a sparsely occupied metapopulation. No rigorous proof of this criterion in continuous time has been available so far. Here, we show that this criterion can be mathematically justified from standard Jacobian arguments. A summary of the key elements of this proof emphasizes the assumptions under which this criterion is valid. Examples illustrate how to generally compute metapopulation fitness in continuous time models. The underlying assumptions behind the criterion are discussed, as well as theoretical puzzles surrounding the concept of metapopulation fitness.

L'étude thermique globale du Rhône, lancée en 2000 à l'initiative de la DRIRE Rhône-Alpes en partenariat avec la DIREN, l'agence de l'eau RM&C, le Service de la Navigation et EDF, a pour objectif de déterminer l'incidence des rejets de chaleur cumulés sur le régime thermique du fleuve et ses conséquences hydrobiologiques. Après une caractérisation du régime thermique du Rhône (phase 1), puis une évaluation de l'échauffement apporté par les centres nucléaires de production d'électricité (CNPE) au cours de la phase 2, la phase 3 concerne l'impact hydrobiologique de ces échauffements cumulés. Cet article reprend, avec quelques éléments nouveaux, le rapport de synthèse de la phase 3 paru en avril 2006. Le Rhône est un fleuve totalement aménagé pour la production hydro-électrique et la navigation. Ces aménagements ont modifié les conditions hydro-morphologiques originelles et créé de nouveaux milieux (canaux, retenues, sections court-circuitées à débit régulé). À ces facteurs hydro-morphologiques contemporains qui structurent l'habitat physique des espèces, se superposent depuis la fin des années 70 des changements de la qualité chimique de l'eau (réduction de la pollution organique et de certaines pollutions toxiques). Par ailleurs, l'apparition et le développement d'espèces exogènes modifient la structure biologique et le fonctionnement de l'écosystème rhodanien. Au cours des trois dernières décennies, le régime thermique du Rhône a été affecté par le changement climatique. Il s'est traduit par un échauffement moyen d'environ 1,5 °C sur le Haut-Rhône et de 3,0 °C sur le Bas-Rhône. Dans cette dérive générale des températures, sur les quinze dernières années les échauffements résiduels moyens cumulés liés aux rejets thermiques des CNPE sont estimés à environ 0,6 °C à l'amont de Saint-Alban et 1,4 °C à l'amont d'Aramon. L'étude des chroniques de la surveillance hydro-écologique à long terme des CNPE indique que les modifications constatées sur les peuplements de macro-invertébrés et de poissons s'expliquent en premier lieu par les effets du changement climatique. En réponse à l'élévation de température, une modification générale dans la structure des peuplements de macro-invertébrés et de poissons a été enregistrée sur le Haut-Rhône au cours des 25 dernières années et particulièrement pendant la dernière décennie. Les espèces thermophiles et lénitophiles sont favorisées alors que les espèces sténothermes d'eau froide et rhéophiles régressent. À Bugey, ces tendances sont plus nettement visibles dans les stations exposées en permanence à des échauffements plus élevés (environ + 5 °C et + 9 °C) que dans celles situées après mélange du rejet. Sur le Bas-Rhône, où les peuplements sont déjà dominés par des taxons thermophiles et lénitophiles, une dérive moins marquée est également observée. Dans les tronçons court-circuités et les annexes hydrauliques, le régime thermique est en grande partie indépendant de la température du Rhône en période estivale. Dans les conditions actuelles, ces milieux à haute valeur écologique ne sont pas affectés par les rejets thermiques des CNPE. Cette étude formule également quelques recommandations pour des ajustements des programmes de surveillance hydro-écologique des CNPE et du programme de surveillance renforcé en cas de crise climatique ainsi que sur de nouvelles actions de recherche. Dans ce domaine, il est préconisé de développer des modèles hydrodynamiques d'habitat sur les secteurs à fort enjeu écologique couplant les conditions hydrologiques et thermiques. / The global thermal study of the Rhone which was launched in 2000 at the initiative of the Rhone-Alps DRIRE (Regional Board for Industry, Research and Environment), in partnership with the DIREN Regional Environment Office, the RM&C water board, the Rhone Navigation Authorities and EDF, marked an attempt to determine the impact of cumulative warm water releases on the thermal regime of the river as a whole, and the resulting hydrobiological effects. Following the description of the thermal regime of the Rhone (phase 1) and an assessment of warming generated by the nuclear power plants (CNPE) on the river (phase 2), phase 3 bears on the hydrobiological impact of the cumulative warming. This article summarizes, with some updates, the report on phase 3 which was issued in April 2006. The French section of the Rhone is equipped with hydropower and navigation installations which create hydro-morphological conditions which are quite distinct, ranging from semi-natural rapid flow to reservoirs with slower flow and including canals and bypass sections with controlled discharge, in the original bed of the river. These habitat-structuring hydro-morphological factors, since the end of the Seventies, have been compounded by changes in the chemical quality of the water (a reduction in organic pollution and in certain toxic pollutants) and the development of exogenous species which influence the biological structure and the dynamics of the Rhone ecosystem. Over the last three decades, the thermal regime of the Rhone has essentially been affected by climate change, which has resulted in warming on the order of 1.5 °C in the upper Rhone and 3.0 °C in the lower Rhone. Within this general shift in temperature, it is estimated that the mean contribution of releases from the nuclear plants is on the order of 0.6 °C upstream Saint-Alban and 1.4 °C upstream Aramon. Statistical processing of long-term hydro-ecological monitoring data from the nuclear plants has shown that the changes observed in macro-invertebrate and fish stocks can first be explained by the effects of climate change. In response to the rise in temperature, a general modification in the structure of macro-invertebrate and fish stocks has been found in the upper Rhone over the last 25 years, most particularly in the last decade: species that prefer warm water and slow flows are favored, while cold-water stenothermic and rheophilic species show a tendency to regress. These changes are markedly more visible at the downstream sites close to the Bugey plant, permanently exposed to greater warming (around + 5 °C and + 9 °C) than that found further downstream after complete mixing of the power plant releases. In the lower Rhone, where stocks were already dominated by thermophilic and slow-flow taxons, the same shift is found, though it is less marked. In the bypass sections and the secondary channels, the thermal regime is largely independent of the temperature in the Rhone in summer; under present conditions, these reaches of great ecological importance are not affected by the thermal releases from the nuclear power plants. Lastly, a few recommendations are formulated. These bear on changes to be made in programs for hydro-ecological monitoring of the nuclear plants and the stepped-up monitoring program in case of climate crisis, as well as on possible research. In this latter regard, the recommendation is made to develop hydrodynamic habitat models of sectors with high ecological importance, coupling hydrological and thermal conditions.

