Scaling and balancing carbon dioxide fluxes in a heterogeneous tundra ecosystem of the Lena River Delta

The current assessments of the carbon turnover in the Arctic tundra are subject to large uncertainties. This problem can (inter alia) be ascribed to both the general shortage of flux data from the vast and sparsely inhabited Arctic region, as well as the typically high spatiotemporal variability of carbon fluxes in tundra ecosystems. Addressing these challenges, carbon dioxide fluxes on an active flood plain situated in the Siberian Lena River Delta were studied during two growing seasons with the eddy covariance method. The footprint exhibited a heterogeneous surface, which generated mixed flux signals that could be partitioned in such a way that both respiratory loss and photosynthetic gain were obtained for each of two vegetation classes. This downscaling of the observed fluxes revealed a differing seasonality in the net uptake of bushes (−0.89 µmol m−2 s−1) and sedges (−0.38 µmol mm−2 s−1) in 2014. That discrepancy, which was concealed in the net signal, resulted from a comparatively warm spring in conjunction with an early snowmelt and a varying canopy structure. Thus, the representativeness of footprints may adversely be affected in response to prolonged unusual weather conditions. In 2015, when air temperatures on average corresponded to climatological means, both vegetation-class-specific flux rates were of similar magnitude (−0.69 µmol m−2 s−1). A comprehensive set of measures (e.g. phenocam) corroborated the reliability of the partitioned fluxes and hence confirmed the utility of flux decomposition for enhanced flux data analysis. This scrutiny encompassed insights into both the phenological dynamic of individual vegetation classes and their respective functional flux to flux driver relationships with the aid of ecophysiologically interpretable parameters. For comparison with other sites, the decomposed fluxes were employed in a vegetation class area-weighted upscaling that was based on a classified high-resolution orthomosaic of the flood plain. In this way, robust budgets that take the heterogeneous surface characteristics into account were estimated. In relation to the average sink strength of various Arctic flux sites, the flood plain constitutes a distinctly stronger carbon dioxide sink. Roughly 42 % of this net uptake, however, was on average offset by methane emissions lowering the sink strength for greenhouse gases. With growing concern about rising greenhouse gas emissions in high-latitude regions, providing robust carbon budgets from tundra ecosystems is critical in view of accelerating permafrost thaw, which can impact the global climate for centuries

Aquí vienen las novias: leyendo las pinturas neolíticas de Uan Derbuaen (Tasili n’Ajer, Argelia)

The Tassil-n-Ajjer mountain range is well known for its phenomenal richness in rock-shelters and cave paintings. Generations of researchers have surveyed, mapped, drafted and discussed different facets of these Tassili paintings. The diversity and versatility of the paintings traditions of the Tassili make difficult any attempt at straightforward generalization, whether stylistic or thematic. Each painting’s station appears to be unique and conveys its own suggestions that have to be studied extensively and systematically. In the approach outlined in this paper –the iconographic approach–, paintings are viewed as complex sets of ‘artifacts’ arranged by the creative minds of the actual artists. How did these artists practice their crafts? What iconic elements did they choose to represent and why? How and why are these selected elements arranged and combined? These are some of the questions addressed in this paper. The new readings of the Uan Derbuaen paintings allow to suggest a staging and grand representation of matrimonial arrangements, the final travel of the brides.La cordillera montañosa del Tasili n’Ajer es bien conocida por su fenomenal riqueza en abrigos y cuevas pintados. Generaciones de investigadores han prospectado, cartografiado, dibujado y discutido diferentes facetas de estas pinturas del Tasili. La diversidad y versatilidad de las tradiciones pictóricas del Tasili hace difícil cualquier intento de generalización directa ya sea estilística o temática. Cada estación pintada parece ser única y expresiva de sugerencias propias que deben ser estudiadas extensa y sistemáticamente. En el enfoque esbozado en este artículo, un enfoque iconográfico, las pinturas son consideradas como series complejas de “artefactos” organizados por las mentes creativas de los artistas reales. ¿Cómo desarrollaban sus habilidades esos artistas? ¿Qué elementos icónicos escogieron para la representación y por qué? ¿Cómo y por qué esos elementos seleccionados se organizaron y combinaron? La nueva lectura de las pinturas de Uan Derbuaen permite sugerir una puesta en escena y una gran representación de los arreglos matrimoniales, el viaje final de las novias

Tailoring restoration interventions to the grassland-savanna-forest complex in central Brazil

Made available in DSpace on 2019-09-18T00:41:29Z (GMT). No. of bitstreams: 1 Schmidtetal2019RestorationEcology.pdf: 228617 bytes, checksum: f2e62c1741a1f02b90f6b15189f85175 (MD5) Previous issue date: 2019bitstream/item/202063/1/Schmidt-et-al-2019-Restoration-Ecology.pd

