1,721,041 research outputs found
Nitrate availability modulates the temperature effect on N<sub>2</sub>O and N<sub>2</sub> production from denitrification
No full textNitrous oxide (N2O) can be both produced and subsequently reduced to dinitrogen gas (N2) via canonical denitrification, making the balance between these steps a key control on the net flux of this potent climate gas. Through a meta-analysis, we showed that net N2O and N2 production from denitrification respond differently to temperature, exhibiting distinct temperature sensitivities. In addition, nitrate availability plays a critical role in regulating this balance, yet only few studies have examined the combined effects of temperature and nitrate availability in natural sediments. Using 15N-isotope labelling and anoxic sediment incubations, we found that temperature effects on N2O and N2 production from denitrification were evident only under high nitrate levels (100 μM), while no significant temperature response occurred under low nitrate concentration (10 μM). At high nitrate availability, N2 production increased at higher temperatures, whereas net N2O production declined, leading to a lower production ratio of N2O to N2 at warmer temperatures. These findings suggest that in nitrogen-limited ecosystems, substrate availability plays a stronger role than temperature in regulating denitrification. More broadly, they provide insights into how nutrient loading and climate warming interact to shape nitrogen cycling and greenhouse gas emissions in aquatic ecosystems
Direct biological fixation provides a freshwater sink for N2O
Get PDFNitrous oxide (N2O) is a potent climate gas, with its strong warming potential and ozone-depleting properties both focusing research on N2O sources. Although a sink for N2O through biological fixation has been observed in the Pacific, the regulation of N2O-fixation compared to canonical N2-fixation is unknown. Here we show that both N2O and N2 can be fixed by freshwater communities but with distinct seasonalities and temperature dependencies. N2O fixation appears less sensitive to temperature than N2 fixation, driving a strong sink for N2O in colder months. Moreover, by quantifying both N2O and N2 fixation we show that, rather than N2O being first reduced to N2 through denitrification, N2O fixation is direct and could explain the widely reported N2O sinks in natural waters. Analysis of the nitrogenase (nifH) community suggests that while only a subset is potentially capable of fixing N2O they maintain a strong, freshwater sink for N2O that could be eroded by warming
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Nutrient fluxes through the Humber estuary - past, present and future
No full textThe geomorphology of the present day and Holocene (3000 years ago) Humber estuary, United Kingdom, are described. More than 90% of the intertidal area and sediment accumulation capacity of the estuary has been lost to reclamation over this period. A similar situation prevails in many other urbanized estuaries. Nutrient budgets for the modern estuary are presented demonstrating little trapping of nutrients, due to the loss of intertidal areas. A speculative budget for the Humber during the Holocene is constructed, which suggests that the estuary was then an efficient sink for nitrogen and phosphorus. A budget is presented describing how nutrient cycling might operate in the Humber with contemporary nutrient loadings, but with the pre-reclamation geography. This suggests that in this form the estuary would significantly attenuate nutrient fluxes to the North Sea. The results are discussed in terms of options for managed realignment of estuaries in response to predicted sea-level rise
Modelling flow and inorganic nitrogen dynamics on the Hampshire Avon: Linking upstream processes to downstream water quality
Get PDFManaging diffuse pollution in catchments is a major issue for environmental managers planning to meet water quality standards and comply with the EU Water Framework Directive. A major source of diffuse pollution is from nitrogen, with high nitrate concentrations affecting water supplies and in-stream ecology. A dynamic, process based model of flow, nitrate and ammonium (INCA-N) has been applied to the Hampshire Avon as part of the NERC Macronutrient Cycles Programme to link upstream and downstream measurements of water chemistry. The model has been calibrated and validated against Environment Agency discharge and solute chemistry data, as well as a data set collected from a river site immediately upstream of the estuary tidal limit. Upstream measurements of denitrification at six sites have been used to evaluate nitrate removal rates in vegetated and non-vegetated conditions. Results show that sediments underlying vegetation were associated with significantly higher rates of nitrate removal than un-vegetated sediments (with an average increase of 245%). These data have been used to scale up rates of nitrate loss to the whole catchment scale and have been implemented via the model. The effects of streambed geology and macrophyte cover on catchment-scale nitrogen dynamics are explored and nutrient fluxes entering the estuary are evaluated. The model is used to test a strategy for nitrogen reduction assessed using a nitrate vulnerable zone (NVZ) methodology. It suggests that nitrate and ammonium concentrations could be reduced by 10% in 10 years and much lower nitrogen level can be achieved but only over a long time perio
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