Sabkha Ecosystems

The United Arab Emirates is situated in the hyper-arid dry land system where the aridity index (P/PET) is less than 0.05, and hence it is a water stress country. To offset the crop water requirements, irrigation is accomplished mainly with saline/brackish ground water, few progressive farmers use desalinated water using small scale reverse osmosis plants. Mismanagement of these resources leads to soil salinization in the agriculture regions, and in the coastal lands through sea water intrusion. Owing to better management of salt-affected soils to optimize agriculture production, it is essential to characterize root zone salinity as spatial distribution. Regular monitoring identifies future spread of the salinity problem and leads to informed decisions. We attempted to assess soil salinity in the Northern Emirates through a soil survey by investigating 10,200 observation sites on a grid basis, and measuring water and root zone salinity of some agricultural farms. We used a combination of techniques, i.e., remote sensing, GIS, grid survey observation at a depth of 50 cm, and laboratory analyses of soil samples. The electrical conductivity “EC” of 1:1 soil:water suspension was measured for all the observation sites and correlated to EC of soil saturation extract (ECe). Based on the USDA salinity classes (0–2, 2–4, 4–8, 8–6, 16–40 & >40 dS m⁻¹), the NE is divided into six salinity zones, revealing large area (83 %) as non-saline, 10 % (very slightly saline), 4 % (slightly saline), and 3 % moderately, strongly, and very strongly saline, the latter two types are confined to the coastal sabkha (due to sea water intrusion), and at the edge of the mountain and inter-dunal sabkhas. Salinity is also observed in agricultural farms irrigated with saline waters, where it has been diagnosed that root zone salinity is not managed properly. We have outlined the management aspects for these saline soils which can be used as a guide for future management and land use planning in the study area.

Prismatic and acicular crystals of large and thick size are the dominant habits in the deposits within the Sabkha. Pyramidal, lenticular and sub-lenticular crystals are less dominant and occur mainly in the locations of fine sediments saturated by halite, whereas the crystals of desert raised shape are dominant in the sand dune area in the southwestern part of the Sabkha. The crystals formed above groundwater level and a few centimeters depth from the surface.

Shallow groundwater level, saturation of sediments by brines, high temperature, high evaporation and saturation of brines by SO₄ ⁻² and CaO₃ ²⁻ provide suitable conditions for the formation of gypsum crystals in the sediments. In addition, the type of host sediments plays an important role in the amount and habit of gypsum crystals in the Sabkha. The general elevation of Umm Said Sabkha above sea level (+1) leads to greater rates of evaporation over groundwater recharge in the Sabkha.

Mangroves refer to an ecological group of evergreen woody plants distributed in a zone of tidal influence – both on sheltered coasts and at the banks of estuaries. They provide a variety of ecosystem goods and services to human society and also prevent coastal areas from hazards of hurricanes and Tsunamis. Mangroves usually grow in variable flooding regimes but salinity appears to be the most important factor affecting their growth and distribution. Best growth of mangroves is found in half strength seawater while a 50 % growth reduction is found in full strength seawater. However, survival of different mangrove species in hyper-saline conditions could vary with different morphological and physiological adaptations. This review is an attempt to gather information on distribution, growth dynamics and eco-physiology of mangroves in Pakistan. Information gathered with the help of past and present researches would help in the restoration and methodical care of the mangroves along the coast of Pakistan besides developing them as source of commercial products and spot for a burgeoning ecotourism industry.

