<p>Tl⁺ is thought to be toxic to cells due to ionic mimicry of K⁺. The aims of this study were two-fold. First, to identify whether K⁺ and Tl⁺ were interacting in isolated guts, whole animals and tissues in <em>Chironomus riparius, </em>and second, to determine the strategies of Tl⁺ tolerance. <em>C. riparius. </em>were very tolerant towards Tl⁺with a 48-hr LC₅₀ of 723 μmol l^-1. The Scanning Ion-selective Technique (SIET) allowed us to identify the caecae, AMG and PMG as the major K⁺-transporting regions of isolated guts. Evidence for an interaction was based on the finding that Tl⁺ was transported in the same directions at these segments (and others), and that 50 μmol l^-1Tl⁺ decreased K⁺ flux at the AMG and PMG. In addition, exposure to Tl⁺ prior to flux measurements had significant effects on net K⁺ transport by the gut. Measurements of Tl⁺ and K⁺ concentrations in the whole animal, gut and hemolymph by Atomic Absorption Spectroscopy (AAS) indicated that Tl⁺ uptake was saturable in the whole animal and gut, and non-saturable in the hemolymph. Together with the SIET measurements, the AAS data suggests that high levels of Tl⁺ can perturb K⁺ transport and homeostasis. The absorption of Tl⁺ from the gut to hemolymph, measured by SIET, was confirmed by hemolymph measurements of Tl⁺ using AAS. This indicated that Tl⁺ gains access to the hemolymph and that sensitive tissues (such as the nervous system) are thus exposed. However, survival of <em>C. riparius</em> at these concentrations implies efficient mechanisms for detoxification of Tl⁺. This tolerance may involve sequestration in the gut, metal-binding proteins and increased secretion by the anal papillae and MTs. In addition, loss of K⁺ from the muscle may prevent hypokalemia in the hemolymph and gut.</p> / Master of Science (MSc)

M.Sc. (Aquatic Health) / Sediments can contain a variety of organic and inorganic contaminants. These contaminants accumulate, resulting in extremely high concentrations even once the overlying water concentrations are at or below acceptable water quality guidelines. Any changes in the physical parameters'of the overlying water can cause these pollutants to be released back into solution. Accumulated contaminants can be released at even higher concentrations than previously detected. In recent years, sediment contamination has highlighted the need to monitor these previously overlooked pollutant sources that have accumulated in aquatic ecosystems. South Africa does not currently have standardised methods to assess sediment toxicity. Although international methods exist, they are largely untested in South Africa and the organisms needed to conduct these tests are not readily available. Over the years numerous culture methods have been develop globally for culturing organism to be used for water and sediment toxicity tests. In South Africa, the focus has mainly been on culturing organisms for water. toxicity testing. Sediment toxicity testing with indigenous organism however, was not developed. Established international culture methods from the United States Environmental Protection Agency, the Organisation for Economic Cooperation and Development, and Environment Canada were taken into consideration when developing the laboratory culture method for two (2)of the selected organisms (Chironomus spp. & Hydra sp.) from this study. A preliminary culture method was also developed for the third selected organism, Melanoides tuberculata (gastropod). The organisms cultured in this study were selected based on their extent of contact with the substrate, ease of handling, availability, culture maintenance as well as their reproductive cycle. The Hydra, Chironomids and M. tuberculata cultures were successfully breeding under laboratory conditions and remained stable. The Chironomus sp. and M. tuberculata maintain contact with the sediment making them suitable as ecologically relevant organisms for use in whole sediment toxicity testing in South Africa.

No description available.

