scholarly journals La stabilité des formes fluviales de l’Orange, entre variabilité naturelle et impacts des grands barrages (secteur Boegoeberg-Augrabies, Afrique du Sud)

2009 ◽  
Vol 61 (1) ◽  
pp. 21-37 ◽  
Author(s):  
David Blanchon ◽  
Jean-Paul Bravard
Keyword(s):  
Nous Avons ◽  
Phragmites Australis ◽  
Arundo Donax ◽  
Afrique Du Sud

RésuméLe fleuve Orange (Afrique du Sud) est l’un des systèmes fluviaux les plus aménagés au monde : les barrages hydroélectriques ont modifié le volume d’écoulement du fleuve et son débit solide a diminué depuis les années 1930. Plus encore, dans son cours moyen inférieur (secteur d’Upington), le fleuve a été contraint entre des digues de 5 à 10 m de hauteur, des chenaux secondaires ont été remplis pour permettre le développement agricole et plus de 10 déversoirs de bas niveau ont été construits à travers le chenal. Dans des conditions similaires, des changements géomorphologiques visibles et rapides (incision du chenal, alluvionnement, etc.) ont été enregistrés dans divers systèmes fluviaux en région semi-aride. Pourtant, l’étude de cartes anciennes (des années 1920) et de photographies aériennes (à partir de 1937) montre une stabilité remarquable des formes fluviales, et ce, même à petite échelle : des bancs sableux et des seuils rocheux sont facilement reconnaissables dans le chenal principal. L’objectif de cet article est d’explorer les différentes hypothèses expliquant cette stabilité, en utilisant le concept de discontinuité et la théorie de la catastrophe, et de confronter les résultats avec les travaux récents sur le fleuve Orange. Notre recherche est basée sur le calcul des puissances spécifiques des crues vicennales, la reconnaissance de terrain (entre 2000 et 2003) et le prélèvement de sédiments, en utilisant la méthode de la courbe de Passega. Nous avons également effectué des comparaisons entre les photographies aériennes et les cartes anciennes et les photographies aériennes les plus récentes à l’aide des outils SIG (MapInfo). À micro-échelle, la progression et la destruction des roseaux (Phragmites australisetArundo donax) a été utilisée comme indicateur des changements géomorphologiques du chenal. Les résultats montrent que les concepts de stabilité et d’équilibre, et les changements géomorphologiques fluviaux sont plus complexes qu’une simple comparaison statique.

scholarly journals Distribution des vitesses radiales des regions HII dans la direction du centre galactique

1964 ◽  
Vol 20 ◽  
pp. 199-208
Author(s):  
G. Courtes
Keyword(s):  
Nous Avons ◽  
Afrique Du Sud

La Station Française de Zeekoegat (Province du Cap—Afrique du Sud), construite dans le cadre de l'Observatoire Européen Austral est consacrée à l'étude des vitesses radiales par le prisme objectif de Fehrenbach. Parallèlement aux observations du prisme objectif, nous avons, avec P. Cruvellier, conduit un programme d'observations des régions HII de l'Hémisphère Sud.

scholarly journals Biorefining Potential of Wild-Grown Arundo donax, Cortaderia selloana and Phragmites australis and the Feasibility of White-Rot Fungi-Mediated Pretreatments

2021 ◽  
Vol 12 ◽  
Author(s):  
Ricardo M. F. da Costa ◽  
Ana Winters ◽  
Barbara Hauck ◽  
Daniel Martín ◽  
Maurice Bosch ◽  
...  
Keyword(s):  
Phragmites Australis ◽  
High Performance ◽  
Enzymatic Saccharification ◽  
White Rot Fungi ◽  
Fungal Species ◽  
Arundo Donax ◽  
White Rot ◽  
Neutral Sugar ◽  
Sugar Release ◽  
Cortaderia Selloana

Arundo donax, Cortaderia selloana and Phragmites australis are high-biomass-producing perennial Poalean species that grow abundantly and spontaneously in warm temperate regions, such as in Mediterranean-type climates, like those of Southern Europe, Western United States coastal areas, or in regions of South America, South Africa and Australia. Given their vigorous and spontaneous growth, biomass from the studied grasses often accumulates excessively in unmanaged agro-forestry areas. Nonetheless, this also creates the demand and opportunity for the valorisation of these biomass sources, particularly their cell wall polymers, for biorefining applications. By contrast, a related crop, Miscanthus × giganteus, is a perennial grass that has been extensively studied for lignocellulosic biomass production, as it can grow on low-input agricultural systems in colder climates. In this study Fourier transform mid-infrared spectroscopy (FTIR), high-performance anion-exchange chromatography (HPAEC) and lignin content determinations were used for a comparative compositional characterisation of A. donax, C. selloana and P. australis harvested from the wild, in relation to a trial field-grown M. × giganteus high-yielding genotype. A high-throughput saccharification assay showed relatively high sugar release values from the wild-grown grasses, even with a 0.1M NaOH mild alkali pretreatment. In addition to this alkaline pretreatment, biomass was treated with white-rot fungi (WRF), which preferentially degrade lignin more readily than holocellulose. Three fungal species were used: Ganoderma lucidum, Pleurotus ostreatus and Trametes versicolor. Our results showed that neutral sugar contents are not significantly altered, while some lignin is lost during the pretreatments. Furthermore, sugar release upon enzymatic saccharification was enhanced, and this was dependent on the plant biomass and fungal species used in the treatment. To maximise the potential for lignocellulose valorisation, the liquid fractions from the pretreatments were analysed by high performance liquid chromatography – photodiode array detection – electrospray ionisation tandem mass spectrometry (HPLC-PDA-ESI-MSn). This study is one of the first to report on the composition of WRF-treated grass biomass, while assessing the potential relevance of breakdown products released during the treatments, beyond more traditional sugar-for-energy applications. Ultimately, we expect that our data will help promote the valorisation of unused biomass resources, create economic value, while contributing to the implementation of sustainable biorefining systems.

