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Thin section and argon-ion polishing scanning electron microscope observations were used to analyze the sedimentary and diagenetic environments and main diagenesis of the Permian Fengcheng Formation shales in different depositional zones of Mahu Sag in the Junggar Basin, and to reconstruct their differential diagenetic evolutional processes. The diagenetic environment of shales in the lake-central zone kept alkaline, which mainly underwent the early stage (Ro<0.5%) dominated by the authigenesis of Na-carbonates and K-feldspar and the late stage (Ro>0.5%) dominated by the replacement of Na-carbonates by reedmergnerite. The shales from the marginal zone underwent a transition from weak alkaline to acidic diagenetic environments, with the early stage dominated by the authigenesis of Mg-bearing clay and silica and the late stage dominated by the dissolution of feldspar and carbonate minerals. The shales from the transitional zone also underwent a transition from an early alkaline diagenetic environment, evidenced by the formation of dolomite and zeolite, to a late acidic diagenetic environment, represented by the reedmergnerite replacement and silicification of feldspar and carbonate minerals. The differences in formation of authigenic minerals during early diagenetic stage determine the fracability of shales. The differences in dissolution of minerals during late diagenetic stage control the content of free shale oil. Dolomitic shale in the transitional zone and siltstone in the marginal zone have relatively high content of free shale oil and strong fracability, and are favorable "sweet spots" for shale oil exploitation and development. [ABSTRACT FROM AUTHOR]

Magnesium carbonates have been identified within the landing site of the Perseverance rover mission. This study reviews terrestrial analog environments and textural, mineral assemblage, isotopic, and elemental analyses that have been applied to establish formation conditions of magnesium carbonates. Magnesium carbonates form in five distinct settings: ultramafic rock‐hosted veins, the matrix of carbonated peridotite, nodules in soil, alkaline lake, and playa deposits, and as diagenetic replacements within lime—and dolostones. Dominant textures include fine‐grained or microcrystalline veins, nodules, and crusts. Microbial influences on formation are recorded in thrombolites, stromatolites, crinkly, and pustular laminites, spheroids, and filamentous microstructures. Mineral assemblages, fluid inclusions, and carbon, oxygen, magnesium, and clumped isotopes of carbon and oxygen have been used to determine the sources of carbon, magnesium, and fluid for magnesium carbonates as well as their temperatures of formation. Isotopic signatures in ultramafic rock‐hosted magnesium carbonates reveal that they form by either low‐temperature meteoric water infiltration and alteration, hydrothermal alteration, or metamorphic processes. Isotopic compositions of lacustrine magnesium carbonate record precipitation from lake water, evaporation processes, and ambient formation temperatures. Assessment of these features with similar analytical techniques applied to returned Martian samples can establish whether carbonates on ancient Mars were formed at high or low temperature conditions in the surface or subsurface through abiotic or biotic processes. The timing of carbonate formation processes could be constrained by 147Sm‐143Nd isochron, U‐Pb concordia, 207Pb‐206Pb isochron radiometric dating as well as 3He, 21Ne, 22Ne, or 36Ar surface exposure dating of returned Martian magnesium carbonate samples. Plain Language Summary: Magnesium carbonate minerals rarely form large deposits on Earth and because they constitute such a small proportion of the terrestrial carbonate record in comparison to calcium‐rich carbonates, they have received little attention. In contrast, the largest carbonate deposit detected on Mars has magnesium carbonate, and it has been detected at the landing site of the 2020 mission where the Perseverance rover will collect samples for return to Earth. We synthesized the field observations and laboratory experiments that pertain to magnesium carbonates formed on Earth and find that they form in five types of environments as follows: within veins or in the bulk volume of magnesium‐rich rocks, soils, alkaline or salty lakes, and as replacements of previously formed calcium‐rich carbonate minerals. Conceptually, these environments may be analogs for ancient Martian magnesium carbonate‐forming environments. Magnesium carbonates formed in some environments are capable of preserving remnants of microbes, especially if magnesium carbonates formed characteristic large‐scale clotted or vertical column shapes or microscale spherical and laminated textures. If life had ever originated on Mars, these would be key materials to investigate for biosignatures. Finally, a number of analytical techniques are discussed that can be performed on magnesium carbonate rocks collected by Perseverance when returned to Earth. Key Points: On Earth, magnesium carbonates of distinct textures form in ultramafic rock hosted veins, listvenites, soils, alkaline lakes, and playasThe isotopic and elemental composition of terrestrial magnesium carbonate reveal timing and chemistry of fluid conditionsThrough the Mars 2020 sample return mission, the reviewed methods can be used to analyze carbonate‐forming conditions on ancient Mars [ABSTRACT FROM AUTHOR]

