30 research outputs found

    Restauration morpho-dynamique et redynamisation de la section court-circuitée du Rhin en aval du barrage de Kembs (projet INTERREG / EDF)

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    National audienceThe Upper Rhine River has been heavily impacted by channelization for flood protection and navigation, and then by damming for hydropower generation. In normal non flooding conditions, most of the flows are diverted in a canalized section whereas the regulated “old Rhine” bypassed reach runs a minimum flow. Between Huningue and Neuf-Brisach, engineering works induced simplification and stabilization of the channel pattern from a formerly braiding sector to a single incised channel, hydrological modifications, bottom armouring due to bedload decrease, and thus ecological alterations. Two complementary and interdisciplinary projects have been initiated to restore alluvial morphodynamics: i) the international “INTERREG IV - Redynamisation of the old Rhine” project (2009-2012) coordinated by the Alsace region, France; ii) the left bank “controlled erosion” project launched by ElectricitĂ© de France (EDF) within Kembs hydroelectric station relicensing process since 2003-2004. The purpose of these projects is to evaluate the feasibility of an important hydro-morphological and ecological restoration plan on a 45 km long reach, through both field testing of bank erosion techniques at favourable locations, and artificial sediments input from right bank excavations. This will help define possible long term prospective scenarios, in order to restore sustainable sediment transport, morphodynamics variability and associated ecological functions. The study will involve historical analysis, hydro-morphological / hydraulic physical and numerical modelling, physical and ecological monitoring, and sociological aspectsLe Rhin alsacien-allemand a enregistrĂ© de profondes modifications morphologiques et hydrologiques Ă  la suite de sa correction et de sa rĂ©gularisation pour la protection contre les crues et la navigation, puis aprĂšs la construction de barrages hydro-Ă©lectriques. Les amĂ©nagements rĂ©alisĂ©s entre Huningue et Neuf-Brisach ont engendrĂ© une simplification et une stabilisation du style fluvial. Un fleuve en tresses a cĂ©dĂ© la place Ă  un chenal unique incisĂ©. Le fond de chenal est devenu pavĂ© Ă  cause d’une diminution des apports de charge de fond et des altĂ©rations Ă©cologiques ont Ă©tĂ© observĂ©es (simplification des habitats aquatiques et riverains). Deux projets complĂ©mentaires et interdisciplinaires ont Ă©tĂ© engagĂ©s afin de restaurer une dynamique des formes alluviales : i) le projet international INTERREG IV – Redynamisation du Vieux Rhin (2009-2012) sous l’impulsion de la rĂ©gion Alsace ; ii) le projet d’érosion maitrisĂ©e des berges de la rive gauche conduit par ElectricitĂ© de France (EDF) dans le cadre du renouvellement de la concession de l’amĂ©nagement de Kembs. L’objectif des deux projets est de dĂ©finir un plan de restauration hydro-morphologique et Ă©cologique conduisant Ă  la redynamisation d’un tronçon de 45 km. L’étude repose sur une analyse historique, l’exploitation de modĂšles Ă  la fois physiques et numĂ©riques, et les suivis morphologiques in situ d’une recharge artificielle en sĂ©diments et d’érosions de berge contrĂŽlĂ©es. Ces Ă©tudes de faisabilitĂ© sont complĂ©tĂ©es par des analyses Ă©cologique et sociologique pour apprĂ©cier l’impact socio-environnemental de ces projets

    Relations between assemblages of carpological remains and modern vegetation in a shallow reservoir in southern Poland

