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Plant life in the Umm as Samim, Oman – A case study in a major inland sabkha
Journal of Arid Environments 85 (2012) 122e127
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Plant life in the Umm as Samim, Oman e A case study in a major inland sabkha P. König* University of Greifswald, Institute of Botany and Landscape Ecology, Grimmerstr. 88, D-17487 Greifswald, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 March 2010 Received in revised form 25 April 2012 Accepted 13 June 2012 Available online xxx
The Umm as Samim is a vast salt flat of central Oman, in which many wadis which flow south-westwards from the central sector of the northern mountains converge. Most of the area is devoid of vegetation due to extraordinary salinity (sabkha). Significant plant growth is possible chiefly on miniature dunes, called nabkhas, which enable the plants to prosper in an otherwise harsh environment. The site conditions are depicted by mapping of miniature dunes and vegetation, accompanied by an account of morphometric parameters, i.e. height of nabkha, height of plant growth, and status of plant life. Within the chosen sample plot, 12.3% of the sabkha is covered by nabkhas. The total plant cover amounts to 5.0%, but only 3.1% of it is alive, while 2.0% is dead or lifeless. Two nabkhas were longitudinally excavated to examine the salinity of soil samples in relation to dune structure and root and shoot system position. The salinity analysis was done via electrical conductivity (EC1:5 extract). Extremely high EC values were found on current or former sabkha surfaces and on the periphery of nabkhas, whereas central nabkha parts and bottom soil offer more favourable salinity values for plant and root growth. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Arabian peninsula Aeluropus lagopoides Nabkha Salinity Tetraena qatarensis
1. Introduction Flat silty depressions with salt accumulation are a typical feature of arid regions and are called sabkha in Arabian countries. They stretch over vast areas and are the object of special knowledge surveys in the region (Barth and Böer, 2002; Deil, 1998; Friedman and Krumbein, 1985; Khan et al., 2006). Sabkhas are more or less bare of vegetation over most of their area. Only along their outskirts and near runnels is modest plant growth possible. On the Arabian peninsula, sabkhas are found along coastal plains and inland depressions. In Oman, too, sabkhas are a typical constituent of the landscape. A general presentation is given by Ghazanfar (2002). The largest sabkha of Oman is the Umm as Samim, situated in the central part of the Sultanate. This inland sabkha has an area of about 2400 km2 and borders on Saudi Arabia. The vast plain is delimited by the foothills of the Hajar mountains in the north, the “empty quarter desert” Rub’ al-Khali in the south and west, and the Jiddat al-Harasis desert in the east. Whereas various aspects of Omanian coastal sabkhas have been described by Kürschner (1986), Ghazanfar (1995, 1999) and König (2007), knowledge about inland sabkhas is scarce e aside from
* Tel.: þ49 3834861130; fax: þ49 3834861129. E-mail address: [email protected]. 0140-1963/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jaridenv.2012.06.007
a more geologically based study by Heathcote and King (1998) e and precise investigations are lacking to date. Thereby it is evident that plant growth is often concentrated on or even limited to micro-dunes, and it was suspected that salinity is less extreme within such stands. The present study deals with a detailed analysis of soil and vegetation to determine the influence of micro-dunes on salinity gradients and growth capacity. 2. Study area The development of the Umm as Samim as we know it today started around 30,000 BP. Today, dry, hot conditions are predominant. The climatic situation is outlined by an ecological climate diagram of the nearest station available, Fahud (Fig. 1). Annual precipitation is approximately 24 mm, far below the 100 mm level relevant for plant growth. The mean annual temperature is given as 28.8 C. Thus, the climate is typified as hyper-arid. Most precipitation occurs during spring but is rather erratic. A typical feature of salty depressions are overgrown miniature dunes called nabkhas or nebkhas, a term that has received general acceptance in the literature (e.g., Khalaf et al., 1995). They develop predominantly at the edges of sabkhas, where the salt content is lower. Some species in the Umm as Samim filter out sand blown by the wind and trap it in their branches or stems. Obviously, sand accumulation allows plants to remain viable when growing in soil zones with lower salinity, while plant growth is impossible on salt
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Fig. 1. Map of Oman with relevant ecological regions, location of the study site at the Umm as Samim, and climatic diagram of Fahud, as the nearest representative station (data source: Fisher and Membery, 1998).
crusts. Thus, nabkhas of the Umm as Samim are result of special adaptations of plant growth. In contrast, in other regions, nabkhas are reported as a consequence of human impact (grazing, population pressure), which has resulted in a dramatic increase in wind erosion (e.g., Nickling and Wolfe, 1994). 3. Materials and methods The study area is situated in the northern part of the Umm as Samim (21 53.7550 N, 55 52.1060 E). The particular site conditions were analysed by means of vegetation mapping, microdune surveys, and soil analysis. The studies were conducted throughout February 2007 and March 2008. The nomenclature follows Cope (2007), Ghazanfar (2003, 2007) and Miller and Cope (1996). For the documentation of vegetation structures, a representative 20 20 m ¼ 400 m2 sample plot was chosen and subdivided into 2 2 m grids for detailed and convenient analysis. The nabkhas present within the plot were mapped regarding height, length and width. Furthermore, the size of the plants was recorded, and they were classified into living and dead specimens.
The nabkha surveys were performed by digging a 50-cm-deep ditch along the main axis of the relevant miniature dunes, which is given by the main wind direction, to obtain the shape of a particular dune section. Dune and plant height as well as root depth were recorded every 10 cm for two representative microdunes. Furthermore, soil samples were collected in a grid system for the evaluation of electrical conductivity (EC), with each square measuring 20 20 cm, and samples were taken at the grid’s intersecting points. This reflects the salinity distribution inside the nabkhas and their immediate surroundings. A slurry was made of the soil samples with distilled water at a ratio of 1:5 and allowed to sediment for 1.5 h. Thereafter, EC was identified with a WTW Cond 340i conductivity gauge as a measure of the amount of total dissolved salts for the temperature reference of 25 C (Rowell, 1997). Since there is a linear relationship between EC and salt concentration, all literature values are converted to EC1:5 extract. ECe (soil saturation paste extract) values must be divided by 6.4 to emulate EC1:5 extract values (Rowell, 1997). Conversion may not match properly in every case, but it is a simple and sufficient tool for comparison.
