No description available.

Limnologische Charakterisierung ausgewählter Ackerhohlformen (Sölle) des nordostdeutschen Jungmoränengebietes als Grundlage von Schutzmaßnahmen* *) gefördert durch die Deutsche Bundesstiftung Umwelt und die FAZIT-Stiftung, Frankfurt a.M. 160 S.: 64 Abbn., 24 Tab., 3 gezeichnete Tafeln, 4 mikroskopische Tafeln Humboldt-Universität zu Berlin Institut für Biologie AG Ökologie Die Untersuchungen konzentrierten sich auf das Plankton von Söllen der Jungmorä nenlandschaft Nordostdeutschlands. Ziel war es, die qualitative und quantitative Phyto- und Zooplanktonstruktur verschiedener Sölle unter dem Gesichtspunkt der nterschiedlichen Landnutzung, des Wasserhaushaltes und des Stoffeintrages in zwei Untersuchungsgebieten zu erfassen, mit einem weitgehend ursprünglichen Forstsoll zu vergleichen und daraus Schlußfolgerungen für den Erhalt und den Schutz dieser Kleingewässer abzuleiten. Es wurden sieben repräsentative Sölle monatlich über drei Vegetationsperioden (1994-1997) untersucht. Neben dem Artenspektrum und dem Abun danzwechsel des Phyto- und Zooplanktons erfolgte eine Erfassung des Chlorophyll a -Gehaltes der Mikroalgenzellen, der hydrochemischen und physikalischen Grundparameter und der Pegelstände des Sollwassers. Trotz der großen Individualität der Untersuchungsgewässer konnten aus den Erg ebnissen die Sölle in drei Gruppen statistisch signifikant zusammengefaßt werden. Für deren Abgrenzung sind die Nährstoffverhältnisse (N oder P-Überschüsse, Nitrifikationsgrad), die Sauerstoffsättigungswerte und das Artenspektrum des Phyto- und Zooplanktons bedeutsam. Hohe Leitfähigkeit des Wassers besonders in den Söllen des Gebietes um Lietzen-Döbberin wird durch hohe Sulfat- und Chloridgehalte bedingt. Im Vergleich zu den Seen sind die Chlorophyll a -Konzentrationen als Biomasseäquivalent für die Mikroalgen in Relation zu den Phosphatgehalten auffallend gering. Aus den Ergebnissen lassen sich Maßnahmen zur Erhaltung und dem Schutz der Sölle ableiten. Es wird die konsequente Verminderung der externen Nährstoffeinträge durch die Schaffung und/ oder Pflege von Pufferzonen sowie gegebenenfalls die Umwidmung des Einzugsgebietes in Dauergrünland empfohlen. Weitere Maßnahmen, die auf die Reduzierung der internen Nährstoffreserven zielen, sind erst nach zusätzlichen Untersuchungen insbesondere zum Phosphorbindungsvermögen der Sedimente für die Sölle ableitbar. / Limnological characterization of selected ponded depressions of the north German young moraine site as a basis for conservation* *) sponsored by the Deutsche Bundesstiftung Umwelt and the FAZIT-Stiftung, Frankfurt a.M. 160 S.: 64 Abbn., 24 Tab., 3 graphic Tables, 4 microscope tables Humboldt-Universität zu Berlin Institut für Biologie AG Ökologie The main geographical feature of the ground and terminal moraines of northern Germany are the numerous small depressions, many of which are water-filled. They represent a typical geographical element of this region and in the German language are usually referred to as "Sölle" (Singular = "Soll"). These small bodies of water were created either glacially through the melting of dead-ice pieces (natural depressions or dead-ice depressions) or later (circa 12th or 13th century) in the course of the clearing of large tracts of forested land through the partial and permanent damming of depressions (pseudo depressions). The study concentrated on the plankton levels of ponded depressions in the recent moraines of northern Germany. The goal of the study was to record the qualitative and quantitative phytoplankton and zooplankton make-up of several different ponded depressions with consideration of the various land uses, management of water, and introduction of nutrients in two research areas and to compare these findings with a mostly unaltered forested ponded depression (ponded depression in a forested area) for the purpose of deriving conclusions about the preservation and protection of these small water ways. Seven representative ponded depressions were examined monthly over the span of three vegetation periods (1994-1997). In addition to the variety of vegetational species and the variation in amounts of phytoplankton and zooplankton, data about the amount of chlorophyll a in the micro algae cells, the hydro-chemical and physical ground parameters, and the water level of the ponds was recorded. In spite of the considerable uniqueness of each of the ponds under examination, the results of the study allowed for the classification of the ponded depressions into three statistically significant groupings.The proportions of nutrients (a surplus of N or P or the level of nitrification), the oxygen saturation values, and the vegetational spectrum of phytoplankton and zooplankton proved meaningful for the differentiation of the groupings. High conductivity of the water, especially in the ponds in the area around Lietzen-Döbberin, is caused by high levels of sulfate and chloride. In comparison to lakes, the concen trations of Chlorophyll a as a biomass equivalent for the micro algae are noticeably smaller in relation to the phosphate levels. The results of the research suggest measures for the preservation and protection of the ponded depressions. The intentional reduction of external nutrients through the creation of and/or care for buffer zones and, if necessary, the redesignation of areas zoned for development into permanent nature conservation zones is recommended. Further preservation measures, aimed at reducing the reserves of internal nutrients, will only be deduced after further study of the ponded depressions, especially in relation to the ability of the sediment to absorb phosphors.