We discuss the potential of using halophytes as a source for producing liquid biofuels. We review the potential pathways for converting oilseeds into biodiesel and bio-derived synthetic paraffinic kerosene and presents some preliminary data on biomass composition and pretreatment of the halophyte Salicornia bigelovii. Six samples of S. bigelovii cultivated at three fertilizer levels (F1: 1 gN/m², F2: 1.5 gN/m² and F3: 2 gN/m²) and two salinity levels (S1: 10 ppt and S5: 50 ppt salt) were analyzed with regard to chemical composition and bioethanol potential. Chemical characterization showed that S. bigelovii contained, 16.31–55.67 g/100gTS (total solids) of carbohydrates, 5.42–16.60 g/100gTS of lignin, 27.85–66.37 g/100gTS of total extractives (including extractable ash), and 2.18–9.68 g/100gTS of structural ash, depending on the plant fraction and cultivation conditions. Enzymatic hydrolysis of the pretreated samples revealed high glucose recoveries of up to 90 % (of glucose in raw S. bigelovii) corresponding to ethanol yield of 111 kg ethanol/dry ton S. bigelovii.

We discuss the process of domesticating wild halophytes to serve as crop plants using seawater irrigation. First steps in this domestication involve determining whether halophyte species exist that may produce significant amounts of a usable product under seawater irrigation and that this is a sustainable agronomic practice. This is followed by development of strategies to improve crop productivity via selecting appropriate species for domestication and then affecting agronomic traits through plant breeding. We demonstrate that halophytes may be productive under seawater irrigation, that this management system may be sustainable, and there are demonstrated pathways toward domestication.

Some halophytes of the subtropical arid deserts produce fruits have a transient seed bank. The time of fruit ripening and shedding in these plants coincides with the onset of suitable conditions for germination and seedling establishment. Economic uses of plants with transient seed bank necessitate understanding environmental factors that would affect seed longevity under different storage conditions. Fresh seeds of both Salsola imbricata and Haloxylon salicornicum have high germination level and germination speed, and form a transient seed bank in nature. The impacts of storage period and condition on germination level and speed were assessed in the two species. In both species, 9 months storage did not affect germination percentage of seeds in fridge, but completely inhibited it in field seeds. The impacts of room and warm temperatures were in between cold and field storage. Storage significantly increased germinate rate index of seeds stored in all conditions till 17 months in S. imbricata and till 12 months in H. salicornicum. In both species, fridge storage had little effects on final germination and germination speed of seeds incubated at the different temperatures, compared to fresh seeds. However, room temperature and warm storages significantly reduced final germination and germination speed at the different temperatures, so the reduction was more pronounced at 35 °C, especially in H. salicornicum.

In general, saline and arid environments are poor in species. A total of 728 taxa of halophytes are recorded for SW Asia belonging to 68 families (compared to 117 plant families worldwide). The majority of halophytes belong to the families Chenopodiaceae, Poaceae, Leguminosae (Papiliondeae), Asteraceae and Cyperaceae. Chenopodiaceae has the largest number of species and genera of all families only exceeded by Poaceae which has more genera but fewer species. These numbers are in accordance with those found for halophytes of the world. From the data available, Turkey has the most halophytes (±600 taxa), followed by Pakistan (±361 taxa), Iran ± 350 taxa), Afghanistan, Saudi Arabia, Oman and Yemen (±120 taxa). Halophytes in SW Asia constitute about half the number of halophyte taxa (and families) recorded for the world.

Information on halophytes is collated from published sources, and names of accepted taxa (and synonyms) are compiled in the database BRAHMS. A preliminary checklist (of names only) produced from this database is provided in this chapter.

The need for halophytes in saline agriculture is rising, as the increasing population seeks to feed itself with ever-decreasing soil sources and dwindling freshwater supplies. Two main steps are needed to establish sustainable halophyte farming: (i) the selection of an economically important and ecologically relevant halophyte and (ii) the development of good management practices for irrigation. The success of both steps will depend on the efforts of many actors in science, technology, environment, agronomy, industry and farming.

Crucial halophyte scientific missions are to work on the multiple uses of halophytes and their salt tolerance limits. Those investigations should also contribute to the understanding of salt mechanisms in halophytes.

In this chapter, we will show recent findings on the use of halophytes and their behavior under saline conditions, and discuss how the farmers, the industrials and consumers can benefit from such scientific knowledge to enhance the development of halophyte farming.

