1,720,962 research outputs found
Vers l'intégration des cours d'eau non-pérennes dans la gestion durable des écosystèmes d'eau douce
No full textVirtually every river network on Earth includes non-perennial rivers and streams (NPRs) that periodically cease to flow or dry. The recurrence of flowing, non-flowing and dry phases that characterize NPRs uniquely supports high biodiversity and biogeochemical cycles in entire river networks. Consequently, changing these hydrological cycles can threaten the integrity of riverine ecosystems and the people that depend on them for their livelihood and culture. Despite their prevalence and importance, NPRs are largely excluded from management practices, conservation laws, and scientific research that have been tailored to perennial rivers. This bias, which stems from a historical lack of consideration for the value and distinctiveness of NPRs, is resulting in their rapid degradation. The aim of this thesis is to advance our understanding of the global prevalence and diversity of NPRs, and to improve their integration in river policy and sustainable management. Leveraging an interdisciplinary perspective integrating hydrology, ecology, geography, and data science, this thesis addresses three main objectives through four articles (Chapters 2 to 5). I) Chapter 2 and 3 provide the first robust quantitative estimate of the prevalence, distribution, and diversity of NPRs worldwide. Using a machine learning model informed by global data on hydrology, climate, geology, and land cover, Chapter 2 reveals that water ceases to flow for at least one day per year along 51%–60% of the world’s rivers by length. This finding demonstrates that non-perennial rivers and streams are the rule rather than the exception on Earth, and that they occur within all climates and biomes, and on every continent. Chapter 3 identifies nine hydrological types of NPRs globally which differ in how often, how long, when and why they stop to flow. II) Chapter 4 highlights the inadequate protection of NPRs by environmental protection laws. Through a case study of regulatory maps defining which watercourses are protected under the Water Law in France, this chapter sheds light on the socio-political factors influencing regulatory cartography, exposes the disproportionate exclusion of NPRs from regulatory frameworks, and discusses the implications of this exclusion for river network integrity. III) Chapter 5 introduces a novel conceptual and operational framework to enhance the effectiveness of flow management programs to sustain freshwater ecosystems (i.e., environmental flows) in river networks with a high prevalence of NPRs. It proposes to broaden the set of ecological processes integrated into the design, implementation, and monitoring of environmental flows with the end goal of better protecting the distinct ecological structure and dynamics of NPRs. This thesis challenges the prevailing conceptual models of river ecosystems by demonstrating the global prevalence and diversity of NPRs, and by supporting their integration into science, policy, and management frameworks. In doing so, it contributes to an ongoing paradigm shift towards an integrated view of river networks. This integrated view involves studying and managing all reaches, their floodplain, and contributing catchment as a dynamically interconnected meta-ecosystem whose components span the aquatic-terrestrial continuum.Pratiquement tous les réseaux fluviaux de la planète comprennent des rivières et des ruisseaux non pérennes (RNP) qui cessent périodiquement de couler ou s'assèchent. Les cycles répétés de phases d’écoulement, de non-écoulement et d’assèchement qui caractérisent les RNP est un facteur clef contribuant à la grande biodiversité et cycles biogéochimiques des réseaux fluviaux. Par conséquent, la modification de ces cycles hydrologiques peut menacer l'intégrité des écosystèmes fluviaux, leur biodiversité et les populations humaines qui en dépendent pour leur subsistance et leur culture. Malgré leur prévalence et leur importance, les RNP sont souvent exclus des pratiques de gestion, des lois sur la conservation et de la recherche scientifique, qui sont basées sur le fonctionnement des rivières pérennes. Ce biais provient d’une perception négative des RPN chez les gestionnaires et le public, et d'un manque historique de considération de leurs spécificités. En conséquence, les RNP souffrent d’une mauvaise gestion chronique et se dégradent à un rythme alarmant. L'objectif de cette thèse est de faire progresser notre compréhension de la prévalence et de la diversité des RNP à l'échelle mondiale, et d'améliorer leur intégration dans les politiques publiques et dans les mesures de gestion durable de l’eau. S'appuyant sur une perspective interdisciplinaire intégrant l'hydrologie, l'écologie, la géographie, et la science des données, cette thèse aborde trois objectifs principaux en quatre articles (Chapitres 2 à 5). I) Les Chapitres 2 and 3 fournissent la première estimation quantitative robuste de la prévalence, de la distribution et de la diversité des RNP dans le monde. En utilisant un modèle de machine learning basé sur des données mondiales sur l'hydrologie, le climat, la géologie et l'occupation des sols, le Chapitre 2 révèle que l'eau cesse de couler au moins un jour par an dans 51 % à 60 % des cours d’eau du monde. Ce résultat démontre que les rivières et les ruisseaux non pérennes sont la règle plutôt que l'exception sur Terre, et qu'ils sont présents dans tous les climats et biomes, et sur tous les continents. En outre, le Chapitre 3 identifie neuf types hydrologiques de RNP à l'échelle mondiale, qui diffèrent par la fréquence, la durée, la saisonnalité et la raison de l'arrêt de l'écoulement. II) Le Chapitre 4 met en évidence la protection inadéquate des RNP dans la législation environnementale. À travers une étude de cas portant sur les cartes réglementaires définissant les cours d'eau protégés par la Loi sur L'eau en France, ce chapitre révèle une exclusion disproportionnée des RNP des cadres réglementaires, les