In het kader van het Europese project FAME is een methode ontwikkeld om op eenvoudige wijze de ecologische toestand van beken en rivieren vast te stellen aan de hand van de visstand. Deze methode, European Fish Index (EFI) genaamd, voldoet aan de eisen van de Kaderrichtlijn Water. De EFI is een belangrijke toevoeging aan het Nederlandse instrumentarium, omdat de methode op Europese schaal toetsbaar is en voor allerlei typen beken en rivieren zinvolle vergelijkingen mogelijk maakt met (vrijwel) ongestoorde situaties die in Nederland zo goed als verdwenen zijn

In het kader van het Europese project FAME is een methode ontwikkeld om op eenvoudige wijze de ecologische toestand van beken en rivieren vast te stellen aan de hand van de visstand. Deze methode, European Fish Index (EFI) genaamd, voldoet aan de eisen van de Kaderrichtlijn Water. De EFI is een belangrijke toevoeging aan het Nederlandse instrumentarium, omdat de methode op Europese schaal toetsbaar is en voor allerlei typen beken en rivieren zinvolle vergelijkingen mogelijk maakt met (vrijwel) ongestoorde situaties die in Nederland zo goed als verdwenen zijn

The first objective of the present study is to analyze the biodiversity of the aquatic ditch vegetation in relation to various envirotunental factors. A second objective is to test whether macrophyte biodiversity is highest at an intermediate level of ditch cleaning frequency

The Niger River inland delta in Mali constitutes a vast 36,000 km2 area of wetlands, producing numerous natural resources, exploited by fishermen, pastoralists and fanners. It is also a humid zone protected through the Ramsar convention of 1971. To promote the management of its natural resources, an integrated model has been developed in order to simulate the evolution of this ecosystem in relation to different scenarios of population increase, diminishing natural flooding (climatic droughts, construction of dams), increasing stress on land tenure and access to farming areas, technological advances, current administrative decentralisation policy. Possible applications of the model are illustrated through an analysis of the impact of the construction of dams on the traditional farming systems of the delta (fishing, rice cropping, pastoralism), and through a sensitivity analysis of an evolution in the fishing techniques on the revenues of fishermen. The validity of the results of the modelling is discussed and its use for other studies in the field of integrated natural resources management analysed. (Resume d'auteur)

UItleg over een nieuw ecologisch beoordelingssysteem voor brakke binnenwateren, aansluitend bij de al bestaande STOWA-beoordelingssystemen voor andere watertypen. Op grond van het ecologisch functioneren en een geformuleerd ecologisch streefbeeld worden beïnvloedingsfactoren, karakteristieken en maatstaven onderscheiden, waarmee voor verschillende hoofdtypen en subtypen brakke binnenwateren een ecologisch profiel kan worden opgesteld. Zowel het zoutgehalte als de dynamiek blijken belangrijke differentiërende factoren tussen brakwatersystemen; morfologie en voedselrijkdom spelen een ondergeschikte rol

UItleg over een nieuw ecologisch beoordelingssysteem voor brakke binnenwateren, aansluitend bij de al bestaande STOWA-beoordelingssystemen voor andere watertypen. Op grond van het ecologisch functioneren en een geformuleerd ecologisch streefbeeld worden beïnvloedingsfactoren, karakteristieken en maatstaven onderscheiden, waarmee voor verschillende hoofdtypen en subtypen brakke binnenwateren een ecologisch profiel kan worden opgesteld. Zowel het zoutgehalte als de dynamiek blijken belangrijke differentiërende factoren tussen brakwatersystemen; morfologie en voedselrijkdom spelen een ondergeschikte rol

A dam on a river course induces numerous changes in the aquatic environment both in the newly formed reservoir and in the river downstream. These changes modify the food resources available to fishes. As a consequence, fish communities undergo rapid transformations particularly in terms of trophic organization. Tucurui Dam, closed on the Tocantins River, Brazil, in September 1984, formed a large reservoir of approximately 2200 km2. Analyses of fish stomach contents were performed before and after the completion of the dam in the downstream section of the river as well as in the reservoir. Resource availability was seen through the relative contribution of food items in supporting the biomass. Main changes caused by the dam consisted of an increase in fishes as a food resource and of a parallel decrease of sediment both in the reservoir and in the downstream part of the river. In addition, in the downstream section, the relative contribution of plankton as a food resource diminished after dam closure. We identified 8 feeding regimes before dam closure. From them the trophic structure of fish communities were established and compared. Most of the community biomass was from specialist feeders. Contribution of piscivores increased after closure; planktivores became unimportant after closure downstream. Some species were shown to change their diet in the transformed environments either downstream or in the reservoir. However, these changes in individual species diet did not seem to play a major role in the transformation of trophic structure of the fish communities.