Suaeda salsa is an annual herbaceous halophyte in the family Chenopodiaceae which produces dimorphic seeds on the same plant under natural conditions, the seed germination is often affected by salinity as well as drought or both. The objective of this study was to determine the effects of salt, drought and their interaction on germination of dimorphic seed of S. salsa and the recovery when stress was removed.

The germination response of dimorphic seeds was studied under stress created by salt (NaCl) and polyethylene glycols 6000 (PEG) singly and in combination. Results showed that the seed germination decreased with an increase in the stress. The black seeds showed greater inhibition than the brown ones. Addition of moderate amount PEG (isotonic to 50 and 100 mM NaCl solutions) in the medium with high salinity (above 300 mM NaCl) increased the germination of both kinds of seeds compared with no PEG addition. This increase was greater in black seeds than in brown seeds. The rate of germination was higher in brown seeds than that in black seeds in all the treatments, while germination recovery and total germination percentage was higher in black seeds than in brown seeds after their exposure to NaCl and PEG and then transferring to distilled water. In conclusion, brown seeds might germinate better under higher salt and drought stress than black seeds, however black seeds showed higher viability under such conditions. Moderate PEG might alleviate the detrimental effect of high salinity on seed germination.

Kochia (Kochia scoparia) have recently been considered as forage and fodder crop in marginal lands. Under severe drought and salinity kochia (35 dS m^-1) could produce up to 16 and 8 t DM ha^-1 biomass in spring and summer cropping, respectively. Kochia produce 90 % biomass at 75 % water application in comparison to 100 % water application. Therefore, deficit irrigation is a useful management technique for Kochia even under saline conditions. Seeds of Kochia can germinate in a wide range of temperature, different levels of water potential, salinity, pH and depth of flooding and showed a high recovery from stress condition. Quick germination and growth of Kochia and its desirable drought, salinity and extreme temperature tolerance indicate that it can be considered as a valuable forage plant in case of shortage of conventional forage occurs, particularly in arid and semiarid regions. Cultivation of Kochia using saline waters for rehabilitation of saline areas, that have been left barren, can be regarded as an approach in sustainable and low-input agriculture. Biomass and seeds of Kochia can help in food production for people settled in these regions and their animals. Kochia in addition to be a forage crop can also be used bioremediation, oilseed and biofuel crop.

Freshwater resources will become limited in near future and it is necessary to develop sustainable biological production systems, which can tolerate hyper-osmotic and hyper-ionic salinity. Plants growing in saline conditions primarily have to cope with osmotic stress followed by specific ion effects, their toxicities, ion disequilibrium and related ramifications such as oxidative burst. This is an exclusion criterion for the majority of our common crops. In order to survive under such conditions, suitable adjustments are necessary. Beside the control of the entrance on root level, the ability to secrete ions (excreter) or to dilute ions (succulents) helps to preserve a vital ion balance inside the tissues.

Sadly, traditional approaches of breeding crop plants with improved abiotic stress resistance have met limited success so far. Failures were due to two problem areas, lack of easy to detect traits and too many genes that had to be transferred at a time. These arguments underline the advantage of utilizing suited halophytes as crops on saline lands and to improve their individual crop potential. Because of their diversity, halophytes have been regarded as a rich source of potential germplasm. A variety of halophytic plant species already has been utilized as nonconventional cash-crops. Lieth H, Mochtchenko M (Cash crop halophytes: recent studies. Tasks for vegetation science, vol 38. Kluwer, Dordrecht, 2003) described the utilization of halophytic species for the improvement of sustainable agriculture as well as sources of income.

However, knowing that saline irrigation always comprises the risk of increasing salinity up to levels where no plants (even no halophytes) can exist anymore, it is important to achieve sustainable conditions. Therefore it is essential to study the interaction among soil salinity, individual species (to study heterogeneity within the halophytes and plant diversity), biotic interactions, and atmosphere at distinct conditions before application.

