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Peatland degradation indicated by stable isotope depth profiles and soil carbon loss
Get PDFPeatlands play a significant role in the global carbon cycle. Since the last glacial maximum, peatlands in the northern hemisphere have accumulated organic matter as peat with about 550 Pg carbon in their soils. The degradation of peatlands either by anthropogenic activities or by changing climatic conditions results in changes of the biogeochemical cycles. Increasing temperatures, especially in the high northern latitudes, lead to the accelerated permafrost thaw and the degradation of palsa peatlands and may lead to a positive carbon-climate feedback. Peatland drainage induces oxic conditions and causes increasing carbon dioxide emissions resulting in a decline of soil organic carbon. In Europe more than 50 % of the former peatland area has been drained for agricultural or forestry use contributing a significant proportion to the national greenhouse gas emissions.
The main objectives of this study were to use depth patterns of stable isotopes, both carbon and nitrogen, as indicators of peatland degradation, and to calculate the carbon balance of degraded peatlands by different profile-based methods. Various depth profiles from peatlands in Northern Sweden, Central Finland and Northern Germany were sampled to investigate these research questions. These peatlands present different causes of peatland degradation, including changes in climatic conditions in the subarctic region, drainage for forestry in the boreal region and drainage for grassland management in the temperate region.
The natural abundance of stable isotopes, particularly stable carbon and nitrogen isotopes, is a commonly used indicator in soil sciences to investigate biogeochemical processes in soils and soil degradation. Depth profiles of stable carbon isotopes generally reflect organic matter dynamics in soils with an increase of δ13C with depth during aerobic decomposition and stable or decreasing δ13C values with depth during anaerobic decomposition of organic matter. In addition, the δ15N values are assumed to increase with depth in degraded peatlands due to aerobic decomposition and show uniform depth patterns under anaerobic decomposition in natural peatlands.
In the palsa peatlands in Northern Sweden, stable carbon isotope depth profiles indicated changes in the decomposition processes over time. Recent degradation due to accelerated permafrost thaw as well as historical changes in decomposition processes from anaerobic to aerobic are displayed in the δ13C depth profiles. The historical changes indicated the uplifting of the palsa peatlands by permafrost. Furthermore, the time of the permafrost uplifting was determined by peat accumulation rates between 100 and 800 years ago. In addition, stable nitrogen isotope depth profiles indicated the change in decomposition processes and showed perturbation of the soil when relating to C/N ratios. The mean ages of permafrost uplifting of the two palsa peatlands identified by the stable nitrogen isotope depth profiles fall in the period of the Little Ice Age.
A land use gradient was investigated in Northern Germany including a near-natural wetland, an extensively managed and an intensively managed grassland site, which have all formed in the same peatland complex. Vertical depth profiles of δ13C, δ15N, ash content, C/N ratio, bulk density and radiocarbon ages were studied to identify peat degradation and to calculate carbon loss. The δ13C depth profiles indicated aerobic decomposition in the upper horizons at all sites. Moreover, depth profiles of δ15N differed significantly between the sites with increasing δ15N values of the upper horizons concurrent to increasing land use intensity due to differences in peat decomposition and fertilizer application.
There are different methods and approaches to determine the carbon balance of degraded peatlands. The profile-based methods compare the degraded soil with a reference soil. Differences in biogeochemical soil parameters, such as ash content, bulk density and radiocarbon age, are used by the profile-based methods to estimate the soil carbon balance of degraded peatland sites.
Peat and carbon loss could be quantified by the combination of ash content and bulk density and is supported by the radiocarbon ages. Increasing carbon loss with increasing land use intensity was calculated by two different profile-methods with 11.5, 18.8-38.2 and 42.9 52.8 kg C m-2 at the near-natural site, the extensively used grassland site and the intensively used grassland site, respectively. However, current greenhouse gas fluxes measured by the chamber technique indicated a carbon gain at the near-natural site, a neutral carbon balance at the extensive used grassland site and a carbon source at the intensive used grassland site. The historical carbon balance was assessed by the profile-based methods whereas the present changes in the carbon balance are captured by the flux measurements. Moreover, the combination of both approaches pointed out that the carbon balance of the peatland has changed over time. All biogeochemical soil parameters indicated peat degradation at all investigated sites along the land use gradient, however, at varying degrees.