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4. Results During the study period, only perennial species were recognised, i.e. Aeluropus lagopoides (L.) Trin. ex Thwaites and Phragmites australis (Cav.) Trin. ex Steud. among the Poaceae, Anabasis setifera Moq., Arthrocnemum macrostachyum (Moric.) K. Koch, Cornulaca monacantha Del., Haloxylon salicornicum (Moq.) Bunge ex Boiss., Salsola rubescens Franchet (all Chenopodiaceae), Tamarix aucheriana (Decne.) Baum (Tamaricaceae), Tetraena qatarensis (Hadidi) Beier et Thulin (formerly Zygophyllum qatarense Hadidi, Zygophyllaceae). First, the dominance of Chenopodiaceae species is evident. Within the photosynthetic pathway types, the C4 plants are predominant (5 of 9 species). Succulence is found in 5 species as well. Although spring 2007 was an extraordinarily rainy year with ephemeral plant growth across great areas in most parts of the United Arab Emirates and northern Oman, is was not possible to find any annuals in the study area or its surroundings. Various aspects of the situation are depicted from a bird’s-eye view in Fig. 2 for a 20 20 m sample area. The vegetation is mainly characterised by the grass A. lagopoides and the dwarf shrub T. qatarensis. Fig. 2a illustrates plant species composition and the individual condition of the constituents in a selected plot. The total plant cover is sparse and amounts to as much as 5.0%. The oversanded area, that is sand covered and captured by nabkhas, accounts for 12.3%. Numerous dead plant specimens document the harsh conditions in the struggle for survival. The strong correlation between dead and living specimens to dune structures is evident, for instance, there’s a correlation between dead plants and relatively smaller nabkhas. In the case of a dead plant, it is not clear whether an established plant died or a new plant had started to grow and accumulate a nabkha but then it died before the nabkha could accumulate much sand. The plant status of some A. lagopoides specimens were not definitely distinguishable in the field due to extreme desiccation (plants appear lifeless). Fig. 2b and c give impressions of nabkha and plant size, respectively. Generally, Aeluropus seems to be the more effective sand binder due to dense rhizomatous growth and ready regrowth after oversanding (and browsing). Thus, the overall height of Aeluropus nabkhas is superior to Tetraena nabkhas. Otherwise, the growth capacity is very limited in the case of the creeping grass A. lagopoides, but is more obvious in the dwarf shrub T. qatarensis due to its morphology. Nabkha structure and salinity allocation is illustrated for A. lagopoides in Fig. 3a. On the windward side, nabkha height increases rapidly to a maximum of 45 cm within the first 70 cm of length. Most of the plant is buried in sand. On the lee side, the nabkha tapers off more slowly and needs 90 cm to cross the zero line (¼ sabkha level). The nabkha shows a total length of 160 cm and represents the typical form of a miniature dune. The entire nabkha is interspersed with shoot material of A. lagopoides. The bottom, from 0 to 6 cm, is shoot-free, and is probably the foundation of nabkha growth. Root depths vary from 25 to 42 cm within nabkha range. The quantified conductivity of the 20 cm samples did not differ significantly from each other. EC ranged from 1.5 to 4.3 mS/cm with a mean range of 2e3 mS/cm. The sample at 40 cm exhibited a conductivity of 2.7 mS/cm. The situation on the soil surface is much more diverse, both in range and amount of salinity. Especially the salinity situation of the soil surface outside the nabkha is quite harmful and characterised by extremely high EC values (between 50 and 55 mS/cm) due to ascending water evaporation supported by finely grained soils. Sand tail values of the zero surface line of the downwind side vary from 46.8 to 29.8 mS/cm. Inside the nabkha, the salinity situation is quite heterogeneous due to sand drift and salt entry, but conspicuously less hostile than outside. Together
Fig. 2. Plant species composition and status (a). Height of miniature dunes below plant growth in four categories (b). Height of plant growth in three categories (c). Main wind direction from NW to SE (i.e. bottom to top), unmarked interdune space is sabkha surface.
with the fact that water is retained by the sandy soil, nabkhas provide favourable microhabitats within the surrounding salt desert. Crossing the nabkha from windward to lee side on the 0 cm line, a distinctive course of conductivity is obvious, starting with 55.1 mS/cm in front, modest values of 4.8e5.5 mS/cm inside, and a high level of 53 mS/cm behind the nabkha again. The samples of the 20- and 40-cm level vary between 6.3 and 19.3 mS/cm. The T. qatarensis nabkha exhibits a length of 320 cm and a maximum height of 34.2 cm (Fig. 3b). The plant cover is found within the first 130 cm (¼ 40%) of the nabkha. Tetraena grows up to 54 cm, root depths are found between 9 and 30 cm.
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Fig. 3. Longitudinal section and analysis of an Aeluropus lagopoides (a) and a Tetraena qatarensis nabkha (b). Volume of electrical conductivity spheres represents amount of salinity, maximum and minimum are given representatively. Vertical position 0 cm ¼ sabkha level.
The EC values of the 20 cm line are virtually identical and range from a modest 1.1 to 1.6 mS/cm. The 20 cm level shows considerable salinity of 4e8.2 mS/cm. Again, variability is most pronounced within the 0-cm level, ranging from 2.1 to 34.2 mS/cm. The allocation of salinity is remarkable. The lowest values (2.1e4.3 mS/cm) are indeed found in the rooting zone of T. qatarensis. Outside this zone, i.e. the former sabkha surface before the formation of the nabkha, EC rises markedly (9e34.2 mS/cm). Altogether, from 20 cm depth onwards, the soil became more damp and there were no salt crystals visible to the naked eye. This impression is confirmed by the measurements of conductivity. Here, too, monocotyledons and dicotyledons show the same tendencies. As expected, the EC is greatest at surface level and, accordingly, salinity is highest. Here, no plants or roots are found in either nabkha. The plants avoid this area, since the salts accumulate to toxic concentrations in the surface region. Thus, the salinity decreases with increasing depth.
