1,720,959 research outputs found
Pore water velocity and ionic strength effects on DOC release from peat-sand mixtures: Results from laboratory and field experiments
Full text linkOrganic soils are the most important source of dissolved organic carbon (DOC) in surface water. To date, most studies have focused on natural and re -wetted peatlands, but in Central Europe a large proportion of organic soils are drained and under agricultural use. Furthermore, measures such as deep ploughing or sand addition have been conducted to improve trafficability and have resulted in topsoil horizons consisting of a peat -sand mixture. Very little is known about DOC losses" from such soils. Moreover, peat soils frequently feature both mobile zones, characterised by active water and solute transport, and immobile zones, which.exchange solutes with the mobile zone by diffusion. Surprisingly, however, the effects of this dual porosity on DOC transport have not yet been explored. This study investigated the physicochemical controls on DOC concentrations in a peat -sand mixture by means of a saturated column experiment with undisturbed columns. The soil came from a former bog in northern Germany where peat layers remaining after peat extraction were mixed with the underlying mineral soil by ploughing. Three pumping rates and two levels of electrical conductivity (EC) were applied. The transport properties of the soil were obtained by analysing breakthrough curves of potassium bromide using the transport model STANMOD, which is based on the two -region non -equilibrium concept. The results of the column study were compared to DOC concentrations measured bi-weekly for two years at the field site from where the columns were taken. Despite a similar texture and soil organic carbon (SOC) content, the fraction of the mobile zone in the columns varied between 51% and 100% of total porosity. Thus even heavily degraded organic soils mixed with sand still showed a dual porosity comparable to degraded peat soils. Percolating the columns with the high EC solution caused low pH values, probably due to ion exchange and cation bridging. The combination of high EC and low pH greatly decreased DOC concentrations at the outlet of the columns. DOC concentrations decreased and fluxes increased as the pumping rates increased. Taking pore water velocity in the mobile zone into account could help to explain the differences between the columns. Overall, transport of DOC did not seem to be limited by production of DOC, but by rate -limited exchange processes. In contrast to the column experiment, field concentrations of DOC were much higher and were not related to pH, but increased with higher electrical conductivity. These higher concentrations could be explained by low pore water velocities and the slightly higher SOC content in the field. This first experiment on DOC transport in peat -sand mixtures taking the dual -porosity nature of organic soils into account clearly demonstrated the importance of pore water velocity and thus the residence time for DOC concentrations. While hydrochemical conditions are frequently addressed in laboratory studies, there is a need for improved understanding of their interaction with hydrology and soil physical properties, especially when attempting to interpret DOC data on different spatial and temporal scales.(C) 2017 The Author(s). Published by Elsevier B.V
Loess-palaeosol sections along the Rhône Rift Valley (SE France) as Late Quaternary palaeoenvironmental archives
Full text linkLoess-palaeosol sections (LPSs) represent ideal archives for gaining knowledge of past
climatic conditions and changes, as their intermediate loess deposits and buried palaeosols
reflect climate conditions of their specific locations. Detailed knowledge of past climatic
changes is also beneficial for accurate modelling and forecasting since such past changes
must have already shown similar trends. Although climate reconstructions from LPS from the
last decades have improved our understanding concerning the cross-regional Pleistocene
climate changes, there are wide knowledge gaps regarding reconstructions linking the central
temperate and Mediterranean Europe. According to climate projections, the region between
the Mediterranean and the temperate climate zone of central Europe is most vulnerable in
Europe, as a northern expansion of Mediterranean conditions (e.g. higher temperatures, more
arid months) is expected. Within this context, the climate reconstruction of the expansion of
the Last Interglacial (Eemian) conditions is especially relevant, as this area is assumed to be
several degrees warmer than current climate, a condition that is also expected for the future
climate within the European vulnerable climatic transition zone.
The LPSs of the Rhône Rift Valley in southeast (SE) France were chosen for this investigate
as the recent climate transition zone is located in the centre of this valley (Valence, ~45° N).
Thus, the LPS present important tie-points between the central European and the
Mediterranean LPS region. Previous investigations on the LPS in the Rhône Rift Valley were
mainly based on observations, and provided only limited insights into the lithological properties
of the loess deposits, the intercalated palaeosols and the resulting pedostratigraphy. This
limitation also applied to the understanding of the changing degree of weathering and
interpretations of the palaeosols with respect to their relative palaeoenvironments. In particular,
numerical ages of the loess deposition and soil formation phases were scarce. We aimed in
this thesis to fill these gaps by reconstructing the Last Interglacial-Glacial landscape evolution
changes along the climate-sensitive transition zone from LPS of the Rhône Rift Valley. The
results were linked with known European LPS in order to (i) verify our findings with LPS of
similar conditions (e.g. climate conditions, valley position) and (ii) to identify where possible
climatic boundaries were located during the Late Pleistocene, and how these boundaries may
have fluctuated over time. We focused thereby on identifying possible stratigraphic marker
horizons/complexes in the LPS, and establishing a reliable chronostratigraphy.
