Solar Lake Research Articles

Immunological studies on microbial mats from Solar Lake (Sinai)— A contribution to the organic geochemistry of sediments

Immunological and biochemical techniques were used to investigate organic matter in microbial mats from Solar Lake (Sinai, Egypt). Antibodies, elicited in rabbits against samples taken at different depths from a core of these mats, were used for the detection of immunological determinants preserved in these samples. Special attention was given to an antiserum directed against a top mat fraction (3–10 mm depth) and an antiserum against a fraction from a lower section of the core (380–390 mm depth). Both antisera, tested in a dot-blot immunobinding assay, were found to give positive reactions with organic matter from different depths of the sediment. An immunohistochemical experiment with the antisera points to antigenic determinants on Recent and subfossil sheaths of Microcoleus. In addition, extracts of sediment samples were submitted to electrophoresis in polyacrylamide gels in order to characterize the separated macromolecules by immunological means. The results showed a rapid decrease in the number of antigenic determinants from Recent to subfossil samples. However, even in the deepest layers of the sediment (690–700 mm depth) intact biopolymers were detected.

Methanogenesis in the hypersaline Solar Lake (Sinai)

Enrichment studies on microbial mat sediments (potential stromatolites) from the hypersaline Solar Lake (Sinai) indicated high numbers of methanogenic bacteria (up to 105 ml−1 sediment) in spite of the high sulfate reduction rate, sulfate concentration and salinity. Among H2/CO2, acetate and monomethylamine, the methylated amine was the preferred substrate. The predominant species enriched was a Methanosarcina sp. The findings indicate that methanogenic bacteria play an important role in hypersaline sulfate-enriched anoxic sediments and stromatolithic microbial mats.

Methanogenesis in the hypersaline Solar Lake (Sinai)

Enrichment studies on microbial mat sediments (potential stromatolites) from the hypersaline Solar Lake (Sinai) indicated high numbers of methanogenic bacteria (up to 105 ml−1 sediment) in spite of the high sulfate reduction rate, sulfate concentration and salinity. Among H2/CO2, acetate and monomethylamine, the methylated amine was the preferred substrate. The predominant species enriched was a Methanosarcina sp. The findings indicate that methanogenic bacteria play an important role in hypersaline sulfate-enriched anoxic sediments and stromatolithic microbial mats.

Carbohydrates in recent marine sediments—II. Occurrence and fate of carbohydrates in a recent stromatolitic deposit: Solar Lake, Sinai

In a study on the diagenesis of carbohydrates in a recent stromatolitic deposit (Solar Lake, Sinai) monosaccharides are quantitated after mild acid hydrolysis and gas chromatographic analysis as alditol acetates. From the depth profiles of the individual monosaccharides relative to the total organic carbon three categories of carbohydrates can be distinguished. The behaviour of the various categories upon burial is discussed in terms of their potential to become a part of the organic matter that survives geological periods. The distribution patterns of especially the mono- O-methyl monosaccharides at various depths are characteristics for the bacterial communities present in the corresponding parts of the sediment column.

The Great salt lake: Artificial pycnocline andsolar lake

This paper deals with a man-made pycnocline which was induced by a causeway constructedacross the Great Salt Lake. The pycnocline is stable with a density gradient of 100 kg/m 4, and the mixing across it is characterized by a diffusion coefficient which is one quarter of the molecular heat conductance. It is shown that the conversion rate of kinetic to potential energy by mixing is a good parameter with small variations. It is argued that protection of the southern arm by wind breaks will bring the pycnocline to the surface and will convert the Great Salt Lake into a solar lake.

Calcification of cyanobacterial mats in Solar Lake, Sinai

Pore-water samples were obtained from the shallow-water part of Solar Lake (Sinai) where luxurious cyanobacterial mats grow. These samples were analyzed for Ca/sup 2 +/, Mg/sup 2 +/, Sr/sup 2 +/, Cl/sup -/, SO/sub 4//sup 2 -/, and titration alkalinity (TA) to determine the role of cyanobacterial growth and degradation on the calcification of the mats. The data are modeled thermodynamically to predict mineral-pore-water equilibria. The data support earlier bacterial and sedimentological studies suggesting that the degradation of the cyanobacterial mat via sulfate reduction is of major importance in the calcification process. 34 references, 1 figure, 2 tables.