Responses of periphyton and phytoplankton productivity in the lower Sulphur River (Texas-Arkansas) to bleach-kraft mill effluent (BKME) were monitored using in situ ¹⁴C incubation. Carbon assimilation rates measured downstream of mill discharge were substantially reduced from upstream levels. Periphyton and phytoplankton chlorophyll a concentrations remained relatively unchanged by the presence of BKME. Periphyton ash-free dry weight increased near the mill outfall, but decreased further downstream. Calculated productivity efficiencies (productivity:biomass) varied with variations in ¹⁴C rates. A laboratory bioassay was designed to determine the effect of BKME light-attenuation on photosynthetic rates of upstream Sulphur River periphyton and Selenastrum capricornutum Prinz. Pooled results of bioassay runs indicated a 20 per cent BKME concentration effectively reduced control ¹⁴C-assimilation levels by 50 per cent. The downstream reduction observed for in situ productivity was 5 per cent lower than that predicted by the color bioassay.

Understanding and modeling microbial responses and feedbacks to climate change is hampered by a lack of a framework in the pelagic environment by which to link local mechanism to large scale patterns. Where terrestrial ecology draws from landscape theory and practice to address issues of scale, the pelagic seascape concept is still in its infancy. We have applied the patch mosaic paradigm of landscape ecology to the study of the seasonal and interannual variability of the North Pacific to facilitate comparative analysis between pelagic ecosystems and provide spatiotemporal context for eulerian time-series studies. Using multivariate, 13-year climatologies of sea surface temperature, photosynthetically active radiation, and chlorophyll a derived from remote sensing observations, we classified hierarchical seascapes at monthly and interannual scales. These dynamic, objectively-determined seascapes offer improved hydrographic coherence relative to oceanic regions with subjectively defined and static boundaries (Chapter 2) and represent unique biogeochemical functioning (Chapter 2) and microbial communities (Chapter3). Furthermore they provide consilience between satellite studies and in situ observations (Chapter 4) and allow for objective comparison of ecosystem forcing (Chapters, 4 and 5). In Chapter 2, we rigorously tested the assumption that satellite-derived seascapes describe regions of biogeochemical coherence. The seasonal cycle of the North Pacific was characterized at three levels of spatiotemporal hierarchy and broader relevance of monthly ���resolved seascapes was assessed through analysis of variance (ANOVA) and multiple linear regression (MLR) analyses of nutrient, primary productivity, and pCO��� data. Distinct nutrient and primary productivity regimes were well-characterized in the coarsest two levels of hierarchy (ANOVA, R�� = 0.5-0.7). Finer scale partitioning was more relevant for pCO���. MLR analyses revealed differential forcing on pCO��� across seascapes and hierarchical levels and a 33 % reduction in mean model error with increased partitioning (from 18.5 ��atm to 12.0 ��atm pCO���). In Chapter 3 we verified the seascapes with in situ collections of microbial abundance and structure. Flow cytometry data was collected from two long term time series and several cruises spanning thousand kilometers of the NE Pacific; these data allowed us to quantify spatiotemporal patterns. In addition, multiple response permutation analysis revealed differences in community structure across discrete seascapes, in terms of both absolute and relative abundances. Principal component analysis of the assemblage supported seascape divisions and revealed structure along environmental gradients with strong associations with chlorophyll a and sea surface temperature and, to a lesser extent, with mixed layer depth and mean photosynthetically active radiation in the mixed layer. Differences of assemblage structure between seascapes and strength of environmental forcing were strong in the subarctic and transition zones, but less pronounced in the subtropics, suggesting satellite-detected changes in bulk properties that may be associated with local physiology or interannual shifts in seascape boundaries. Based on the work presented in Chapter 4, we discovered