The heterogeneity within halophytes (biotic factor) is often ignored but biotic interactions can be in this context an ideal accessory to stabilize sustainable populations on saline lands. The aspect, that dicotyledonous halophytes, when grown in saline soils, generally accumulate more NaCl in shoot tissues than monocotyledonous halophytes (especially grasses) has several consequences on their suitability as crops and their culture conditions (procedure to apply salinity). The implementation of an intercropping system (halophyte culture) is such a way to use saline land and brackish water for producing an economically viable and environmentally sound agriculture. It was estimated that 15 % of undeveloped land in the world’s coastal and inland salt deserts could be suitable for growing crops using saltwater agriculture. This amounts to 130 million hectares of new cropland that could be brought into human or animal food production chain - without cutting down forests or consuming more scarce freshwater for irrigation.

This study attempts to understand whether changes in edaphic factors are key players in regulating ecophysiological parameters in coastal plants. Some ecophysiological parameters of selected populations along the coastal gradient (dune and salt marsh zones) were investigated. Significant variation in soil parameters such as ECe, moisture and organic matter were found between dune and marsh zones. However, populations mostly displayed plant-type specific variations in ecophysiological parameters i.e., dicot species had more negative xylem pressure potential and higher chlorophyll and transpiration rates than monocots. In addition, some species specific responses were also observed. Despite these differences all the species displayed almost similar water-use efficiency. Significance of results obtained in this study is discussed.

The extensive natural coastal sabkha ecosystems along the Arabian Gulf’s southern and western shoreline are detailed and their incorporation as part of saline agro-systems is outlined. This chapter is intended to showcase the inherent natural values of saline coastal sabkha, saline water resources and halophytic plants and provide sustainable alternatives for their utilization. It also discusses the alternative use of industrial brine water being discharged along the Arabian Gulf coast for saline agro-systems within sabkha landforms.

Critical fresh water shortages are occurring in population centers worldwide. Overuse of fresh water resources, coupled with effects of global warming such as salt water intrusion and desertification, are resulting in salinization of water and soil resources. Rapid urban population growth has put enormous pressures on limited freshwater supplies, and many governments have responded by placing restrictions on the use of fresh water for irrigating turfgrass landscapes, instead requiring use of reclaimed, or other secondary saline water sources. Issues facing landscape managers using saline water sources are soil salinization, resulting in direct salt injury, and secondary problems of loss of soil structure ensuing from sodium and bicarbonate effects, resulting in loss of salt leaching potential and soil anaerobiosis. Long-term solutions to the salinity problem will require development of improved salinity tolerant turfgrasses. Progress has been made in understanding turfgrass salinity tolerance mechanisms, and in development of salinity tolerant turfgrass cultivars and alternate native species.

Salicornia, belonging to the family Chenopodiaceae, can tolerate total immersion in salt water absorbing the salt dissolved in the water without any harm. It is an ideal, high quality edible-oil yielding plant and its high economic value is attributed to the content of poly-unsaturated oil. In order to solve a number of global problems, this salt-tolerant crops should better be grown on millions of hectares of unproductive, arid land, and in all salty, marshy coastal area of the earth, while conserving freshwater and providing food, fodder, oil and valuable byproducts. For this reasons, knowledge of the ecology and ecophysiology of Salicornia europea can help to evaluate its salt tolerance and potential as crop, but also to give insight into the optimal agronomic conditions for cultivation. In this regard, we evaluated the effects of salinity on S. europaea growth to obtain insight in its performance. Our results showed that S. europaea grows rapidly at moderate salt concentrations (150 and 300 mM NaCl) and can survive at extreme salinities, including seawater concentrations. The results evidenced also that salinity triggered inorganic ions (Na⁺) accumulation. In conclusion, germination responses to salinity of S. europaea seem likely to influence their colonisation capacities down the tidal gradient and hence may be important in the maintenance of taxa zonation in salt marshes. In addition seedling growth data and biochemical analysis suggest that this taxa may be successfully used to reclaim highly salinized areas in semi-arid and arid regions of the world.

