Insecticides have long been used as the main method in limiting agricultural pests, but their widespread use hasresulted in environmental pollution, development of resistances, and biodiversity reduction. The effects of insecticides at low residual doses on both the targeted crop pest species and beneficial insects have become a major concern. In particular, these low doses can induce unexpected positive (hormetic) effects on pest insects, such as surges in population growth exceeding what would have been observed without pesticide application. Methomyl and chlorpyrifos are two insecticides commonly used to control the population levels of the cotton leafworm Spodoptera littoralis, a major pest moth. The aim of the present study was to examine the effects ofsublethal doses of these two pesticides, known to present a residual activity and persistence in the environment, on the moth physiology. Using a metabolomic approach, we showed that sublethal doses of methomyl and chlorpyrifos have a systemic effect on the treated insects. We also demonstrated a behavioral disruption of S. littoralis larvae exposed to sublethal doses of methomyl, whereas no effects were observed for the same doses of chlorpyrifos. Interestingly, we highlighted that sublethal doses of both pesticides did not induce a change in acetylcholinesterase activity in head of exposed larvae.

Wind waves are responsible for some of the spatio-temporal gradients observed in the biotic and abiotic variables in large shallow lakes. However, their effects on the phytoplankton community composition are still largely unexplored especially in freshwater systems such as lakes. In this paper, using field observations and mesocosm bioassay experiments, we investigated the impact of turbulence generated by wind waves on the phytoplankton community composition (especially on harmful cyanobacteria) in Lake Taihu, a large, shallow eutrophic lake in China. The composition of the phytoplankton community varied with the intensity of wind waves in the different areas of the lake. During summer, when wind waves were strong in the central lake, diatoms and green algae seemed to dominate while harmful cyanobacteria dominated in the weakly influenced Meiliang Bay. Turbulence bioassays also showed that diatoms and green algae were favoured by turbulent mixing. The critical time for the shift of the phytoplankton community composition was approximately 10 days under turbulent conditions. However, short-term (6 days) turbulence is rather beneficial for the dominance of cyanobacteria. This study suggests that the duration of wind events and their associated hydrodynamics are key factors to understanding the temporal and spatial changes of phytoplankton communities.

Nous développons un modèle à générations emboîtées dans lequel l’évolution de la pollutionet la formation de la préoccupation environnementale sont endogènes. D’un côté, despersonnes concernées de façon hétérogène par les questions environnementales participentvolontairement à la dépollution. D’un autre côté, la transmission des attitudes vis-à-vis del’environnement résulte d’un choix économique qui dépend lui-même de la pollution. Lemodèle prédit que la proportion à long terme d’individus préoccupés par l’environnement seraforte dans tous les cas. Cependant, selon la nature de la technologie qui génère la pollution, latransition d’une société peu préoccupée par l’environnement vers une société fortementpréoccupée par l’environnement s’accompagne de deux effets différents sur le niveau depollution à long terme. Si la technologie est « propre », on aboutit à un niveau d’équilibrestable de pollution. A l’inverse, si elle est « sale », la pollution connaît une croissanceillimitée qui finit par causer un désastre environnemental. Ce résultat reproduit les faitsstylisés observés quant à l’évolution conjointe de la préoccupation environnementale et lapollution dans les pays en développement. Dans le deuxième cas, nous montrons que destransferts intergénérationnels de la génération âgée vers la génération active jeune rétablissentla possibilité d’atteindre un état stationnaire de pollution. | We develop an overlapping generations model within which the evolution of pollution and theformation of environmental concern are endogenous. On the one hand, peopleheterogeneously concerned with environmental issues contribute to pollution which is apublic bad. On the other hand, the transmission of environmental attitudes is the result ofsome economic choice which is affected by pollution. The model predicts that the long runproportion of environmentally concerned individuals will always be high. Though, dependingon the pollution-generating technology, the transition from a low-environmentally concernedsociety to a high-environmentally concerned one is accompanied by two different outcomesregarding the long run level of pollution. If the technology is “clean”, there is a stable steadystate level of pollution. However, if it is “dirty”, pollution experiences an unlimited growthwhich eventually causes an environmental disaster. This result captures some stylized factsregarding the joint evolution of environmental concern and pollution in developing nations. Inthe latter case, we show that intergenerational transfers from the older generation to the youngworking one restore the possibility to reach a stationary level of pollution.

This text focuses on the identification, efficiencies, classification and management of landscape features having a potential buffer function regarding diffuse phosphorus, because of their specific structure (vegetation-soil) and of their location at the interface between sources (farm infrastructures, emitting fields…) and surface water bodies. These buffers are very diverse and correspond to natural landscape features (wetlands, riparian areas…) as well as manmade structures (constructed buffer strips or intermediate cases such as field margins, hedgerows). Their role and efficiency depends on the local factors controlling the retention processes (internal organisation and properties of the buffer), on the position within the watershed, and on the landscape context which reciprocally determines the overall buffer capacity of a watershed. On that basis, we recognize the diversity of the buffers in structure and functioning and thus in the way they attenuate the signal, their limitations (sustainability, side effects) and their hierarchic organisation at the watershed scale.

