The Dead Sea and Arava Science Center

Tamar Regional Council, Israel

The Dead Sea and Arava Science Center

Tamar Regional Council, Israel
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Katra I.,Ben - Gurion University of the Negev | Yizhaq H.,Ben - Gurion University of the Negev | Yizhaq H.,The Dead Sea and Arava Science Center
Aeolian Research | Year: 2017

The commonly used grain size analysis technique which applies moments (sorting, skewness and kurtosis) is less useful in the case of sediments with bimodal size distributions. Herein we suggest a new simple method for analyzing the degree of grain size segregation in sand-sized sediment that has clear bimodal size distributions. Two main features are used to characterize the bimodal distribution: grain diameter segregation, which is the normalized difference between coarse and fine grain diameters, and the frequency segregation which is the normalized difference in frequencies between two modes. The new defined indices can be calculated from frequency plot curves and can be graphically represented on a two dimensional coordinate system showing the dynamical aspects of the size distribution. The results enable comparison between granular samples from different locations and/or times to shed new light on the dynamic processes involved in grain size segregation of sediments. We demonstrate here the use of this method to analyze bimodal distributions of aeolian granular samples mostly from aeolian megaripples. Six different aeolian cases were analyzed to highlight the method's applicability, which is relevant to wide research themes in the Earth and environmental sciences, and can furthermore be easily adapted to analyze polymodal grain size distributions. © 2017

Adar O.,The Dead Sea and Arava Science Center | Kaplan-Levy R.N.,Israel Oceanographic And Limnological Research | Banet G.,The Dead Sea and Arava Science Center
European Journal of Phycology | Year: 2016

Two algal cultures, TvB and SH, were isolated from extreme habitats along the Syrian-African rift Valley (Israel). These cultures were initially identified as Chlorella spp. according to their morphology and lack of bristles, but following molecular phylogenetic analyses, re-identified as Micractinium spp. closely related to Chlorella. The strains were subjected to a bi-factorial study in the search for algae that grow well at elevated temperatures and salinities for future biotechnological uses. Cell density (CD) and optical density (OD) were measured for each strain at three temperatures: 35, 40 and 45ºC, and five salinities of seawater (SW): 34.8 ppt (100% SW), 26.5 ppt (75% SW), 18.3 ppt (50% SW) 10 ppt (25% SW) and 1.8 ppt (0% SW). Both strains grew best at 35–40ºC and at 0–50% SW. Increased salinity enhanced temperature tolerance to 45ºC, particularly for strain TvB. At 45ºC, following a short initial growth spurt, cultures underwent a lag period of c. 7 days, followed by a significant growth phase. During the lag period, algae underwent a substantial increase in average cell diameter (ACD). These enlarged or gigantic cells with diameters of up to ~20 μm, produced and eventually released multiple autospores. By day 13, original size distribution was almost restored. The observed morphological alterations appear to enable these strains to survive and grow autotrophically at supra-optimal temperatures (SOT). These natural adjustments may be exploited for reducing costs associated with both cooling and desalination in future cultivation. © 2016 British Phycological Society

Mischke S.,University of Iceland | Opitz S.,University of Cologne | Kalbe J.,University of Potsdam | Ginat H.,The Dead Sea and Arava Science Center | Al-Saqarat B.,University of Jordan
Quaternary International | Year: 2015

Sedimentological, palaeontological and mineralogical analyses of sediments from the endorheic Al Jafr Basin were conducted to better understand the depositional and hydrological conditions on the southern Jordan Plateau in the late Quaternary. Surficially exposed carbonate-rich sediments in the western part of the basin contain ostracod (micro-crustacean) shells of Ilyocypris cf. bradyi, Candona neglecta, Heterocypris salina, Fabaeformiscandona fabaeformis, Pseudocandona sp. and Herpetocypris brevicaudata. The shells of these and other more rare species, and charophyte and mollusc remains indicate that the sediments were formed in a wetland setting of shallow freshwater to slightly oligohaline ponds, streams and swamps. The present more northern distribution of some of the recorded taxa implies that climate conditions were probably cooler during the wetland formation. Radiocarbon age data for biogenic carbonate from two locations suggest that the wetland setting existed during the second half of Marine Isotope Stage (MIS) 3 or possibly earlier. A significantly higher water table must have existed in the basin during wetland formation; and wetter climate conditions are inferred for the catchment or at least for its highest and most humid westernmost part. Deflation and local sediment accumulation by wind and occasional sheet-wash events apparently prevailed in the region since MIS 2. Our newly presented data and inferences do not support the reconstruction of a previously reported large and relatively deep Pleistocene lake in the Al Jafr Basin. However, more extensive studies are certainly required for a detailed assessment of the Quaternary hydrological conditions in southern Jordan. © 2014 Elsevier Ltd and INQUA.