A. lagopoides stretches from the Mediterranean to the Indian subcontinent with presence in all countries of the Arabian peninsula. The species, provided with clonal growth, salt glands which reduce the salt charge readily, and the water-efficient C4 photosynthetic pathway, is a typical constituent of coastal halophytic communities, but is also found in damp and arid places with a tendency to salinisation. T. qatarensis is an endemic of the Arabian peninsula and found from Qatar through the Emirates and Oman to Socotra. It is a characteristic part of the desert vegetation and known for its sophisticated water economy, because leaf quantity and structure are controlled by the moisture status of the environment (Ismail, 1983). The absence of annuals would seem to disagree with the results of Brown and Porembski (1998), who found a high percentage of annuals on the nabkhas of Haloxylon salicornicum in the Kuwait desert; however, these settle on non-saline ground and under somewhat wetter conditions of about 120 mm rainfall per year. 5.2. Propagation and establishment
5. Discussion 5.1. Floristic composition and vegetation pattern The vegetation is dominated by Aeluropus lagopoides and Tetraena qatarensis. Both species are widely distributed in arid regions.
Especially for A. lagopoides, it is apparent that old plant material can function as the substrate for new growth of the same species, because almost the entire nabkha is interspersed with Aeluropus shoots. The spread can be generative or vegetative. Beneath the surface of a T. qatarensis nabkha, plant material is only found below
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the assimilating sections. Nevertheless, shoot and leaf sections of Aeluropus, formerly aboveground plant parts, occur only from a height of several centimetres onward. The salinity results clearly indicate that a certain amount of sand has to accumulate initially to offer a salt level low enough for plant survival or germination facilities (Fig. 2). The surface samples tended to show higher salinity and lower soil moisture than did the bottom samples (Fig. 3). Surface conditions are important during the time of generative propagation/ reproduction of the species in view of the high osmotic potential of the medium which might inhibit the germination of seeds. A. lagopoides is known to be highly salt tolerant during germination. Gulzar and Khan (2001) and Gulzar et al. (2003) studied the effects of various salinity treatments on biomass production, longitudinal growth and germination. Little inhibition was found in media containing 200 mM NaCl, but 400 mM NaCl (and more) inhibited growth, and plants survived in 600 mM NaCl with low mortality and reduced growth. The highest germination is obtained under non-saline conditions, and an increase in NaCl concentration progressively inhibits germination. 30% of seeds germinated under moderate temperatures (20/30 C) at 500 mM NaCl, a salinity concentration approaching seawater (600 mM NaCl). Bodla et al. (1995) reported that A. lagopoides could survive up to 110 mS/cm NaCl (z1500 mM NaCl) to a certain extent. Increasing salinity is responsible for decreasing shoot length and number of leaves, both reducing the biomass production considerably. Germination experiments with T. qatarensis showed that seeds failed to germinate when NaCl concentration was above 300 mM (Zaman et al., 2006). Altogether, Aeluropus lagopides exhibits a greater tolerance to salinity than T. qatarensis from an autecological point of view. According to Mahmood et al. (1996), a NaCl concentration of 309 mM represents an EC of 30 mS/cm, a numerical value which is not reached by most of the nabkha EC1:5 extracts soil samples (Fig. 3a, b) and enables plant growth, given sufficient rain. This strategy is well-known from other typical constituents of Arabian halophytic vegetation (e.g., Mahmoud et al., 1983). Furthermore, the shed seeds of T. qatarensis were found to experience day temperatures at the soil surface and 1 cm below the soil surface between 52e68 C and 50e64 C, respectively (Ismail and El-Ghazaly, 1990). Seeds may remain viable for a long period and create an enormous seed-bank, ready to germinate when conditions are right. Seeds usually germinate after leaching of salt due to rainfall, which is rather erratic in the Umm as Samim area. Thus, it is assumed that propagation by seeds is a rare event in the study area. Plants with perennial and/or clonal growth hence have an advantage in this situation. 5.3. Nabkha shape and plant growth A. lagopoides and T. qatarensis show a similar nabkha profile. Both species reduce wind speed and allow sand deposition within the plant bodies and in the tail on the downwind side. The form is somewhat elliptical, and more or less tapered on the leeward side. The nabkha size depends on plant height and density of branching. The length of the nabkha seems to correlate with plant size, an interrelationship which Khalaf et al. (1995) found to be significant. The monocotyledonous A. lagopoides, in contrast, grows rather net-like on the dune surface level and therefore does not generate much wind protection for the leeward side. T. qatarensis, however, extends up to 30 cm above the nabkha surface and can affect a larger part of its slipstream. A. lagopoides probably compensates this “lack” by the fact that the nabkha is thoroughly pervaded by the shoot system and reaches a greater height than that of Tetraena. Thus, sand capture strategy and form of the nabkha is somewhat different. It is assumed that A. lagopoides cannot unfold its full
potential due to excessive browsing; the species is particularly reported to be a favourite forage plant (Gulzar and Khan, 2001). In contrast, T. qatarensis is not readily grazed by livestock, and camels feed on it only when other fresh fodder is unavailable (Ghazanfar, 2007). The assessment by Mandaville (1990) is somewhat different, reporting that it is a useful summer grazing plant for camels, which are accustomed to its salinity and purgative effects. However, the local Bedouins consider excessive grazing on it unhealthy. This might result in more successful sand capturing due to less damage caused by browsing animals. The roots of the plants typically find their way into the zone between sabkha surface and 35 cm soil depth, with a mean rooting depth of 36.1 cm (A. lagopoides) and 22.9 cm (T. qatarensis). 