An ecological study of wetlands was undertaken in northern Lake Victoria (East Africa) between 1993 and 1996 with a major aim of characterising shallow vegetation-dominated interface habitats, and evaluating their importance for fish, in particular, for the stocked and socio-economically important Oreochromis niloticus LINNÉ (the Nile tilapia). From field and laboratory experiments, five major habitat types could be defined by the type of the dominant emergent macrophyte at the shore from the more than 40 identified plant species along a 110 km shoreline. These were: Cyperus papyrus L. (papyrus), Phragmites mauritianus Kunth (reeds), Typha domingensis Pers. (bulrush), Vossia cuspidata (Roxb.) (hippo grass), and the alien floating Eichhornia crassipes (Martius) Solms-Laubach (water hyacinth).From digital data, considerable long term changes in the shoreline wetland landscape of the lake were discerned and appeared to be primarily associated with increasing human activity (e.g., agriculture, biomass harvests) which had resulted into a 5 % reduction of wetland cover. Inspite of the absence of a well developed euhydrophyte community (e.g., Potamogeton and Ceratophyllum ), and increasing infestations with E. crassipes mats, the width of the littoral zone was established by secchi transparency as being about 50 - 70 m away from the shallow (less than 1 m deep) vegetation fringe sloping to between 2 and 4 m in depth at its outer fringe. Hydrological influences associated with seasonal changes (the alternation of rainy with dry periods) explained most of the observed variation in abiotic (e.g., Si, tot.-P, soluble reactive-P, NO 3 -N, pH, temperature) and biotic (phytoplankton, macrofauna, fish) factors, but there was also significant (p < 0.05) variation due to vegetation, distance from the shore out towards open water and interaction effects between these factors.At least 30 species of fish were identified from the shallower (2.5 m) vegetated habitats in contrast to 10 species from the deeper (4 - 8 m) open water habitats. There were other significant (p < 0.05) spatial and temporal differences in habitat use by fish. Species diversity was dominated by haplochromine species but three stocked species (the Nile perch, Lates niloticus L., O. niloticus and Tilapia zilli ) contributed at least 90% of the estimated numerical and biomass densities of which, the Nile tilapia was the most important component making up 45 - 65 % of the biomass of all fish. Season was a major factor in size-related abundance patterns but generally, most of the Nile tilapia biomass was associated with Phragmites-Vossia-Typha -dominated habitats which were also important for small (

The social and biophysical processes entailed in environmental deterioration are the subject of intense debate in Honduras, one of the poorest countries of Latin America. This book analyses the political ecology of precarious farming in mountainous areas. The author evaluates a rich array of social and agronomic data in order to assess existing theories that purport to explain environmental deterioration and agrarian change in Honduras. It explores the relationships between land tenure patterns, shifting agricultural practices, changing social relations of production, and producers' knowledge. Special attention is given to differential perceptions and responses of producers to environmental deterioration, and to the broader knowledge struggles of different actors about issues such as burning, the fallow crisis, biocide use, and deforestation. This detailed case study draws on political economy, human ecology, critical realism, and social constructionism and constitutes an original contribution to current debates on political ecology.The central argument of this book is that land degradation through present agricultural practices is not simply an effect of poverty, inconsiderate acting or a direct consequence of a modernisation process which is orchestrated and imposed upon the Honduran peasantry by external capitalist development. Instead, the social causation of environmental change in mountainous areas of Honduras should be understood in terms of a complex mixture of local patterns of access to resources, forms of state intervention, the heterogeneous paths of technological change and knowledge generation, divisions of labour, and the specific interactions of emerging commodity markets and the organization of production.Chapter two focuses on issues of land tenure and property rights. It compares local histories of land distribution in El Zapote with widely used models of the latifundio-minifundio complex and the colonial legacy of the large landholding. Subsequently, it explores how local rules and cultural notions, local government and state laws, and state interventions through land reform and land titling projects, mediate the relation between people and the land. Conclusions deal with the multiple land histories which explain the complexity of conflicts, and with the many factors shaping the meaning villagers attribute to the value of land.Chapter three explores technological changes in crop production and cattle husbandry and compares the findings in El Zapote with recent studies dealing with heterogeneity and diversity in agriculture, thus criticizing approaches which maintain a duality of traditional and modern agricultural technology. It stresses the recognition of the multiplicity of factors causing technological change.This exploration of technological change serves as a starting point for the discussion of how different environmental problems are perceived by different actors. Chapter four identifies different perspectives on the fallow crisis, the use of fire to clear fields, vegetation and climatic change, and the use of new agro-chemicals. It deals with the paradox that agronomy cannot encompass the many factors involved in environmental deterioration, but that an alternative strategy of validating producers' environmental perceptions cannot provide a coherent theory of the causes of environmental deterioration as well.In Chapters two, three, and four, it will be shown that environmental behaviour and perceptions about environmental change relate to access to, and distribution of, resources. Chapter five gives further consideration to the different aspects of the social relations of production in El Zapote, in order to understand the processes of social differentiation.Chapter six broadens the issue of social differentiation with a discussion of local agricultural knowledge. The argument is put forward that we need an understanding of both the practical character of knowledge, (that local knowledge generation responds to environment and social context), and its discursive character. Knowledge is not only embedded in narratives on the epistemological level, but also in concrete natural environments and social relations. An important conclusion is that current `local knowledge approaches' overestimate the potential of local knowledge for environmental conservation or restoration.The concluding chapter starts by commenting on various explanations of environmental deterioration in Honduran mountain agriculture. Using the case study of El Zapote it presents an alternative explanation with the main argument that a linear relation between the distribution of the means of production and labour relations on the one hand, and use of the environment on the other, cannot be justified, but that, nevertheless, an inquiry into changing patterns of social differentiation may provide insight into important mechanisms of human interaction with nature. The final section challenges theoretical (epistemological and ontological) confusions about social and biophysical causation of environmental deterioration in environmental social science.

