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Aggregate formation in chloritic and serpentinitic alpine soils
No full textVariations in soil-water and mineralogical composition of clay particles are important factors governing the formation and stabilization of soil aggregates. We evaluated the effects of these factors on aggregate genesis in two soils with different mineralogical compositions. One developed from chlorite-rich schists and the other from serpentinite, but they have similar organic matter and Fe oxides contents. The <2-mm fractions were submitted to one cycle of wetting and drying, producing two classes of newly formed aggregates (2–5 and 95 mm in diameter). The aggregates differed in water stability, with those from serpentinitic soil being more stable. The amounts of water-dispersible clay (WDC) were lower in the more stable aggregates than in the original <2 mm fraction, and the WDC showed more positive electrophoretic mobility values, indicating its stabilization during aggregation. In the aggregates obtained from chlorite-rich soil, the WDC amounts were similar to those of the <2-mm fractions, and the electrophoretic mobility values were more negative. The aggregation and stabilization processes differed in the two soils and were affected by the clay dispersion/flocculation behavior. The variations in aggregate stabilization were therefore attributed to different clay-clay and clay-sand interactions caused by the mineralogical differences in the clay fractions involved. No differences were found when comparing the two size classes of newly formed aggregates from the same soil. This indicates that the same mechanism produced aggregates of a variety of sizes
Anthropogenic disturbance and effects on the organic matter migration in a clear-cut boreal forest soil.
No full textThe practice of clear cutting in boreal forests is often based on heavy caterpillar harvesting machinery, strongly damaging forest soils. Large areas of European Northern Russian countries face these disturbances and the risk of loss of productive forest soils. The objective of this work was to evaluate the effect of high intensity human disturbance on soil carbon balance, and on the migration capacity of the organic matter.
A 35-40 years old clear-cut Russian boreal forest was studied (Ust-Kulom, Komi Republic). In this area, the forest road built to collect wood was still visible from the concentration of birch trees. Two soil profiles were selected: one was representative of low level anthropogenic disturbance (clear-cut forest), and the other was opened in the most disturbed area (forest road). In the most disturbed profile, the presence of a B horizon enriched in C clearly documented the migration of organic matter. The soils were sampled and analysed for the main chemical and physical characteristics. The total extractable carbon (TEC) was obtained by NaOH, and fractionated into humic (HA) and fulvic acids (FA), which were purified and freeze-dried. The carbon content (CHA and CFA) in the fractions was determined by wet oxidation. The spectroscopic analyses, the determination of the E4/E6 ratio, and the elemental composition were carried out on the humic fractions.
In the less disturbed site, the C stock calculated down to 60 cm in soil horizons was 4.4 kg m-2, while in the most disturbed soil, the amount was 8.0 kg m-2. The effect of disturbance on the organic fraction was evident also on the distribution of C in the profile: in the clear-cut site the carbon content decreased with depth, while in the profile of the forest road a translocation of organic matter with an accumulation of carbon in the deep horizons (EBh and Bh) was evident. The C to N ratios were different between the soils. In fact, at depth, N was twice as much in the FA from forest road than in the FA from the forest profile, and the molar C/N ratios were very low. In the forest profile, the FA from the clay-depleted surface horizons were richer in oxygen-containing functional groups than those from the clay-richer deepest horizons, as deduced by the elemental analyses and by the E4/E6 ratios.
In the most disturbed profile the FA were generally more oxidised and richer in aromatic moieties with depth. The FT-IR spectra confirmed the higher aromaticity of the deepest FAs from the EBh and Bh horizons, as evident from the decrease of the 1720 to 1630 cm-1 bands ratio.
From the quantitative point of view, the CFA/CHA ratio indicated an increase of the low molecular weight humic substances with depth in the forest profile, while in the road profile the FA increase was evident down to horizon overlying the EBh horizon.