5.4. Salinity comparison In the nabkha area, the salinity at the 0-cm level drops significantly compared to the surroundings (55e3 mS/cm). This demonstrates the effectiveness of sand accumulation. It is noteworthy that the salinity at 20 cm and for the one sample taken at 40 cm is lower than that at 20 cm and 40 cm. Indeed, the substrate of the nabkha is accumulated sand, where the salinity is much lower than that of the underlying clayey soil, which is enriched with salt by evaporation and rising soil water. As drying occurs, salts crystallise out of solution producing a salt efflorescence on the sabkha soil surface. As a result, salt crystals drift along with the sand and are likewise deposited. Electrical conductivity values of the 20-cm level differ significantly between the two nabkha types, because conductivity of the T. qatarensis nabkha is generally almost 10 mS/cm lower than that of the A. lagopoides nabkha. The locations of the two nabkhas were situated very close together and the substrates showed no obvious differences, so it is very unlikely that the drifting sand which accumulated differs decisively in salt content and consistency. However, desalinization glands in Aeluropus contribute to salinity because plant material is enclosed in the sandmass. In contrast, salt-accumulating Tetraena leaves are shed and blown away. The 40-cm level is reached by the Aeluropus nabkha only. The results of salinity measurements of A. lagopoides and T. qatarensis sites of other regions and authors are sometimes difficult to compare due to different measurement specifications. A. lagopoides sites were sampled by Al-Jaloud et al. (2001) in Saudi Arabia, with results varying from 4.0 to 6.2 mS/cm, depending on soil depth. König (2007) reported 0.2 mS/cm for 30 cm soil depth and 1.1 mS/cm for soil surface in a coastal area of Dhofar/Oman. For T. qatarensis, Al-Jaloud et al. (2001) mentioned a range of 2.2e3.0 mS/cm for Saudi Arabia. From the Arabian Gulf coast of Saudi Arabia, Böer (1996) reported 0.4e7.6 mS/cm directly underneath the plants at a depth of 35e40 cm. König (2007) recorded values for coastal sites near Duqm, central Oman. For the halophytic site, the EC amounted to 13.1e22.0 mS/cm and 30.8e31.0 mS/cm for 30 cm soil depth and soil surface, respectively. The nonhalophytic, but spray-influenced site showed 4.3e6.3 and 3.3e5.6 mS/cm, respectively. Altogether, the values largely correspond with those of the core areas of growth, i.e. the rooting zones of excavated A. lagopoides and T. qatarensis nabkhas of the Umm as Samim, aside from the exceptional halophytic site near Duqm. 6. Conclusion Under arid conditions, ascending soil water flow and evaporation will lead to salt accumulation at the soil surface, especially in depressions and locations with high proportions of fine earth. Apart from a few specialists, plant life is mostly possible on sand accumulations which rise a certain distance above the sabkha surface. In
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summary, it can be reasonably stated that sand accumulation is an effective strategy of halophytes to survive in extreme habitats like Umm as Samim. This was validated by soil samples in various microzones of nabkhas. Thus, the hypothesis that salinity is less extreme within nabkhas was confirmed. Such sites are microhabitats and offer a minimum of livelihood. Furthermore, nabkhas enable establishment which is the greatest obstacle to plant development. Otherwise, site conditions are hostile due to extreme soil salinity. This strategy, of course, has its limits. Wide areas of Umm as Samim are devoid of vegetation. EC values at the surface of those areas reaches 167 mS/cm e far beyond ranges in which plants can grow. Acknowledgements I am indebted to Natalie Breidenbach and Oliver Fried for assistance during field work and soil analysis. Thanks go to Ulrich Möbius for competent laboratory assistance and Kathleen Splieth for the English review. References Al-Jaloud, A.A., Al-Saiady, M.Y., Assaeed, A.M., Chaudhary, S.A., 2001. Some halophyte plants of Saudi Arabia, their composition and relation to soil properties. Pakistan Journal of Biological Sciences 4, 531e534. Barth, H.-J., Böer, B. (Eds.), 2002. Sabkha ecosystems. Vol. I, The Arabian Peninsula and Adjacent Countries. Tasks for Vegetation Science, vol. 36. Kluwer, Dordrecht. Bodla, M.A., Chaudhry, M.R., Shamsi, S.R.A., Baig, M.S., 1995. Salt tolerance in some dominant grasses of Punjab. In: Khan, M.A., Ungar, I.A. (Eds.), The Biology of Salt Tolerant Plants. Department of Botany, University of Karachi/Pakistan, pp. 190e198. Böer, B., 1996. Plants as soil indicators along the Saudi coast of the Arabian Gulf. Journal of Arid Environments 33, 417e423. Brown, G., Porembski, S., 1998. Flora and vegetational aspects of miniature dunes in a sand-depleted Haloxylon salicornicum community in the Kuwait desert. Flora 193, 133e140. Cope, T.A., 2007. Flora of the Arabian Peninsula and Socotra, vol. 5(1). Univ. Press, Edinburgh. Deil, U., 1998. Coastal and sabkha vegetation. In: Ghazanfar, S.A., Fisher, M. (Eds.), Vegetation of the Arabian Pensinsula. Geobotany, vol. 25, pp. 209e228. Fisher, M., Membery, D.A., 1998. Climate. In: Ghazanfar, S.A., Fisher, M. (Eds.), Vegetation of the Arabian Peninsula. Geobotany, vol. 25, pp. 5e38. Friedman, G.M., Krumbein, W.E. (Eds.), 1985. Hypersaline Ecosystems. The Gavish Sabkha. Ecological Studies, vol. 53. Springer, Berlin.
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Ghazanfar, S.A., 1995. Vegetation of coastal sabhkas: an analysis of the vegetation of Barr al Hikman, Sultanate of Oman. In: Khan, M.A., Ungar, I.A. (Eds.), The Biology of Salt Tolerant Plants. Department of Botany, University of Karachi/Pakistan, pp. 277e283. Ghazanfar, S.A., 1999. Coastal vegetation of Oman. Estuarine, Coastal and Shelf Science 49, 21e27. Ghazanfar, S.A., 2002. The sabkha vegetation of Oman. In: Barth, H., Boer, B. (Eds.), Sabkha Ecosystems. Kluwer, Dordrecht, pp. 99e107. Ghazanfar, S.A., 2003. Flora of the Sultanate of Oman. Vol. 1: Piperaceae to Primulaceae. Scripta Botanica Belgica, vol. 25. National Botanic Garden, Meise. Ghazanfar, S.A., 2007. Flora of the Sultanate of Oman. Vol. 2: Crassulaceae e Apiaceae. With contributions by A. Patzelt. Scripta Botanica Belgica, vol. 36. National Botanic Garden, Meise. Gulzar, S., Khan, M.A., 2001. Seed germination of a halophytic grass Aeluropus lagopoides. Annals of Botany 87, 319e324. Gulzar, S., Khan, M.A., Ungar, I.A., 2003. Effects of salinity on growth, ionic content, and plant-water status of Aeluropus lagopoides. Communications in Soil Science and Plant Analysis 34, 1657e1668. Heathcote, J.A., King, S., 1998. Umm as Samim, Oman. A sabkha with evidence for climate change. In: Al-Sharhan, A.S., Glennie, K.W., Whittle, G.L., Kendall, C.G.S.C. (Eds.), Quaternary Deserts and Climatic Change. Balkema, Rotterdam and Brookfield, pp. 141e153. Ismail, A.M., 1983. Some factors controlling the water economy of Zygophyllum qatarense Hadidi growing in Qatar. Journal of Arid Environments 6, 239e246. Ismail, A.M.A., El-Ghazaly, G.A., 1990. Phenological studies on Zygophyllum qatarense Hadidi from contrasting habitats. Journal of Arid Environments 18, 195e205. Khalaf, F.I., Misak, R., AI-Dousari, A., 1995. Sedimentological and morphological characteristics of some nabkha deposits in the northern coastal plain of Kuwait, Arabia. Journal of Arid Environments 29, 267e292. Khan, M.A., Böer, B., Kust, G.S., Barth, H.