The social and biophysical processes entailed in environmental deterioration are the subject of intense debate in Honduras, one of the poorest countries of Latin America. This book analyses the political ecology of precarious farming in mountainous areas. The author evaluates a rich array of social and agronomic data in order to assess existing theories that purport to explain environmental deterioration and agrarian change in Honduras. It explores the relationships between land tenure patterns, shifting agricultural practices, changing social relations of production, and producers' knowledge. Special attention is given to differential perceptions and responses of producers to environmental deterioration, and to the broader knowledge struggles of different actors about issues such as burning, the fallow crisis, biocide use, and deforestation. This detailed case study draws on political economy, human ecology, critical realism, and social constructionism and constitutes an original contribution to current debates on political ecology.The central argument of this book is that land degradation through present agricultural practices is not simply an effect of poverty, inconsiderate acting or a direct consequence of a modernisation process which is orchestrated and imposed upon the Honduran peasantry by external capitalist development. Instead, the social causation of environmental change in mountainous areas of Honduras should be understood in terms of a complex mixture of local patterns of access to resources, forms of state intervention, the heterogeneous paths of technological change and knowledge generation, divisions of labour, and the specific interactions of emerging commodity markets and the organization of production.Chapter two focuses on issues of land tenure and property rights. It compares local histories of land distribution in El Zapote with widely used models of the latifundio-minifundio complex and the colonial legacy of the large landholding. Subsequently, it explores how local rules and cultural notions, local government and state laws, and state interventions through land reform and land titling projects, mediate the relation between people and the land. Conclusions deal with the multiple land histories which explain the complexity of conflicts, and with the many factors shaping the meaning villagers attribute to the value of land.Chapter three explores technological changes in crop production and cattle husbandry and compares the findings in El Zapote with recent studies dealing with heterogeneity and diversity in agriculture, thus criticizing approaches which maintain a duality of traditional and modern agricultural technology. It stresses the recognition of the multiplicity of factors causing technological change.This exploration of technological change serves as a starting point for the discussion of how different environmental problems are perceived by different actors. Chapter four identifies different perspectives on the fallow crisis, the use of fire to clear fields, vegetation and climatic change, and the use of new agro-chemicals. It deals with the paradox that agronomy cannot encompass the many factors involved in environmental deterioration, but that an alternative strategy of validating producers' environmental perceptions cannot provide a coherent theory of the causes of environmental deterioration as well.In Chapters two, three, and four, it will be shown that environmental behaviour and perceptions about environmental change relate to access to, and distribution of, resources. Chapter five gives further consideration to the different aspects of the social relations of production in El Zapote, in order to understand the processes of social differentiation.Chapter six broadens the issue of social differentiation with a discussion of local agricultural knowledge. The argument is put forward that we need an understanding of both the practical character of knowledge, (that local knowledge generation responds to environment and social context), and its discursive character. Knowledge is not only embedded in narratives on the epistemological level, but also in concrete natural environments and social relations. An important conclusion is that current `local knowledge approaches' overestimate the potential of local knowledge for environmental conservation or restoration.The concluding chapter starts by commenting on various explanations of environmental deterioration in Honduran mountain agriculture. Using the case study of El Zapote it presents an alternative explanation with the main argument that a linear relation between the distribution of the means of production and labour relations on the one hand, and use of the environment on the other, cannot be justified, but that, nevertheless, an inquiry into changing patterns of social differentiation may provide insight into important mechanisms of human interaction with nature. The final section challenges theoretical (epistemological and ontological) confusions about social and biophysical causation of environmental deterioration in environmental social science.