Crossed effects between climate change and chemical pollutions were identified on community structure and ecosystem functioning. Temperature rising affects the toxic properties of pollutants and the sensitiveness of organisms to chemicals stress. Inversely, chemical exposure may decrease the capacity of organisms to respond to environmental changes. The aim of our study was to assess the individual and crossed effects of temperature rising and pesticide contamination on fish. Goldfish, Carassius auratus, were exposed during 96 h at two temperatures (22 and 32 °C) to a mixture of common pesticides (S-metolachlor, isoproturon, linuron, atrazine-desethyl, aclonifen, pendimethalin, and tebuconazol) at two environmentally relevant concentrations (total concentrations MIX1 = 8.4 μg L(-1) and MIX2 = 42 μg L(-1)). We investigated the sediment reworking behavior, which has a major ecological functional role. We also focused on three physiological traits from the cellular up to the whole individual level showing metabolic status of fish (protein concentration in liver and muscle, hepatosomatic index, and Fulton's condition factor). Individual thermal stress and low concentrations of pesticides decreased the sediment reworking activity of fish and entrained metabolic compensation with global depletion in energy stores. We found that combined chemical and thermal stresses impaired the capacity of fish to set up an efficient adaptive response. Our results strongly suggest that temperature will make fish more sensitive to water contamination by pesticides, raising concerns about wild fish conservation submitted to global changes.

Les écosystèmes lacustres sont de plus en plus soumis à de multiples perturbations maisleur réponse est encore trop rarement considérée de façon globale. En effet, au traversd’un jeu d’interactions complexes, chaque perturbation peut moduler l’intensité del’impact des autres sur les lacs, et de ce fait, leur réponse. Dans ce contexte, ce travaildoctoral est axé sur l’approfondissement de notre compréhension de la réponse des lacs àun contexte de perturbations multiples, sur le long terme. Pour cela, trois grands lacsprofonds (le lac Léman, du Bourget et d’Annecy), soumis à une perturbation régionalesimilaire (i.e., le réchauffement climatique) et à deux perturbations locales (i.e., leschangements dans le statut trophique et dans les pratiques de gestion piscicole)d’intensités différentes, ont été choisis. La réponse de ces lacs à ces changements a étéabordée au travers d’une approche paléolimnologique, basée sur les cladocères. En effet,la capacité de ceux-ci à intégrer les changements temporels dans le réseau trophiquepélagique en réponse aux trois perturbations environnementales en fait un modèle adéquatpour reconstruire les changements à l’échelle de la communauté pélagique. Plusprécisément, nous avons abordé (i) les changements dans les communautés de cladocères,au cours du siècle dernier, en réponse aux trois perturbations environnementales et (ii)l’impact de ces perturbations sur les stratégies de reproduction des Daphnies. Cependant,le manque de connaissance dans les grands lacs profonds sur la représentativité descommunautés sources de cladocères par les assemblages de restes archivés dans lessédiments a tout d’abord conduit à faire un point méthodologique. Ce dernier a abouti à lamise en évidence de différences dans le niveau de représentation de communautés sourcesde cladocères selon le type de restes utilisés. La composition taxonomique et la structureen taille des restes parthénogénétiques (i.e., exosquelettes) reflètent relativement biencelle des communautés sources. Quant aux éphippies (oeufs de dormance), elles serévèlent des indicateurs fiables pour reconstruire les comportements de reproduction.Suite à ces résultats, les reconstructions paléolimnologiques des communautés decladocères montrent que leur trajectoire écologique était contrôlée par des interactionscomplexes entre les trois pertubations différentes, selon les périodes de temps et entre leslacs. De plus, la réponse des communautés de cladocères au climat était différente entreles trois lacs comme une fonction de l’intensité des forçages locaux. Ces observationssuggèrent qu’il est important d’inclure le rôle des perturbations locales dans la prédictionde l’impact futur des changements climatiques sur les lacs. L’impact des perturbationsenvironnementales sur le comportement de reproduction des Daphnies est tel que desévènements d’hybridation interspécifique ont été observés. Cependant, ces évènementsd’hybridation sont issus de sensibilité aux trois perturbations environnementalesdifférentes entre les espèces de Daphnies.

Soil carries out functions that are crucial for theenvironment and life on earth and is therefore an essential non renewableresource for mankind. Recently, the European Soil Framework Directive proposalindicated that soil is under increasing environmental pressure mostly due tothe intensification of human activities, which are damaging the capacity ofsoil to continue to perform in full its broad variety of crucial functions.Most of these soil functions are depending on micro-organisms inhabiting the soil.The diversity of soil micro-organisms is the highest on earth with estimates ofseveral thousand to several million different genomes per gram of soil. Howeverfundamental knowledge of the diversity and ecology of microbial communitiescarrying out soil functions is still limited. Understanding the impact ofanthropogenic activities on microbial communities and how this relates to soilfunctioning is therefore a major challenge in soil microbiology. The revolutionin the techniques available to date offer exciting opportunities for a betterunderstanding of the relationships between microbial diversity and soilfunctions. This talk will focus on the novel insights into the impact of humanactivities on microbial communities and potential consequences for ecosystemprocesses.