-J., 2006. Sabkha Ecosystems. Vol. II: West and Central Asia. Tasks for Vegetation Science, vol. 42. Kluwer, Dordrecht. König, P., 2007. Soil and vegetation studies in coastal halophytic communities of Oman. Nova Hedwigia, Beiheft 131, 247e264. Kürschner, H., 1986. A study of the vegetation of the Qurm Nature Reserve, Muscat Area, Oman. Arab Gulf Journal of Scientific Research 4, 23e52. Mahmood, K., Malik, K.A., Lodhi, M.A.K., Sheikh, K.H., 1996. Seed germination and salinity tolerance in plant species growing on saline wastelands. Biologia Plantarum 38, 309e315. Mahmoud, A., El-Sheikh, A.M., Abdul Baset, S., 1983. Germination of two halophytes: Halopeplis perfoliata and Limonium axillare from Saudi Arabia. Journal of Arid Environments 6, 87e98. Mandaville, J.P., 1990. Flora of Eastern Saudi Arabia. Kegan Paul, London. Miller, A.G., Cope, T.A., 1996. Flora of the Arabian Peninsula and Socotra, vol. 1. Univ. Press, Edinburgh. Nickling, W.G., Wolfe, S.A., 1994. The morphology and origin of Nabkhas, Region of Mopti, Mali, West Africa. Journal of Arid Environments 28, 13e30. Rowell, D.L., 1997. Bodenkunde. Untersuchungsmethoden und ihre Anwendungen. Springer, Berlin. Zaman, S., Padmesh, S., Bhat, N.R., Tawfiq, H., 2006. Germination of some Kuwait’s native plants under saline conditions. American-Eurasian Journal of Agricultural and Environmental Sciences 1, 146e148.
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Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv
Short communication
Plant life in the Umm as Samim, Oman e A case study in a major inland sabkha P. König* University of Greifswald, Institute of Botany and Landscape Ecology, Grimmerstr. 88, D-17487 Greifswald, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 March 2010 Received in revised form 25 April 2012 Accepted 13 June 2012 Available online xxx
The Umm as Samim is a vast salt flat of central Oman, in which many wadis which flow south-westwards from the central sector of the northern mountains converge. Most of the area is devoid of vegetation due to extraordinary salinity (sabkha). Significant plant growth is possible chiefly on miniature dunes, called nabkhas, which enable the plants to prosper in an otherwise harsh environment. The site conditions are depicted by mapping of miniature dunes and vegetation, accompanied by an account of morphometric parameters, i.e. height of nabkha, height of plant growth, and status of plant life. Within the chosen sample plot, 12.3% of the sabkha is covered by nabkhas. The total plant cover amounts to 5.0%, but only 3.1% of it is alive, while 2.0% is dead or lifeless. Two nabkhas were longitudinally excavated to examine the salinity of soil samples in relation to dune structure and root and shoot system position. The salinity analysis was done via electrical conductivity (EC1:5 extract). Extremely high EC values were found on current or former sabkha surfaces and on the periphery of nabkhas, whereas central nabkha parts and bottom soil offer more favourable salinity values for plant and root growth. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Arabian peninsula Aeluropus lagopoides Nabkha Salinity Tetraena qatarensis
1. Introduction Flat silty depressions with salt accumulation are a typical feature of arid regions and are called sabkha in Arabian countries. They stretch over vast areas and are the object of special knowledge surveys in the region (Barth and Böer, 2002; Deil, 1998; Friedman and Krumbein, 1985; Khan et al., 2006). Sabkhas are more or less bare of vegetation over most of their area. Only along their outskirts and near runnels is modest plant growth possible. On the Arabian peninsula, sabkhas are found along coastal plains and inland depressions. In Oman, too, sabkhas are a typical constituent of the landscape. A general presentation is given by Ghazanfar (2002). The largest sabkha of Oman is the Umm as Samim, situated in the central part of the Sultanate. This inland sabkha has an area of about 2400 km2 and borders on Saudi Arabia. The vast plain is delimited by the foothills of the Hajar mountains in the north, the “empty quarter desert” Rub’ al-Khali in the south and west, and the Jiddat al-Harasis desert in the east. Whereas various aspects of Omanian coastal sabkhas have been described by Kürschner (1986), Ghazanfar (1995, 1999) and König (2007), knowledge about inland sabkhas is scarce e aside from
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a more geologically based study by Heathcote and King (1998) e and precise investigations are lacking to date. Thereby it is evident that plant growth is often concentrated on or even limited to micro-dunes, and it was suspected that salinity is less extreme within such stands. The present study deals with a detailed analysis of soil and vegetation to determine the influence of micro-dunes on salinity gradients and growth capacity. 2. Study area The development of the Umm as Samim as we know it today started around 30,000 BP. Today, dry, hot conditions are predominant. The climatic situation is outlined by an ecological climate diagram of the nearest station available, Fahud (Fig. 1). Annual precipitation is approximately 24 mm, far below the 100 mm level relevant for plant growth. The mean annual temperature is given as 28.8 C. Thus, the climate is typified as hyper-arid. Most precipitation occurs during spring but is rather erratic. A typical feature of salty depressions are overgrown miniature dunes called nabkhas or nebkhas, a term that has received general acceptance in the literature (e.g., Khalaf et al., 1995). They develop predominantly at the edges of sabkhas, where the salt content is lower. Some species in the Umm as Samim filter out sand blown by the wind and trap it in their branches or stems. Obviously, sand accumulation allows plants to remain viable when growing in soil zones with lower salinity, while plant growth is impossible on salt
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Fig. 1. Map of Oman with relevant ecological regions, location of the study site at the Umm as Samim, and climatic diagram of Fahud, as the nearest representative station (data source: Fisher and Membery, 1998).
crusts. Thus, nabkhas of the Umm as Samim are result of special adaptations of plant growth. In contrast, in other regions, nabkhas are reported as a consequence of human impact (grazing, population pressure), which has resulted in a dramatic increase in wind erosion (e.g., Nickling and Wolfe, 1994). 3. Materials and methods The study area is situated in the northern part of the Umm as Samim (21 53.7550 N, 55 52.1060 E). The particular site conditions were analysed by means of vegetation mapping, microdune surveys, and soil analysis. The studies were conducted throughout February 2007 and March 2008. The nomenclature follows Cope (2007), Ghazanfar (2003, 2007) and Miller and Cope (1996). For the documentation of vegetation structures, a representative 20 20 m ¼ 400 m2 sample plot was chosen and subdivided into 2 2 m grids for detailed and convenient analysis. The nabkhas present within the plot were mapped regarding height, length and width. Furthermore, the size of the plants was recorded, and they were classified into living and dead specimens.