The characteristics of organic matter in the two sites clearly indicated that migration has been more effective in the most disturbed site. On the other hand, the differences in the humic material present in the deep horizons of the two sites suggest that other processes may have contributed to accumulation of organic matter in the forest road
Surface charge of the clay fraction in newly formed soil aggregates of different size
No full textThe complexes of clay-polyvalent cations-organic matter are building blocks of soil microaggregates, which in turn cohere yielding larger units of various size. In natural systems, this process is influenced by various factors such as environmental conditions, cementing agents, soil properties. Being the clay fraction the primary floccule, a study was conduced to characterize the surface charge of water dispersible clays isolated from aggregates of different size, obtained in the laboratory, and to evaluate the effects of the formation contions. The <2mm fraction of two alpine soils different in clay contents and in mineralogy (one dominated by serpentine and the other by chlorite), was incubated for two weeks after the addition of water with or without small quantities (5g kg-1) of humic acids (HA): At the end, three fractions of aggregates were separated by dry sieving (<2, 2-5 and >5mm) and the water dispersible clay was analysed for electrophoretic mobility and mineralogical composition. Incubation without the addition of HA did not affect the surface charge values of the clay remaing in the non-agregated fraction (<2mm), with respect to the initial samples. Water dispersible clay in the 2-5 and >5mm aggregates showed instead differences both in surface charge and in mineralogical composition. When serpentine dominated, the clay was more positively charged than that of the nn-aggregates fraction, with a shift in PZC from pH 2.5 to 3.2. The other soil sample behave in the opposite way, shifting from pH 3.3 to 2.6. The average size of the clay ranged from 0.6μm at pH 6 to 1.2-1.3μm at pH 2, with a similar tren in all samples. At pH below PZC the positively charged Si-OH or Al-OH edge sites can interact with the negative basal paltes froming edge-to-face aggregates. The addition of HA affected clay surface properties of all samples: the PZC was reached at lower pH than in the water-only system of the same size. The particle dimensions varied from 0.5 to 1.4μm, indicating a weak effect of HA on dispersion or aggregation of particles. The wetting treatment differentiated the water dispersible clay of the aggregates from that of the non-aggregated fraction. In fact, the latter maintained the surface properties of the <2mm sample before the incubation, while the former presented a different net surface charge, with a different effect on the basis of the mineralogical composition of the soil. Upon the addition of moderate amounts, humic acids cause a specific modification of the clay surface properties, independently of mineralogical composition and aggregate size
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
Organic matter after clear-cutting: decrease, increase or translocation?
No full textIn podzolic environments the distribution of organic matter (SOM) in soil is related to the characteristics of the litter and to the dynamics of water percolating through the profile. SOM distribution may be therefore influenced by disturbances to tree cover and site hydrologic conditions, such as those occurring after clear-cutting. In a 35 years old clear-cut boreal forest stand (Ust-Kulom, Russian Federation) we selected two soil profiles and evaluated SOM stocks and characteristics: P1 is located within the stand and little influenced by physical disturbances to soil cover, P2 was opened where the forest road built for harvesting was still visible
The C stock calculated down to 60 cm was 4.4 kg m-2 in P1, and 8.0 kg m-2 in P2. The increase was associated to changes in profile morphology and development of EBh and Bh horizons. These horizons have formed through an enhancement of SOM migration which was only partially related to the classical process of podzolisation. In fact, while the elemental composition of fulvic acids (FA) in organic layers was similar in P1 and P2, in P2 the FA from deep mineral horizons were enriched in N and polysaccharides, and less enriched in aromatic compounds. The thin sections confirmed the process of SOM migration: homogeneous brown coatings of monomorphic organic matter were the dominant features in the Bh horizon of P2.
After clear-cutting SOM migration capacity has been enhanced, but the process was only partially related to the chemical properties of organic compounds. As the accumulation has involved also a less decomposed and less mobile fraction, an important pool of SOM has been translocated at the borders of the stand, probably because of the development of preferential water flows with physical soil disturbances. These movements have determined a mosaic of different SOM concentrations in the landscape
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
Diritto/diritti
No full textIl saggio ricostruisce il passaggio dall'ordine di un lungo medioevo 'maschio', poggiante sulle differenze di status, ai limiti e contraddizione dell'uguaglianza codicistica, alla Cotsituzione del 1948, con particolare riferimento alla polarità, uguaglianza/differenz
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
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