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Humid Areas (humid + area)
Selected AbstractsPhysiological and biochemical traits involved in the genotypic variability to salt tolerance of Tunisian Cakile maritimaAFRICAN JOURNAL OF ECOLOGY, Issue 4 2009Megdiche Wided Abstract Cakile maritima (family: Brassicaceae) was collected from three provenances belonging to different bioclimatic stages (humid, semi arid and arid) in Tunisia to study their eco-physiological and biochemical responses to salinity. Seedlings were cultivated on inert sand for 20 days under NaCl treatments (0, 100, 200, 400 mm NaCl). Plant response to salinity was provenance- and salt-dependent. At 100 mm NaCl, growth parameters (leaf biomass, area, number per plant and relative growth rate) were improved in plants from Jerba (originating from arid bioclimatic stage) compared with the control, while growth was reduced in those from Tabarka (from humid area). High salt levels (400 mm NaCl) decreased the plant growth in the three provenances, but plants in Tabarka were the most salt sensitive. The relative salt tolerance of plants from Jerba and Bekalta provenances was associated with low levels of malondialdehyde as well as of electrolyte leakage and endoproteolytic activity. Salt reduced leaf hydration, the decrease in water content being dose-dependent and more pronounced in Tabarka. Increase in salinity led to significant increase in leaf succulence and decrease in leaf water potential, especially in Jerba plants. The plants from the latter displayed the highest leaf levels of Na+ and Cl,, proline, soluble carbohydrates, soluble proteins, and polyphenols. Overall, the higher salt tolerance of plants from Jerba provenance, and to a lower extent of those from Bekalta, may be partly related to their better capacity for osmotic adjustment and to limit oxidative damage when salt-challenged. Résumé Cakile maritima a été collecté (famille des Brassicaceae) dans trois provenances appartenant à des étages bioclimatiques différentes (humide, semi-aride et aride) de la Tunisie, dans le but d'étudier leurs réponses éco-physiologique et biochimique à la salinité. Des plantules ont été cultivées dans du sable inerte pendant vingt jours avec des doses croissantes de NaCl (0, 100, 200 et 400 mm NaCl). La réponse de Cakile maritima dépend de la provenance et de la salinité du milieu. A 100 mm de NaCl, les paramètres de croissance (biomasse, surface et nombre des feuilles par plante ainsi que le taux de la croissance relative) ont été améliorés chez Djerba (zone bioclimatique aride) par comparaison aux plantes témoins, tandis que la croissance a été réduite chez Tabarka (zone humide). A la plus forte dose de sel (400 mm), une réduction de la croissance des trois provenances a été enregistrée avec une nette sensibilité chez les plantes de la provenance Tabarka. La tolérance relative des deux provenances Djerba et Bekalta est associée à une faible teneur en malondialdéhyde ainsi qu'une fuite d'électrolyte et activité endo-protéolytique modérées. Le traitement salin a réduit l'hydratation des feuilles et cette diminution du contenu en eau est dose-dépendante et elle est plus prononcée chez Tabarka. En outre, l'augmentation de la salinité du milieu a entrainé une élévation de la succulence des feuilles concomitante à une diminution du potentiel hydrique notamment chez Djerba. Les plantes de cette dernière ont été les plus riches en Na+ et Cl - , en proline, carbohydrates, en protéines solubles et en polyphénols. En général, la tolérance au sel de la provenance Djerba, et à moindre degré Bekalta, est en partie reliée à la meilleure capacité d'ajustement osmotique et la limitation des dommages oxydatifs sous stress salin. [source] Hydrological connectivity of soil pipes determined by ground-penetrating radar tracer detectionEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2004Joseph Holden Abstract Soil pipes are common and important features of many catchments, particularly in semi-arid and humid areas, and can contribute a large proportion of runoff to river systems. They may also signi,cantly in,uence catchment sediment and solute yield. However, there are often problems in ,nding and de,ning soil pipe networks which are located deep below the surface. Ground-penetrating radar (GPR) has been used for non-destructive identi,cation and mapping of soil pipes in blanket peat catchments. While GPR can identify subsurface cavities, it cannot alone determine hydrological connectivity between one cavity and another. This paper presents results from an experiment to test the ability of GPR to establish hydrological connectivity between pipes through use of a tracer solution. Sodium chloride was injected into pipe cavities previously detected by the radar. The GPR was placed downslope of the injection points and positioned on the ground directly above detected soil pipes. The resultant radargrams showed signi,cant changes in re,ectance from some cavities and no change from others. Pipe waters were sampled in order to check the radar results. Changes in electrical conductivity of the pipe water could be detected by the GPR, without data post-processing, when background levels were increased by more than approximately twofold. It was thus possible to rapidly determine hydrological connectivity of soil pipes within dense pipe networks across hillslopes without ground disturbance. It was also possible to remotely measure travel times through pipe systems; the passing of the salt wave below the GPR produced an easily detectable signal on the radargram which required no post-processing. The technique should allow remote sensing of water sources and sinks for soil pipes below the surface. The improved understanding of ,owpath connectivity will be important for understanding water delivery, solutional and particulate denudation, and hydrological and geomorphological model development. Copyright © 2004 John Wiley & Sons, Ltd. [source] Impact of wastewater discharge on the channel morphology of ephemeral streamsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2001Marwan A. Hassan Abstract The impact of wastewater flow on the channel bed morphology was evaluated in four ephemeral streams in Israel and the Palestinian Territories: Nahal Og, Nahal Kidron, Nahal Qeult and Nahal Hebron. Channel changes before, during and after the halting of wastewater flow were monitored. The wastewater flow causes a shift from a dry ephemeral channel with intermittent