In den Jahren 2005 bis 2010 erfolgte im Rahmen der Erarbeitung der vorliegenden Dissertationsschrift eine ökologische Untersuchung der Chironomidenfauna in der Talsperre Saidenbach (Sachsen, Erzgebirge). Drei Arten mit hoher Abundanz konnten bei der umfassenden Artenanalyse im Jahr 2005 ermittelt werden: Procladius crassinervis, P. choreus und Chironomus anthracinus. Zusätzlich wurde die Art C. plumosus aufgrund ihrer engen Verwandtschaft zu C. anthracinus in die Untersuchung einbezogen. Die Arbeit ist auf vier Schwerpunkte fokussiert, wobei die Larven und Puppen der vier Arten analysiert wurden. (1) Die Erarbeitung einer zuverlässigen Methode zur Unterscheidung der Larven der beiden eng verwandten Procladius-Arten basierend auf morphologischen Kriterien (Imaginalscheiden-entwicklung, Kopfkapselgröße und Körperlänge) sowie die Tiefenverteilung der Puppen waren eine Vorbedingung für weiterführende Analysen des Lebenszyklus (LZ) dieser beiden Arten. (2) Die Untersuchung des LZ war der zweite Schwerpunkt. Der LZ wurde stark von abiotischen Faktoren wie Temperatur, Sauerstoff und Biovolumen des Phytoplanktons kontrolliert. (3) Die raum-zeitlichen Verteilungsmuster der vier Arten wurden zunächst bezüglich großräumiger Unterschiede über einen Tiefengradienten innerhalb eines Transektes analysiert. Hierbei zeigte sich bei allen vier Arten eine zeitliche Änderung im jeweiligen Hauptverbreitungsgebiet. Die jungen Larven von C. anthracinus, C. plumosus und P. choreus wanderten im Verlauf ihrer Entwicklung bis zur Verpuppung in flachere Bereiche, P. crassinervis wanderte in tiefere Bereiche. Die Analyse der Verteilungsunterschiede der Larven zwischen zwei verschieden stark eutrophierten Buchten ergab höhere Dichten der beiden Chironomus-Arten in der Bucht mit dem größeren Zulauf und der höheren Phytoplanktonkonzentration im Vergleich mit den anderen Arten. Eine Analyse des kleinräumigen Verteilungsmusters fokussierte auf der Frage, ob die Larven gleichmäßig verteilt oder aggregiert auftraten. Die Untersuchung des vertikalen Verteilungsmusters erforschte das Schwimmverhalten der Larven. (4) Der letzte Aspekt war eine experimentelle Untersuchung, die am Beispiel von C. anthracinus durchgeführt wurde mit dem Ziel, den Proximatfaktor für die beobachtete Wanderung der Larven zu ermitteln, der letztendlich die Temperatur war. Puppen bevorzugten im Experiment wärmere Temperaturen und junge Larven kühlere Temperaturen. Die fünfjährige Untersuchung der Chironomiden in der Talsperre Saidenbach beschreibt insgesamt die komplexe Verhaltensreaktion der Chironomiden, die einen wesentlichen Teil der benthischen Lebensgemeinschaft darstellen, bezüglich der Lebenszyklusmuster (Voltinismus, Verpuppung), der Abundanzänderungen (inner- und zwischenjährlich) sowie der groß- und kleinräumigen Verteilung unter der Einwirkung der wichtigsten Umweltfaktoren. / In the context of the present dissertation an ecological study was performed about chironomids in Saidenbach Reservoir in the Saxony Ore Mountains, Germany during the five years from 2005 to 2010. A preliminary overall species analysis in 2005 showed that three species were most abundant: Procladius crassinervis, P. choreus and Chironomus anthracinus. Additionally, the species C. plumosus was examined because of its close relationship to C. anthracinus. The study is focussed on four subjects, whereby larvae and pupae of the four species were analysed. (1) The elaboration of a reliable method to distinguish the larvae of the two closely related species P. crassinervis and P. choreus on the basis of morphological criteria (imaginal disc development, larval head capsule size and body length) as well as the depth distribution of their pupae was a precondition to the profound analysis of their life cycles. (2) The investigation of the life cycle pattern of the four species was the second focus. The life cycle of the four species was found to be strongly influenced by abiotic conditions such as temperature, oxygen and biovolume of the phytoplankton. (3) The spatial and temporal distribution pattern of the four species was analysed in view of large scale differences over a depth gradient in one transect. Here, in all four species a shift in the mainly settled lake bottom area occurred. The young larvae of C. anthracinus, C. plumosus and P. choreus migrated during maturing and pupation towards shallower areas; P. crassinervis migrated to deeper areas. The distribution differences between two different bays showed that the two Chironomus species had higher densities in the bay with the higher inflow which resulted in a higher phytoplankton standing stock compared to the other species. A small scale distribution pattern analysis focussed on finding out whether the larvae were aggregated or randomly distributed. The vertical distribution analysis examined the swimming behaviour of the larvae. (4) The last aspect was an experimental setup exemplarily driven with C. anthracinus which showed that the migration was stimulated by the proximate factor temperature as pupae preferred warmer temperatures and young larvae colder temperatures. Altogether, the five year study about chironomids in Saidenbach Reservoir pointed out the complex reaction in the behaviour of an important part of the benthic community concerning the life cycle pattern (voltinism, pupation pattern), the changing in abundances (inter-annual and intra-annual) and the large scale and small scale distribution pattern under the rule of the most important environmental factors.