The decay constant of the first excited pion from lattice QCD

We review the theory that predicts that the decay constant of the excited light pseudo-scalar mesons are suppressed in the chiral limit relative to the pion decay constant. We compute the decay constant of the first excited pion ($\pi^\prime$) using unquenched QCD at a fixed lattice spacing with sea quarks of mass as low as a third the mass of the strange quark. The final result is very sensitive to the improvement conditions. We obtain $f_{\pi^\prime} / f_{\pi}$ = 0.078(93) in the chiral limit.Comment: Updated references. Clarified discussion around equations 2 and

The Midpoint Rule as a Variational--Symplectic Integrator. I. Hamiltonian Systems

Numerical algorithms based on variational and symplectic integrators exhibit special features that make them promising candidates for application to general relativity and other constrained Hamiltonian systems. This paper lays part of the foundation for such applications. The midpoint rule for Hamilton's equations is examined from the perspectives of variational and symplectic integrators. It is shown that the midpoint rule preserves the symplectic form, conserves Noether charges, and exhibits excellent long--term energy behavior. The energy behavior is explained by the result, shown here, that the midpoint rule exactly conserves a phase space function that is close to the Hamiltonian. The presentation includes several examples.Comment: 11 pages, 8 figures, REVTe

Ignoring carbon emissions from thermokarst ponds results in overestimation of tundra net carbon uptake

Arctic permafrost landscapes have functioned as a global carbon sink for millennia. These landscapes are very heterogeneous, and the omnipresent water bodies within them act as a carbon source. Yet, few studies have focused on the impact of these water bodies on the landscape carbon budget. We deepen our understanding of carbon emissions from thermokarst ponds and constrain their impact by comparing carbon dioxide and methane fluxes from these ponds to fluxes from the surrounding tundra. We use eddy covariance measurements from a tower located at the border between a large pond and semi-terrestrial tundra. When we take the open-water areas of thermokarst ponds into account, our results show that the estimated summer carbon uptake of the polygonal tundra is 11g lower. Further, the data show that open-water methane emissions are of a similar magnitude to polygonal tundra emissions. However, some parts of the pond's shoreline exhibit much higher emissions. This finding underlines the high spatial variability in methane emissions. We conclude that gas fluxes from thermokarst ponds can contribute significantly to the carbon budget of Arctic tundra landscapes. Consequently, changes in the water body distribution of tundra landscapes due to permafrost degradation may substantially impact the overall carbon budget of the Arctic. © 2022 Lutz Beckebanze et al

Coverage, efficacy or dosing interval: which factor predominantly influences the impact of routine childhood vaccination for the prevention of varicella? A model-based study for Italy

Background: Varicella is a highly infectious disease with a significant public health and economic burden, which can be prevented with childhood routine varicella vaccination. Vaccination strategies differ by country. Some factors are known to play an important role (number of doses, coverage, dosing interval, efficacy and catch-up programmes), however, their relative impact on the reduction of varicella in the population remains unclear. This paper aims to help policy makers prioritise the critical factors to achieve the most successful vaccination programme with the available budget. Methods: Scenarios assessed the impact of different vaccination strategies on reduction of varicella disease in the population. A dynamic transmission model was used and adapted to fit Italian demographics and population mixing patterns. Inputs included coverage, number of doses, dosing intervals, first-dose efficacy and availability of catch-up programmes, based on strategies currently used or likely to be used in different countries. The time horizon was 30 years. Results: Both one- and two-dose routine varicella vaccination strategies prevented a comparable number of varicella cases with complications, but two-doses provided broader protection due to prevention of a higher number of milder varicella cases. A catch-up programme in susceptible adolescents aged 10-14 years old reduced varicella cases by 27-43 % in older children, which are often more severe than in younger children. Coverage, for all strategies, sustained at high levels achieved the largest reduction in varicella. In general, a 20 % increase in coverage resulted in a further 27-31 % reduction in varicella cases. When high coverage is reached, the impact of dosing interval and first-dose vaccine efficacy had a relatively lower impact on disease prevention in the population. Compared to the long (11 years) dosing interval, the short (5 months) and medium (5 years) interval schedules reduced varicella cases by a further 5-13 % and 2-5 %, respectively. Similarly, a 10 % increase in first-dose efficacy (from 65 to 75 % efficacy) prevented 2-5 % more varicella cases, suggesting it is the least influential factor when considering routine varicella vaccination. Conclusions: Vaccination strategies can be implemented differently in each country depending on their needs, infrastructure and healthcare budget. However, ensuring high coverage remains the critical success factor for significant prevention of varicella when introducing varicella vaccination in the national immunisation programme

P04-36. HIV-1-speficic antibody dependant cellular cytotoxicity (ADCC) médiated by primary NK cells

International audiencen.