Environmental factors (e.g., temperature and pH) shaping the distribution of microbial communities in hot springs have been extensively studied, whereas how hydrochemical formation mechanisms and hydrological circulation processes affect microbial community composition is not comprehensively elucidated. In the present study, hydrochemical, isotopic, and high‐throughput sequencing methods were employed to investigate hydrochemical characteristics and evolution of springwater as well as their underlying roles in shaping the microbial community in multiple acidic and alkaline hot springs in southwestern Yunnan, China. Distinct hydrochemical (e.g., pH, temperature, sulfate, SiO2, and trace metals) and isotopic (δ2H and δ18O) characteristics revealed the recharge sources and circulation processes of springwater were different in alkaline, high‐temperature and acidic, moderate‐temperature hot springs. Two acidic, moderate‐temperature springs (43°C–55°C), characterized by high sulfate, showed shallow circulation depths and were potentially heated by upwelling hot, high H2S abundance gases, and sulfur oxidation might be one of the main underlying hydrochemical processes. Seven alkaline, high‐temperature springs (>70°C), in contrast, which originated from a different recharge source as indicated by the lighter isotopic compositions (δ2H and δ18O), showed characteristics of deeper circulation. Hydrogenobacter sp. is the most abundant microorganism in alkaline, high‐temperature springs, whereas acidic, moderate‐temperature springs are mainly composed of Chlorobiaceae, Thiomonas sp., Halothiobacillus sp., Sulfurihydrogenibium sp., and Hydrogenobaculum sp. which have been reported to possess the potentials to cycle sulfur. The hydrochemical constraints on shaping microbial communities may help us better understand biogeochemical cycles across a range of temperatures in acidic and alkaline springs. Key Points: Hydrochemical characteristics of alkaline, high‐temperature and acidic, moderate‐temperature springs reflect distinct circulation pathsMicrobial communities respond to hydrochemical constraints on alkaline, high‐temperature and acidic, moderate‐temperature springsHydrogenobacter sp. dominates in alkaline springs and Chlorobiaceae and Sulfurihydrogenibium sp. dominate in acidic springs [ABSTRACT FROM AUTHOR]

Soda lakes are saline alkaline lakes characterized by high concentrations of sodium carbonate/bicarbonate which lead to a stable elevated pH (>9), and moderate to extremely high salinity. Despite this combination of extreme conditions, biodiversity in soda lakes is high, and the presence of diverse microbial communities provides a driving force for highly active biogeochemical cycles. The sulfur cycle is one of the most important of these and bacterial sulfur oxidation is dominated by members of the obligately chemolithoautotrophic genus Thioalkalivibrio. Currently, 10 species have been described in this genus, but over one hundred isolates have been obtained from soda lake samples. The genomes of 75 strains were sequenced and annotated previously, and used in this study to provide a comprehensive picture of the diversity and distribution of genes related to dissimilatory sulfur metabolism in Thioalkalivibrio. Initially, all annotated genes in 75 Thioalkalivibrio genomes were placed in ortholog groups and filtered by bi-directional best BLAST analysis. Investigation of the ortholog groups containing genes related to sulfur oxidation showed that flavocytochrome c (fcc) , the truncated sox system, and sulfite:quinone oxidoreductase (soe) are present in all strains, whereas dissimilatory sulfite reductase (dsr ; which catalyzes the oxidation of elemental sulfur) was found in only six strains. The heterodisulfide reductase system (hdr), which is proposed to oxidize sulfur to sulfite in strains lacking both dsr and soxCD , was detected in 73 genomes. Hierarchical clustering of strains based on sulfur gene repertoire correlated closely with previous phylogenomic analysis. The phylogenetic analysis of several sulfur oxidation genes showed a complex evolutionary history. All in all, this study presents a comprehensive investigation of sulfur metabolism-related genes in cultivated Thioalkalivibrio strains and provides several avenues for future research. [ABSTRACT FROM AUTHOR]