Zaady E.,Israel Agricultural Research Organization | Katra I.,Ben - Gurion University of the Negev | Yizhaq H.,Ben - Gurion University of the Negev | Yizhaq H.,The Dead Sea and Arava Science Center | And 2 more authors.
Aeolian Research | Year: 2014

The aims of this study were to investigate the impact of biological soil crusts' (biocrust) developmental stage on soil physical structures in sand dunes under two different rainfall regimes. It was hypothesized that biocrust's developmental stage and function, as affected by the aridity level, may impact soil surface properties, pedogenesis and hydrology. Bio-physiological parameters of the biocrust (polysaccharide, protein and chlorophyll contents) were studied for the determination of its developmental stage. The soil physical surface properties that were measured included the surface breaking pressure and granulometry. Hydrological measurements included the infiltration rate and soil moisture regime in deep layers and structure granulometry. These measurements were taken over two years, in scraped top soil surfaces and in homogeneous sandy dunes, and were compared with natural biocrust surfaces. Higher precipitation at the northern site, with a more advanced developmental stage of the natural biocrust compared to the southern site, has affected the structure granulometry by increasing the cohesive fractions of clay and very-fine silt within the soil surface layer. Higher infiltration rates and soil moisture (%) below the biocrust were obtained with the cyanobacterial crust at the dry southern site. Biocrust controls water infiltration into the soil sub-surface by affecting the surface penetrability. The infiltration controlled by the crust was inversed to the rainfall gradient. The novelty of this study is that by characterizing the bio-physiological parameters of biocrusts as affected by aridity levels, it is possible to imitate climate change scenarios on soil moisture in specific sites. © 2014 Elsevier B.V.

Yizhaq H.,Ben - Gurion University of the Negev | Yizhaq H.,The Dead Sea and Arava Science Center | Ashkenazy Y.,Ben - Gurion University of the Negev
Aeolian Research | Year: 2016

We show that the system of biocrust and vegetation on sand dunes modeled by two coupled ordinary nonlinear differential equations exhibits self-sustained oscillations. Such oscillations can occur on vegetated linear dunes that are mostly covered by biocrust. The vegetation-biocrust interaction underlies these oscillations and these do not occur if only vegetation dynamics is considered. The oscillations are "relaxation oscillations" which are characterized by two alternating attraction processes to equilibrium states with high low vegetation covers. The complex dynamics of the biocrust-vegetation model leads to unexpected scenarios, such as vegetation rehabilitation induced by drought or by grazing during which the system shifts to one of the bistable state dominated by a higher vegetation cover, or rehabilitation of vegetation that is induced by decrease in precipitation. The oscillation periods range from decades to millennia and they can interact and be affected by the climate system variability. © 2015 Elsevier B.V.

Leibowitz M.P.,Ben - Gurion University of the Negev | Chettri J.K.,Copenhagen University | Ofir R.,The Dead Sea and Arava Science Center | Zilberg D.,Ben - Gurion University of the Negev
Journal of Fish Diseases | Year: 2010

Antibacterial and antiparasitic agents and a cysteine protease inhibitor (E-64) were tested against Tetrahymena infection, a serious problem in guppy production worldwide. Chemicals were tested in vitro by a colorimetric assay for Tetrahymena survival. The most effective were niclosamide, albendazole and chloroquine, with 23%, 35% and 60% survival, respectively, following 2-h exposure to 100 ppm. Longer incubation periods resulted in greater reductions in survival. Niclosamide was further studied in vivo at different dosages, administered orally to Tetrahymena-infected guppies. Mortality rates were significantly lower in all treatment groups; in trial I, 30% and 33% mortality in 5 and 40 mg kg-1 niclosamide-fed fish vs. 59% mortality in controls; in trial II, 35%, 13% and 10% in 50, 100 and 200 mg kg-1 niclosamide-fed fish vs. 64% in controls. The effect of the cysteine protease inhibitor E64 was tested in tissue culture, by measuring histolytic activity of the parasite (Tet-NI) on a guppy-fin cell line, based on cell depletion. Tet-NI feeding activity was significantly reduced following pretreatment with E-64 relative to non-treated Tet-NI. E-64-pretreated Tet-NI was injected i.p. into guppies: recorded mortality rates were significantly lower (35%) than that in non-treated Tet-NI (60%), suggesting inhibition of the parasite's cysteine protease as a possible therapeutic approach. © 2010 Blackwell Publishing Ltd.