The nabkha surveys were performed by digging a 50-cm-deep ditch along the main axis of the relevant miniature dunes, which is given by the main wind direction, to obtain the shape of a particular dune section. Dune and plant height as well as root depth were recorded every 10 cm for two representative microdunes. Furthermore, soil samples were collected in a grid system for the evaluation of electrical conductivity (EC), with each square measuring 20 20 cm, and samples were taken at the grid’s intersecting points. This reflects the salinity distribution inside the nabkhas and their immediate surroundings. A slurry was made of the soil samples with distilled water at a ratio of 1:5 and allowed to sediment for 1.5 h. Thereafter, EC was identified with a WTW Cond 340i conductivity gauge as a measure of the amount of total dissolved salts for the temperature reference of 25 C (Rowell, 1997). Since there is a linear relationship between EC and salt concentration, all literature values are converted to EC1:5 extract. ECe (soil saturation paste extract) values must be divided by 6.4 to emulate EC1:5 extract values (Rowell, 1997). Conversion may not match properly in every case, but it is a simple and sufficient tool for comparison.
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4. Results During the study period, only perennial species were recognised, i.e. Aeluropus lagopoides (L.) Trin. ex Thwaites and Phragmites australis (Cav.) Trin. ex Steud. among the Poaceae, Anabasis setifera Moq., Arthrocnemum macrostachyum (Moric.) K. Koch, Cornulaca monacantha Del., Haloxylon salicornicum (Moq.) Bunge ex Boiss., Salsola rubescens Franchet (all Chenopodiaceae), Tamarix aucheriana (Decne.) Baum (Tamaricaceae), Tetraena qatarensis (Hadidi) Beier et Thulin (formerly Zygophyllum qatarense Hadidi, Zygophyllaceae). First, the dominance of Chenopodiaceae species is evident. Within the photosynthetic pathway types, the C4 plants are predominant (5 of 9 species). Succulence is found in 5 species as well. Although spring 2007 was an extraordinarily rainy year with ephemeral plant growth across great areas in most parts of the United Arab Emirates and northern Oman, is was not possible to find any annuals in the study area or its surroundings. Various aspects of the situation are depicted from a bird’s-eye view in Fig. 2 for a 20 20 m sample area. The vegetation is mainly characterised by the grass A. lagopoides and the dwarf shrub T. qatarensis. Fig. 2a illustrates plant species composition and the individual condition of the constituents in a selected plot. The total plant cover is sparse and amounts to as much as 5.0%. The oversanded area, that is sand covered and captured by nabkhas, accounts for 12.3%. Numerous dead plant specimens document the harsh conditions in the struggle for survival. The strong correlation between dead and living specimens to dune structures is evident, for instance, there’s a correlation between dead plants and relatively smaller nabkhas. In the case of a dead plant, it is not clear whether an established plant died or a new plant had started to grow and accumulate a nabkha but then it died before the nabkha could accumulate much sand. The plant status of some A. lagopoides specimens were not definitely distinguishable in the field due to extreme desiccation (plants appear lifeless). Fig. 2b and c give impressions of nabkha and plant size, respectively. Generally, Aeluropus seems to be the more effective sand binder due to dense rhizomatous growth and ready regrowth after oversanding (and browsing). Thus, the overall height of Aeluropus nabkhas is superior to Tetraena nabkhas. Otherwise, the growth capacity is very limited in the case of the creeping grass A. lagopoides, but is more obvious in the dwarf shrub T. qatarensis due to its morphology. Nabkha structure and salinity allocation is illustrated for A. lagopoides in Fig. 3a. On the windward side, nabkha height increases rapidly to a maximum of 45 cm within the first 70 cm of length. Most of the plant is buried in sand. On the lee side, the nabkha tapers off more slowly and needs 90 cm to cross the zero line (¼ sabkha level). The nabkha shows a total length of 160 cm and represents the typical form of a miniature dune. The entire nabkha is interspersed with shoot material of A. lagopoides. The bottom, from 0 to 6 cm, is shoot-free, and is probably the foundation of nabkha growth. Root depths vary from 25 to 42 cm within nabkha range. The quantified conductivity of the 20 cm samples did not differ significantly from each other. EC ranged from 1.5 to 4.3 mS/cm with a mean range of 2e3 mS/cm. The sample at 40 cm exhibited a conductivity of 2.7 mS/cm. The situation on the soil surface is much more diverse, both in range and amount of salinity. Especially the salinity situation of the soil surface outside the nabkha is quite harmful and characterised by extremely high EC values (between 50 and 55 mS/cm) due to ascending water evaporation supported by finely grained soils. Sand tail values of the zero surface line of the downwind side vary from 46.8 to 29.8 mS/cm. Inside the nabkha, the salinity situation is quite heterogeneous due to sand drift and salt entry, but conspicuously less hostile than outside. Together
Fig. 2. Plant species composition and status (a). Height of miniature dunes below plant growth in four categories (b). Height of plant growth in three categories (c). Main wind direction from NW to SE (i.e. bottom to top), unmarked interdune space is sabkha surface.
with the fact that water is retained by the sandy soil, nabkhas provide favourable microhabitats within the surrounding salt desert. Crossing the nabkha from windward to lee side on the 0 cm line, a distinctive course of conductivity is obvious, starting with 55.1 mS/cm in front, modest values of 4.8e5.5 mS/cm inside, and a high level of 53 mS/cm behind the nabkha again. The samples of the 20- and 40-cm level vary between 6.3 and 19.3 mS/cm. The T. qatarensis nabkha exhibits a length of 320 cm and a maximum height of 34.2 cm (Fig. 3b). The plant cover is found within the first 130 cm (¼ 40%) of the nabkha. Tetraena grows up to 54 cm, root depths are found between 9 and 30 cm.