Sodiomyces alkalinus is one of the very few alkalophilic fungi, adapted to grow optimally at high pH. It is widely distributed at the plant‐deprived edges of extremely alkaline lakes and locally abundant. We sequenced the genome of S. alkalinus and reconstructed evolution of catabolic enzymes, using a phylogenomic comparison. We found that the genome of S. alkalinus is larger, but its predicted proteome is smaller and heavily depleted of both plant‐degrading enzymes and proteinases, when compared to its closest plant‐pathogenic relatives. Interestingly, despite overall losses, S. alkalinus has retained many proteinases families and acquired bacterial cell wall‐degrading enzymes, some of them via horizontal gene transfer from bacteria. This fungus has very potent proteolytic activity at high pH values, but slowly induced low activity of cellulases and hemicellulases. Our experimental and in silico data suggest that plant biomass, a common food source for most fungi, is not a preferred substrate for S. alkalinus in its natural environment. We conclude that the fungus has abandoned the ancestral plant‐based diet and has become specialized in a more protein‐rich food, abundantly available in soda lakes in the form of prokaryotes and small crustaceans. [ABSTRACT FROM AUTHOR]

Algal blooms in lakes are often associated with anthropogenic eutrophication; however, they can occur without the human introduction of nutrients to a lake. A rare bloom of the alga Picocystis sp. strain ML occurred in the spring of 2016 at Mono Lake, a hyperalkaline lake in California, which was also at the apex of a multiyear-long drought. These conditions presented a unique sampling opportunity to investigate microbiological dynamics and potential metabolic function during an intense natural algal bloom. We conducted a comprehensive molecular analysis along a depth transect near the center of the lake from the surface to a depth of 25 m in June 2016. Across sampled depths, rRNA gene sequencing revealed that Picocystis-associated chloroplasts were found at 40 to 50% relative abundance, greater than values recorded previously. Despite high relative abundances of the photosynthetic oxygenic algal genus Picocystis, oxygen declined below detectable limits below a depth of 15 m, corresponding with an increase in microorganisms known to be anaerobic. In contrast to previously sampled years, both metagenomic and metatranscriptomic data suggested a depletion of anaerobic sulfatereducing microorganisms throughout the lake's water column. Transcripts associated with photosystem I and II were expressed at both 2 m and 25 m, suggesting that limited oxygen production could occur at extremely low light levels at depth within the lake. Blooms of Picocystis appear to correspond with a loss of microbial activity such as sulfate reduction within Mono Lake, yet microorganisms may survive within the sediment to repopulate the lake water column as the bloom subsides. [ABSTRACT FROM AUTHOR]

A sediment core covering the last millennium from Lake Aktaş, a shallow alkaline soda lake in the northeast Anatolian highland of Turkey, was studied for pollen and physical and chemical proxies to reconstruct past climate change. The sediments were dated by AMS radiocarbon dating of bulk organic carbon. Among arboreal pollen (AP) from around 930 years ago, dominant trees were Pinus sylvestris , Picea orientalis , Abies , Betula , Fagus , and Quercus . AP exceeded NAP (non-arboreal pollen) in this time, whereas the opposite is the case in a pollen trap in the same region collecting the pollen for one year in 2015–2016. The comparison of modern and fossil pollen influx indicates that in that period trees were more widely distributed around the lake than today, where steppe vegetation now prevails. Inferred causes for the disappearance of trees are anthropogenic impacts and climatic change towards more continental conditions. The results also identify the onset of the Little Ice Age in the NE Anatolian highland of Turkey. [ABSTRACT FROM AUTHOR]