An ecological study of wetlands was undertaken in northern Lake Victoria (East Africa) between 1993 and 1996 with a major aim of characterising shallow vegetation-dominated interface habitats, and evaluating their importance for fish, in particular, for the stocked and socio-economically important Oreochromis niloticus LINNÉ (the Nile tilapia). From field and laboratory experiments, five major habitat types could be defined by the type of the dominant emergent macrophyte at the shore from the more than 40 identified plant species along a 110 km shoreline. These were: Cyperus papyrus L. (papyrus), Phragmites mauritianus Kunth (reeds), Typha domingensis Pers. (bulrush), Vossia cuspidata (Roxb.) (hippo grass), and the alien floating Eichhornia crassipes (Martius) Solms-Laubach (water hyacinth).From digital data, considerable long term changes in the shoreline wetland landscape of the lake were discerned and appeared to be primarily associated with increasing human activity (e.g., agriculture, biomass harvests) which had resulted into a 5 % reduction of wetland cover. Inspite of the absence of a well developed euhydrophyte community (e.g., Potamogeton and Ceratophyllum ), and increasing infestations with E. crassipes mats, the width of the littoral zone was established by secchi transparency as being about 50 - 70 m away from the shallow (less than 1 m deep) vegetation fringe sloping to between 2 and 4 m in depth at its outer fringe. Hydrological influences associated with seasonal changes (the alternation of rainy with dry periods) explained most of the observed variation in abiotic (e.g., Si, tot.-P, soluble reactive-P, NO 3 -N, pH, temperature) and biotic (phytoplankton, macrofauna, fish) factors, but there was also significant (p < 0.05) variation due to vegetation, distance from the shore out towards open water and interaction effects between these factors.At least 30 species of fish were identified from the shallower (2.5 m) vegetated habitats in contrast to 10 species from the deeper (4 - 8 m) open water habitats. There were other significant (p < 0.05) spatial and temporal differences in habitat use by fish. Species diversity was dominated by haplochromine species but three stocked species (the Nile perch, Lates niloticus L., O. niloticus and Tilapia zilli ) contributed at least 90% of the estimated numerical and biomass densities of which, the Nile tilapia was the most important component making up 45 - 65 % of the biomass of all fish. Season was a major factor in size-related abundance patterns but generally, most of the Nile tilapia biomass was associated with Phragmites-Vossia-Typha -dominated habitats which were also important for small (

A survey is given of the work and life of Cornelis den Hartog up to the date in 1996 on which he retired from his position as a professor at the University of Nijmegen. Cornelis (Kees) den Hartog made important contributions to aquatic ecology in the widest sense, e.G. On brackish water typology, meiofauna (microturbellaria), macroinvertebrates, littoral algae, sea-grasses and aquatic macrophytes. He favoured the ecosystem approach in aquatic ecology by studying structure and functioning in an integrated way. He led 31 students to their doctor's degrees (PhD).

Onderdeel natuurbeleidsplan

Life cycles of Rhyacophila fasciata Hagen and R. nubila Zettersdedt are studied. The first species is found in Qab Ilias, a small river on the east side of Mount Lebanon, the second one lives in Yahfufah on the west side of the Anti Lebanon. Length and width of the head were measured. The average size for larvae in the fifth instar are 1.81 and 1.4 mm and 1.58 and 1.17 mm respectively. Flying periods, laying eggs and hatching occur the year round with a resting period in winter. The first species needs more than one year to accomplish its life cycle and the second one less than one year., Les cycles de vie de Rhyacophila fasciata Hagen et R. nubila Zettersdedt sont étudiés. La première espèce colonise la rivière Qab Ilias (versant est du mont Liban) et la seconde colonise la rivière Yahfufah (versant ouest de l’Anti Liban). Ces deux cours d’eau appartiennent au haut bassin du Litani. Les dimensions moyennes, longueur et largeur, de la capsule céphalique du 5ème stade larvaire sont de 1,81 et 1,4 mm et de 1,58 et 1,17 mm respectivement. Les périodes de vol, de ponte et d’éclosion s’observent toute l’année avec un repos hivernal. R. fasciata est une espèce printanière et a besoin de plus d’une année pour accomplir son cycle biologique. R. nubila a une période de vol printanière précoce et une autre estivo-automnale et parachève son cycle en moins d’une année., Alouf Nicolas J. Cycle de développement de deux Rhyacophila (Insecta : Trichoptera) au Liban. In: Ecologia mediterranea, tome 17,1991. pp. 11-17.

