| 21. |
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| 22. |
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| 23. |
- Ardö, Jonas, et al.
(författare)
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Assessment of soil organic carbon in semi-arid Sudan using GIS and the CENTURY model
- 2003
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Ingår i: Journal of Arid Environments. - : Elsevier BV. - 1095-922X .- 0140-1963. ; 54:4, s. 633-651
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Tidskriftsartikel (refereegranskat)abstract
- Using the UNFCCC as a basis, and the objectives of estimating soil organic carbon (SOC) changes during the period 1900-2100, a spatially explicit database of climate, land cover and soil texture was compiled for a 262,000 km(2) region in semi-arid Sudan. The area is characterized by low input cultivation of millet, sorghum and sesame combined with livestock grazing. By integrating the database with the CENTURY ecosystem model, we were able to estimate historical, current and future pools of SOC as a function of land management and climate. The SOC (upper 20 cm) decrease from 1900 to 2000 was estimated to be 6.8 Mt and the maximum potential carbon sink (SOC increase) for the period 2000 to 2 100 was estimated to be 17 Mt. Cropland and grassland lost 293 and 152t SOC km(-2) respectively whereas the savannahs gained 76t SOC km(-2) from 1900 to 2000. The SOC sequestration scenario simulated during 2000-2100 recovered 94, 84 and 75 tkm(-2) for cropland, grassland and savannah respectively. In addition to climate and soils, cropping intensity, fallow periods, fire frequency and grazing intensity also influence cropland SOC variation. Grassland and savannah SOC variations depend on grazing intensity and fire return interval. Land management may affect future amounts of SOC in semi-arid areas thereby turning them from sources into sinks of carbon. SOC estimates were reasonably consistent with measurements (r(2) = 0.70, n = 13).
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| 24. |
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| 25. |
- Ardö, Jonas, et al.
(författare)
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Soil carbon sequestration in traditional farming in Sudanese dry lands
- 2004
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Ingår i: Environmental Management. - : Springer Science and Business Media LLC. - 0364-152X .- 1432-1009. ; 33, s. 318-329
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Tidskriftsartikel (refereegranskat)abstract
- Do altered land management practices offer possibilities to sequester carbon in the soil and thereby mitigate increasing atmospheric CO2 as well as improve local soil fertility? This study investigates the impact of fallow periods on soil organic carbon in semiarid subsistence agroecosystems on sandy and poor soils in Kordofan, Sudan. The area is characterized by low-input cultivation of millet and sorghum in combination with livestock grazing. Recently, cultivation intensity has increased and the fallow periods have been shortened. Soil carbon contents were assessed for sites that have been under various cultivation intensities, ranging from 30 years of fallow to 30 years of continuous cultivation. Soil organic carbon showed a significant negative relationship with cultivation intensity. Measurements indicate a mean increase of approximately 4 g soil organic carbon (SOC) per square meter per year during fallow periods. The possibilities of increasing soil organic carbon by land management were also estimated through simulations using the Century model. Modeling suggested that reverting an intensely cropped millet site to permanent grassland would sequester approximately 1-2 g SOC/m(2)/yr, with higher rates during the early part of the period. Continuous intense cultivation could decrease the currently low soil carbon levels even further. These results indicate that altered land management could contribute to transforming degraded semiarid agroecosystems from a source to a weak sink for atmospheric CO2. Possible data improvements and uncertainties are discussed.
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| 26. |
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| 27. |
- Arneth, Almut, et al.
(författare)
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Restoring Degraded Lands
- 2021
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Ingår i: Annual Review of Environment and Resources. - : Annual Reviews. - 1543-5938 .- 1545-2050. ; 46, s. 569-599
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Forskningsöversikt (refereegranskat)abstract
- Land degradation continues to be an enormous challenge to human societies, reducing food security, emitting greenhouse gases and aerosols, driving the loss of biodiversity, polluting water, and undermining a wide range of ecosystem services beyond food supply and water and climate regulation. Climate change will exacerbate several degradation processes. Investment in diverse restoration efforts, including sustainable agricultural and forest land management, as well as land set aside for conservation wherever possible, will generate co-benefits for climate change mitigation and adaptation and morebroadly for human and societal well-being and the economy. This review highlights the magnitude of the degradation problem and some of the key challenges for ecological restoration. There are biophysical as well as societal limits to restoration. Better integrating policies to jointly address poverty, land degradation, and greenhouse gas emissions and removals is fundamental to reducing many existing barriers and contributing to climate-resilient sustainable development.
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| 28. |
- Asad Ayoubi, Mehran, et al.