Six strains of extremely halophilic and alkaliphilic euryarchaea were enriched and isolated in pure culture from surface brines and sediments of hypersaline alkaline lakes in various geographical locations with various forms of insoluble cellulose as growth substrate. The cells are mostly flat motile rods with a thin monolayer cell wall while growing on cellobiose. In contrast, the cells growing with cellulose are mostly nonmotile cocci covered with a thick external EPS layer. The isolates, designated AArcel, are obligate aerobic heterotrophs with a narrow substrate spectrum. All strains can use insoluble celluloses, cellobiose, a few soluble glucans and xylan as their carbon and energy source. They are extreme halophiles, growing within the range from 2.5 to 4.8 M total Na + (optimum at 4 M) and obligate alkaliphiles, with the pH range for growth from 7.5 to 9.9 (optimum at 8.5–9). The core archaeal lipids of strain AArcel5 T were dominated by C 20 –C 20 dialkyl glycerol ether (DGE) (i.e. archaeol) and C 20 –C 25 DGE in nearly equal proportion. The 16S rRNA gene analysis indicated that all six isolates belong to a single genomic species mostly related to the genera Saliphagus-Natribaculum-Halovarius . Taking together a substantial phenotypic difference of the new isolates from the closest relatives and the phylogenetic distance, it is concluded that the AArcel group represents a novel genus-level branch within the family Natrialbaceae for which the name Natronobiforma cellulositropha gen. nov., sp. nov. is proposed with AArcel5 T as the type strain (JCM 31939 T = UNIQEM U972 T ). [ABSTRACT FROM AUTHOR]

In recent years, global warming has led to a growing number of Vibrio cholerae infections in bathing water users in regions formerly unaffected by this pathogen. It is therefore of high importance to monitor V. cholerae in aquatic environments and to elucidate the main factors governing its prevalence and abundance. For this purpose, rapid and standardizable methods that can be performed by routine water laboratories are prerequisite. In this study, we applied a recently developed multiplex quantitative PCR (qPCR) strategy (i) to monitor the spatiotemporal variability of V. cholerae abundance in two small soda pools and a large lake that is intensively used for recreation and (ii) to elucidate the main factors driving V. cholerae dynamics in these environments. V. cholerae was detected with qPCR at high concentrations of up to 970,000 genomic units 100 ml-1 during the warm season, up to 2 orders of magnitude higher than values obtained by cultivation. An independent cytometric approach led to results comparable to qPCR data but with significantly more positive samples due to problems with DNA recovery for qPCR. Not a single sample was positive for toxigenic V. cholerae, indicating that only nontoxigenic V. cholerae (NTVC) was present. Temperature was the main predictor of NTVC abundance, but the quality and quantity of dissolved organic matter were also important environmental correlates. Based on this study, we recommend using the developed qPCR strategy for quantification of toxigenic and nontoxigenic V. cholerae in bathing waters with the need for improvements in DNA recovery. [ABSTRACT FROM AUTHOR]

During the last decade, the distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in lacustrine sediments has been widely used to reconstruct past variations in lake temperature. A prerequisite for the application of brGDGTs to lacustrine paleoclimate reconstructions is to understand the sources of brGDGTs in lake systems and the processes that influence their distribution. In this study, we investigated the distribution of brGDGTs in core-top sediments from 35 lakes across China, with a broad mean annual air temperature (MAAT) range, but a constrained pH range, to explore the effect of temperature. The results reveal a contrasting response of MBT′ 5ME and MBT′ 6ME to temperature in lake environments compared to that in soils. The sedimentary distributions of 5- and 6-methyl brGDGTs exhibit different relationships with temperature, with most of the latter being correlated to MAAT while the former responding to temperature by only hexamethylated compounds. In both global and Chinese soils, most 6-methyl brGDGTs have no relationship with MAAT, but the distribution of 5-methyl brGDGTs is correlated with MAAT. The different behaviors suggest that communities producing 5- or 6-methyl brGDGTs might be different in lakes and soils. In addition, in lakes from cold regions (MAAT < 5 °C), the brGDGT distributions correlate only with warm season temperatures (April to October) but exhibit no correlation with cold seasons, suggesting a seasonal bias in brGDGT production in these lakes. This bias towards the warm season is not found in lakes from warmer regions (MAAT > 5 °C). Based on these results we propose new temperature calibrations for paleotemperature reconstructions in Chinese alkaline lakes. [ABSTRACT FROM AUTHOR]