In several field campaigns, two main LPS, i.e. Baix LPS (in the climate transition zone) and
Collias LPS (in the Mediterranean zone) and several aside profiles, have been investigated
with multiple state-of-the-art-methods to establish reliable chronostratigraphies. The two LPS
displayed several loess and weakly to strongly developed palaeosol horizons. Based on the field observations and the laboratory analyses, both main LPS were subdivided in up to four
pedo-stratigraphic units, interlaced by two main loess units, respectively and formation and
deposition times of soils and sediments were correlated with various OSL ages.
Both LPSs begin from bottom to top with an Last Interglacial/Early Glacial soil-complex (MIS
5) represent by a mainly truncated Luvisol formation (Baix LPS: Stagnic Luvisol; Collias LPS:
Chromic Luvisol + several Bw horizons), also well-know from other European LPSs (e.g.
Rocourt complex). However, in contrast to European LPSs no humic-rich layer for late MIS 5
were observed in Rhône Rift Valley LPS. The following loess unit of the Lower Pleniglacial
(MIS 4) comprises of least weathered silty and sandy loess (partly olive-ish at Collias LPS) and
loess-like sediment horizons. At Baix LPS also a brown MIS 4 /MIS 3 Bw horizon was identified
(lower interstadial soil), which may correlate with known palaeosol relicts of the Cambisol or
Regosol-Cambisol types (e.g. Gräselberger Soil, Jackerath Soil, Reisberg Soil) from central
Europe LPSs. The overlain pedo-unit, at both sites, is represented by a truncated Cambisol-
complex (upper interstadial soil) with prominent in situ carbonate nodules and a striking former
biopores system (mainly at Collias LPS). The soil remain is assumed to represents a pedo-
complex spanning from (GI 15.1 or) GI 14 to GI 9 and correlates well with brown soil horizons
(e.g. Remagen Soils, Gräselberg Soils) of European LPSs. Thus, the striking Cambisol soil-
complex may be regarded as a stratigraphic marker horizon within the Rhône Rift Valley and
serve as a Middle Pleniglacial-unit for supra-regional correlation of central European and
Mediterranean LPS. In contrast to central European LPSs with further Cambisol formation (e.g.
Lohne Soil complex, Sinzig Soils) for the milder climate periods GI 8 to GI 4 (ca 38–29 ka)
during upper MIS 3, at Baix and Collias LPSs no significant soil formation could be detected
or may not exist. Thus, times favourable of soil formation (and soil conservation) appear to
alternate between the Mediterranean (early MIS 3 prior to Heinrich 4 event) and the central
European loess landscapes (later MIS 3, after the Heinrich 4 event). The deposits of the
following Upper Pleniglacial (MIS 2) are represented at both LPSs mainly by silt and sand sized
loess with varying intensity of weathering. Also no further (weak) soil formation, e.g. tundra
gley soils, especially redoximorphic features related to freeze-thaw dynamics, was observed,
thus agree with assumed less severe climate conditions during loess accumulations at both
LPS sites compared to central Europe. The Holocene soil formation displays similar to
European LPSs a Cambisol formation, although the conditions for a Luvisol formation along
the entire climatic transect is given, but the difference in terms of disturbance and duration of
time period have to be respected.
Based on our findings we could show that the main (pedo) -stratigraphies of Collias and Baix
LPSs generally agree with the central and western European LPSs (e.g. MIS 5, MIS 3 pedo-
stratigraphic marker horizons). However, the syn-sedimentary, intensively reworked and bioturbated character of the Rhône Rift Valley loess deposits as well as their partly polygenetic
soils and soil-complexes reflect clearly a gradient of decreasing magnitude of Late Pleistocene
climate changes from central Europe to southern Europe.
Furthermore, no clear northern expansion of Mediterranean conditions based solely on soil
characteristics during the Last Interglacial could be unambiguous verified. However, other
archives do support a northern expansion of Mediterranean conditions in the northern Rhône
Rift Valley and we can concluded that the climate conditions in the central and southern Rhône
Rift Valley seemed to be significantly more humid than today. The comparison of the Last
Interglacial and the recent soil formation to determine similarities and differences of the climate
conditions within the Rhône Rift Valley is challenging due to various factors (e.g. different
insolation, geomorphological position, intense anthropogenic use). As our results are
inconclusive concerning the Last Interglacial climate conditions within the recent climatic
transition zone, statements how these boundaries within the Rhône Rift Valley respond to
future climate changes have to be carefully made and thus, more research to conclusively
verify the intensity of rubefication under similar conditions, regionally and within the climate
transect is needed.2024-03-0
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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