that interannual shifts in the boundaries of a transition seascape and two distinct oligotrophic subtropical seascapes affect the variability observed at benchmark time series Station ALOHA; the latter two seascapes oscillate in their contributions to the expansion of the entire subtropics. On interannual scales, in situ phytoplankton abundance (as measured by chl-a), net primary productivity (NPP), and the relative abundance of eukaryotic phytoplankton and Synechococcus sp. increased during periods of encroachment by the transition seascape. Conversely, the relative abundance of Prochlorococcus increased and chl ���a and NPP decreased when the highly oligotrophic seascape encroached on Station ALOHA. The dynamic range (~6 million km��) of subtropical expansion is born almost entirely by the transition zone - resulting in a transfer of ~1.2 Pg of total primary C production between a system primed for export production and one dominated by the microbial loop. In Chapter 5, we investigated multiple factors that contribute to the effectiveness of the biological pump in the transition seascape. Near-continuous measurements of net primary production (NPP), net community production (NCP) and several ecophysiological variables were collected in across subarctic, transition, and subtropical seascapes of the Northeast Pacific during August and September of 2008. Mesoscale processes and shifts in community structure contributed to high export efficiency in the subtropical seascape; the convergence of assemblage structure, high biomass, moderate NPP: NCP and high NCP contributed to biologically mediated air-sea exchange in the transition seascape. Furthermore, NPP and NCP were strongly spatially coupled in both the transition (r[subscript 1, 39]=0.70; p<0.0001) and subtropical seascapes (r[subscript 1, 45]= 0.68, p<0.0001), suggesting the possibility for empirical modeling efforts. This dissertation provides a first step to characterize the seascape variability in the NE Pacific and to understand the modulation of primary and export production in a critical transition region. The multivariate seascape approach described here provides spatiotemporal context for in situ studies and allows objective comparisons of systems' responses to climatic forcing. An integrated ocean observing system will require insight from in situ observations and experiments, ecosystem models, and satellite remote sensing. The results highlighted in this dissertation suggest that the pelagic seascape framework, through its capacity to scale both context and mechanism, may serve as an important and unifying component of such an observing system. / Graduation date: 2013

In light of increasing harmful algal blooms and the need to protect human health and aquatic resources, proactive management approaches merit further study. For this purpose I conducted field samplings to characterize plankton community composition and laboratory experiments to test some approaches to new management schemes in the lower Rincon Delta. On site measurements and microscopic analysis showed that environmental parameters and plankton community composition varied considerably among sampling stations and sampling dates. A recent modeling study suggested that manipulation of freshwater inflow to estuaries might prevent phytoplankton blooms and enhance secondary productivity. To test this theory I conducted three semi-continuous design and flow-through incubation design experiments using natural plankton assemblages. I investigated the effect of two different pulsing regimes of inflow and nutrient loading on zooplankton densities, and phytoplankton biomass and diversity. Despite differences in zooplankton structure and phytoplankton community composition between the two experiment designs, the results confirmed that pulsed inflows might alter plankton dynamics. My findings showed that 3-day pulse treatments consistently supported greater zooplankton densities and higher phytoplankton species diversity when compared to 1-day pulse treatments. In addition, accumulation of phytoplankton biovolume remained low during 3-day pulse treatments. Differences in zooplankton performance between 3-day pulse and 1-day pulse inflow treatments were likely due to the ability of phytoplankton to uptake and store greater amounts of nutrients under conditions of 3-day pulse inflow. This resulted in food of higher quality for zooplankton, and might have supported greater zooplankton population growth rates. Additionally, in an attempt to understand the mechanisms leading to high biodiversity in aquatic ecosystems, I built a resource-storage model and studied the effects of resource-storage on competition of multiple phytoplankton species on multiple abiotic resources. I compared this model with a well-established multi-species competition model. My results showed that for certain species combinations a resource-storage-based model can generate dissimilar outcomes when compared to a model without resource-storage.