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Fig. 3. Longitudinal section and analysis of an Aeluropus lagopoides (a) and a Tetraena qatarensis nabkha (b). Volume of electrical conductivity spheres represents amount of salinity, maximum and minimum are given representatively. Vertical position 0 cm ¼ sabkha level.
The EC values of the 20 cm line are virtually identical and range from a modest 1.1 to 1.6 mS/cm. The 20 cm level shows considerable salinity of 4e8.2 mS/cm. Again, variability is most pronounced within the 0-cm level, ranging from 2.1 to 34.2 mS/cm. The allocation of salinity is remarkable. The lowest values (2.1e4.3 mS/cm) are indeed found in the rooting zone of T. qatarensis. Outside this zone, i.e. the former sabkha surface before the formation of the nabkha, EC rises markedly (9e34.2 mS/cm). Altogether, from 20 cm depth onwards, the soil became more damp and there were no salt crystals visible to the naked eye. This impression is confirmed by the measurements of conductivity. Here, too, monocotyledons and dicotyledons show the same tendencies. As expected, the EC is greatest at surface level and, accordingly, salinity is highest. Here, no plants or roots are found in either nabkha. The plants avoid this area, since the salts accumulate to toxic concentrations in the surface region. Thus, the salinity decreases with increasing depth.
A. lagopoides stretches from the Mediterranean to the Indian subcontinent with presence in all countries of the Arabian peninsula. The species, provided with clonal growth, salt glands which reduce the salt charge readily, and the water-efficient C4 photosynthetic pathway, is a typical constituent of coastal halophytic communities, but is also found in damp and arid places with a tendency to salinisation. T. qatarensis is an endemic of the Arabian peninsula and found from Qatar through the Emirates and Oman to Socotra. It is a characteristic part of the desert vegetation and known for its sophisticated water economy, because leaf quantity and structure are controlled by the moisture status of the environment (Ismail, 1983). The absence of annuals would seem to disagree with the results of Brown and Porembski (1998), who found a high percentage of annuals on the nabkhas of Haloxylon salicornicum in the Kuwait desert; however, these settle on non-saline ground and under somewhat wetter conditions of about 120 mm rainfall per year. 5.2. Propagation and establishment
5. Discussion 5.1. Floristic composition and vegetation pattern The vegetation is dominated by Aeluropus lagopoides and Tetraena qatarensis. Both species are widely distributed in arid regions.
Especially for A. lagopoides, it is apparent that old plant material can function as the substrate for new growth of the same species, because almost the entire nabkha is interspersed with Aeluropus shoots. The spread can be generative or vegetative. Beneath the surface of a T. qatarensis nabkha, plant material is only found below
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the assimilating sections. Nevertheless, shoot and leaf sections of Aeluropus, formerly aboveground plant parts, occur only from a height of several centimetres onward. The salinity results clearly indicate that a certain amount of sand has to accumulate initially to offer a salt level low enough for plant survival or germination facilities (Fig. 2). The surface samples tended to show higher salinity and lower soil moisture than did the bottom samples (Fig. 3). Surface conditions are important during the time of generative propagation/ reproduction of the species in view of the high osmotic potential of the medium which might inhibit the germination of seeds. A. lagopoides is known to be highly salt tolerant during germination. Gulzar and Khan (2001) and Gulzar et al. (2003) studied the effects of various salinity treatments on biomass production, longitudinal growth and germination. Little inhibition was found in media containing 200 mM NaCl, but 400 mM NaCl (and more) inhibited growth, and plants survived in 600 mM NaCl with low mortality and reduced growth. The highest germination is obtained under non-saline conditions, and an increase in NaCl concentration progressively inhibits germination. 30% of seeds germinated under moderate temperatures (20/30 C) at 500 mM NaCl, a salinity concentration approaching seawater (600 mM NaCl). Bodla et al. (1995) reported that A. lagopoides could survive up to 110 mS/cm NaCl (z1500 mM NaCl) to a certain extent. Increasing salinity is responsible for decreasing shoot length and number of leaves, both reducing the biomass production considerably. Germination experiments with T. qatarensis showed that seeds failed to germinate when NaCl concentration was above 300 mM (Zaman et al., 2006). Altogether, Aeluropus lagopides exhibits a greater tolerance to salinity than T. qatarensis from an autecological point of view. According to Mahmood et al. (1996), a NaCl concentration of 309 mM represents an EC of 30 mS/cm, a numerical value which is not reached by most of the nabkha EC1:5 extracts soil samples (Fig. 3a, b) and enables plant growth, given sufficient rain. This strategy is well-known from other typical constituents of Arabian halophytic vegetation (e.g., Mahmoud et al., 1983). Furthermore, the shed seeds of T. qatarensis were found to experience day temperatures at the soil surface and 1 cm below the soil surface between 52e68 C and 50e64 C, respectively (Ismail and El-Ghazaly, 1990). Seeds may remain viable for a long period and create an enormous seed-bank, ready to germinate when conditions are right. Seeds usually germinate after leaching of salt due to rainfall, which is rather erratic in the Umm as Samim area. Thus, it is assumed that propagation by seeds is a rare event in the study area. Plants with perennial and/or clonal growth hence have an advantage in this situation. 5.3. Nabkha shape and plant growth A. lagopoides and T. qatarensis show a similar nabkha profile. Both species reduce wind speed and allow sand deposition within the plant bodies and in the tail on the downwind side. The form is somewhat elliptical, and more or less tapered on the leeward side. The nabkha size depends on plant height and density of branching. The length of the nabkha seems to correlate with plant size, an interrelationship which Khalaf et al. (1995) found to be significant. The monocotyledonous A. lagopoides, in contrast, grows rather net-like on the dune surface level and therefore does not generate much wind protection for the leeward side. T. qatarensis, however, extends up to 30 cm above the nabkha surface and can affect a larger part of its slipstream. A. lagopoides probably compensates this “lack” by the fact that the nabkha is thoroughly pervaded by the shoot system and reaches a greater height than that of Tetraena. Thus, sand capture strategy and form of the nabkha is somewhat different. It is assumed that A. lagopoides cannot unfold its full