Microelectrode studies of the photosynthesis and O2, H2S, and pH profiles of a microbial mat1

The profiles of O2, H2S, and pH within a microbial mat of the hypersaline pond Solar Lake, Sinai, were measured by 2–200‐µm‐thick microelectrodes during diurnal and artificial light cycles. The oxygen concentration in the photic layer varied from a maximum of 1,400 µM during the day to 0 during the night. The pH in the same layer varied between 9.6 in the early afternoon and 7.7 in the early morning. Sulfide was not present in the photic zone during the day, but built up to about 50 µM during the night. The diffusion gradients of sulfide and oxygen were very steep and the two compounds coexisted in a layer only 0.25 mm thick during the day. Diffusion flux calculations showed that the average turnover time of sulfide within this layer was 21 s. The rapid turnover indicated that the oxidation of sulfide must be biologically mediated. Oxygenic photosynthesis was measured by a new oxygen microprofile method which accurately determines the vertical distribution of photosynthetic activity. There was no difference in the efficiency of photosynthesis between morning and afternoon. The photosynthetic efficiency of the whole mat was about fourfold higher at low light intensities, <120 µEinst· m‒2·s‒1, than at high light intensities, 120–1,600 µEinst·m‒2·s‒1. Anoxygenic photosynthesis within the mat was not quantitatively important.

Photosynthesis and structure of benthic microbial mats: Microelectrode and SEM studies of four cyanobacterial communities1

The microzonation of photosynthetic organisms in four cyanobacterial mats of Solar Lake, Sinai, was studied by light and scanning electron microscopy. The zonation was compared to the distribution of photosynthesis and of O2, H2S, and pH. Microelectrodes were used to measure the chemical gradients as well as the photosynthetic rates by a newly developed technique which allows a spatial resolution of 100 µm. In one of the mats, the photic zone was only 0.8 mm thick and there was a maximum photosynthetic rate of 50 µmol O2·cm‒3·h‒1 at 0.3–0.4‐mm depth. Three other mats had photosynthesis down to 2.5, 4.5, and >10 mm. Photosynthetic rates in the shallow water mats ranged from 13.3 to 17.6 mmol O2·m‒2·h‒1. Two‐dimensional maps of oxygen and photosynthesis distribution at the mat surface demonstrated a strong heterogeneity with rapid oxygen production within dense diatom tufts of 0.2–0.5‐mm diameter overgrowing the cyanobacteria. The photosynthesis in the tufts reached 100 µmol O2·cm‒3·h‒1, which led to an oxygen turnover time of only 23 s. Gas bubbles within the mat served as dynamic reservoirs for oxygen during light‐dark cycles and buffered against extreme diurnal variations between oxygen and sulfide.

Ecophysiology of the Cyanobacterium Dactylococcopsis salina: Effect of Light Intensity, Sulphide and Temperature

Dactylococcopsis salina is a planktonic gas-vacuolated cyanobacterium that forms a distinct bacterial plate at the metalimnion of Solar Lake, Sinai. Temperature, light intensity and sulphide concentration were examined as possible limiting factors determining the distribution of D. salina during the annual limnological cycle of Solar Lake. Both laboratory cultures and in situ samples were examined for their photosynthetic activity at a wide range of temperature, light intensity and sulphide concentrations. The cyanobacterium showed a considerable light adaptation and a capacity for photosynthetic activity at high light intensities. It also showed anoxygenic photosynthesis using H2S as an alternative electron donor, but this activity was only 4% of oxygenic photosynthesis. Furthermore, H2S was highly toxic to D. salina and no CO2 photoassimilation could be detected at pH 7 and 1 mm-sulphide. Temperature is the primary environmental factor governing the distribution of D. salina in Solar Lake.