floods to a continuous flow pattern similar to that of humid areas. Within a few months, nutrient-rich wastewater flow leads to rapid development of vegetation along channel and bars. The colonization of part of the active channel by vegetation increases flow resistance as well as bank and bed stability, and limits sediment availability from bars and other sediment stores along the channels. In some cases the established vegetation covers the entire channel width and halts the transport of bed material along the channel. During low and medium size flood events, bars remain stable and the vegetation intact. Extreme events destroy the vegetation and activate the bars. The wastewater flow results in the development of new small bars, which are usually destroyed by flood flows. Due to the vegetation establishment, the active channel width decreases by up to 700 per cent. The deposition of fine sediment and organic material changed the sediment texture within the stable bar surface and the whole bed surface texture in Nahal Hebron. The recovery of Nahal Og after the halting of the wastewater flow was relatively fast; within two flood seasons the channel almost returned to pre-wastewater characteristics. The results of the study could be used to indicate what would happen if wastewater flows were introduced along natural desert streams. Also, the results could be used to predict the consequences of vegetation removal as a result of human intervention within the active channel of humid streams. Copyright © 2001 John Wiley & Sons, Ltd. [source] Hydrograph and unit hydrograph derivation in arid regionsHYDROLOGICAL PROCESSES, Issue 8 2007Zekai Abstract Arid and semi-arid regions expose special hydrological features that are distinctive from humid areas. Unfortunately, humid-region hydrological empirical formulations are used directly in the arid and semi-arid regions without care about the basic assumptions. During any storm rainfall in arid regions, rainfall, infiltration and runoff components of the hydrological cycle have impacts on water resources. The basis of the methodology presented in this paper is the ratio of runoff increment to rainfall increment during an infinitesimally small time duration. This is the definition of runoff coefficient for the same infinitesimal time duration. The ratio is obtained through rational, physical and mathematical combination of hydrological thinking and then integrated with the classical infiltration equation for the hydrograph determination. The parameters of the methodology are explained and their empirical estimations are presented. The methodology works for rainfall and runoff from ungauged watersheds where infiltration measurement can be performed. The comparison of the new approach with different classical approaches, such as the rational formula and Soil Conservation Service method, are presented in detail. Its application is performed for two wadis within the Kingdom of Saudi Arabia. Copyright © 2006 John Wiley & Sons, Ltd. [source] An investigation on the Culicoides species composition at seven sites in southern SwitzerlandMEDICAL AND VETERINARY ENTOMOLOGY, Issue 2 2009S. CASATI Abstract In the past decade, there have been regular outbreaks of bluetongue (BT) in many parts of Europe. Owing to the presence of BT disease and its vectors in countries adjacent to Switzerland, an initial entomological survey was conducted in 2003, which established the presence of several midges of the genus Culicoides (Diptera: Ceratopogonidae). Subsequently, a sentinel herd monitoring system was established with the primary entomological aim being the determination and further study of Culicoides population compositions. Insects were collected in 2005 and 2006 at seven sentinel herd sites in the south of Switzerland (canton of Ticino) near the border of Italy, using Onderstepoort-type light traps. This region is botanically and zoologically similar to the Mediterranean and is one of the warmest and most humid areas of the country, hence it is considered a potential access path for BT disease into Switzerland. Collections were made at four cattle farms, two equestrian centres and one goat farm. Sites were sampled four times per month from June to October. Traps were operated from dusk until dawn and samples were collected monthly for analysis through microscopy as well as a Culicoides imicola -specific PCR. Results confirmed the absence of C. imicola (Kieffer) and demonstrated that the potential BT virus vectors are highly abundant, notably: Culicoides obsoletus (Meigen), Culicoides scoticus (Downes & Kettle) and Culicoides dewulfi (Goetghebuer) subgenus Avaritia and Culicoides pulicaris (Linnaeus) subgenus Culicoides. These findings expand the current knowledge of Culicoides population composition in the southern part of the Switzerland. Culicoides cataneii (Clastrier), Culicoides flavipulicaris (Dzhafarov), Culicoides indistinctus (Khalaf), Culicoides nubeculosus (Meigen) and species of the Grisescens complex were reported for the first time in Switzerland. [source] Thermal-contraction-crack networks as evidence for late-Pleistocene permafrost in Inner Mongolia, ChinaPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2004J. Vandenberghe Abstract Numerous wedges on the Ordos Plateau show typical characteristics of periglacial sand wedges that enable them to be distinguished from desiccation cracks in clayey illuviation soil horizons. The sand wedges are organized in two generations of polygonal networks. The older generation is a large-scale network with a diameter of 8 to 9,m and wedge depths up to more than 2,m. The younger generation has a mean diameter of 3 to 4,m and is formed within the large networks. It consists of shallow (0.6 to 1,m deep) but relatively wide wedges. In contrast to the typical sand wedges that form within continuous permafrost, the shallow wedges formed probably as ,ground wedges' by seasonal freezing. Ice wedges and cryoturbations developed only rarely, and exclusively in the most humid areas. Thermal-contraction cracking occurred mainly between 26 and 20,ka BP, indicating mean annual temperatures at least 13°C lower than present. Before and after that period mean annual temperatures were at least 7 to 8.5° lower than today. The presence of these periglacial phenomena show that the southern limit of continuous permafrost in Inner Mongolia occurred south of 38°N during the Last Glacial Maximum. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||