The East Mediterranean includes Turkey, Syria, Lebanon, Palestine, Jordan and Israel. It is a typical transition zone between the Saharo-Arabian desert biome and temperate climates. A total of 304 halophytic taxa from 50 families belonging to 172 genera are distributed in the region. The families with the highest number of taxa are; Chenopodiaceae (51 taxa-16.78 %), Poaceae (44 taxa-14.47 %), Asteraceae (23 taxa-7.57 %), Fabaceae (22 taxa-7.24 %), Cyperaceae (17 taxa-5.59 %) and Plumbaginaceae (13 taxa-4.28 %) respectively. They constitute 55.93 % of the halophytes distributed in the East Mediterranean. The genera with the highest number of species are; Limonium (13), Juncus (11), Atriplex, Salsola (8 each), Suaeda (7), Tamarix, Plantago, Silene (6 each) and Euphorbia, Centaurium, Bromus (5 each). Out of 304 taxa 9 are endemics, 24 are rare plants, 16 taxa are vulnerable, 9 taxa endangered, 6 taxa critical and two taxa have lower risk. These taxa can be grouped as; Xerophytes (79), Psammohalophytes (73), Hygrohalophytes (68), Halophytes (56), Xerohalophytes (22) and ruderals (6). Out of the halophyte taxa listed 124 taxa (40.79 %) are of economic importance. The most widely used parts of the plants are leaves (28.24 %) and roots (21.18 %). The most common preparation of the traditional folk medicine is decoction (42.55 %), followed by infusion (11.70 %), poultice (10.64 %) and powder (8.51 %). In addition to these some plants are consumed fresh for the treatment of some ailments, their percentage lies around 10.64, but consumption as cooked meal is 8.51 %. A majority of these plants are used for the treatment of urinary system disorders (21.74 %). Many halophytic species are used as either forage or fodder, even as ornamentals, but some are poisonous. These taxa play an important role in the control of soil erosion. They are also used to clean contaminated soils and water. Similarly Cynodon dactylon, Ruppia maritima and Inula crithmoides can be used to produce biomass through biosaline agriculture.

Two experiments were performed to determine the effects of temperature and NaCl concentration on seed germination and early seedling growth of Atriplex lentiformis and Atriplex verrucifera collected from salt deserts in Isfahan and Shiraz, Iran. These species help prevent soil erosion. Seeds were germinated from 5 to 30 °C at 5 °C intervals. Optimum temperature for seed germination in A. lentiformis and A. verrucifera was 15 and 10 °C, respectively. Germination was lowest at 30 °C for both species. Seeds were also germinated at 100–500 mMol/L NaCl at 100 mMol/L increments. Germination decreased as NaCl concentration increased from over 85 % germination at 0 mMol/L NaCl to less than 5 % germination at 500 mMol/L for A. lentiformis, and from over 60 to 0 % for A. verrucifera at the same salt concentrations. Ungerminated seeds in high NaCl concentrations had a higher percent recovery germination in distilled water than seeds in lower salt concentrations. For A. lentiformis there was 42.5 % recovery at 500 mMol NaCl, but only 13 % recovery germination at 100 mMol. Similar values were found for A. verrucifera. Early growth reflected germination responses in each experimental group. Hypocotyl length was significantly and strongly negatively correlated with salinity.

Estuaries and coastal lagoons around the world are wetlands of great importance and they are regularly targeted as prime conservation sites. Many include wildlife refuges and have nature reserves that were set up in areas preserved from development in order to keep valuable species and habitats, while maintaining traditions and sustained use.

Tidal wetlands are often mentioned in the literature as natural habitats with high biological productivity. The net primary production in a salt marsh is often higher than in temperate or tropical forests and this productivity is directly linked to the important role halophytes play in estuaries, in terms of the value-added.