In Finland more than half of the peatland area was drained during the 20th century for forestry use. The Lakkasuo peatland, Central Finland, includes a minerotrophic and an ombrotrophic part, both of which were partially drained for forestry. In addition to the δ13C depth profiles, four different profile-based methods were applied, using differences in ash content or radiocarbon dated peat samples to calculate the carbon balance of the soil. The δ13C depth profiles indicated that both undrained sites are in a natural state and that both drained sites are enriched in 13C in the topsoil indicating aerobic decomposition. At the minerotrophic drained site all four profile-based methods indicated a carbon loss but of different magnitude (0.058 to 0.272 kg C m-2 yr-1). However, at the ombrotrophic drained site both radiocarbon methods suggested a carbon gain (0.139 to 0.182 kg C m-2 yr-1) whereas the two other methods indicated a carbon loss (0.061 to 0.270 kg C m-2 yr-1). The results confirm that in boreal peatlands drainage for forestry leads to a higher risk of losing carbon when the peatland is minerotrophic.
This thesis demonstrates that examining stable carbon isotopes is a useful way of identifying peatland degradation by various causes, and this approach can be used as indicator of the natural state of a peatland. The carbon balance calculations by different profile-based methods help determining the long-term carbon changes of degraded peatlands since the beginning of peatland drainage
Relevance of functional organic matter fractions for soil denitrification [Kumulative Dissertation]
No full textMenge und Qualität des organischen Materials (OM) können das Denitrifikationspotenzial von Böden stark beeinflussen. Insbesondere die Bedeutung von OM-Fraktionen mit unterschiedlicher Bioverfügbarkeit (wasserlösliches OM – WEOM, partikuläres OM – POM und mineral-assoziiertes OM – MOM) für die Denitrifikation ist noch ungeklärt. Die Inkubation verschiedener Böden und OM-Typen ergab, dass begrenzte OM-Quellen vollständig denitrifizierende Organismen begünstigen. Der wasserextrahierbare organische Kohlenstoff (WEOC) in POM, insbesondere in frischen Pflanzenresten, hat ein viel höheres Potenzial kurzfristige Denitrifikationsaktivität in einer typischen ˈhot spot–hot momentˈ-Situation zu fördern als MOM. In OC-reichen Böden mit hohem Tongehalt kann MOM jedoch eine wichtige Rolle bei der Bereitstellung organischer Substrate während der Denitrifikation spielen. Insgesamt ist WEOC, das leicht bioverfügbares OM repräsentiert, ein direkter Indikator für das Denitrifikationspotenzial von Böden.Content and quality of organic matter (OM) may strongly affect the denitrification potential of soils. In particular, the impact of soil OM fractions of differing bioavailability (water-extractable – WEOM, particulate – POM, and mineral-associated OM – MOM) on denitrification remains unresolved. Incubation of different soils and OM types revealed that limited OM sources favored a microbial community more efficient in resource use, i.e., complete denitrifying organisms. The water-extractable organic carbon (WEOC) in POM, especially in largely undecomposed plant residues, has a much higher potential to support short-term denitrification activity in a typical ˈhot spot–hot momentˈ situation than MOM. However, in OC-rich soils with high clay contents MOM can play an important role in providing organic substrates during denitrification. Overall, WEOC, representing readily bioavailable OM, is a straightforward indicator of the denitrification potential of soils
Stabilization mechanisms of organic matter in four temperate soils: Development and application of a conceptual model
No full textBased on recent findings in the literature, we developed a process-oriented conceptual model L that integrates all three process groups of organic matter (OM) stabilization in soils namely (1) selective preservation of recalcitrant compounds, (2) spatial inaccessibility to decomposer organisms, and (3) interactions of OM with minerals and metal ions. The model concept relates the diverse stabilization mechanisms to active, intermediate, and passive pools. The formation of the passive pool is regarded as hierarchical structured co-action of various processes that are active under specific pedogenetic conditions. To evaluate the model, we used data of pool sizes and turnover times of soil OM fractions from horizons of two acid forest and two agricultural soils. Selective preservation of recalcitrant compounds is relevant in the active pool and particularly in soil horizons with high C contents. Biogenic aggregation preserves OM in the intermediate pool and is limited to topsoil horizons. Spatial inaccessibility due to the occlusion of OM in clay microstructures and due to the formation of hydrophobic surfaces stabilizes OM in the passive pool. If present, charcoal contributes to the passive pool mainly in topsoil horizons. The importance of organo-mineral interactions for OM stabilization in the passive pool is well-known and increases with soil depth. Hydrophobicity is particularly relevant in acid soils and in soils with considerable inputs of charcoal. We conclude that the stabilization potentials of soils are site- and horizon-specific. Furthermore, management affects key stabilization mechanisms. Tillage increases the importance of organo-mineral interactions for OM stabilization, and in Ap horizons with high microbial activity and C turnover, organo-mineral interactions can contribute to OM stabilization in the intermediate pool. The application of our model showed that we need a better understanding of processes causing spatial inaccessibility of OM to decomposers in the passive pool