The biology of a new gas-vacuolate cyanobacterium, Dactylococcopsis salina sp. nov., in Solar Lake

Several gas-vacuolate microorganisms have been found in Solar Lake, a stratified heliothermal saline pool in Sinai. The most abundant of these organisms is a new cyanobacterium Dactylococcopsis salina . It has been isolated and grown in a defined culture medium, and its biology has been studied in the lake throughout two annual periods of stratification. The Dactylococcopsis dominated the lake plankton between depths of 1 and 4 m during December 1979 to April 1980 but disappeared during summer holomixis. It reappeared in November and again persisted through to May 1981 but during this second period of stratification it was distributed only in a narrow band around a depth of 1 m. By determining the physical and chemical requirements of Dactylococcopsis in culture it has been possible to explain the changes in its abundance and vertical distribution in the lake, as follows. (i) Salinity provides no barrier to its distribution as it is able to grow over a wider range, 5-20% , than that encountered in the lake. (ii) The cyanobacterium is killed by prolonged exposure to temperatures exceeding 46 °C. This temperature was exceeded at depths below 1.5 m as the lake heated up in April 1980 and at depths below 2 m throughout the November 1980 to May 1981 period of stratification Dactylococcopsis was absent from these layers. (iii) While the Dactylococcopsis is able to photosynthesize under anaerobic conditions in the presence of sulphide, its efficiency is less than 4% of the aerobic rate. Its inability to compete effectively with other photosynthetic microorganisms in the presence of sulphide may explain its absence from depths below 4 m during the winter of 1980. (iv) Dactylococcopsis is able to adapt to very high light intensities. The natural population has a photosynthetic I k of 900 µE m -2 s -1 and it survives light intensities of 800 µE m -2 s -1 for prolonged periods. However, the combination of even higher intensities and high oxygen concentrations at the lake surface may contribute to its absence there. (v) The absence of Dactylococcopsis from the top 0.7 m of the lake can be explained by grazing pressure from Artemia salina , the brine shrimp. The shrimp effectively filters the cyanobacterium from the epilimnetic water and is able to assimilate it. Artemia is unable to graze the metalimnetic population during stratification because it cannot withstand the elevated temperatures there. (vi) Dactylococcopsis resides in the stratified metalimnion for many months. Losses by sinking, or floating, are minimized by light intensity-regulated buoyancy control in which gas vacuoles provide an essential part.

Origin of Dolomite and Its Spatial and Chronological Distribution--A New Insight: ABSTRACT