Nowadays many surface waters in The Netherlands tend to become ecologically uniform with the same mediocre quality. A differentiated approach to water management is necessary to stop this process of impoverishment of aquatic ecosystems. In The Netherlands the provincial authorities represent the appropriate level at which this differentiated approach to water management can be put into practice. Such an approach has been realized by the Department of Water Management of the Province of Overijssel. As a part of this approach the project 'Ecological characterization of surface waters in the province of Overijssel (EKOO)' was formulated in 1981.The aims of the EKOO-project are to develop a regional ecological characterization of surface waters based on macrofauna composition and to reach a better understanding of the variety and the structure of the macrofauna communities present in the waters of the province of Overijssel. The project thus provides knowledge of aquatic ecosystems on a regional scale and a basis for the development of water management policies. An additional aim of this study is to develop the typological approach used in water management.The typological approach used can be interpreted as an integration of the zonal concept and the continuum concept. Taxon combinations will be described as types. Within a limited range of environmental conditions, these types are representative of communities, but at the same time they together form a continuum. Due to hierarchical relations between major environmental variables (master factors) and evolutionary and historical factors, a type can only be described within a biogeographical region.The study was designed as a qualitative survey but organized as much as possible along quantitative lines. Macrofauna composition (taxon composition and abundance) was chosen as a basic parameter. About 70 variables that were considered physically, chemically or biologically relevant, were measured at each sampling site. In total 664 sites were sampled, distributed over about twenty physico- geographical water types. These twenty types include all the major environmental variables relevant to this region; they overlap in abiotic features. The physico-geographical water typology was used as a practical tool for carrying out the survey, but was not used in obtaining the ecological typology. The ecological typology was derived from the collected biotic and abiotic data alone.A study on the reproducibility of the standard macrofauna sample was carried out. The standard pond net macrofauna sampling technique used in The Netherlands appears to present only a semi-quantitative picture of the more common taxa. With this technique only about 55% of all the taxa present at a site at the moment of sampling were collected. However, when the standard pond net was used for a regional typological study it appeared that seasonal differences as well as inconsistencies due to sample technique were of little significance compared with differences between types. It was concluded that the reproducibility of a macrofauna sample is sufficient for typological purposes.For data analysis, the twenty physico-geographical water types were combined into five main categories. The abiotic and biotic data were processed for these five main categories. Later, all the data were processed together to obtain an ecological water typology for the province of Overijssel. Multivariate analysis techniques are appropriate in data analysis for typologi~-al purposes. Different multivariate analysis techniques (cluster analysis and canonical ordination) were used to derive and describe site groups in terms of taxon composition and mean environmental conditions. Sites intermediate between groups were manually relocated by using information from other sources (e.g. literature) about the ecology of the constituent taxa. The resulting site groups were termed cenotypes.Six cenotypes were distinguished among helocrene springs. The main differences between the cenotypes were related to hydrology (mainly duration of drought) and acidity. Furthermore, the nutrient content and/or the load of organic material differed between related cenotypes. Each cenotype contained its own microhabitat group(s). The microhabitat groups, except for two, were associated with the duration of the drought period. The other two groups were associated with the spring source and the spring stream, respectively. The natural reference situation for helocrene springs probably resembles some of the actual helocrene springs investigated. The most important human activities causing disturbance are those which cause changes in the chemical composition of the groundwater. The management of springs should be directed at this factor.Eleven cenotypes were distinguished among the streams. The main differences between the cenotypes were related to dimensions, "stream-character", duration of drought and the load of organic material. All the streams were more or less influenced by human activities. Stream regulation, especially, has caused a dramatic change in the taxon composition. Only about 2% of the total length of streams is still more or less natural in 'stream-character' and its corresponding community. These 2% are only preserved because of their geographical position on the steepest slopes. In general, efforts at improvement of the ecological character should be directed at the physical and hydraulic conditions.Eleven cenotypes were distinguished among the ditches. The main differences between the cenotypes were related to dimensions, duration of drought, acidity and current. Furthermore, the nutrient content and/or load of organic material differed between related cenotypes . It is illustrated that the taxon combination found in a ditch reflects a stage of succession in space (profile structure) and time (maturity). Therefore, an overlap in taxon combination between cenotypes occurred (continuum). Ditches are artificial ecosystems which mainly occur in cultivated areas (which implies eutrophication) and depend on regular human interference (cleaning, dredging). The ecological management of ditches should be based upon the relationbetween profile structure, succession stage and human interference.Eleven cenotypes were distinguished among the rivers, canals and large lakes. They showed great overlap in taxa (mostly opportunists) and in environmental circumstances. Increasing dimensions of the line-shaped more or less running waters go together with an increasing drainage area. These large-sized water bodies function as collectors of nutrients, organic material and toxicants. This results in chronic stress and probably the disappearance of most taxa occurring originally. The chronic stress also overrules the natural master factors of current and dimensions. Only a few taxa are still characteristic for the reach of a river or the gradient in size of canals.Nine cenotypes were distinguished among the ponds and small lakes. The main differences between the cenotypes were related to duration of drought, acidity, morphology and nutrient load. In particular, the four cenotypes within the group of stagnant, pH-neutral ponds/lakes showed an overlap in taxon compostion. These cenotypes represent a web-shaped continuum dominated by dimensions (relation of width to depth), nutrient load, and bottom composition (especially mesotrophic peat). The most important processess induced by men are acidification, eutrophication, and changes in the original hydrology.Cenotypes of different main physico-geographical watertypes can be very similar. Therefore they should be combined or rearranged. This is done by processing all abiotic and biotic data together. Again, cluster analysis and canonical ordination were applied. After each ordination along two axes, the distinctive cenotypes were removed and the remaining sites were reordinated. Through this progressive removal of groups of sites, finally, 42 cenotypes were distinguished. Some notes on the ecology of the typifying taxa and the most important environmental variables were made for each cenotype.The mutual relations between the cenotypes are shown in a hierarchical dendrogram based on biological similarity as well as in a web of cenotypes (Figure 11.1).The hierarchical dendrogram shows, among others, that a group of cenotypes related to middle and lower reaches of regulated streams, small rivers, ditches and some of the medium-sized, more or less stagnant waters, - all hypertrophic, mesosaprobic environments -, has a fair number of the macrofauna in common. Apparantly, human activity (e.g. by regulation of streams, discharge of wastes and agricultural activity in the watershed) leads to a decreasing role of the factor current in running waters and the factors dimensions (in fact shape and depth) and bottom type in the stagnant waters and leads to an impoverishment of the macrofauna.The web of cenotypes illustrates the mutual position of the cenotypes, the transitions between the cenotypes (the continuum) and the major environmental gradients. The four most dominant factors are 'stream-character', acidity, duration of drought, and dimensions.To evaluate a given water body, even subjectively, it is necessary to compare it with other water bodies in different states. This scale of evaluation needs a reference water. The reference water is not necessarily an endpoint of succession nor a pristine situation, but it should at least represent a situation that can be used to indicate the desired direction of improvement. In choosing the reference communities for water management one must focus on communities present in waters where major environmental conditions are less disturbed. Such waters are the undisturbed streams, the oligotrophic moorland pools, and the mesotrophic old meanders cut off from streams.The regional ecological typology presented (Figure 11.1) offers a tool for establishing the developmental direction from a community observed in the field towards the reference community. It is also a tool to determine the reference community for a particular water body. Because the factors in the web of cenotypes are a result of a descriptive study, the web cannot be used without caution as a predictive tool; the factors are purely indicative. The typology and associated ecological concepts are a tool to help solving water management problems. It is a basis, among others, for monitoring and assessment of waterquality, it indicates potential capacities Of surface waters and it provides guidelines for management and restoration of surface waters. May it be serve to the advantage of the environment around us.