facteurs sociopolitiques qui influencent la cartographie réglementaire et ses implications pour l'intégrité du réseau hydrographique. III) Le Chapitre 5 développe un cadre conceptuel et opérationnel pour améliorer l'efficacité des programmes de gestion des débits écologiques (e-flows) qui visent à protéger les écosystèmes d'eau douce, particulièrement dans les réseaux fluviaux avec une forte prévalence de RNP. Dans ce chapitre, je propose d'élargir le panel de processus écologiques intégrés dans la conception, la mise en oeuvre et le suivi des débits écologiques dans le but de mieux protéger la structure et la dynamique particulières des écosystèmes de RNP. En conclusion, cette thèse remet en question les modèles conceptuels dominants des écosystèmes fluviaux en démontrant la prévalence et la diversité mondiale des RNP et en promouvant leur intégration dans les cadres scientifiques, de politiques publiques et de gestion. Ce faisant, elle contribue à un changement de paradigme vers une vision intégrée des réseaux fluviaux. Ce nouveau paradigme repose sur l'étude et la gestion de tous les segments, de leur plaine d'inondation et des bassins versants qui y contribuent comme un méta-écosystème dynamiquement interconnecté dont les composants couvrent le continuum aquatique-terrestre
Understanding and predicting the leading edge dynamics of invasive rusty crayfish (Orconectes rusticus) in the John Day River
No full textThesis (Master's)--University of Washington, 2017Continued ecological impacts of invasive species on freshwater ecosystems is one of the main challenges confronting ecologists and decision makers in conserving biodiversity and ecosystem function today. Efforts to prohibit the initial introduction of nonnative species are widely recognized to be the most cost-effective management and policy strategy. However, when aquatic invasive species become established and start spreading through the landscape, efforts to slow their proliferation remain severely limited by a lack of adequate forecasting tools and understanding of their secondary spread. My thesis aims to address these challenges by improving our understanding of and predicting the leading edge dynamics of the invasive rusty crayfish Orconectes rusticus (now Faxonius rusticus) in the John Day River (JDR) basin, a major tributary of the Columbia River in northeastern Oregon. In Chapter 1, I demonstrate the use of a spatially explicit individual-based model to recreate the invasion history of rusty crayfish in the JDR and forecast its future distribution. This study shows that controlling the spread of invasive species is possible even after their establishment, when control efforts can be effectively allocated, and that spatially explicit individual-based models can provide unique insight into the secondary spread of aquatic invasive species and concretely support decision makers in choosing optimal control strategies. Chapter 2 investigates whether phenotypic differences exist between rusty crayfish individuals at the boundary of their invasion range compared to their conspecifics closer to their initial location of introduction. I show that rusty crayfish in the JDR have developed less competitive morphology and better physiological condition as they spread towards the edge of their current invasion range and feed lower in the food web in invasion front populations than in core areas. By accounting for variations in temperature, primary productivity, and macroinvertebrate biomass throughout the invasion gradient of rusty crayfish, my research suggests that low conspecific densities and natural selection by spatial sorting are the primary drivers of these phenotypic changes, which suggests that these trends are likely to grow stronger over time as rusty crayfish keep spreading. Together, these chapters not only improve our understanding of the leading edge dynamics of aquatic invasive species such as rusty crayfish but also improve our ability to control their spread and reduce their impact on invaded ecosystems
Increased streamflow intermittence in europe due to climate change projected by combining global hydrological modeling and machine learning
No full textInternational audienceFreshwater biodiversity and ecosystem services are under stress as climate change alters streamflow intermittence. We present the first continental‐scale quantification of future climate change impacts on streamflow intermittence, achieved for Europe at a high spatial resolution that captures headwater streams. A hybrid modeling approach combines physics‐based and data‐based modeling, with a random forest model, trained on historical streamflow observations, using predictors representing the impact of climate change on high‐resolution (500 m) streamflow. These predictors were derived from a low‐resolution (50 km) global hydrological model, WaterGAP, which was driven by the outputs of five global climate models. The generated monthly time series of intermittence status for over 1.5 million reaches were used to calculate five ecologically relevant indicators of streamflow intermittence change. In Europe, the number of non‐perennial reach‐months is projected to increase in the future, for both low (SSP1‐RCP2.6) and high (SSP5‐RCP8.5) greenhouse gas emissions scenarios, in almost all climate zones, particularly in August and September. Under SSP1‐RCP2.6, 3.8% of all reach‐months may experience no‐flow conditions in 2071–2100, only a small increase from 3.5% in 1985–2014. Under SSP5‐8.5, however, a larger increase to 4.8% of all reach‐months is expected; 2.8% of European reaches are projected to shift from being perennial to non‐perennial, even where annual precipitation increases, while 0.7% are projected to shift from non‐perennial to perennial. These shifts represent a fundamental change in ecological habitat and connectivity i.e. bound to erode aquatic species diversity and alter ecosystem functions across more than 87.000 km of river segments
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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