In den Jahren 2005 bis 2010 erfolgte im Rahmen der Erarbeitung der vorliegenden Dissertationsschrift eine ökologische Untersuchung der Chironomidenfauna in der Talsperre Saidenbach (Sachsen, Erzgebirge). Drei Arten mit hoher Abundanz konnten bei der umfassenden Artenanalyse im Jahr 2005 ermittelt werden: Procladius crassinervis, P. choreus und Chironomus anthracinus. Zusätzlich wurde die Art C. plumosus aufgrund ihrer engen Verwandtschaft zu C. anthracinus in die Untersuchung einbezogen. Die Arbeit ist auf vier Schwerpunkte fokussiert, wobei die Larven und Puppen der vier Arten analysiert wurden. (1) Die Erarbeitung einer zuverlässigen Methode zur Unterscheidung der Larven der beiden eng verwandten Procladius-Arten basierend auf morphologischen Kriterien (Imaginalscheiden-entwicklung, Kopfkapselgröße und Körperlänge) sowie die Tiefenverteilung der Puppen waren eine Vorbedingung für weiterführende Analysen des Lebenszyklus (LZ) dieser beiden Arten. (2) Die Untersuchung des LZ war der zweite Schwerpunkt. Der LZ wurde stark von abiotischen Faktoren wie Temperatur, Sauerstoff und Biovolumen des Phytoplanktons kontrolliert. (3) Die raum-zeitlichen Verteilungsmuster der vier Arten wurden zunächst bezüglich großräumiger Unterschiede über einen Tiefengradienten innerhalb eines Transektes analysiert. Hierbei zeigte sich bei allen vier Arten eine zeitliche Änderung im jeweiligen Hauptverbreitungsgebiet. Die jungen Larven von C. anthracinus, C. plumosus und P. choreus wanderten im Verlauf ihrer Entwicklung bis zur Verpuppung in flachere Bereiche, P. crassinervis wanderte in tiefere Bereiche. Die Analyse der Verteilungsunterschiede der Larven zwischen zwei verschieden stark eutrophierten Buchten ergab höhere Dichten der beiden Chironomus-Arten in der Bucht mit dem größeren Zulauf und der höheren Phytoplanktonkonzentration im Vergleich mit den anderen Arten. Eine Analyse des kleinräumigen Verteilungsmusters fokussierte auf der Frage, ob die Larven gleichmäßig verteilt oder aggregiert auftraten. Die Untersuchung des vertikalen Verteilungsmusters erforschte das Schwimmverhalten der Larven. (4) Der letzte Aspekt war eine experimentelle Untersuchung, die am Beispiel von C. anthracinus durchgeführt wurde mit dem Ziel, den Proximatfaktor für die beobachtete Wanderung der Larven zu ermitteln, der letztendlich die Temperatur war. Puppen bevorzugten im Experiment wärmere Temperaturen und junge Larven kühlere Temperaturen. Die fünfjährige Untersuchung der Chironomiden in der Talsperre Saidenbach beschreibt insgesamt die komplexe Verhaltensreaktion der Chironomiden, die einen wesentlichen Teil der benthischen Lebensgemeinschaft darstellen, bezüglich der Lebenszyklusmuster (Voltinismus, Verpuppung), der Abundanzänderungen (inner- und zwischenjährlich) sowie der groß- und kleinräumigen Verteilung unter der Einwirkung der wichtigsten Umweltfaktoren.:1. GENERAL INTRODUCTION 2. MORPHOLOGICAL DIFFERENTIATION OF TWO PROCLADIUS AND TWO CHIRONOMUS SPECIES IN THE MESOTROPHIC SAIDENBACH RESERVOIR 2.1 Introduction 2.2 Material and methods 2.2.1 Sampling of larvae 2.2.2 Species identification 2.2.3 Differentiation of the Procladius species by means of head capsule size and depth distribution 2.2.4 Other morphological criteria 2.2.5 Development of imaginal discs 2.3. Results 2.3.1 Procladius crassinervis and P. choreus 2.3.2 Chironomus anthracinus and C. plumosus 2.4. Discussion 2.4.1 Method discussion 2.4.2 Head capsule width 2.4.3 Larval growth 3. FIVE - YEAR LIFE