1,720,973 research outputs found
Hydroperiod, Physicochemistry and Seasonal Change of Macroinvertebrate Communities in Intermittent Prairie Streams
No full textRecent literature has stressed the importance of headwater streams in freshwater ecosystem health and biodiversity. These streams contribute a globally significant amount of runoff, nutrients, and biological diversity to downstream rivers and lakes. Over half of stream kilometers assessed in South Dakota did not meet their beneficial uses and headwater streams may be an initial source of impairments. Many headwater streams are intermittent and contain flowing water seasonally. Intermittent streams comprise over 90% (136,800 kilometers) of river kilometers in South Dakota. Intermittent streams typically progress from flowing water conditions to interstitial, pooled, and dry streambed depending on local climate. Physicochemical characteristics change along with the hydrologic condition. This alters macroinvertebrate communities as in-stream conditions become too harsh for certain species. The objectives of this research were to describe the hydroperiod (flow duration), macroinvertebrate communities and identify changes in physicochemical parameters and community composition associated with different hydrologic conditions in intermittent streams. Sixty intermittent headwater streams were selected in South Dakota’s Northern Glaciated Plains (NGP) ecoregion. Streams were located within 7 level IV ecoregions including the Big Sioux Basin, Drift Plains, Glacial Lake Basins, James River Lowland, Minnesota River Prairie, Prairie Coteau and Prairie Coteau Escarpment. All study sites were 1st-3rd Strahler Order (1st NHDPlus), with watershed areas ≤6 km2, defined bed and bank features, intermittent flow most years, and none were lake outlets. Macroinvertebrates and physicochemical parameters were sampled monthly at each site from April−August or until streams dried. A quantitative bucket technique and petite 500-μm dip net were used to collect macroinvertebrate samples. Streams began to flow in April following spring snowmelt and 83% of streams were either pooled or dry by early September; one sampling site remained dry throughout. The majority of drying occurred in June and July. HOBO (Onset Inc.) temperature loggers were used to track daily temperature amplitudes and allowed the detection of drying dates. Streams commonly fluctuated between hydrologic phases and several study sites were re-wetted after initial drying. Dissolved oxygen significantly decreased and water temperature increased as streams entered the pooled phase. Conductivity, total dissolved solids, total kjehldahl nitrogen (TKN) and total phosphorus had highest means while streams were in the pooled phase. Ammonia, total Kjehldahl nitrogen, and total phosphorus all increased significantly in pooled phases. A significant decrease in total suspended solids, turbidity, and chloride were also seen as stream drying progressed. A total of 199 genera from 20 orders and 75 families of aquatic invertebrates were identified from 40 reference sites within the NGP. Aedes (Culicidae), Pseudosuccinea (Lymnaeidae), Paraleptophlebia (Leptophlebiidae), Micropsectra (Chironomidae), and Tvetnia (Chironomidae) were the most abundant invertebrates collected. Burrowers and collector-gatherers were the most abundant habit and functional feeding guild found, comprising 42% and 66% of total abundance, respectively. The average Hilsenhoff Biotic Index score for sites was 6.9 and 50% of invertebrate taxa found are considered intolerant of organic pollution. Changes in macroinvertebrate abundance and community structure during the study period were coupled with changing hydrologic states. Pooled streams had the lowest macroinvertebrate abundance, significantly lower Diptera and Trichoptera abundance, and significantly lower burrower and collector-gatherer abundance. Hilsenhoff Biotic Index scores were highest in pooled streams but did not differ significantly from flowing and interstitial streams. Aedes (Culicidae), Pseudosuccinea (Lymnaeidae), Paraleptophlebia (Leptophlebiidae), Hydrobaenus (Chironomidae), Sphaerium (Sphaeriidae), and Diplocladius (Chironomidae) were found in high numbers while streams were in the pooled phase despite high water temperatures and low dissolved oxygen concentrations. Several taxa were characterized as having fast seasonal life cycles, high dispersal ability, and the ability to diapause. These attributes allow for survival in intermittent streams and make community composition unique from perennial streams and rivers. Changes in stream physicochemical properties and community structure through hydrologic phases must be considered when designing bioassessment studies in headwaters
The hyporeic zone as a primary source of invertebrate community resilience in intermittent alluvial rivers : evidence from field and mesocosm experiments