One of the oldest problems in sedimentology is the origin of dolomite. Dolomite, CaMg (CO3)2, is one of the most common sedimentary carbonate minerals. Its density is 2.866, and calcite's density is 2.710. The absolute abundance of dolostones, as well as the dolostone/limestone ratio, increase with geologic age. Changes in seawater magnesium concentration were invoked to explain these observations. During the last 30 years, for both scientific and economic reasons, many attempts were made to explain the scarcity of recent dolomites. Carbonate rocks composed mainly of dolomite generally have high porosities, and are important reservoir rocks for oil. Dolomite is the thermodynamically stable carbonate phase in seawater. Its relative scarcity in recent marine carbonate sediments, therefore, cannot be explained simply by the thermodynamic properties of dolomite; dolomite formation appears to be inhibited by seawater. Most sedimentologists assumed that the formation of dolomite is mainly controlled by the dissolved magnesium/calcium (Mg2+/Ca2+) ratio in seawater; the molar (Mg2+/Ca2+) ratio in seawater is 5.3. It was therefore assumed that dolomite formation requires a still higher ratio. This explanation, however, had to be abandoned when primarily during the last 2 to 3 years, dolomite was observed as an important constituent of many modern marine organic-rich sediments; for example, in th California borderlands, Gulf of California, the Japan Trench, Cariaco basin off the coast of Venezuela, and the Solar Lake in Israel. In the Guaymas basin, for example, dolomite actively forms from pore fluids with Mg2+/Ca2+ ratios of 1 to 2. Similar dolomite formed in the Miocene Monterey Formation, either as penecontemporaneous or early diagenetic nodules or as laminated dolomite. The ^dgr18O values of these dolomites range from -6 to +7 ^pmil (PDB), and their ^dgr13C values range from -30 to +20 ^pmil. Experiments conducted recently in our laboratory have shown that the important condition of dolomite formation is not high Mg2+/Ca2+ ratios, but low dissolved sulfate (SO4-4) content, which inhibits dolomite formation, seawater contains 28 mMSO42-. Dolomitization of calcite is already inhibited at sulfate concentrations of approximately 5 to 7% of seawater value. Aragonite dolomitization, however, though strongly retarded at these low dissolved SO42- concentration values, is inhibited at sulfate concentrations of approximately 50% of seawater's value. We have also shown that dolomitization of CaCO3 proceeds through protodolomite, a calcium-rich disordered dolomite which would transform t dolomite if equilibrium were established. Dissolved SO42- also retards the rates of protodolomite transformation to dolomite and dedolomitization. Sulfate ions adsorbed to the surfaces of calcite, dolomite, or aragonite may affect the kinetics of phase transformations in the carbonate system. In a sulfate-depleted environment, sulfate is rapidly desorbed; at 15° to 35°C (59° to 95°F), the process is completed in 1 to 2 days. Thus, favorable sites for dolomite formation in the marine environment are those where dissolved SO42- concentrations are low. The most effective processes of sulfate removal from or its dilution in marine pore fluids are microbial reduction in organic-rich sediments and mixing of seawater with large amounts of fresh water. This happens, for example, in continental margin sediments with high rates of deposition, as in the Gulf of California, or in deeper water sediments associated with black shales. The presence of much dissolved SO42- in seawater also explains the almost absence of dolomite in apparently highly favorable environments, for example, in open marine carbonates. The relative paucity of dolomite-rich carbonate rocks (dolostones) formed during the last 100 to 120 million years, as compared with their abundance in older sediments, in particular in the Precambrian and early Paleozoic, could be explained on the basis of changes in the depositional environments and in the carbonate mineralogy of the primary calcareous sediments. These differences do not necessarily reflect changes in seawater magnesium concentrations. End_of_Article - Last_Page 2156------------

Predation of Arternia cysts by water-tiger larvae of the genus Anacaena (Coleoptera, Hydrophilidae)

Artemia cysts are preyed upon by the larvae of Anacaena (Coleoptera, Hydrophilidae) in the wet supralittoral of the hypersaline Solar Lake near Elat. The larvae are specialized feeders of the cysts, as shown by laboratory experiments.

Ecology of the bacteria of the sulphur cycle with special reference to anoxic-oxic interface environments.

H2S is produced as a main end-product of anaerobic mineralization in anoxic, sulphate-rich environments by a diverse population of sulphate-reducing bacteria. The sulphate reducers can carry out an almost complete oxidation of detrital organic matter to CO2. The H2S consequently becomes an important electron carrier from the anoxic to the oxic world. Thiobacilli and other colourless sulphur bacteria have the potential to oxidize the H2S at the oxic-anoxic interface in sediments or stratified waters, but their role is still poorly understood. A comparison of sulphide oxidation processes in the chemoclines of the Black Sea, the Solar Lake and in A beggiatoa mat indicated that depth scales and retention times of coexisting O2 and H2S regulate the bacterial involvement in the sulphide oxidation. The H2S specialists, Beggiatoa and Thiovulum, are optimally adapted to compete with the autocatalytic oxidation of H2S by O2. Microelectrode measurements show retention times of O2-H2S in the bacterial mats or veils of less than 1 s. In photic chemoclines of stratified waters or sulfureta, the phototrophic sulphur bacteria or cyanobacteria interact with the sulphide oxidation at the O2-H2S interface. Short cycles between H2S and intermediate oxidation products, So or S2O2 3-, are created. The bacteria of the sulfuretum are highly adapted to the diurnal rhythm of light, O2 and H2S.