In light of increasing harmful algal blooms and the need to protect human health and aquatic resources, proactive management approaches merit further study. For this purpose I conducted field samplings to characterize plankton community composition and laboratory experiments to test some approaches to new management schemes in the lower Rincon Delta. On site measurements and microscopic analysis showed that environmental parameters and plankton community composition varied considerably among sampling stations and sampling dates. A recent modeling study suggested that manipulation of freshwater inflow to estuaries might prevent phytoplankton blooms and enhance secondary productivity. To test this theory I conducted three semi-continuous design and flow-through incubation design experiments using natural plankton assemblages. I investigated the effect of two different pulsing regimes of inflow and nutrient loading on zooplankton densities, and phytoplankton biomass and diversity. Despite differences in zooplankton structure and phytoplankton community composition between the two experiment designs, the results confirmed that pulsed inflows might alter plankton dynamics. My findings showed that 3-day pulse treatments consistently supported greater zooplankton densities and higher phytoplankton species diversity when compared to 1-day pulse treatments. In addition, accumulation of phytoplankton biovolume remained low during 3-day pulse treatments. Differences in zooplankton performance between 3-day pulse and 1-day pulse inflow treatments were likely due to the ability of phytoplankton to uptake and store greater amounts of nutrients under conditions of 3-day pulse inflow. This resulted in food of higher quality for zooplankton, and might have supported greater zooplankton population growth rates. Additionally, in an attempt to understand the mechanisms leading to high biodiversity in aquatic ecosystems, I built a resource-storage model and studied the effects of resource-storage on competition of multiple phytoplankton species on multiple abiotic resources. I compared this model with a well-established multi-species competition model. My results showed that for certain species combinations a resource-storage-based model can generate dissimilar outcomes when compared to a model without resource-storage.