Full text linkUnderstanding community response to disturbance is essential to identifying processes that determine their assembly and to predicting the future effects of climate change on biodiversity and ecosystem functions. Drying (complete loss of surface water) is a natural disturbance affecting 50% of rivers worldwide and is occurring more in perennial rivers due to climate change. However, its effects on aquatic invertebrate communities and the underlying processes contributing to their resilience (i.e. return to pre-drying or undisturbed levels) have not been well quantified. Using 4 congruous field and mesocosm experiments to quantify community resilience and identify its primary sources in environmentally harsh alluvial rivers. First, I found communities in 8 alluvial rivers were highly resilient to moderate and severe drying. Second, I showed that the hyporheic zone (saturated interstitial sediments) can be the primary source of colonists, promoting high community resilience. Third, I found high water temperature and intraspecific competition caused Gammarus pulex, a common benthic detritivore, to migrate into the hyporheic zone. Fourth, I found increasing depth to the water table diminished the hyporheic zone’s role as a source of colonists by reducing survival of G. pulex. My results support an emerging concept that harsh ecosystems are highly resilient and indicate that the effects of drying on biodiversity and ecosystem functions could vary across river systems. In alluvial rivers, the hyporheic zone can contribute strongly to community resilience and management should focus on protecting and restoring vertical connectivity to maximize resilience to climate changeUn paradigme émergent prédit que les perturbations influencent les processus qui déterminent l'organisation des communautés. L'assèchement des rivières (disparition complète d'eau de surface pour une durée déterminée) est une perturbation naturelle affectant les cours d'eau dans de nombreuses régions du monde. De plus en plus de cours d'eau pérenne s'assèchent en réponse aux changements globaux. Toutefois, l'effet de ces assèchements sur les communautés aquatiques et les processus impliqués dans leur résilience restent mal quantifié et mal compris. A travers quatre études allant de suivis de terrain à des expérimentations in-situ et des mésocosmes en laboratoire, une résilience exceptionnelle des communautés d'invertébrés a été mesurée dans huit rivières alluviales. La zone hyporhéique semble être la principale source de recolonisation expliquant la forte résilience de ces communautés. En laboratoire, l'augmentation de la température et de la compétition intra-spécifique entraine une migration de Gammarus pulex dans la zone hyporhéique. L'augmentation de la profondeur de la zone hyporhéique lors d'assèchements pourrait réduire la résilience et avoir des effets sur les fonctions de l'écosystème (décomposition de litière). Ces résultats montrent que les assèchements n'ont pas toujours des effets sévères sur les communautés d'invertébrés des rivières alluviales qui semblent même très résilientes. La zone hyporhéique joue un rôle primordial dans la résilience des communautés des cours d'eau. Un accent devrait être mis sur la protection de la zone hyporhéique dans les rivières alluviales afin de préserver cette capacité de résilience face aux changements globau
La zone hyporhéique favorise la résilience des communautés d'invertébrés dans les rivières alluviales intermittentes : expériences de terrain et mésocosmes en laboratoire
No full textUn paradigme émergent prédit que les perturbations influencent les processus qui déterminent l'organisation des communautés. L'assèchement des rivières (disparition complète d'eau de surface pour une durée déterminée) est une perturbation naturelle affectant les cours d'eau dans de nombreuses régions du monde. De plus en plus de cours d'eau pérenne s'assèchent en réponse aux changements globaux. Toutefois, l'effet de ces assèchements sur les communautés aquatiques et les processus impliqués dans leur résilience restent mal quantifié et mal compris. A travers quatre études allant de suivis de terrain à des expérimentations in-situ et des mésocosmes en laboratoire, une résilience exceptionnelle des communautés d'invertébrés a été mesurée dans huit rivières alluviales. La zone hyporhéique semble être la principale source de recolonisation expliquant la forte résilience de ces communautés. En laboratoire, l'augmentation de la température et de la compétition intra-spécifique entraine une migration de Gammarus pulex dans la zone hyporhéique. L'augmentation de la profondeur de la zone hyporhéique lors d'assèchements pourrait réduire la résilience et avoir des effets sur les fonctions de l'écosystème (décomposition de litière). Ces résultats