CYCLE PATTERN OF TWO PROCLADIUS AND TWO CHIRONOMUS SPECIES IN THE MESOTROPHIC SAIDENBACH RESERVOIR 3.1 Introduction 3.2 Material and methods 3.2.1 Study area 3.2.2 Sampling of chironomid larvae 3.2.3 Sampling of chironomid pupae 3.2.4 Mortality 3.2.5 Abiotic conditions and phytoplankton 3.3 Results 3.3.1 Abiotic conditions and phytoplankton 3.3.1.1 Temperature 3.3.1.2 Oxygen 3.3.1.3 Phytoplankton 3.3.2 Life cycle analysis 3.3.2.1 Composition of instars 3.3.2.2 Procladius crassinervis 3.3.2.3 Procladius choreus 3.3.2.4 Chironomus anthracinus 3.3.2.5 Chironomus plumosus 3.3.2.6 Tanytarsini 3.3.2.7 Other species 3.3.3 Influence of abiotic conditions on pupation and life cycle 3.3.3.1 Procladius crassinervis 3.3.3.2 Procladius choreus 3.3.3.3 Chironomus anthracinus 3.3.3.4 Chironomus plumosus 3.3.3.5 Tanytarsini 3.3.4 Mortality of larvae during pupation 3.4 Discussion 3.4.1 Method discussion 3.4.2 Life cycle 3.4.3 Influence of controlling factors 3.4.4 Larval mortality and chironomid pupae as prey 4. SMALL AND LARGE SCALE DISTRIBUTION ASPECTS AND MIGRATION OF TWO PROCLADIUS AND TWO CHIRONOMUS SPECIES IN THE MESOTROPHIC SAIDENBACH RESERVOIR 4.1 Introduction 4.2 Study area 4.3 Material and methods 4.3.1 Sampling of chironomid pupae 4.3.2 Sampling of chironomid larvae 4.3.3 Large scale distribution 4.3.3.1 Depth gradient of the larval abundance 4.3.3.2 Distribution between different lake areas 4.3.4 Small scale distribution - patchiness 4.3.5 Vertical distribution 4.3.5.1 Residence depth in the sediment 4.3.5.2 Larvae in the water column 4.4 Results 4.4.1 Large scale distribution 4.4.1.1 Depth gradient of the larval abundance 4.4.1.2 Distribution between different lake areas 4.4.2 Small scale distribution - patchiness 4.4.3 Vertical distribution 4.4.3.1 Residence depth in the sediment 4.4.3.2 Larvae in the water column 4.5 Discussion 4.5.1 Large scale distribution 4.5.1.1 Depth gradient of the larval abundance 4.5.1.2 Distribution between different lake areas 4.5.2 Small scale distribution - patchiness 4.5.3 Vertical distribution 4.5.3.1 Residence depth in the sediment 4.5.3.2 Larvae in the water column 5. INVESTIGATIONS ON THE PREFERENCE TEMPERATURE OF C. ANTHRACINUS FROM THE MESOTROPHIC SAIDENBACH RESERVOIR 5.1 Introduction 5.2 Material and methods 5.2.1 Influence of temperature on the timing of pupation 5.2.2 Preference temperature 5.2.3 Locomotory activity of larvae 5.3 Results 5.3.1 Migratory activity of C. anthracinus in the field 5.3.2 Influence of temperature on the timing of pupation 5.3.3 Preference temperature 5.3.4 Locomotory activity of larvae 5.4 Discussion 5.4.1 Influence of temperature on the timing of pupation 5.4.2 Preference temperature 5.4.3 Agitation activity of larvae 6. OVERALL SUMMARY AND FUTURE PROSPECTS 7. REFERENCES EIDESSTATTLICHE ERKLÄRUNG DANKSAGUNG / In the context of the present dissertation an ecological study was performed about chironomids in Saidenbach Reservoir in the Saxony Ore Mountains, Germany during the five years from 2005 to 2010. A preliminary overall species analysis in 2005 showed that three species were most abundant: Procladius crassinervis, P. choreus and Chironomus anthracinus. Additionally, the species C. plumosus was examined because of its close relationship to C. anthracinus. The study is focussed on four subjects, whereby larvae and pupae of the four species were analysed. (1) The elaboration of a reliable method to distinguish the larvae of the two closely related species