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    This paper explores relations between assemblages of carpological remains and vegetation in and around a small, shallow reservoir in southern Poland. The study was conducted from 2006 to 2008. Quantity and distribution of species in the reservoir were recorded annually during the growing season. In October 2008, 40 samples of surface sediment (top 2 cm) were collected along transects at 10 m intervals. Samples of 100 cm3 were prepared for analysis of plant macroremains. Assemblages of carpological remains generally reflect local vegetation well. In some cases, however, even analysis of numerous samples failed to fully capture the species composition or reflect plant ratios in the parent phytocenosis. Reasons for this include factors that affect seed production, transport and fossilization, which differ among species. Among the best-represented macroremains were plants of the rush phytocenosis. In analysed samples, macroremains of 68.8 % of extant rushes were identified. Sixty percent of submerged and floating-leaf taxa were found in carpological samples, whereas 26.7 % of the trees and bushes were represented in sediment deposits. Species composition of phytocenoses in the reservoir and in surrounding areas was best reflected by macroremains from the nearby reed bed. Numbers of diaspores of Mentha aquatica, Hippuris vulgaris and Carex reflected well their relative abundance in phytocenoses. Chara sp., Juncus inflexus and Eupatorium cannabinum were overrepresented, whereas Typha latifolia and Sparganium minimum were poorly represented in relation to contemporary plant cover. There were no diaspores of Phragmites australis, which dominates the contemporary reed bed. Besides the shape of a reservoir, the key factor influencing diaspore numbers is distribution of plant cover. In many cases, single diaspores (Potentilla erecta, Myosotis scorpioides, Lythrum salicaria, Scutellaria galericulata), or higher concentrations (Hippuris vulgaris, Mentha aquatica, Eleocharis palustris, Schoenoplectus tabernaemontani, Chara sp.) reflected well the location of parent vegetation. The findings indicate that carpological remains in sediments can be an important source of information about plants in and around lakes. They generally reflect well local vegetation and in some cases may be used to identify taxa that dominated in the past

    Plants in aquatic ecosystems: current trends and future directions

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    Aquatic plants fulfil a wide range of ecological roles, and make a substantial contribution to the structure, function and service provision of aquatic ecosystems. Given their well-documented importance in aquatic ecosystems, research into aquatic plants continues to blossom. The 14th International Symposium on Aquatic Plants, held in Edinburgh in September 2015, brought together 120 delegates from 28 countries and six continents. This special issue of Hydrobiologia includes a select number of papers on aspects of aquatic plants, covering a wide range of species, systems and issues. In this paper we present an overview of current trends and future directions in aquatic plant research in the early 21st century. Our understanding of aquatic plant biology, the range of scientific issues being addressed and the range of techniques available to researchers have all arguably never been greater; however, substantial challenges exist to the conservation and management of both aquatic plants and the ecosystems in which they are found. The range of countries and continents represented by conference delegates and authors of papers in the special issue illustrate the global relevance of aquatic plant research in the early 21st century but also the many challenges that this burgeoning scientific discipline must address

    Réponse des communautés végétales aux conditions environnementales : perturbations ou contraintes.

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    National audienceIn aquatic environments, disturbances can be floods which induce the flow velocities sufficient to cause erosion of the substrate and the uprooting of plant communities, or that promote alluvial deposits. Thus they create heterogeneity of habitats which results in a wide variety of plant communities whose composition is related to the variability of the intensity of exchanges hydrological, quality and origin of waters. The species develop strategies adapted to the fluctuating water levels with variable intensity and frequency. In rivers not subject to flooding, plant communities that are expanding are organized as a sequence of vegetation according to a gradient of natural trophic level upstream downstream. Physical or chemical impairments (morphological changes in the bed, hydroelectric impoundment) change or even destroy this sequence. It shows that plant communities may be descriptors of hydrological functioning of the watercourse and/or biondicators of physical or chemical impairments.Dans les milieux aquatiques, des perturbations peuvent ĂȘtre des crues qui induisent des vitesses d'Ă©coulement suffisantes pour provoquer l'Ă©rosion du substrat et l'arrachage des communautĂ©s vĂ©gĂ©tales fixĂ©es, ou qui favorisent des dĂ©pĂŽts d'alluvions. Elles crĂ©ent ainsi une hĂ©tĂ©rogĂ©nĂ©itĂ© des habitats qui se traduit par une grande diversitĂ© de communautĂ©s vĂ©gĂ©tales dont la composition est liĂ©e Ă  la variabilitĂ© de l'intensitĂ© des Ă©changes hydrologiques, Ă  la qualitĂ© et Ă  l'origine des eaux. Les espĂšces dĂ©veloppent des stratĂ©gies adaptĂ©es Ă  ces fluctuations des niveaux d'eau d'intensitĂ© et de frĂ©quence variables. Dans les cours d'eau non soumis aux crues, les communautĂ©s vĂ©gĂ©tales qui s'y dĂ©veloppent s'organisent en sĂ©quence de vĂ©gĂ©tation selon un gradient naturel du niveau trophique amont-aval. Des altĂ©rations physiques (modifications morphologiques du lit, discontinuitĂ© crĂ©Ă©e par les barrages) ou chimiques modifient voire dĂ©truisent cette sĂ©quence. On montre que les communautĂ©s vĂ©gĂ©tales peuvent ĂȘtre des descripteurs du fonctionnement hydrologique du cours d'eau et/ou des bioindicateurs des altĂ©rations physico-chimiques

