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Cl distribution in different terrestrial habitats along hill slope gradients in Forsmark
No full textThe view of chlorine in nature is undergoing a major change as a result of the recent decades of research. It is now clear that chloride (Cl−), that was previously considered non-reactive and the totally dominating Cl species, instead is reactive and does not always constitute the predominant form of chlorine (Cl) (e.g. Bastviken et al. 2013, Svensson et al. 2007). Extensive natural chlorination of organic matter occurs in many terrestrial ecosystems (Gustavsson et al. 2012, Redon et al. 2011). Experiments with radioactive Cl (36Cl) as tracer have confirmed natural chlorination rates corresponding to as much as 50–300 % of the annual wet deposition of Cl in several types of soils (Bastviken et al. 2007, 2009). Substantial chlorination of organic matter occurs in a wide range of agricultural and forest soils (Gustavsson et al. 2012, Redon et al. 2013). The estimates are based on bulk soil excluding roots, which is likely an underestimation of the chlorination potential as it was later shown that the majority of chlorination occurs in the rhizosphere (Montelius et al. 2019). Available evidence indicates that 29–100 % of Cl in soil is organically bound (Clorg) (Bastviken et al. 2013, Redon et al. 2011). Therefore, it is not surprising that Clorg in soils frequently exceeds the level of Cl−. This dominance of Clorg in soils has been observed in several different types of soils. A study in France reported that > 80 % of the total chlorine was Clorg across grassland, arable and forest soils (Redon et al. 2013)
Relationship between ?13C of chironomid remains and methane flux in Swedish lakes
No full text1.?Methanogenic carbon can be incorporated by methane-oxidising bacteria, leading to a 13C-depleted stable carbon isotopic composition (?13C) of chironomids that feed on these microorganisms. This has been shown for the chironomid tribe Chironomini, but very little information is available about the ?13C of other abundant chironomid groups and the relationship between chironomid ?13C and methane production in lakes.2.?Methane flux was measured at the water surface of seven lakes in Sweden. Furthermore, fluxes from the sediments to the water column were measured in transects in two of the lakes. Methane fluxes were then compared with ?13C of chitinous chironomid remains isolated from the lake surface sediments. Several different chironomid groups were examined (Chironomini, Orthocladiinae, Tanypodinae and Tanytarsini).3.?Remains of Orthocladiinae in the seven study lakes had the highest ?13C values (?31.3 to ?27.0‰), most likely reflecting ?13C of algae and other plant-derived organic matter. Remains of Chironomini and Tanypodinae had lower ?13C values (?33.2 to ?27.6‰ and ?33.6 to ?28.0‰, respectively). A significant negative correlation was observed between methane fluxes at the lake surface and ?13C of Chironomini (r = ?0.90, P = 0.006). Methane release from the sediments was also negatively correlated with ?13C of Chironomini (r = ?0.67, P = 0.025) in the transect samples obtained from two of the lakes. The remains of other chironomid taxa were only weakly or not correlated with methane fluxes measured in our study lakes (P > 0.05).4.?Selective incorporation of methane-derived carbon can explain the observed correlations between methane fluxes and ?13C values of Chironomini. Remains of this group might therefore have the potential to provide information about past changes in methane availability in lakes using sediment records. However, differences in productivity, algal ?13C composition and the importance of allochthonous organic matter input between the studied lakes may also have influenced Chironomini ?13C. More detailed studies with a higher number of analysed samples and detailed measurement of ?13C of different ecosystem components (e.g. methane, dissolved inorganic carbon) will be necessary to further resolve the relative contribution of different carbon sources to ?13C of chironomid remains
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
The stable carbon isotopic composition of Daphnia ephippia in small, temperate lakes reflects in-lake methane availability