potential due to excessive browsing; the species is particularly reported to be a favourite forage plant (Gulzar and Khan, 2001). In contrast, T. qatarensis is not readily grazed by livestock, and camels feed on it only when other fresh fodder is unavailable (Ghazanfar, 2007). The assessment by Mandaville (1990) is somewhat different, reporting that it is a useful summer grazing plant for camels, which are accustomed to its salinity and purgative effects. However, the local Bedouins consider excessive grazing on it unhealthy. This might result in more successful sand capturing due to less damage caused by browsing animals. The roots of the plants typically find their way into the zone between sabkha surface and 35 cm soil depth, with a mean rooting depth of 36.1 cm (A. lagopoides) and 22.9 cm (T. qatarensis). 5.4. Salinity comparison In the nabkha area, the salinity at the 0-cm level drops significantly compared to the surroundings (55e3 mS/cm). This demonstrates the effectiveness of sand accumulation. It is noteworthy that the salinity at 20 cm and for the one sample taken at 40 cm is lower than that at 20 cm and 40 cm. Indeed, the substrate of the nabkha is accumulated sand, where the salinity is much lower than that of the underlying clayey soil, which is enriched with salt by evaporation and rising soil water. As drying occurs, salts crystallise out of solution producing a salt efflorescence on the sabkha soil surface. As a result, salt crystals drift along with the sand and are likewise deposited. Electrical conductivity values of the 20-cm level differ significantly between the two nabkha types, because conductivity of the T. qatarensis nabkha is generally almost 10 mS/cm lower than that of the A. lagopoides nabkha. The locations of the two nabkhas were situated very close together and the substrates showed no obvious differences, so it is very unlikely that the drifting sand which accumulated differs decisively in salt content and consistency. However, desalinization glands in Aeluropus contribute to salinity because plant material is enclosed in the sandmass. In contrast, salt-accumulating Tetraena leaves are shed and blown away. The 40-cm level is reached by the Aeluropus nabkha only. The results of salinity measurements of A. lagopoides and T. qatarensis sites of other regions and authors are sometimes difficult to compare due to different measurement specifications. A. lagopoides sites were sampled by Al-Jaloud et al. (2001) in Saudi Arabia, with results varying from 4.0 to 6.2 mS/cm, depending on soil depth. König (2007) reported 0.2 mS/cm for 30 cm soil depth and 1.1 mS/cm for soil surface in a coastal area of Dhofar/Oman. For T. qatarensis, Al-Jaloud et al. (2001) mentioned a range of 2.2e3.0 mS/cm for Saudi Arabia. From the Arabian Gulf coast of Saudi Arabia, Böer (1996) reported 0.4e7.6 mS/cm directly underneath the plants at a depth of 35e40 cm. König (2007) recorded values for coastal sites near Duqm, central Oman. For the halophytic site, the EC amounted to 13.1e22.0 mS/cm and 30.8e31.0 mS/cm for 30 cm soil depth and soil surface, respectively. The nonhalophytic, but spray-influenced site showed 4.3e6.3 and 3.3e5.6 mS/cm, respectively. Altogether, the values largely correspond with those of the core areas of growth, i.e. the rooting zones of excavated A. lagopoides and T. qatarensis nabkhas of the Umm as Samim, aside from the exceptional halophytic site near Duqm. 6. Conclusion Under arid conditions, ascending soil water flow and evaporation will lead to salt accumulation at the soil surface, especially in depressions and locations with high proportions of fine earth. Apart from a few specialists, plant life is mostly possible on sand accumulations which rise a certain distance above the sabkha surface. In
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summary, it can be reasonably stated that sand accumulation is an effective strategy of halophytes to survive in extreme habitats like Umm as Samim. This was validated by soil samples in various microzones of nabkhas. Thus, the hypothesis that salinity is less extreme within nabkhas was confirmed. Such sites are microhabitats and offer a minimum of livelihood. Furthermore, nabkhas enable establishment which is the greatest obstacle to plant development. Otherwise, site conditions are hostile due to extreme soil salinity. This strategy, of course, has its limits. Wide areas of Umm as Samim are devoid of vegetation. EC values at the surface of those areas reaches 167 mS/cm e far beyond ranges in which plants can grow. Acknowledgements I am indebted to Natalie Breidenbach and Oliver Fried for assistance during field work and soil analysis. Thanks go to Ulrich Möbius for competent laboratory assistance and Kathleen Splieth for the English review. References Al-Jaloud, A.A., Al-Saiady, M.Y., Assaeed, A.M., Chaudhary, S.A., 2001. Some halophyte plants of Saudi Arabia, their composition and relation to soil properties. Pakistan Journal of Biological Sciences 4, 531e534. Barth, H.-J., Böer, B. (Eds.), 2002. Sabkha ecosystems. Vol. I, The Arabian Peninsula and Adjacent Countries. Tasks for Vegetation Science, vol. 36. Kluwer, Dordrecht. Bodla, M.A., Chaudhry, M.R., Shamsi, S.R.A., Baig, M.S., 1995. Salt tolerance in some dominant grasses of Punjab. In: Khan, M.A., Ungar, I.A. (Eds.), The Biology of Salt Tolerant Plants. Department of Botany, University of Karachi/Pakistan, pp. 190e198. Böer, B., 1996. Plants as soil indicators along the Saudi coast of the Arabian Gulf. Journal of Arid Environments 33, 417e423. Brown, G., Porembski, S., 1998. Flora and vegetational aspects of miniature dunes in a sand-depleted Haloxylon salicornicum community in the Kuwait desert. Flora 193, 133e140. Cope, T.A., 2007. Flora of the Arabian Peninsula and Socotra, vol. 5(1). Univ. Press, Edinburgh. Deil, U., 1998. Coastal and sabkha vegetation. In: Ghazanfar, S.A., Fisher, M. (Eds.), Vegetation of the Arabian Pensinsula. Geobotany, vol. 25, pp. 209e228. Fisher, M., Membery, D.A., 1998. Climate. In: Ghazanfar, S.A., Fisher, M. (Eds.), Vegetation of the Arabian Peninsula. Geobotany, vol. 25, pp. 5e38. Friedman, G.M., Krumbein, W.E. (Eds.), 1985. Hypersaline Ecosystems. The Gavish Sabkha. Ecological Studies, vol. 53. Springer, Berlin.
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