Wahbeh B.,Ben - Gurion University of the Negev | Hamed T.A.,The Dead Sea and Arava Science Center | Hamed T.A.,Arava Institute for Environmental Studies | Kasher R.,Ben - Gurion University of the Negev
Renewable Energy | Year: 2012

Hydrolysis of boron is investigated as a part of a boron/boron oxide solar water splitting-thermochemical cycle. Boron was hydrolyzed and boron oxide was gasified with steam in a tubular reactor. The effects of the reactor temperature and water flow rate on hydrogen production and boron oxide gasification were studied at different furnace set point temperatures and water flow rates. The produced hydrogen was measured by inline gas chromatography. Results show that the hydrogen production rate increased by increasing the reaction temperature and water flow rate. The range of hydrogen production efficiency of 95-100% was obtained for all experiments, as well as a full conversion of the boron particles to boron oxide, and the boron oxide to orthoboric acid. It was observed that the hydrogen production rate was high at the beginning of the hydrolysis process and decreased gradually with time. The X-ray analysis showed that the boron was converted into boron oxide and boric acid. The formation of a boric acid layer on the reactor walls was attributed to the gasification of the boron oxide. © 2012 Elsevier Ltd.

Sagie H.,Ben - Gurion University of the Negev | Sagie H.,Arava Institute for Environmental Studies | Morris A.,Arava Institute for Environmental Studies | Morris A.,The Dead Sea and Arava Science Center | And 4 more authors.
Journal of Arid Environments | Year: 2013

This research explores local resident perspectives on ecosystem services (ES) in the hyper-arid Arava Valley/Wadi Araba, which spans across both Israel and Jordan. Identifying and characterizing ES, an increasingly popular precursor for crafting sustainable natural resource management and land use policy, is an inherently multi-disciplinary endeavor. Our goal is to apply social research tools, in particular in-depth interviews with local residents, to understand their perspectives concerning ES. Since the research is conducted on two sides of an international border, it also illuminates the potential role of culture, nationality and economics in formulating perceptions on ES in deserts.The results show that, although deserts are often considered to be lacking in ES, local residents feel that their environment is abundant in services, particularly cultural services. Furthermore, although they live in a nearly identical ecosystem, local residents from two sides of the border showed distinct differences, as well as some shared patterns, in how they use and value ES. The study highlights the importance of applying social methods for ES identification and characterization in tandem with other disciplinary approaches, in order to avoid common problems including disregard of the importance of social and cultural perspectives, leading to undervaluing of intangible cultural services. © 2013 Elsevier Ltd.

Yizhaq H.,Ben - Gurion University of the Negev | Yizhaq H.,The Dead Sea and Arava Science Center | Katra I.,Ben - Gurion University of the Negev
Earth and Planetary Science Letters | Year: 2015

Megaripples are distinguished from regular ripples by their larger dimensions and bimodal grain-size distributions. The interplay between wind, grain size and ripple morphology (height and wavelength) controls their development. Two main mechanisms limit megaripple height. The first, megaripple flattening due to winds that are above the fluid threshold of the coarse grains, destroys the armoring layer of the megaripple. The second is megaripple erosion by the impacts of fast-moving, fine saltating grains that propel the coarse grains constituting the armoring layer. For any given wind regime and grain size distribution, the potential megaripple dimensions are limited by these two mechanisms. Here we study the first mechanism and estimate the duration of strong winds (sustained above the fluid threshold) needed to flatten megaripples. Strong gusts of wind, in contrast, cannot destroy the megaripples but can cause ripple migration. Based on data from previous works on megaripples, we find a scaling law between the ripple morphology and the coarse mode of grains at the crest. Using this scaling relation allows us to calculate the wind velocity and duration needed for megaripple flattening. In general, the coarser the particles at the megaripple crest, the stronger the wind needed to flatten the megaripples. Moreover, the greater the strength of the wind required to flatten the megaripples, the lower the recurrence probability. Taken together, these findings increase the longevity of megaripples. We apply the results for a megaripple field in the southern Arava valley (Israel). © 2015 Elsevier B.V.

Winters G.,The Dead Sea and Arava Science Center | Shklar G.,Israel Agricultural Research Organization | Korol L.,Israel Agricultural Research Organization
Conservation Genetics Resources | Year: 2013

Nuclear microsatellite markers were developed for Acacia tortilis to study patterns of population genetic structure across the species' distribution. Twelve dinucleotide repeat loci were developed and tested on 20 individuals sampled from four populations. The number of alleles per locus ranged from 5 to 15, expected heterozygosities from 0.701 to 0.873 and the polymorphism information content (PIC) ranged from 0.675 to 0.861. © 2013 Springer Science+Business Media Dordrecht.

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