54 research outputs found
How to halt the global decline of lands
The assessment of land degradation and restoration by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services shows that land degradation across the globe is a wide and severe issue and is showing no signs of slowing down. This trend must be halted and reversed
Cluster Lenses
Clusters of galaxies are the most recently assembled, massive, bound
structures in the Universe. As predicted by General Relativity, given their
masses, clusters strongly deform space-time in their vicinity. Clusters act as
some of the most powerful gravitational lenses in the Universe. Light rays
traversing through clusters from distant sources are hence deflected, and the
resulting images of these distant objects therefore appear distorted and
magnified. Lensing by clusters occurs in two regimes, each with unique
observational signatures. The strong lensing regime is characterized by effects
readily seen by eye, namely, the production of giant arcs, multiple-images, and
arclets. The weak lensing regime is characterized by small deformations in the
shapes of background galaxies only detectable statistically. Cluster lenses
have been exploited successfully to address several important current questions
in cosmology: (i) the study of the lens(es) - understanding cluster mass
distributions and issues pertaining to cluster formation and evolution, as well
as constraining the nature of dark matter; (ii) the study of the lensed objects
- probing the properties of the background lensed galaxy population - which is
statistically at higher redshifts and of lower intrinsic luminosity thus
enabling the probing of galaxy formation at the earliest times right up to the
Dark Ages; and (iii) the study of the geometry of the Universe - as the
strength of lensing depends on the ratios of angular diameter distances between
the lens, source and observer, lens deflections are sensitive to the value of
cosmological parameters and offer a powerful geometric tool to probe Dark
Energy. In this review, we present the basics of cluster lensing and provide a
current status report of the field.Comment: About 120 pages - Published in Open Access at:
http://www.springerlink.com/content/j183018170485723/ . arXiv admin note:
text overlap with arXiv:astro-ph/0504478 and arXiv:1003.3674 by other author
Long-term impacts of season of grazing on soil carbon sequestration and selected soil properties in the arid Eastern Cape, South Africa
BACKGROUND AND AIMS : The karoo biomes of South Africa are major feed resources, yet soil nutrient depletion
and degradation is a major problem. The objective of this study was to assess impacts of long-term (>75 years)
grazing during spring (SPG), summer (SUG), winter (WG) and exclosure (non-grazed control) treatments on
soil nutrients, penetration resistance and infiltration tests.
METHODS : A soil sampling campaign was carried out to collect soil to a depth of 60 cm to analyse bulk density,
soil physical and chemical parameters as well as soil compaction and infiltration.
RESULTS : Generally, grazing treatments reduced soil organic C (SOC) stocks and C:N ratios, and modified soil
properties. There was higher SOC stock (0.128 Mg ha-1 yr-1) in the exclosure than in the SPG (0.096 Mg ha-1 yr-
1), SUG (0.099 Mg ha-1 yr-1) and WG (0.105 Mg ha-1 yr-1). The C:N ratios exhibited similar pattern to that of C.
From the grazing treatments, the WG demonstrated 7 to 10% additional SOC stock over the SPG and SUG,
respectively.
CONCLUSIONS : Short period animal exclusion could be an option to be considered to improve plant nutrients in
sandy soils of South Africa. However, this may require a policy environment which supports stock exclusion
from such areas vulnerable to land degradation, nutrient and C losses by grazing-induced vegetation and
landscape changes.Department of Science and Technology University of Pretoria) and the European Communities, 7th framework program under the grant agreement No.
266018, ANIMALCHANGE project.http://link.springer.com/journal/111042016-12-31hb201
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