The oxidation state diagram: stability of dissolved sulphur species in seawater

Oxidation state diagrams have been constructed for different sulphur species. Sulphur oxyacids are stressed with respect to their key role in the cycling of inorganic sulphur species, besides sulphides and elemental sulphur. Following the stable sulphate species in seawater, metastable species are S 4O 6 2−, S 2O 3 2− and S 0. Stability of different species found from these diagrams were compared with the earlier literature. A case study, from Solar Lake (Sinai) is inconcurrent with the results of the present diagrams.

Ciliates of solar lake on the red sea shore

Solar Lake, about 20 km south of Elat, is a mesothermal, monomictic lake heated heliothermally. Its turnover occurs in the summer months, during July and August. During the rest of the year the lake is layered. The epilimnion is about 1 m thick, the metalimnion lying at a depth of 90–120 cm. The hypolimnion is anaerobic and can be heated to a maximum of 56.6 °C. The water is 4 to 6 m deep, depending on the season. During the stagnation period in the spring of 1978 qualitative measurements were made of the ciliate fauna in the lake. Samples were taken from the pelagic and benthic regions, from the shore to the middle of the lake. No ciliates were found in the entire pelagic region. All the 16 species found in the benthic region were in the zone of layered algal mats (Zone IV) and in the “pinacle algal mat” (Zone III) ( Krumbein and Cohen 1974). These two zones extend to the lower boundary of the epilimnion. In the algal mats of the deeper Zones II and I no ciliates were found. This result is apparently due to the high water temperatures prevailing at these depths and to the anaerobic conditions, for adequate food (algae and bacteria) is present. Stephanopogon apogon, Uronema nigricans, Uronema filificum, Parauronema virginianum, Pseudocohnilembus marinus, Halteria grandinella, Euplotes rariseta and Uronychia transfuga are bacteriophagous; the alga-eaters include Frontonia marina, Condylostoma reichi n. spec, Condylostoma patulum, Tachysoma spec, and Holosticha diademata. Enchelyodon trepida and Litonotus lamella are predators on other ciliates. One ecological characteristic shared by the species found is their high salinity tolerance. L. lamella, U. nigricans, H. grandinella and H. diademata are known to live in fresh water and in the ocean, and the main range of the other species covers a great variety of marine biotopes. The infraciliature of all the ciliates was studied with AgNO 3 (by the method of Chatton-Lwoff ) or protargol ( Wilbert ). Condylostoma reichi (Fig. 7) is new to science. New species and genus characteristics of Uronychia transfuga (Fig. 10, Fig. 11) are described, on the basis of infraciliature and morphogenetic stages.

Microbial transformations of sulfur compounds in a stratified lake (Solar Lake, Sinai)1

Microbiological and chemical aspects of the sulfur cycle were studied in the chemocline of a tropical salt lake. Oxygen and sulfide coexisted in a 0–10‐cm layer which migrated up and down during a diurnal cycle. Sulfide was rapidly oxidized by oxygen, with a half‐life of 5–10 min, to produce mainly sulfate and thiosulfate. Thiosulfate and elemental sulfur had concentration maxima in the chemocline while polysulfide was abundant throughout the sulfide zone. Radiotracer experiments showed that the elemental sulfur was produced by anoxygenic photosynthesis in cyanobacteria. The elemental sulfur was further oxidized or again reduced, depending on the presence or absence of oxygen. Cyanobacteria in the chemocline shifted between anoxygenic photosynthesis in the morning and oxygenic photosynthesis in the afternoon. A high dark CO2 fixation was found in the chemocline which could be stimulated by sulfide, elemental sulfur, and thiosulfate. The oxidation rate of sulfide in the chemocline was dependent on the presence of bacteria.