montrent que les assèchements n'ont pas toujours des effets sévères sur les communautés d'invertébrés des rivières alluviales qui semblent même très résilientes. La zone hyporhéique joue un rôle primordial dans la résilience des communautés des cours d'eau. Un accent devrait être mis sur la protection de la zone hyporhéique dans les rivières alluviales afin de préserver cette capacité de résilience face aux changements globauxUnderstanding community response to disturbance is essential to identifying processes that determine their assembly and to predicting the future effects of climate change on biodiversity and ecosystem functions. Drying (complete loss of surface water) is a natural disturbance affecting 50% of rivers worldwide and is occurring more in perennial rivers due to climate change. However, its effects on aquatic invertebrate communities and the underlying processes contributing to their resilience (i.e. return to pre-drying or undisturbed levels) have not been well quantified. Using 4 congruous field and mesocosm experiments to quantify community resilience and identify its primary sources in environmentally harsh alluvial rivers. First, I found communities in 8 alluvial rivers were highly resilient to moderate and severe drying. Second, I showed that the hyporheic zone (saturated interstitial sediments) can be the primary source of colonists, promoting high community resilience. Third, I found high water temperature and intraspecific competition caused Gammarus pulex, a common benthic detritivore, to migrate into the hyporheic zone. Fourth, I found increasing depth to the water table diminished the hyporheic zone’s role as a source of colonists by reducing survival of G. pulex. My results support an emerging concept that harsh ecosystems are highly resilient and indicate that the effects of drying on biodiversity and ecosystem functions could vary across river systems. In alluvial rivers, the hyporheic zone can contribute strongly to community resilience and management should focus on protecting and restoring vertical connectivity to maximize resilience to climate chang
Is drift the primary process promoting the resilience of river invertebrate communities? A manipulative field experiment in an intermittent alluvial river
No full textInternational audience1. In river systems, aquatic invertebrate communities are surprisingly persistent over time and gener- ally recover quickly from disturbances. Drift has long been viewed as the primary process promoting this resilience, and it plays a important role in predictive models of community composition and concepts in lotic ecology. More recently, other processes such as vertical migration from the hypor- heic zone, aerial oviposition from distant refuges and the use of resistance forms (e.g. diapause) have received greater recognition and support for their importance.2. In this study, the view that drift is the primary process promoting invertebrate community resili- ence was challenged in an intermittent alluvial river using reach-scale flow manipulations. First, six treatment channels were completely dried for 1 week, while three others were left flowing to be used as controls. Second, flow was re-established in channels and drift was either allowed or blocked for a 4-week period. Third, during this period the resilience of community structure, composition and function was compared between treatments, and the potential for colonisation from the drift, hypor- heic zone, aerial oviposition and resistance forms was measured.3. Communities recovered after only 2 weeks in all of the previously dried channels, and contrary to our hypotheses, invertebrate community structure, composition and functional trait composition were not altered by blocking drift, indicating it was not the primary process promoting resilience in this river.4. Three lines of evidence suggested colonisation from the hyporheic zone and not aerial oviposition nor resistance forms promoted resilience following rewetting including the following: (i) finding all common benthic taxa in the hyporheic zone during the drying event, (ii) a distinct decrease in inver- tebrate size upon rewetting in all treatment channels and (iii) a negative correlation between resili- ence and water table depth.5. This experiment highlighted the potential importance of the hyporheic zone as a key source of colonisation in alluvial rivers and emphasises the need for a three-dimensional perspective when considering community resilience in rivers. Adaptive management approaches are needed to direct attention to sources (e.g. hyporheic zone) that are essential to promoting community resilience in riv- ers facing increased pressures due to climate change, water abstraction and flow regime alteration
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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