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
Changes in minerals and organic-mineral associations during paddy soil development
Get PDFReisböden unterliegen alternierenden Redoxbedingungen, die zur Transformation von Tonmineralen und Eisenoxiden führen. Entsprechende Effekte auf die Speicherung organischer Bodensubstanz (OBS) sind noch wenig erforscht. Daher wurden Reisböden aus Indonesien und China untersucht, die seit mehreren Dekaden Redoxfluktuation ausgesetzt waren und aus verschiedenen Bodentypen (Vertisol, Andosol, Alisol) hervorgegangen sind. Ein Teil der Böden wurde zudem mit Reisstroh und 8 Redoxzyklen zur Simulation von Reisbodenentwicklung inkubiert. Der Umsatz von Stroh in Böden unter Redoxfluktuation scheint weitgehend unabhängig vom Bodentyp zu verlaufen, während die Netto-Akkumulation von OBS teilweise vom Bodentyp abhängt, was auf einen Einfluss der Mineralzusammensetzung des Bodens hindeutet. Insgesamt konnte gezeigt werden, dass durch Reisanbau induzierte biogeochemische Veränderungen zum Teil vom Ausgangsboden beeinflusst sind. Die Haupteigenschaften der Ausgangsbodentypen blieben jedoch erhalten.Rice paddy soils are characterized by redox fluctuations resulting in clay mineral and Fe oxide transformations. Corresponding effects on soil organic carbon (SOC) storage are poorly understood. Hence, paddy soils from Indonesia and China that have been exposed to redox fluctuations for several decades and that derived from three different soil types (Vertisols, Andosols, Alisols) were studied. Some of the soils were further incubated with rice straw and 8 redox cycles mimicking paddy soil development. The overall turnover of straw OC in soils under redox fluctuation seems to be independent of soil type, while net accumulation of SOC may in part depend on soil type, suggesting an impact of the soil’s mineral composition. Overall, biogeochemical changes induced by paddy management were partly influenced by the original soil and the parent material. However, the main characteristics of the initial soil types were preserved and not overridden by several decades of paddy management
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
The relevance of root growth for spatiotemporal patterns of chemical gradients in the rhizosphere
Get PDFThe soil ecosystem provides space for complex, interlinked biochemical and biophysical processes which, in their entirety, ensure human nutrition, e.g. in the form of agricultural systems. Plant roots play a dominant role in the regulation of many soil processes alongside a multitude of other soil organisms. The rhizosphere, influenced by plant roots, plays a key role in nutrient uptake and carbon sequestration. This work investigates how roots and root hairs interact with differently textured soil. The results show a plastic response to soil texture and altered nutrient uptake due to root hairs. In summary, this work provides an insight into the complex field of soil-plant interaction at different scale levels. In addition to new scientific findings, a new approach for the non-destructive investigation of chemical gradients in the 3D context of the rhizosphere is presented.Das Ökosystem Boden bietet Raum für komplexe, ineinandergreifende biochemische und biophysikalische Prozesse, die in ihrer Gesamtheit z.B. in Form von Agrarsystemen die Ernährung des Menschen sichern. Pflanzenwurzeln spielen neben einer Vielzahl anderer Bodenlebewesen eine dominante Rolle bei der Regulation vieler Bodenprozesse. Die Rhizosphäre, beeinflusst von Pflanzenwurzeln, spielt eine Schlüsselrolle bei Nährstoffaufnahme und Kohlenstoffbindung. Diese Arbeit untersucht, wie Wurzeln und Wurzelhaare mit unterschiedlich texturiertem Boden interagieren. Die Ergebnisse zeigen eine plastische Reaktion auf die Bodentextur und eine veränderte Nährstoffaufnahme bedingt durch Wurzelhaare. Zusammenfassend bietet diese Arbeit einen Einblick in das komplexe Feld der Boden-Pflanzen-Interaktion auf verschiedenen Skalenebenen. Neben neuen wissenschaftlichen Erkenntnissen wird ein neuer Ansatz zur nahezu zerstörungsfreien Untersuchung chemischer Gradienten im 3D-Kontext der Rhizosphäre vorgestellt
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
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