Nowadays many surface waters in The Netherlands tend to become ecologically uniform with the same mediocre quality. A differentiated approach to water management is necessary to stop this process of impoverishment of aquatic ecosystems. In The Netherlands the provincial authorities represent the appropriate level at which this differentiated approach to water management can be put into practice. Such an approach has been realized by the Department of Water Management of the Province of Overijssel. As a part of this approach the project 'Ecological characterization of surface waters in the province of Overijssel (EKOO)' was formulated in 1981.The aims of the EKOO-project are to develop a regional ecological characterization of surface waters based on macrofauna composition and to reach a better understanding of the variety and the structure of the macrofauna communities present in the waters of the province of Overijssel. The project thus provides knowledge of aquatic ecosystems on a regional scale and a basis for the development of water management policies. An additional aim of this study is to develop the typological approach used in water management.The typological approach used can be interpreted as an integration of the zonal concept and the continuum concept. Taxon combinations will be described as types. Within a limited range of environmental conditions, these types are representative of communities, but at the same time they together form a continuum. Due to hierarchical relations between major environmental variables (master factors) and evolutionary and historical factors, a type can only be described within a biogeographical region.The study was designed as a qualitative survey but organized as much as possible along quantitative lines. Macrofauna composition (taxon composition and abundance) was chosen as a basic parameter. About 70 variables that were considered physically, chemically or biologically relevant, were measured at each sampling site. In total 664 sites were sampled, distributed over about twenty physico- geographical water types. These twenty types include all the major environmental variables relevant to this region; they overlap in abiotic features. The physico-geographical water typology was used as a practical tool for carrying out the survey, but was not used in obtaining the ecological typology. The ecological typology was derived from the collected biotic and abiotic data alone.A study on the reproducibility of the standard macrofauna sample was carried out. The standard pond net macrofauna sampling technique used in The Netherlands appears to present only a semi-quantitative picture of the more common taxa. With this technique only about 55% of all the taxa present at a site at the moment of sampling were collected. However, when the standard pond net was used for a regional typological study it appeared that seasonal differences as well as inconsistencies due to sample technique were of little significance compared with differences between types. It was concluded that the reproducibility of a macrofauna sample is sufficient for typological purposes.For data analysis, the twenty physico-geographical water types were combined into five main categories. The abiotic and biotic data were processed for these five main categories. Later, all the data were processed together to obtain an ecological water typology for the province of Overijssel. Multivariate analysis techniques are appropriate in data analysis for typologi~-al purposes. Different multivariate analysis techniques (cluster analysis and canonical ordination) were used to derive and describe site groups in terms of taxon composition and mean environmental conditions. Sites intermediate between groups were manually relocated by using information from other sources (e.g. literature) about the ecology of the constituent taxa. The resulting site groups were termed cenotypes.Six cenotypes were distinguished among helocrene springs. The main differences between the cenotypes were related to hydrology (mainly duration of drought) and acidity. Furthermore, the nutrient content and/or the load of organic material differed between related cenotypes. Each cenotype contained its own microhabitat group(s). The microhabitat groups, except for two, were associated with the duration of the drought period. The other two groups were associated with the spring source and the spring stream, respectively. The natural reference situation for helocrene springs probably resembles some of the actual helocrene springs investigated. The most important human activities causing disturbance are those which cause changes in the chemical composition of the groundwater. The management of springs should be directed at this factor.Eleven cenotypes were distinguished among the streams. The main differences between the cenotypes were related to dimensions, "stream-character", duration of drought and the load of organic material. All the streams were more or less influenced by human activities. Stream regulation, especially, has caused a dramatic change in the taxon composition. Only about 2% of the total length of streams is still more or less natural in 'stream-character' and its corresponding community. These 2% are only preserved because of their geographical position on the steepest slopes. In general, efforts at improvement of the ecological character should be directed at the physical and hydraulic conditions.Eleven cenotypes were distinguished among the ditches. The main differences between the cenotypes were related to dimensions, duration of drought, acidity and current. Furthermore, the nutrient content and/or load of organic material differed between related cenotypes . It is illustrated that the taxon combination found in a ditch reflects a stage of succession in space (profile structure) and time (maturity). Therefore, an overlap in taxon combination between cenotypes occurred (continuum). Ditches are artificial ecosystems which mainly occur in cultivated areas (which implies eutrophication) and depend on regular human interference (cleaning, dredging). The ecological management of ditches should be based upon the relationbetween profile structure, succession stage and human interference.Eleven cenotypes were distinguished among the rivers, canals and large lakes. They showed great overlap in taxa (mostly opportunists) and in environmental circumstances. Increasing dimensions of the line-shaped more or less running waters go together with an increasing drainage area. These large-sized water bodies function as collectors of nutrients, organic material and toxicants. This results in chronic stress and probably the disappearance of most taxa occurring originally. The chronic stress also overrules the natural master factors of current and dimensions. Only a few taxa are still characteristic for the reach of a river or the gradient in size of canals.Nine cenotypes were distinguished among the ponds and small lakes. The main differences between the cenotypes were related to duration of drought, acidity, morphology and nutrient load. In particular, the four cenotypes within the group of stagnant, pH-neutral ponds/lakes showed an overlap in taxon compostion. These cenotypes represent a web-shaped continuum dominated by dimensions (relation of width to depth), nutrient load, and bottom composition (especially mesotrophic peat). The most important processess induced by men are acidification, eutrophication, and changes in the original hydrology.Cenotypes of different main physico-geographical watertypes can be very similar. Therefore they should be combined or rearranged. This is done by processing all abiotic and biotic data together. Again, cluster analysis and canonical ordination were applied. After each ordination along two axes, the distinctive cenotypes were removed and the remaining sites were reordinated. Through this progressive removal of groups of sites, finally, 42 cenotypes were distinguished. Some notes on the ecology of the typifying taxa and the most important environmental variables were made for each cenotype.The mutual relations between the cenotypes are shown in a hierarchical dendrogram based on biological similarity as well as in a web of cenotypes (Figure 11.1).The hierarchical dendrogram shows, among others, that a group of cenotypes related to middle and lower reaches of regulated streams, small rivers, ditches and some of the medium-sized, more or less stagnant waters, - all hypertrophic, mesosaprobic environments -, has a fair number of the macrofauna in common. Apparantly, human activity (e.g. by regulation of streams, discharge of wastes and agricultural activity in the watershed) leads to a decreasing role of the factor current in running waters and the factors dimensions (in fact shape and depth) and bottom type in the stagnant waters and leads to an impoverishment of the macrofauna.The web of cenotypes illustrates the mutual position of the cenotypes, the transitions between the cenotypes (the continuum) and the major environmental gradients. The four most dominant factors are 'stream-character', acidity, duration of drought, and dimensions.To evaluate a given water body, even subjectively, it is necessary to compare it with other water bodies in different states. This scale of evaluation needs a reference water. The reference water is not necessarily an endpoint of succession nor a pristine situation, but it should at least represent a situation that can be used to indicate the desired direction of improvement. In choosing the reference communities for water management one must focus on communities present in waters where major environmental conditions are less disturbed. Such waters are the undisturbed streams, the oligotrophic moorland pools, and the mesotrophic old meanders cut off from streams.The regional ecological typology presented (Figure 11.1) offers a tool for establishing the developmental direction from a community observed in the field towards the reference community. It is also a tool to determine the reference community for a particular water body. Because the factors in the web of cenotypes are a result of a descriptive study, the web cannot be used without caution as a predictive tool; the factors are purely indicative. The typology and associated ecological concepts are a tool to help solving water management problems. It is a basis, among others, for monitoring and assessment of waterquality, it indicates potential capacities Of surface waters and it provides guidelines for management and restoration of surface waters. May it be serve to the advantage of the environment around us.