Phytoplanktonarten unterscheiden sich in ihren Ansprüchen hinsichtlich Ressourcen wie Nährstoffe, Licht und andere physikalische Faktoren. Wechselwirkungen zwischen Nährstoffen und physikalischen Faktoren beeinflussen daher die Artenzusammensetzung einer Phytoplanktongemeinschaft. In der vorliegenden Arbeit wurde der Einfluss von Temperatur und Photoperiode auf das Phytoplanktonwachstum in Abhängigkeit vom Lichtregime und dem Angebot an Phosphor (P) und Silizium (Si) untersucht. Hierfür wurden Wachstums- und Konkurrenzexperimente unter Laborverhältnissen mit Stephanodiscus minutulus, Nitzschia acicularis (beides Bacillariophyceae) und Limnothrix redekei (Cyanophyceae) durchgeführt, ein Modell der Faktorinteraktionen entwickelt sowie ökologische Langzeitdaten des Müggelsees (Berlin) statistisch ausgewertet. Die Effekte von Temperatur und Photoperiode auf die Wachstumsraten unterschieden sich nicht zwischen konstantem und fluktuierendem Licht. Die Auswirkungen der Photoperiode und der Lichtfluktuationen auf die Wachstumsraten waren hierbei additiv. Der Grad der Limitation der Wachstumsraten durch P oder Si wurde durch die Photoperiode nicht signifikant beeinflusst. Wechselwirkungen zwischen Temperatur und P oder Si waren hingegen komplex und artspezifisch. Unabhängig davon, ob die Wachstumsraten durch P, Si oder fluktuierendes Licht gesteuert wurden, war S. minutulus konkurrenzstärker bei niedrigeren Temperaturen und N. acicularis bei höheren Temperaturen. Zusammenfassend zeigen die Ergebnisse, dass die Faktorinteraktionstypen artspezifisch sind, die Adaptation der Arten widerspiegeln und so zur Nischen-Differenzierung beitragen. Kenntnisse dieser Wechselwirkungen fördern deshalb unser Verständnis der Phytoplanktondiversität und ermöglichen es, Reaktionen des Phytoplanktons auf Klimaerwärmung und Trophieveränderung, die mit einer Verschiebung der Verhältnisse zwischen Nährstoffen, Temperatur und Licht einhergehen, besser vorherzusagen. / Phytoplankton species have different resource requirements and different sensitivities to important growth factors. Interactions between nutrients and physical factors, such as temperature and light should therefore influence the species composition. Because these interactions are poorly understood, this study investigated the interactive effects of temperature and photoperiod on phytoplankton growth controlled by fluctuating light, phosphorus (P) and silicon (Si). Growth and competition experiments were performed in the laboratory on Stephanodiscus minutulus, Nitzschia acicularis (both Bacillariophyceae) and Limnothrix redekei (Cyanophyceae). A model of factor interactions was developed and long-term field data from Lake Müggelsee (Berlin) were statistically analysed. Temperature and photoperiod had the same influence on growth under fluctuating light as they did under constant light. The photoperiod and short term light fluctuations caused by mixing had additive effects on growth. P and Si interacted strongly with temperature with respect to growth, but less with the photoperiod. The Droop relation fitted to S. minutulus but not N. acicularis. The Monod equation could not sufficiently account for non-steady dynamics of diatom growth under Si limitation, underestimating uptake rates and overestimating uptake affinity. Estimates based on the Monod model may therefore considerably underestimate the degree of Si limitation. The types of factor interactions were generally species-specific, reflected niche adaptation and enhanced niche differentiation. Interactions between nutrients and physical factors are relevant to growth during spring and contribute to the phytoplankton composition. Understanding the interactions should improve our knowledge of phytoplankton diversity and increase our ability to predict phytoplankton response to climate and trophic change, which shift the relationship between nutrients, temperature and light.

L’objectif de ce travail de thèse vise à analyser les effets de quelques pesticides et d’un adjuvant sur des organismes marins, représentatifs de quatre niveaux trophiques, à savoir des micro-algues, un échinoderme, des bivalves et un poisson. L’analyse de la pollu-sensibilité est basée sur l’utilisation de différents bio-essais existants ou adaptés au contexte de cette étude.Les tests de toxicité ont permis d’évaluer la sensibilité de trois espèces phytoplanctoniques (Chaetoceros calcitrans, Isochrysis aff. Galbana et Tetraselmis suecica) vis-à-vis d’un fongicide l’époxiconazole (pur et en formulation commerciale Opus) et de l’adjuvant nonylphénol. D’une manière générale, la croissance de C. calcitrans et I. aff. Galbana s’avère plus sensible à l’action des contaminants étudiés. Ainsi, en utilisant pour C. calcitrans un milieu reproduisant les conditions naturelles du Golfe de Gabès, des valeurs de CE50 de 2 ,31 mg/L et 2,9 μg/l sont obtenues respectivement avec la substance active époxiconazole, et le produit formulé. Ces