Hydrodynamic modelling for early warning of sanitary risks in open swimming waters

Hydrodynamic

Aquatic ecological modelling with TELEMAC3D: performance of the ecological library AED2 in a natural ecosystem

Hydrodynamic

Open water swimming in urban areas E. coli distribution with TELEMAC-3D

Hydrodynamic

Impact of a flood event on the biogeochemical behaviour of a mesotrophic alpine lake: Lake Bourget (Savoy)

International audienceA flood event which occurred during the onset of thermal stratification and of algal growth (March 1996) was studied in mesotrophic Lake Bourget (France). Both physical and biogeochemical processes occurring during this episode were assessed. The dominant effect was a decrease of nutrient concentrations along the river-lake ecotone. This phenomenon seemed mainly linked to biological factors: stimulation of the spring algal and bacterial growth. After the flood, the algae aggregated with allochthonous particles brought by the river and were rapidly eliminated by sedimentation. The effect of this early spring flood, seemed spatially restricted and rather neutral as regards lake water quality. In the lake region crossed by the river plume, the overall effect after the flood was a decrease of P available for the phytoplankton. In the open water, the P concentration was probably not modified by the load supplied by the flood

Impact of a flood event on the biogeochemical behaviour of a mesotrophic alpine lake: Lake Bourget (Savoy)

International audienceA flood event which occurred during the onset of thermal stratification and of algal growth (March 1996) was studied in mesotrophic Lake Bourget (France). Both physical and biogeochemical processes occurring during this episode were assessed. The dominant effect was a decrease of nutrient concentrations along the river-lake ecotone. This phenomenon seemed mainly linked to biological factors: stimulation of the spring algal and bacterial growth. After the flood, the algae aggregated with allochthonous particles brought by the river and were rapidly eliminated by sedimentation. The effect of this early spring flood, seemed spatially restricted and rather neutral as regards lake water quality. In the lake region crossed by the river plume, the overall effect after the flood was a decrease of P available for the phytoplankton. In the open water, the P concentration was probably not modified by the load supplied by the flood

Fonctionnement biogéochimique du lac du Bourget : phosphore, phytoplancton calcite et taux de sédimentation

8 pagesInternational audienceThe diversion, in 1980, of the main sewers entering Lake Bourget reduced significantly the nutrient loading and the inlake bioavailable phosphorus concentration, Nevertheless, paradoxically, the lake trophic state has not been clearly improved and blooms of toxic cyanobacteria (Planktothrix rubescens), which threaten the use of water, have been frequently observed since 1996, The main processes occurring in the phosphorus cycle have been studied in successive research projects (1988-1998), based on a joined approach of field survey and mathematical modelling. The settling fluxes of particulate matter and associated phosphorus species have been measured at the year and season scales. These results have highlighted that the sedimentation of particulate phosphorus is a very significant transfer process towards the bottom sediment, essential for the lake water quality restoration. Interplays between phosphorus, two types of major autochthonous particles, phytoplankton and calcite, and metallic oxides have been investigated, Nolwithstanding that, the obtained results were unsuccessful to make totally clear the origin of the phosphorus available for summer primary production, these results suggested that other Iwo-dimension, hydrodynamical processes, have to be considered.Les travaux d'assainissement menés dans le bassin versant du lac du Bourget depuis 1980 ont réduit les apports en nutriments et les concentrations en phosphore directement assimilable par les algues. Néanmoins, paradoxalement, l'état trophique du lac ne s'est pas significativement amélioré, des développements de cyanobactéries toxiques (Planktothrix rubescens) observés régulièrement depuis 1996, constituant une menace pour les usages de l'eau, Afin de préciser les processus principaux intervenant dans le cycle du phosphore, plusieurs programmes de recherche successifs, basés sur une double approche de terrain et de modélisation mathématique ont été entrepris de 1988 à 1998, Les flux de sédimentation de la matière particulaire et des formes du phosphore associées ont été quantifiés à l'échelle saisonnière et annuelle, mettant en évidence que la sédimentation du phosphore particulaire constituait un important mécanisme de transfert vers le compartiment sédimentaire de fond, essentiel pour la restauration du lac, Les interactions entre le phosphore et, d'une part deux types de particules dominantes de la matière particulaire autochtone, phytoplancton et calcite, d'autre part les oxydes métalliques ont été étudiées. S'il n'a pas été possible d'élucider totalement l'origine du phosphore utilisé pour la production primaire estivale, les résultats obtenus ont conduit à envisager d'autres mécanismes explicatifs, de nature hydrodynamique et bidimensionnelle

Global warming as a driving factor for cyanobacterial blooms in Lake Karaoun, Lebanon