Gross primary production, community respiration and reaeration coefficient were determined during an annual cycle on the Viroin River (South Belgium), based on the daily variations of dissolved oxygen concentration. Reaeration coefficient remains remarkably constant (0.26 h−1) during the year in spite of discharge variations. The autotrophic community is dominated by ‘Ranunculus fluitans’. Primary production parallels the variations of total solar radiations. It ranges from 0 in winter to 8 g O2 m−2 d−1 in summer. In spring and summer, respiration variations parallel those of primary production (average value: 10 g O2 m−2 d−1); in the dry autumn, decomposition of dying macrophytes considerably enhances the community respiration (15 g O2 m−2 d−1). A P/R diagram is used to characterize the trophic state of the Viroin., info:eu-repo/semantics/published

A method proposed for estimating the rate of bacterial mortality in aquatic environments consists in following the disappearance of radioactive tracer from the macromolecular fraction of 3H-thymidine labeled natural assemblages of bacteria. The data presented in this paper offer a further technical validation of this procedure. Application of the method to North and Mediterranean Sea, estuaries, rivers and lakes yields first order mortality constant in the range 0.008–0.06 h−1. Mortality due to grazing by protozoans retained by 2 μm filtration range from 20 to 90% of the mortality detected by the method., info:eu-repo/semantics/published

Er wordt gepleit voor gerichter onderzoek naar de relatie tussen de ruimtelijke opbouw van een gebied en het voorkomen van bepaalde levensgemeenschappen, zodanig dat dit toepasbaar is bij inrichtingsplannen