(författare)
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Lamellar Microdomains of Block-Copolymer-Based Ionic Supramolecules Exhibiting a Hierarchical Self-Assembly
- 2014
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:10, s. 3428-3435
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Tidskriftsartikel (refereegranskat)abstract
- Based on a parent diblock copolymer of poly(styrene)-b-poly(methacrylic acid), PS-b-PMAA, linear-b-amphiphilic comb (L-b-AC) ionic supramolecules [Soft Matter 2013, 9, 1540-1555] are synthesized in which the poly(methacrylate) backbone of the ionic supramolecular AC-block is neutralized by alkyl (Cn; n = 8, 12, and 16) trimethylammonium counterions (i.e., side chains) at various ion (pair) fractions X [i.e., counterion/side-chain grafting density; X = number of alkyl counterions (i.e., side chains) per acidic group of the parent PMAA block] these L-b-AC ionic supramolecules exhibit a spherical-in-lamellar hierarchical self-assembly. For these systems, (1) the effective Flory-Huggins interaction parameter between L- and AC-blocks chi'(Cn/x) was extracted, and (2) analysis of the lamellar microdomains showed that when there is an increase in X, alkyl counterion (i.e., side chain) length l(sc), or both, there is an increase in both the average interfacial area per block junction Sigma and the thickness of the microlayer of the AC-block d(Ac).
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| 29. |
- Asad Ayoubi, Mehran, et al.
(författare)
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Micro- and nanophase separations in hierarchical self-assembly of strongly amphiphilic block copolymer-based ionic supramolecules
- 2013
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 9:5, s. 1540-1555
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Tidskriftsartikel (refereegranskat)abstract
- By a selective complexation between different alkyltrimethylammonium amphiphiles (C8, C12 and C16) and three different diblock copolymer systems of poly(styrene)-b-poly(methacrylic acid) at various grafting densities X (X = number of alkyl chains per acidic group of the poly(methacrylic acid) PMAA block), a class of ionic supramolecules are successfully synthesized whose molecular architecture consists of a poly(styrene) PS block (Linear block) covalently connected to a strongly amphiphilic comb-like block (AmphComb block), i.e. Linear-b-AmphComb. In the melt state, these ionic supramolecules can show simultaneous microphase (between Linear and AmphComb blocks) and nanophase (within the AmphComb blocks) separations. This leads to the formation of various structure-in-structure two-scale hierarchical self-assemblies, including S-in-S-LL, S-in-S-BCC, S-in-C, S-in-L and C-in-L, where S, S-LL, S-BCC, C and L stand for spherical, spherical in liquid-like state, spherical in body-centered-cubic arrangement, cylindrical and lamellar, respectively. Synchrotron small angle X-ray scattering (SAXS) and crossed polarizers, together with SAXS modelling analysis, were used for a detailed structural study of the samples. The morphology of the microphase separated state was mapped out on 'master' microdomain morphology diagrams as a function of the volume fraction of the AmphComb blocks (Phi(AmphComb)) and the compositional window of each microdomain morphology was determined. It was observed that, (i) within samples based on the same parent diblock copolymer system, the occurrence of a specific microdomain morphology is only dependent on the value of Phi(AmphComb), regardless of the grafting density X and the length of the alkyl side-chains, and (ii) microdomain morphological boundaries occur at Phi(AmphComb) values of similar to 0.20 (S-LL/C and S-BCC/C) and similar to 0.28 (C/L). Finally, the specific influences of the strongly amphiphilic nature of the AmphComb blocks on the observed morphological and hierarchical behaviours of our system are discussed. For reference, stoichiometric strongly amphiphilic comb-like (AmphComb) ionic supramolecules, based on complexation between a homopolymer of PMAA and the various alkyltrimethylammonium amphiphiles, were prepared, which nanophase separated into S (C8) or C (C12 and C16) domains.
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| 30. |
- Asad Ayoubi, Mehran, et al.
(författare)
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Morphological Investigation of Polydisperse Asymmetric Block Copolymer Systems of Poly(styrene) and Poly(methacrylic acid) in the Strong Segregation Regime
- 2013
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Ingår i: Journal of Polymer Science. Part B, Polymer Physics. - : Wiley. - 0887-6266. ; 51:23, s. 1657-1671
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Tidskriftsartikel (refereegranskat)abstract
- Samples of compositionally (highly) asymmetric diblock copolymers and, also, mixtures of diblock and triblock copolymers (the latter obtained as end-coupling products of two diblock molecules of the mixture), composed of (a) monodisperse majority block(s) of poly(styrene) (PS) and a polydisperse minority block of poly(methacrylic acid) (PMAA), microphase separate into spherical PMAA microdomains, either in disordered liquid-like state or body-centered-cubic (BCC) arrangement, at various annealing temperatures T, in the strong segregation regime SSR. We found that (i) the microphase separated state is favored over an anticipated molecularly homogenous state, (ii) the spherical microdomain morphology (with BCC symmetry) is favored over an anticipated hexagonally packed cylindrical morphology, (iii) the extent of the dissolution of short PMAA blocks in the PS material can be quantified, (iv) the spherical microdomains are dilated, and (v) despite molecular-weight (and architectural) polydispersity, well-ordered BCC structures can be obtained. (c) 2013 Wiley Periodicals, Inc.
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