résultats montrent l’importance des adjuvants dans la toxicité et que les micro-algues peuvent être sensibles aux effets non-cibles d’un fongicide triazole.En outre, l’âge des cellules, les conditions d’éclairement et de composition des milieux de culture induisent des changements de sensibilité au fongicide, suggérant que la densité cellulaire est un paramètre important dans les tests de toxicité.L’analyse de quelques paramètres physiologiques montre que les contaminants utilisés induisent une augmentation du volume cellulaire, des échanges gazeux, de la teneur en pigments et en ATP. Il apparaît ainsi que les toxiques utilisés réduisent la vitesse de croissance, prolongeant le cycle cellulaire, sans affecter la production de nouveaux matériaux, nécessaires à la construction de nouvelles cellules.Par ailleurs, une étude réalisée en microcosmes lors d’un bloom de l’algue toxique Karenia selliformis dans le golfe de Gabès, montre que les différents contaminants chimiques (époxiconazole, chlorpyriphos-éthyl, nonylphénol) produisent des modifications drastiques de la structure des communautés phytoplanctoniques, fonction de la nature et de la concentration du contaminant.La toxicité des différents contaminants a été étudiée sur des animaux marins, aux stades embryo-larvaire (oursin, huître, palourde), métamorphose des larves (palourde) et survie des larves (turbot). Les résultats montrent que les larves du turbot sont les plus sensibles à l’action des contaminants avec des CE50 allant de 2,78 à 492 μg/L selon le toxique et que chez la palourde, la métamorphose est le stade le plus sensible parmi les trois stades de développement étudiés. Les contaminants utilisés produisent des anomalies du développement et des malformations embryonnaires qui peuvent induire une réduction de la production naturelle en agissant i) directement sur le développement embryo-larvaire et ii) indirectement sur la qualité et la biodisponibilité de l’aliment à travers la variation de la biomasse phytoplanctonique. Ces résultats soulignent la nécessité d’appliquer les toxiques à différents organismes marins présentant des organisations différentes pour apprécier pleinement leur impact. / This work aims to study the effects of a few pesticides and one adjuvant on marine organisms, representatives of four trophic levels : micro-algae, echinoderm, bivalves and fish. Analysis of the pollu-sensitivity was based on the utilisation of existing bio-assays or adapted to this study.Phytotoxic assessments were conducted on three phytoplanktonic species (Chaetoceros calcitrans, Isochrysis aff. Galbana et Tetraselmis suecica) using the fungicide epoxiconazole and the adjuvant nonylphenol. Sensitivity to these toxicants of C. calcitrans and I. aff. Galbana was high. Thus, when C. calcitrans was grown in a medium simulating pre-winter conditions in Gabès Gulf, EC50 values were respectively, 2.31 mg/L and 2.9 μg/L for epoxiconazole active ingredient and epoxiconazole-formulated. These results questioned the use of ecotoxicological data obtained solely using active molecules of pesticides rather the complete formulation and show that non-target micro-algae may be affected by a triazole fungicide.Moreover, cell age, light and nutrient composition induced changes in epoxiconazole sensitivity, suggesting that cellular density is an important parameter in toxicity tests.Analysis of a few physiological parameters show that contaminants used in this study induce an increase of pigment content, ATP synthesis, and rates of oxygen exchanges while the cell volume enlarges. Consequently, the toxicants might reduce the growth rate, by a prolongation of the cell cycle without affecting the production of new material for the construction of new cells.Bioassays were conducted using microcosms during a bloom of the toxic algae Karenia selliformis in the Gulf of Gabès. The different toxicants (epoxiconazole, chlorpyrifos-éthyl, nonyphenol) produced drastic changes in the phytoplankton communities, depending on the type and concentration of the contaminant.Phytotoxic assessments were conducted on marine animal models, using different developmental stages: embryo-larval development (sea urchin, oyster, and clam), metamorphosis larvae (clam) and larvae survival (turbot). Results show that turbot larvae are most sensitive to the action of contaminants with EC50 values ranging from 2.78 to 492 μg/L depending on the toxic and that the metamorphosis is the stage the most sensitive of the three stages of development of clam studied.The pollutants produced developmental and embryonic abnormalities that might induce a reduction in the natural production by acting i) directly on the development of the marine organisms and ii) indirectly on the quality and bioavailability of food through the variation of phytoplankton biomass.These results underline the need to study pollutant effects on marine organisms having different organizations to evaluate their full impact.