P. crassinervis and P. choreus on the basis of morphological criteria (imaginal disc development, larval head capsule size and body length) as well as the depth distribution of their pupae was a precondition to the profound analysis of their life cycles. (2) The investigation of the life cycle pattern of the four species was the second focus. The life cycle of the four species was found to be strongly influenced by abiotic conditions such as temperature, oxygen and biovolume of the phytoplankton. (3) The spatial and temporal distribution pattern of the four species was analysed in view of large scale differences over a depth gradient in one transect. Here, in all four species a shift in the mainly settled lake bottom area occurred. The young larvae of C. anthracinus, C. plumosus and P. choreus migrated during maturing and pupation towards shallower areas; P. crassinervis migrated to deeper areas. The distribution differences between two different bays showed that the two Chironomus species had higher densities in the bay with the higher inflow which resulted in a higher phytoplankton standing stock compared to the other species. A small scale distribution pattern analysis focussed on finding out whether the larvae were aggregated or randomly distributed. The vertical distribution analysis examined the swimming behaviour of the larvae. (4) The last aspect was an experimental setup exemplarily driven with C. anthracinus which showed that the migration was stimulated by the proximate factor temperature as pupae preferred warmer temperatures and young larvae colder temperatures. Altogether, the five year study about chironomids in Saidenbach Reservoir pointed out the complex reaction in the behaviour of an important part of the benthic community concerning the life cycle pattern (voltinism, pupation pattern), the changing in abundances (inter-annual and intra-annual) and the large scale and small scale distribution pattern under the rule of the most important environmental factors.:1. GENERAL INTRODUCTION 2. MORPHOLOGICAL DIFFERENTIATION OF TWO PROCLADIUS AND TWO CHIRONOMUS SPECIES IN THE MESOTROPHIC SAIDENBACH RESERVOIR 2.1 Introduction 2.2 Material and methods 2.2.1 Sampling of larvae 2.2.2 Species identification 2.2.3 Differentiation of the Procladius species by means of head capsule size and depth distribution 2.2.4 Other morphological criteria 2.2.5 Development of imaginal discs 2.3. Results 2.3.1 Procladius crassinervis and P. choreus 2.3.2 Chironomus anthracinus and C. plumosus 2.4. Discussion 2.4.1 Method discussion 2.4.2 Head capsule width 2.4.3 Larval growth 3. FIVE - YEAR LIFE CYCLE PATTERN OF TWO PROCLADIUS AND TWO CHIRONOMUS SPECIES IN THE MESOTROPHIC SAIDENBACH RESERVOIR 3.1 Introduction 3.2 Material and methods 3.2.1 Study area 3.2.2 Sampling of chironomid larvae 3.2.3 Sampling of chironomid pupae 3.2.4 Mortality 3.2.5 Abiotic conditions and phytoplankton 3.3 Results 3.3.1 Abiotic conditions and phytoplankton 3.3.1.1 Temperature 3.3.1.2 Oxygen 3.3.1.3 Phytoplankton 3.3.2 Life cycle analysis 3.3.2.1 Composition of instars 3.3.2.2 Procladius crassinervis 3.3.2.3 Procladius choreus 3.3.2.4 Chironomus anthracinus 3.3.2.5 Chironomus plumosus 3.3.2.6 Tanytarsini 3.3.2.7 Other species 3.3.3 Influence of abiotic conditions on pupation and life cycle 3.3.3.1 Procladius crassinervis 3.3.3.2 Procladius choreus 3.3.3.3 Chironomus anthracinus 3.3.3.4 Chironomus plumosus 3.3.3.5 Tanytarsini 3.3.4 Mortality of larvae during pupation 3.4 