1,721,031 research outputs found
Changes in the seasonal snow cover of alpine regions and its effect on soil processes: A review
No full textAt its maximum annual development, snow can cover more than half the Northern Hemisphere land area with one-third experiencing seasonal snow cover. The precise conditions that develop during the annual pattern of snowpack development formation have implications for: (i) soil microbiological activity and nutrient transformations; (ii) the capacity of the accumulating snowpack to retain atmospheric derived solutes; (iii) preferential elution and rapid runoff of solutes from the snowpack during periods of thaw; and (iv) leaching of solutes. Long-term records of annual snow accumulation suggest that substantial, regional scale shifts in snowpack characteristics have been occurring. The accompanying changes in the frequency and timing of freeze-thaw episodes and the evidence of their disruptive and selective influence upon soil microbial processes, when human induced, suggests there are wider implications for nutrient cycling and functioning of mountain ecosystems. This review is focused on alpine landscape
Phosphorus Loss in Overfertilized Soils: The Selective P Partitioning and Redistribution Between Particle Size Separates
No full textUsing 12 well-characterised European soils contrasting in their physical and chemical properties, we demonstrate significant differences in the partitioning of phosphorus (P) between various particle size separates. Samples of each soil were subjected to one of three methods of increasingly aggressive dispersion in the order water (WD), mechanical (MD) or chemical (CD). A general, although not exclusive, inverse relationship existed between the concentration of various attributes (these included organic carbon, oxalate and dithionite iron contents, total P, resin and water extractable P) and particle size. The quantity, composition and physico-chemical properties of individual size separates were sensitive to the dispersion method used. This suggested an interaction between the ease of dispersion and particulate properties even within a single size class. Typically the total P concentration was highest in the most easily dispersed (WD) clay fraction. The total P content of the whole soil could be reasonably obtained by summing the appropriate quantities of each particle size material, however, resin and water extractable P were not adequately predicted using this approach. Together these observations have implications for laboratory and field situations where artificial disaggregation and/or selective separation and transport of fine soil material may occur. Finally a comparison of water soluble P between whole soils and their MD dispersed size fractions suggested three broad situations might exist, where either sorption processes, a precipitate or some combined P precipitate and sorption mechanism controlled P release
Labile nitrogen, carbon, and phosphorus pools and nitrogen mineralization and immobilization rates at low temperatures in seasonally snow-covered soils
No full textSurface mineral horizons from four ecosystems sampled in the northwestern Italian Alps were incubated at -3 and +3°C to simulate subnivial and early thaw period temperatures for a seasonally snow-covered area. The soil profiles at these sites represent extreme examples of management, grazed meadow (site M) and extensive grazing beneath larch (site L) or naturally disturbed by avalanche and colonized by alder (site A) and the expected forest climax vegetation beneath fir (site F). Changes in labile pools of nitrogen (N) and phosphorus (P) were active at all sites at both temperatures during 14 days of laboratory incubation. Ammonium was the dominant inorganic form of total dissolved N (TDN), being equivalent to 1.8-9.8 g N m-2 within the mineral horizon. Gross rates of ammonification were similar at the two temperatures but significantly (p<0.05) greater in soil from beneath fir than in the other three. Nitrification occurred in all soils and displayed a wide range in rates, from 2 to 85 mg N m-2 day-1, and was least in the two most acid soils, A and F. Immobilization of NH4+ as microbial N was greater in the fir soil than in the other three. Also, the fir soil showed greatest gross ammonification and least accumulation of NO3- and greatest tendency to retain N. This high N retention capacity in the climax ecosystem contrasted with the managed systems characterized by higher nitrification rates and greater potential spring NO3- loss. Dissolved organic N ranged between 30 and 50% of the TDN, while dissolved organic P was greater than 70% of total dissolved P (TDP). The dissolved organic compounds were important components of the labile pool, in equilibrium with a large reserve of organic N, and may significantly contribute to the soil N availability at low temperatures
Simulating soil freeze/thaw cycles typical of winter alpine conditions: Implications for N and P availability
No full textSeasonally snow-covered alpine soils may be subjected to freeze/thaw cycles, particularly during years having little snow and during the late winter and early spring periods. Freeze/thaw cycles can stimulate soil mineralization and could therefore be one factor regulating nitrogen (N) and phosphorus (P) availability and cycling. In this study laboratory incubation experiments using four soils having contrasting properties have been used to characterize the change in N and P forms (microbial and soluble inorganic/organic) that occur after simulated freeze/thaw cycles. Soil samples were collected from locations representing extreme examples of either direct human management (grazed meadow (site M) and extensive grazing beneath larch (site L)) or those disturbed by more natural events (recent avalanche and colonisation by alder (site A)) and from beneath the expected forest climax vegetation beneath fir (site F). Topsoil from these sites, maintained at two different water contents (20 and 30%, w/w), were exposed to either a single (SF) or four sequential (4SF) freeze/thaw cycles. Each cycle consisted of 12 h at -9 °C and 12 h at +4 °C mimicking a diurnal pattern. A SF cycle reduced microbial N for soils from sites F and A and was accompanied by a significant increase in dissolved organic nitrogen (DON) at both moisture contents. In contrast, the microbial N of soils from M and L was not affected by the freeze/thaw cycles, suggesting a particular adaptation of soil microbes to these extremes in temperature. Freeze/thaw cycles resulted in a significant increase in the net ammonification in all soils. Extractable total dissolved N (TDN) and total dissolved P (TDP) increased in all soils after a SF cycle, however, the relative importance of the different N and P forms differed. At the lower soil moisture content, NO3 - concentrations remained constant or slightly decreased in all soils, except that from site M. In all other soils DON appeared to replace NO3 - as the potentially mobile N source after the freeze/thaw cycles. The relative contribution of dissolved organic P to TDP after freeze/thaw remained significant, and greater than 50% in all soils. Freeze/thaw cycles, in seasonally snow covered soils, are likely to have a selective effect on the microbial biomass. Freezing and thawing resulted in a pulse of net ammonification and DON release, which represent an important influence upon N cycling in these alpine systems
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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