18 pagesInternational audienceThe Middle East region suffers already from the gradual effects of climate change and will be among the most vulnerable regions in the future. As a result, productivity should undergo losses due to high temperatures, drought, floods and soil degradation which threaten food security of Levantine countries. Since water is the critical factor in the region, even slight changes in air temperature and rainfall patterns will have considerable impact. It has been proven that potential climate change may disrupt, on one hand, most ecosystems through changes in their physicochemical conditions, and on the other hand the species which are living in these ecosystems. Then, the biodiversity can be found challenging. In this study, the effects of climate change on population and phytoplankton communities of Lake Karaoun were investigated since 1992. The climate regime shifts have been shown to alter the lake ecosystem. In the past, Lake Karaoun was characterized by a highly diversified microflora dominated by diatoms and green algae. Recent climatic fluctuations, with culmination in 2008-2011 and temperatures exceeding 40˚C have upset this biodiversity. Blooms of cyanobacteria, specifically Microcystis aeruginosa and Aphanizomenon ovalisporum, have occurred and disturbed both the ecosystem and the functioning of the lake

Design and analysis of an urban retention pond database

8 pagesInternational audienceIn conjunction with the urban development in the Ile-de-France region numerous retention ponds were created in the seventies. Because of their number the knowledge concerning the behaviour of these ponds remains quite scarce and it is a weakness for their optimal management. This paper presents a database related to retention ponds in the Ile-de-France region, which gathers all the available data concerning their design, their behaviour in their catchment, their water quality and their maintenance. The objective of this database is precisely to improve their knowledge and to finally help in their management. Data from 55 ponds are presently included in the database. From these data it is possible to infer a high pollution retention potential of the ponds. Despite the heterogeneity of the monitoring strategies, significant relations between the water quality in the ponds and the occupation of the catchment were established.Lors de la création des villes nouvelles en région Ile de France dans les années 70, les bassins de retenue en eau ont été abondamment utilisés pour contrôler l'évacuation des eaux pluviales. Toutefois, en raison de leur nombre, la connaissance du comportement de ces bassins reste limitée, ce qui constitue une faiblesse pour leur gestion optimale. Ce texte présente une base de donnée relative à ces bassins en eau. Elle rassemble toutes les informations disponibles relatives à leur conception, leur fonctionnement, la qualité de leurs eaux et leur entretien. L'objectif de cette base de données est d'améliorer la connaissance de ces plans d'eau et ultérieurement d'aider à leur gestion. Les données de 55 bassins sont actuellement rentrées dans la base de données. A partir de ces données, on peut estimer un potentiel de dépollution élevé. Par ailleurs, des relations significatives entre la qualité des eaux et l'occupation du bassin versant ont été mises en évidence

Urban lakes: interaction between phytoplankton dynamics and trace metal speciation

9 p.International audienceUrban lakes have a particular influence on the water cycle in urban catchments. Thermal stratification and a longer residence time of the water within the lake can boost the phytoplankton production. On the other hand, trace metals are naturally found in environment in trace amounts due to erosion and physic-chemical or biological alteration processes. Trace metals are essential to growth and reproduction of organisms. However, they are also well known for their toxic effects on animals and humans. Their ecotoxicity depends on metal properties and chemical speciation (particulate, dissolved: labile or bioavailable and inert fractions). The interaction between phytoplankton production and trace metal speciation is not well understood until present time. The aim of this research is twofold: (1) to analyze the driving processes of the phytoplankton production in an urban lake through physical-chemical and biological field data collection and (2) simultaneously to survey the chemical speciation of trace metals in this lake. To address these issues, a field survey and laboratory analysis, including physical-chemical, biological variables, organic matter and trace metal concentrations, have been designed and implemented in an urban study site: Lake Créteil in France

An integrated approach for urban water modelling, linking a watershed hydrological model and a cyanobacteria dynamics model in urban lakes

International audienceIn the future, the frequency and the intensity of cyanobacteria blooms in urban lakes are expected to increase in response to climate change and expanding urbanization. In order to study the impacts of watershed changes on cyanobacteria dynamics in urban lakes, a modelling approach, in which an ecological lake model is connected to a hydrological watershed model, is proposed. To validate this approach, the water quality (temperature, transparency, dissolved oxygen and chlorophyll-a) was monitored at high frequency (5-30 min) on two study sites in contrasted regions (climate, land-use...). In the first part of this paper, we show the advantage of using high-frequency data to simulate cyanobacteria dynamics in Lake Enghien (France), a temperate urban lake. In a second part, the methodology used, to link the ecological lake model and the hydrological watershed model is explained for Lake Pampulha (Brazil), a tropical urban lake. Some preliminary results of the ecological modelling of Lake Pampulha are also presented. The integrated modelling approach proposed, will allow us to study the lake response to different future cenarios of the watershed evolution. Furthermore, high-frequency data are expected to provide a better understanding of the lake functioning during extreme meteorological conditions (e.g. heavy rainfall events or drought)