En raison de leur importante capacité de réponse aux changements environnementaux, les producteurs primaires sont depuis longtemps utilisés comme indicateurs biologiques de la qualité des milieux aquatiques. La Directive Cadre Européenne sur l’Eau (2000/60/CE) préconise ainsi l’utilisation du phytoplancton, du phytobenthos et des macrophytes afin de mesurer l’état écologique des écosystèmes lacustres. Dans cette étude, ces trois compartiments ont été utilisés pour déterminer l’état écologique de cinq lacs localisés dans la région Aquitaine (Sud-Ouest de la France), lacs ayant la particularité de présenter des niveaux trophiques différents. Les résultats ont montré qu’au niveau intra-lac la composition floristique dépend fortement des variables physiques dans la plupart des systèmes tandis qu’au niveau inter-lac celle-ci dépend du niveau trophique. Le phytoplancton s’est révélé être l’indicateur de qualité le plus performant et le seul utilisable dans les eaux ouvertes, et le plus précis dans les systèmes où les macrophytes submergés étaient absents. Cependant, dans les lacs humiques, les assemblages phytoplanctoniques semblent répondre davantage à la turbidité et aux brassages fréquents de la colonne d’eau qu’aux nutriments. Dans de telles conditions, afin de mieux caractériser la qualité de l’eau, l’utilisation complémentaire du phytobenthos et des macrophytes se révèle plus pertinente. En conclusion, considérant les trois compartiments biologiques, la présente étude permet une approche complémentaire de l’état écologique des systèmes lacustres. Certaines des méthodes appliquées ici représentent un outil potentiel de détermination de la qualité de l’eau selon les exigences de la DCE, mais elles nécessitent d’être affinées pour une meilleure évaluation de l’état écologique des lacs français. Une attention particulière a été portée aux taxa exotiques observés dans ces lacs tempérés, et cet aspect doit être pris en considération lors de l’évaluation écologique. En effet, ces espèces sensiblement avantagées par les conséquences du changement climatique, peuvent altérer la structure et le fonctionnement des écosystèmes aquatiques en place, et aboutir à une perte de diversité. / Due to their important ability to respond to environmental changes, primary producers have been used for a long time as biological indicators of water quality. The Water Framework Directive (2000/60/EC) recommends the use of the phytoplankton, phytobenthos (diatoms) and macrophytes in the ecological status assessment of lakes. In this study, these three compartments have been used to determine the ecological status of five lakes located in the Aquitaine region (southwest of France) with different trophic status. The results showed that within lakes, the floristic composition in most of the systems strongly depends on physical parameters whereas among lakes it depends on the trophic status. The phytoplankton proved to be the most powerful indicator of quality in open-water areas as well as in systems where submerged macrophytes are absent. However, in the humic lakes, the phytoplankton assemblages seem to respond more to turbidity and mixing than to nutrient load. Under such conditions, water quality could be underestimated and the complementary use of phytobenthos and macrophytes appears more appropriated. In conclusion, considering the three biological elements, the present study allows a complementary approach of the ecological status of the lakes. Some of the methods applied here represent a potential tool for the assessment of the ecological status in the context of WFD, but they need to be refined to assess more properly the ecological status of French lakes. A special attention was paid to exotic taxa observed in these temperate lakes, and this aspect must be taken into account in the ecological assessment. Indeed, these species favoured by the consequences of the climate change, can modify the structure and functioning of the aquatic ecosystems, and lead to a loss of diversity.