Salt marshes may be a sink of heavy metals. The ability to phytostabilize contaminants in the rhizo-sediment is an important aspect in the self-remediative processes and biogeochemistry of this ecosystem, and will help filtering natural and anthropogenic loads of nutrients and pollutants discharged into the wetland.

There is also a provision of rare and unique habitats, which support nursery grounds for commercial fish and wildlife, including vital feeding grounds for many migratory birds. Rediscovered as a new source of amenity and leisure activities for the population living in urban areas, salt marsh halophytes and estuaries have an important role in the preservation of biodiversity.

In this paper we discuss the support of the salt marsh ecosystem to the estuarine birds, and consequently its contribution for biodiversity.

Many seaweeds, seagrasses and many halophytes, grow in the tidal zone in similar environments. Their every-day-life and their life cycle are influenced by regular flooding during high tide and exposure to the air at low tide. Therefore they are confronted with similar daily changes in the osmotic potential and need to take up nutrients from the water and/or from the sediment. In addition, coastal zones and estuaries are often contaminated with high loads of some nutrients and heavy metals. Sulfur-deficiency is a major issue for land-based agriculture, whereas seawater act as a global sulfur reservoir and sulfur does not limit growth of marine plants. Sulfur-containing compounds and proteins seem to play a pivotal in the adaptation to these environmental conditions. This review highlights the putative roles of sulfur-containing compounds in a comparative way in seaweeds, seagrasses and halophytes. Can we observe similar metabolic and proteomic adaptations in regularly flooded coastal plants? The role of sulfur-containing proteins and of sulfur-containing secondary metabolites and their responsible set of enzymes will be analyzed from an evolutionary point of view. New strategies to increase salt-tolerance in higher plants based on sulfur-containing compounds are discussed.

Seagrasses (Zostera marina, Z. noltii, Ruppia cirrosa) and other higher marine plants (Potamogeton pectinatus, etc.) are widely distributed in the ocean, and they occupy large areas of shallow gulfs and bays of the Black Sea. The usage survey of seagrasses in agriculture, industry and pharmacology has been completed, and the results of experiments on the uses of Black Sea seagrass in the diet of livestock are described, including the chemical composition. Zostera marina contains a significant amount of organic matter and nutrients with valuable trace elements whose concentrations are higher than in most terrestrial food plants. However, its organic matter does not have a high nutritional value due to the low protein content, the imbalance of its amino-acid composition and poorly assimilated lignin. The potential for economic seagrass utilization is mainly based in aquaculture, because seagrasses are keystones of the coastal ecosystems, and many of them are protected by various conventions and agreements, and they are biological ocean “hot spots”. Seagrass aquaculture can play a role in biodiversity conservation of the native communities and populations from their extraction for commercial use.

Somebody started developing rice-field terraces a long time ago, and rice is now one of the most important cash crops in the world. Who will try the same with seagrasses under seawater irrigation? Seagrasses can provide highly valuable cash products under full strength seawater salinity. This is a highly valuable research prospect for coastal dry land countries that wish to develop food-security without depending on freshwater.

The international environmental conservation communities know about the immeasurable service-value that mangrove ecosystems provide for ecosystem functioning. Globally mangroves are seriously and rapidly declining in area coverage. The coastal zones are narrow in width, and therefore offer rather limited space for mangroves. UNESCO’s innovative technology offers a new idea that has not yet grasped the attention of the international community: Floating Mangroves for carbon sequestration. A small-scale model has been developed. This concept can reduce atmospheric carbon levels, reduce land-based marine pollution, generate biofuel and other cash crops without any dependency on freshwater, and it can generate jobs and income.

Developing biosaline agriculture more intensively will result in seriously enhanced global food-security, especially in dry land countries. It will assist generating jobs and income. Certain successes have been achieved over the past five decades. However, much more attention is needed, including a full collection of wild halophytic plant species. This short communication suggests that the world needs a World Halophyte Garden.