Diurnal Cycle of Oxygen and Sulfide Microgradients and Microbial Photosynthesis in a Cyanobacterial Mat Sediment

The diurnal variation in the microgradients of O(2), H(2)S, and Eh were studied in the benthic cyanobacterial mats of a hypersaline desert lake (Solar Lake, Sinai). The results were related to light intensity, light penetration into the mat, temperature, pH, NH(4), photosynthetic activity, pigments, and the zonation of the microbial community. Extreme diurnal variation was found, with an O(2) peak of 0.5 mM at 1 to 2 mm of depth below the mat surface during day and a H(2)S peak of 2.5 mM at 2 to 3 mm of depth at night. At the O(2)-H(2)S interface, the two compounds coexisted over a depth interval of 0.2 to 1 mm and with a turnover time of a few minutes. The photic zone reached 2.5 mm into the mat in summer, and the main CO(2) light fixation took place at 1 to 2 mm of depth. During winter, light and photosynthesis were restricted to the uppermost 1 mm. The quantitative dynamics of O(2) and H(2)S were calculated from the chemical gradients and from the measured diffusion coefficients.

Solar Lake (Sinai). 3. Bacterial distribution and production1

The relations between photosynthetic and nonphotosynthetic (chemoorganotrophic and chemolithotrophic) microorganisms in Solar Lake were studied during the annual limnological cycle. Six different bacterial plates were observed during stratification by direct and viable bacterial counts, light and dark CO2 incorporation, chlorophyll a, protein, ATP, and ETS determinations. A maximal dark CO2 incorporation of 1,014 mg C m−3 d−1 may represent as much as 16,900 mg C m−3 d−1 of chemoorganotrophic bacterial production, on the assumption that these bacteria assimilate an average of 6% CO2 of their total carbon uptake. This calculated production is very high in comparison to the recorded photosynthetic maximum of 4,960 mg C m−3 d−1. The organic carbon needed for such a high chemoorganotrophic production may be supplied by the benthic cyanobacterial mats. Extremely high specific activities of ATP and ETS for the layer immediately above the thermocline indicate a very active bacterial plate at this layer.

Solar Lake (Sinai). 1. Physical and chemical limnology1

In Solar Lake, a basin at the edge of the sea filled with brine and shielded from the wind, a pycnocline builds up in September due to seepage of seawater to the surface. Solar heating produces a mesothermic temperature curve with a maximum up to 60.5°C at 2.5–3‐m depth and decreasing temperatures toward the bottom (40°C at 5 m). The temperature profile together with a supply of nutrients from seepage leads to the development of several bacterial plates and a benthic cyanobacterial bloom. A rapid development of anoxic conditions with up to 39 ppm H2S, a decrease in pH from top to bottom (8–6.9), redox potential gradients (+390 to −185 mV), and extremely pronounced light absorption are observed during the period of stratification which lasts from Sepember to July. With increasing solar energy, the seawater supply no longer compensates for the evaporation rate of 3.0 m yr−1 and the mesothermy becomes unstable. During a short period of holomixis, lasting from 4–13 weeks, the temperature is 27°C throughout the water column. The sediments of Solar Lake preserve a record of the last 4,600 years from the conditions of a marine lagoon to the development of the limnological cycle presented here.

Solar Lake (Sinai). 2. Distribution of photosynthetic microorganisms and primary production1

The seasonal and vertical distributions of sulfur photosynthetic bacteria and cyanobacteria in Solar Lake, and their contribution to primary production, are described. During stratification, separate plates of the phototrophic sulfur bacteria Chromatium violescens and Prosthecochloris sp. develop. A bottom cyanobacterial bloom consisting of Oscillatoria spp. and Microcoleus sp. develops H2Sconcentrations up to 39 ppm and under light conditions down to 0.5% of surface light. The occurrence of a cyanobacterial bloom in the hypolimnion is explained by the facultative anoxygenic photosynthesis of Oscillatoria limnetica. Primary production is extremely high during stratification and reaches a maximum of 8,015 mg C m−2 d−1, 91% of which is produced in the metalimnion and hypolimnion. The overall annual production (59.09 g C m−2 yr−1) is low, owing to extremely low primary production in the epilimnion throughout stratification and in the whole column during holomixis. Stagnant conditions in a shallow body of water exposed to high irradiation leads to an inverse productivity profile.