A mistura vertical de águas profundas, ricas em nutrientes e de baixas temperaturas, características da Água Central do Atlântico Sul (ACAS), com águas de baixa d;sponibilidade nutricional, baixa biomassa fitoplanctônica e de temperaturas mais elevadas, características da Água Costeira (AC), da região de Ubatuba, foi simulada através da realização de bioensaios. As águas foram incubadas com as populações fitoplanctônicas naturais, sem enriquecimentos nutricionais, sob diferentes níveis de atenuação radiação solar incidente total (100, 30 e 10% de IL) e temperatura igual a da água do mar de superfície. o potencial quimico e biológico dos dois tipos de água (ACAS e AC) e de uma mistura equitativa de ambas, foi avaliado através do monitoramento diário de aspectos quali- quantitativos do fitoplâncton (Clorofila-a, contagem e identificação das células e taxas de produção primária) e do teor de nutrientes dissolvidos no meio, durante o período de incubação. Foram realizadas três etapas experimentais: em Jul/88, Jan/89 e Jul/89 com durações de 8, 15 e 14 dias, respectivamente. A mistura da ACAS com AC apresentou os melhores rendimentos máximos de Clorofila-a e produção primária, sob os níveis de 100 e 30 % de IL. A 10% de IL, a ACAS mostrou- se mais produtiva do que quando misturada à AC e, em termos de Cl-a integral, teve rendimento superior inclusive ao obtido pela Mistura a 100% de IL. A AC apresentou um rendimento menor que as outras duas águas sob os três niveis de luz utilizados. Sob intensidades luminosas mais altas os nutrientes foram rapidamente assimilados causando uma floração de espécies oportunistas (diatomáceas) logo no inicio do periodo de incubação, o que não foi observado sob intensidades luminosas menores. Os resultados ainda indicam que os \"lag-time\" observados no inverno foram significativamente maiores que os do verão. Foi também possivel observar a existência de uma estratificação fisiológica das populações fitoplanctônicas presentes em uma mesma massa d\' água, em função da profundidade, no inverno. Esta estratificação provavelmente deveu-se à diferentes suprimentos nutricionais de origem orgânica que estariam disponiveis apenas para as populações da água de fundo, possivelmente devido a interação da água com o sedimento. Estes resultados demostram a grande importância da água da ACAS como agente fertilizador para as águas oligotróficas da região, permitindo a ocorrência de produção nova. / The vertical mixing of the rich, low temperature, deep South Atlantic Central Water (SACW), with the low nutrient, low phytoplanktonic biomass and hiSh temperature Coastal Water (CW), irom Ubatuba region, was simulated erforming bioassays. The waters were incubated with the authoctonous phytoplankton without any nutrient addition, under ifferent attenuation levels (100, 30 and 10% ) of the total incident solar radiation and at the same temperature as the urface sea water. The chemical and biological potential of each water (SACW and CW), and of an equivalent mixture of them, wa evaluated by means of a daily monitoring of quali and quantitative phytoplankton aspects (Chl-a, cell counting and photosynthetic rates) and of the dissolved nutrient concentrations durins the incubation period. Three series of experiments were performed: Jul/88, Jan/89 and Jul/89, lasting 8, 15 and 14 days espectively. The mixing of SACW and CW presented the best maximum yield oi chlorophyll and photosyntetic rates under 100 and 30% solar radiation. Under 10% SACW alone waa more productive than mixed with CW and, considering integral chlorophyll-a during the whole period. it preaented a higher yield than the one obtained with Mixed Water under 100% oí solar radiation. CW preaented the lowest yield under the experimental light leveI used. Under high light intensi ties nutrients were quickly assimilated inducing a bloom of opportunist species (diatoms) at the begining of the incubation period, which was not observed under low light intensities.(diatoms) at the begining of the incubation period, which was not observed under low light intensities. Results also indicate that the Ias times observed during winter were ignificantIy higher than those during summer. It was possible to observe the existence of a Physiological atratification among phytoplank.tonic populations from the same water mass, as a function of depht, durins winter. This phenomenon was probably due to diatinct nutricional aupply of orsanic origen that would be avaiIabIe to deep populations only, possibly as a consequence of ater/sediment interactiona. These results demonstrate the great importance of SACW as a fertilizer agent to the oligothrophic waters of the region, allowing the occurrence of new production.