Discussion 3.4.1 Method discussion 3.4.2 Life cycle 3.4.3 Influence of controlling factors 3.4.4 Larval mortality and chironomid pupae as prey 4. SMALL AND LARGE SCALE DISTRIBUTION ASPECTS AND MIGRATION OF TWO PROCLADIUS AND TWO CHIRONOMUS SPECIES IN THE MESOTROPHIC SAIDENBACH RESERVOIR 4.1 Introduction 4.2 Study area 4.3 Material and methods 4.3.1 Sampling of chironomid pupae 4.3.2 Sampling of chironomid larvae 4.3.3 Large scale distribution 4.3.3.1 Depth gradient of the larval abundance 4.3.3.2 Distribution between different lake areas 4.3.4 Small scale distribution - patchiness 4.3.5 Vertical distribution 4.3.5.1 Residence depth in the sediment 4.3.5.2 Larvae in the water column 4.4 Results 4.4.1 Large scale distribution 4.4.1.1 Depth gradient of the larval abundance 4.4.1.2 Distribution between different lake areas 4.4.2 Small scale distribution - patchiness 4.4.3 Vertical distribution 4.4.3.1 Residence depth in the sediment 4.4.3.2 Larvae in the water column 4.5 Discussion 4.5.1 Large scale distribution 4.5.1.1 Depth gradient of the larval abundance 4.5.1.2 Distribution between different lake areas 4.5.2 Small scale distribution - patchiness 4.5.3 Vertical distribution 4.5.3.1 Residence depth in the sediment 4.5.3.2 Larvae in the water column 5. INVESTIGATIONS ON THE PREFERENCE TEMPERATURE OF C. ANTHRACINUS FROM THE MESOTROPHIC SAIDENBACH RESERVOIR 5.1 Introduction 5.2 Material and methods 5.2.1 Influence of temperature on the timing of pupation 5.2.2 Preference temperature 5.2.3 Locomotory activity of larvae 5.3 Results 5.3.1 Migratory activity of C. anthracinus in the field 5.3.2 Influence of temperature on the timing of pupation 5.3.3 Preference temperature 5.3.4 Locomotory activity of larvae 5.4 Discussion 5.4.1 Influence of temperature on the timing of pupation 5.4.2 Preference temperature 5.4.3 Agitation activity of larvae 6. OVERALL SUMMARY AND FUTURE PROSPECTS 7. REFERENCES EIDESSTATTLICHE ERKLÄRUNG DANKSAGUNG

L’eutrophisation et la contamination des sédiments (ex : métaux, nutriments, etc.) sont des problèmes majeurs pour la protection des écosystèmes aquatiques et la protection des ressources d’eau douce. Le lac Saint-Augustin (Québec, Canada) est aux prises avec ces deux problèmes. Depuis 2001, plusieurs épisodes de fleurs d’eau de cyanobactéries sont rapportés durant la saison estivale (P &gt; 70 µg/L). Galvez et collaborateurs ont proposé une méthode de restauration pour ce lac consistant : (I) à réduire la teneur en phosphore de l’eau du lac par coagulation/floculation avec du sulfate d’aluminium et (II) à effectuer un recouvrement actif de roche calcaire et de sable afin d’isoler le floc d’Al, le P et les autres contaminants (ex., métaux) et permettre la recolonisation par le benthos. L’objectif des présents travaux était d’évaluer l’écocompatibilité de cette méthode. Deux approches écotoxicologiques ont été employées : (I) essais de toxicité monospécifiques (croissance de l’algue Pseudokirchneriella subcapitata et de la lentille d’eau Lemna minor; survie et reproduction de la daphnie Daphnia magna et de l’amphipode Hyalella azteca, survie, croissance et émergence de l’invertébré Chironomus riparius ainsi que survie des larves de tête-de-boule Pimephales promelas et des alevins de truites arc-en-ciel Oncorhynchus mykiss) et (II) essai en microcosmes de 2 litres tel qu’adapté par Triffault-Bouchet. La toxicité de l’aluminium et l’impact de la roche calcaire ont été étudiés séparément : d’abord avec eau et sédiments