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

Categorical Models for a Semantically Linear Lambda-calculus

This paper is about a categorical approach to model a very simple Semantically Linear lambda calculus, named Sll-calculus. This is a core calculus underlying the programming language SlPCF. In particular, in this work, we introduce the notion of Sll-Category, which is able to describe a very large class of sound models of Sll-calculus. Sll-Category extends in the natural way Benton, Bierman, Hyland and de Paiva's Linear Category, in order to soundly interpret all the constructs of Sll-calculus. This category is general enough to catch interesting models in Scott Domains and Coherence Spaces

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

Predicting future effects from nutrient abatement and climate change on phosphorus concentrations in Lake Bourget, France

Like many temperate European  lakes, Lake Bourget (France) has suffered from eutrophication during the second half of the last century. Due to a remarkable policy restoration program, the lake has been recovering for the past 25 years after a massive decrease in total phosphorus (TP) loading. TP concentrations have decreased from about 100-120 to 20-25 µg/L. Additional efforts are, however, still required to obtain a perennially sustainable good ecological status and model parameterisation of fluxes can assist in predicting future outcomes, especially in the context of global warming. In this paper, a dynamic model (MeroLakeMab) was developed and tested with the purpose to reconstructthe loading history of Lake Bourget and to predict TP concentrations during scenarios of increased temperature, decreased water runoff and decreased P loading. Simulations suggested that the historical TP loading decrease may have been as extensive as 90%. Decreases in water discharge to Lake Bourget at magnitudes forecasted by the Intergovernmental Panel on Climate Change would not affect TP concentrations notably, but marked concentration changes could, however, occur if decreases in runoff would have a strong impact on the TP loading. Increasing temperature effects on yearly mean TP concentrations in the water column would be very small compared to effects from changes in the TP loading. Predictions such as these could be instrumental for future successful lake management

Predicting future effects from nutrient abatement and climate change on phosphorus concentrations in Lake Bourget, France

Like many temperate European  lakes, Lake Bourget (France) has suffered from eutrophication during the second half of the last century. Due to a remarkable policy restoration program, the lake has been recovering for the past 25 years after a massive decrease in total phosphorus (TP) loading. TP concentrations have decreased from about 100-120 to 20-25 µg/L. Additional efforts are, however, still required to obtain a perennially sustainable good ecological status and model parameterisation of fluxes can assist in predicting future outcomes, especially in the context of global warming. In this paper, a dynamic model (MeroLakeMab) was developed and tested with the purpose to reconstructthe loading history of Lake Bourget and to predict TP concentrations during scenarios of increased temperature, decreased water runoff and decreased P loading. Simulations suggested that the historical TP loading decrease may have been as extensive as 90%. Decreases in water discharge to Lake Bourget at magnitudes forecasted by the Intergovernmental Panel on Climate Change would not affect TP concentrations notably, but marked concentration changes could, however, occur if decreases in runoff would have a strong impact on the TP loading. Increasing temperature effects on yearly mean TP concentrations in the water column would be very small compared to effects from changes in the TP loading. Predictions such as these could be instrumental for future successful lake management

Cyanobacterial bloom termination: the disappearance of Planktothrix rubescens from Lake Bourget (France) after restoration

International audienceLike many large freshwater ecosystems in Europe, Lake Bourget suffered from eutrophication during the second part of the 20th century and since the 1980s has been partially restored by reductions in nutrient loadings. Here, we analyse a data set comprised of field measurements of physicochemical and biological variables in Lake Bourget covering the period from 2004 to 2011 and complement this data set with laboratory experiments, to gain an understanding of the changes in phytoplankton community structure during recent years and drivers of these changes. Between 1995 and 2008, Lake Bourget was characterised by the proliferation of the red-coloured filamentous and toxic cyanobacterium Planktothrix rubescens, comprising 34.1-52.6% of the total phytoplanktonic biomass between 2004 and 2008. In 2009, although the contribution of P.rubescens to the total biomass was still considerable (25.3%), it was significantly lower (P<0.05) compared with previous years. The cyanobacterium disappeared completely during the autumn to winter transition of 2009/2010 and has not been recorded since this time. Concomitantly, total phytoplanktonic biomass declined sharply and a new phytoplanktonic community occurred consisting predominantly of mixotrophic genera, such as Dinobryon spp., Rhodomonas, Cryptomonas and a variety of different diatoms such as Stephanodiscus, Cyclotella and Fragilaria. Our findings suggest declines in phosphorus concentration as a key variable in bloom termination, although a number of other factors could also be important, such as temperature-dependent water column mixing, light availability, zooplankton grazing and seasonal cyanobacterial inoculums

Microbial community structure and dynamics in the largest natural French lake (lake Bourget)

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