Mutual effect of Phragmites australis, Arundo donax and immobilization agents on arsenic and trace metals phytostabilization in polluted soils

Geoderma ◽  
2018 ◽  
Vol 314 ◽  
pp. 63-72 ◽  
Author(s):  
Paola Castaldi ◽  
Margherita Silvetti ◽  
Rebeca Manzano ◽  
Giuseppe Brundu ◽  
Pier Paolo Roggero ◽  
...  
Keyword(s):  
Trace Metals ◽  
Phragmites Australis ◽  
Mutual Effect ◽  
Arundo Donax ◽  
Polluted Soils

scholarly journals Evapotranspiration from Horizontal Subsurface Flow Constructed Wetlands Planted with Different Perennial Plant Species

Water ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 2159 ◽  
Author(s):  
Milani ◽  
Marzo ◽  
Toscano ◽  
Consoli ◽  
Cirelli ◽  
...  
Keyword(s):  
Plant Species ◽  
Phragmites Australis ◽  
Constructed Wetlands ◽  
Crop Coefficient ◽  
Arundo Donax ◽  
Growth Stages ◽  
Cyperus Papyrus ◽  
Chrysopogon Zizanioides ◽  
Perennial Plant ◽  
Crop Coefficients

This paper presents the results of an experiment carried out in Southern Italy (Sicily) on the estimation evapotranspiration (ET) in pilot constructed wetlands planted with different species (Chrysopogon zizanioides, Myscanthus x giganteus, Arundo donax, Phragmites australis, and Cyperus papyrus). In the two monitored growing seasons, reference ET0 was calculated with the Penman-Monteith formula, while actual ET and crop coefficients were measured through a water balance and the FAO 56 approach, respectively. The highest average seasonal ET value was observed in Phragmites australis (17.31 mm d−1) followed by Arundo donax (11.23 mm day−1) Chrysopogon zizanioides (8.56 mm day−1), Cyperus papyrus (7.86 mm day−1), and Myscanthus x giganteus (7.35 mm day−1). For all plants, crop coefficient values showed different patterns in relation to growth stages and were strongly correlated with phenological parameters. Myscanthus x giganteus and Arundo donax showed a water use efficiency values significantly higher than those observed for the other tested species. Results of this study may contribute to select appropriate plant species for constructed wetlands located in semi-arid regions, especially when the use of reclaimed water and/or the use of aboveground biomass are planned.

Testing the Enemy Release Hypothesis on tall-statured grasses in South Africa, using Arundo donax, Phragmites australis, and Phragmites mauritianus as models

2018 ◽  
Vol 109 (3) ◽  
pp. 287-299 ◽  
Author(s):  
K. Canavan ◽  
I.D. Paterson ◽  
M.P. Hill ◽  
T.L. Dudley
Keyword(s):  
South Africa ◽  
Species Richness ◽  
Phragmites Australis ◽  
Native Species ◽  
Arundo Donax ◽  
Enemy Release Hypothesis ◽  
Enemy Release ◽  
Specialist Herbivores ◽  
Enemy Escape ◽  
Phragmites Mauritianus

AbstractThe Enemy Release Hypothesis (ERH) predicts that introduced plant species can escape herbivory and therefore have a competitive advantage over native plants, which are exposed to both generalist and specialist natural enemies. In this study, the ERH was explored using the invasive alien species, Arundo donax and two native tall-statured grasses, the cosmopolitan Phragmites australis and African endemic Phragmites mauritianus in South Africa. It was predicted that A. donax would have reduced species richness of herbivores compared with the native Phragmites spp., that it would be devoid of specialist herbivores and would thus be experiencing enemy escape in the adventive range. The herbivore assemblages were determined from both field surveys and a literature review. The assumptions of the ERH were for the most part not met; 13 herbivores were found on A. donax compared with 17 on P. australis and 20 on P. mauritianus. Arundo donax had two specialist herbivores from its native range, and shared native herbivores with Phragmites spp. Although A. donax had reduced species richness and diversity compared with that found in the native distribution, it has partially re-acquired a herbivore assemblage which is similar to that found on analogous native species. This suggests that enemy release may not fully explain the invasive success of A. donax in South Africa.

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