artificiels et ensuite avec eau et sédiments du lac Saint-Augustin. Les résultats démontrent que les algues et les daphnies sont affectées par l’application d’alun. Aucun effet n’a été observé chez les autres organismes. Ceux-ci ont eu la capacité de recoloniser les milieux traités avec l’alun ou avec la technique complète. Ces résultats tendent à démontrer que la méthode de restauration est prometteuse. L’écocompatibilité de la technique ne pourra cependant être démontrée que par des essais in situ et après un suivi étroit du phytoplancton et du zooplancton dans le lac. Toutefois, dans le cadre des présents travaux, l’efficacité des traitements (en terme de déphosphatation) n’a pas permis d’atteindre le critère de qualité du MDDEP (20 µg/L). Ces paramètres devront être étroitement suivis lors des essais in situ. Mots clés : Eutrophisation, sédiments contaminés, restauration de lac, aluminium, recouvrement actif, évaluation écotoxicologique, bioessais monospécifique, microcosmes. / Eutrophication and contaminated sediments (e.g.: nutrients, metals, etc.) are preoccupying issues in aquatic ecosystems and water resource protection. Saint-Augustin Lake (Quebec, Canada) is affected by both problems in addition to the presence of de-icing salts. This small shallow lake has low renewal time and receives an intensive phosphorus transfer from bottom sediments to the water column. Since 2001, the lake presents cyanobacteria blooms every summer (P &gt; 70 μg/L). Galvez and collaborators has proposed a remediation method for this lake that consists of (i) the precipitation of phosphorus present in the water column by the addition of alum, in association with the deposition of (ii) an active capping layer (limestone + sand) to isolated P, Al and other contaminants (e.g., metals) within bottom sediments and allow recolonisation by benthos. The objective of this study is to assess the ecotoxicological impact of that remediation method. Two ecotoxicological approaches are used to assess the impact of this method: (I) single-species bioassays (algae Pseudokirchneriella subcapitata and duckweed Lemna minor growth; daphnid Daphnia magna and amphipod Hyalella azteca survival and reproduction, invertebrate Chironomes riparius survival, growth and emergence, fathead minnow P. promelas and rainbow trouts O. mykiss survival) and (II) a 2-L microcosm as adapted by Triffault-Bouchet. Alum toxicity and limestone impact were studied separately in laboratory: first with artificial water and sediments and then using actual lake overlying water and sediments. The results show that algae and daphnids are sensitive to alum treatment. No significant effects were observed on the other organisms. These organisms had the ability to recolonize the treated media either with alum treatment or with complete treatment. These results suggest that the restoration method is promising. The environmental compatibility of the technique, would be demonstrated after testing in situ with a close monitoring of phytoplankton and zooplankton in the lake. However, the results of this study showed that the treatments dephosphatation efficacity was not enought to reach the MDDEP quality criteria (20 µg/L). Also, the concentration of residual aluminum after treatments was still over the MDDEP quality criteria after treatments. Keywords : Eutrophication, contaminated sédiments, lake restauration, aluminum, active capping, écotoxicological évaluation, monospécific bioessais, microcosms.