Get PDFDaphnia can ingest methane-oxidizing bacteria and incorporate methanogenic carbon into their biomass, leading to low stable carbon isotope ratios (expressed as δ13C values) of their tissue. Therefore, δ13C analysis of Daphnia resting eggs (ephippia) in lake sediment records can potentially be used to reconstruct past in-lake availability of methane (CH4). However, detailed multilake studies demonstrating that δ13C values of recently deposited Daphnia ephippia (δ13Cephippia) are systematically related to in-lake CH4 concentrations (CH4aq) are still missing. We measured δ13Cephippia from surface sediments of 15 small lakes in Europe, and compared these values with late-summer CH4aq. δ13Cephippia ranged from −51.6‰ to −25.9‰, and was strongly correlated with CH4aq in the surface water and above the sediment (r −0.73 and −0.77, respectively), whereas a negative rather than the expected positive correlation was found with δ13C values of carbon dioxide (CO2) (r −0.54), and no correlation was observed with CO2aq. At eight sites, offsets between δ13 CCO2 and δ13Cephippia exceeded offsets between δ13 CCO2 and δ13Calgae reported in literature. δ13Cephippia was positively correlated with δ13C values of sedimentary organic matter (r 0.54), but up to 20.7‰ lower in all except one of the lakes (average −6.1‰). We conclude that incorporation of methanogenic carbon prior to ephippia formation must have been widespread by Daphnia in our study lakes, especially those with high CH4aq. Our results suggest a systematic relationship between δ13Cephippia values and CH4aq in small temperate lakes, and that δ13Cephippia analysis on sediment records may provide insights into past changes in in-lake CH4aq
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
Taxon-specific ?13C analysis of chitinous invertebrate remains in sediments from Strandsjön, Sweden
Get PDFTaxon-specific stable carbon isotope (δ13C) analysis of chitinous remains of invertebrates can provide valuable information about the carbon sources used by invertebrates living in specific habitats of lake ecosystems (for example, sediments, water column, or aquatic vegetation). This is complementary to δ13C of sedimentary organic matter (SOM), which provides an integrated signal of organic matter produced in a lake and its catchment, and of diagenetic processes within sediments. In a sediment record from Strandsjön (Sweden) covering the past circa 140 years, we analyzed SOM geochemistry (δ13C, C:Natomic, organic carbon content) and δ13C of chitinous invertebrate remains in order to examine whether taxon-specific δ13C records could be developed for different invertebrate groups and whether these analyses provide insights into past changes of organic carbon sources for lacustrine invertebrates available in benthic and planktonic compartments of the lake. Invertebrate taxa included benthic chironomids (Chironomus, Chironomini excluding Chironomus, Tanytarsini, and Tanypodinae), filter-feeders on suspended particulate organic matter (Daphnia, Plumatella and Cristatella mucedo), and Rhabdocoela. δ13C of chironomid remains indicated periodic availability of 13C-depleted carbon sources in the benthic environment of the lake as δ13C values of the different chironomid taxa fluctuated simultaneously between -34.7 and -30.5‰ (VPDB). Daphnia and Bryozoa showed parallel changes in their δ13C values which did not coincide with variations in δ13C of chironomids, though, and a 2-3‰ decrease since circa AD 1960. The decrease in δ13C of Daphnia and Bryozoa could indicate a decrease in phytoplankton δ13C as a result of lower lake productivity, which is in accordance with historical information about the lake that suggests a shift to less eutrophic conditions after AD 1960. In contrast, Rhabdocoela cocoons were characterized by relatively high δ13C values (-30.4 to -28.2‰) that did not show a strong temporal trend, which could be related to the predatory feeding mode and wide prey spectrum of this organism group. The taxon-specific δ13C analyses of invertebrate remains indicated that different carbon sources were available for the benthic chironomid larvae than for the filter-feeding Daphnia and bryozoans. Our results therefore demonstrate that taxon-specific analysis of δ13C of organic invertebrate remains can provide complementary information to measurements on bulk SOM and that δ13C of invertebrate remains may allow the reconstruction of past changes in carbon sources and their δ13C in different habitats of lake ecosystems
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