    Conservation status assessment of aquatic habitats within the Rhine floodplain using an index based on macrophytes

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    The programme LIFE Nature "Conservation and restoration of habitats of the Rhine fringe" (2002-2005) focussed on the assessment of the conservation status of terrestrial and aquatic habitats. Along the Rhine fringe, the degree of connection between waterbodies and the river main channel determined the water flow (surface or phreatic waters, flow velocity) and induced flood disturbances (hydromorphological quality, scouring effect). A new typology based on metrics characterizing the conservation status, was proposed for the upper Rhine floodplain. Seven physical and biological metrics were selected: specific richness, presence or absence of rare, polluto-tolerant and exotic species, species abundance, degree of connection, and trophy level defined by the macrophyte community. Aquatic macrophytes surveys were conducted at 315 sites along the Rhine French fringe. Multiple correspondence analysis and discriminant analysis were used to define metrics scores in a preliminary network of 129 macrophytes surveys stands. Metrics were combined to give a measure of the conservation status of the 315 sites. Five classes of the conservation status have been defined from degraded to excellent status. The mapping of the conservation status was realized to answer the question addressed by the program “Life Nature”. We discuss on the choice of the metrics and their justification in the definition of the conservation status. The method was tested in the fluvial hydrosystem of Ill river, the main tributary of the Rhine river in the Alsace floodplain, and compared to the French trophic index based on macrophytes, IBMR

    Miscanthus

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    Despite their putative invasive potential, Miscanthus taxa have been increasingly viewed as promising crops for bioenergy production. Miscanthus x giganteus is cultivated worldwide due to its high productivity, and its non‐spreading growth limits its risk of invasion. However, the genetic uniformity of its unique cultivated clone has recently been questioned. We used morphometry, nuclear microsatellites, AFLP fingerprints and nrDNA ITS barcoding to assess Miscanthus genotypes cultivated in eastern France. As expected, the globally cultivated clone was the main morphotype and genotype of our samplings; however, we also identified a second genotype, assigned to M. sacchariflorus, in the sampled fields. Morphological differentiation partially overlaps genotypic assignation, probably due to disturbance at the crop edges. We also show that Miscanthus taxa are misidentified in commercial nurseries. Our study confirms previous reports of the occurrence of other accessions in fields of M. x giganteus. These taxonomic confusions limit the certainty that a single clone of M. x giganteus is cultivated. In this context, M. x giganteus crop fields may actually promote the dispersal of invasive Miscanthus taxa

    Miscanthus x giganteus crop fields hide a genotype of the invasive M. sacchariflorus

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    Despite their putative invasive potential, Miscanthus taxa have been increasingly viewed as promising crops for bioenergy production. Miscanthus x giganteus is cultivated worldwide due to its high productivity, and its non‐spreading growth limits its risk of invasion. However, the genetic uniformity of its unique cultivated clone has recently been questioned. We used morphometry, nuclear microsatellites, AFLP fingerprints and nrDNA ITS barcoding to assess Miscanthus genotypes cultivated in eastern France. As expected, the globally cultivated clone was the main morphotype and genotype of our samplings; however, we also identified a second genotype, assigned to M. sacchariflorus, in the sampled fields. Morphological differentiation partially overlaps genotypic assignation, probably due to disturbance at the crop edges. We also show that Miscanthus taxa are misidentified in commercial nurseries. Our study confirms previous reports of the occurrence of other accessions in fields of M. x giganteus. These taxonomic confusions limit the certainty that a single clone of M. x giganteus is cultivated. In this context, M. x giganteus crop fields may actually promote the dispersal of invasive Miscanthus taxa
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