Nhecolândia is a vast sub-region of the Pantanal wetland in Brazil with great diversity in surface water chemistry evolving in a sodic alkaline pathway under the influence of evaporation. In this region, > 15,000 shallow lakes are likely to contribute an enormous quantity of greenhouse gas to the atmosphere, but the diversity of the biogeochemical scenarios and their variability in time and space is a major challenge to estimate the regional contribution. From 4 selected alkaline lakes, we compiled measurements of the physico-chemical characteristics of water and sediments, gas fluxes in floating chambers, and sedimentation rates to illustrate this diversity. Although these lakes have a similar chemical composition, the results confirm a difference between the black-water and green-water alkaline lakes, corresponding to distinct biogeochemical functioning. This difference does not appear to affect lake sedimentation rates, but is reflected in gas emissions. Black-water lakes are CO 2 and CH 4 sources, with fairly constant emissions throughout the seasons. Annual carbon dioxide and methane emissions approach 0.86 mol m − 2 y − 1 and 0.07 mol m − 2 y − 1 , respectively, and no clear trend towards N 2 O capture or emission was observed. By contrast, green-water lakes are CO 2 and N 2 O sinks but important CH 4 sources with fluxes varying significantly throughout the seasons, depending on the magnitude of the phytoplankton bloom. The results highlight important daily and seasonal variations in gas fluxes, and in particular a hot moments for methane emissions, when the O 2 -supersaturation is reached during the afternoon under extreme bloom and sunny weather conditions, provoking an abrupt O 2 purging of the lakes. Taking into account the seasonal variability, annual methane emissions are around 10.2 mol m − 2 y − 1 , i.e., much higher than reported in previous studies for alkaline lakes in Nhecolândia. Carbon dioxide and nitrous oxide consumption is estimated about 1.9 mol m − 2 y − 1 and 0.73 mmol m − 2 y − 1 , respectively. However, these balances must be better constrained with systematic and targeted measurements throughout the seasons. [ABSTRACT FROM AUTHOR]

Abstract: Acidic coal mining lakes (AMLs) are characterized by low pH, low biodiversity, and high concentrations of sulfate and metals. However, to date, knowledge is inadequate on the involvement of the aquatic microbial functions in biogeochemical processes of an AML. Here, we use a natural weakly alkaline lake (WAL) as a reference to investigate the functional gene structure of microbial communities in the aerobic surface waters of an AML by using a metagenomic approach with GeoChip‐based functional gene arrays (GeoChip 5.0). We found significant differences in the compositions of the microbial functional genes between the two lake types. The AML had significantly lower gene diversity than the WAL, and the functional genes detected in the AML were almost a subset of those in the WAL. We also found significant differences in the microbial metabolic potentials between the two lake types. In the AML, the microbial communities had higher functional capacities in phosphorus‐utilization, sulfur oxidation, and metal‐detoxification and had lower metabolic potentials of carbon and nitrogen fixation, and the degradation of starch, hemicellulose, cellulose, chitin, and lignin than those in the WAL. By performing null model and network analyses, we observed stronger deterministic effects of the functional gene assemblages and greater clustering among the co‐occurring functional genes in the AML than those in the WAL. Altogether, we demonstrated contrasting patterns of freshwater microbial metabolic potentials and functional gene interactions between an AML and a WAL, which may advance the understanding of microbial functional response to acidification in freshwater lakes. [ABSTRACT FROM AUTHOR]

Thick Oligocene-Miocene lacustrine limestones of the Lake Mead region in southern Nevada have few adequate modern analogues that can shed light on their origin. We contend that the Lower Pahranagat Lake (LPAH), a spring-fed, alkaline lake in east-central Nevada, provides such an analogue. Through sediment cores, sampling of the lake margin, and characterization of sediment physical and chemical properties, we show that the LPAH shares a number of lithofacies in common with the Late Oligocene to Early Miocene Rainbow Gardens (RGF) and Miocene Horse Spring Formations (HSF) in the Lake Mead area. These include: stratiform stromatolites, domal stromatolites, reed beds, and intermittently laminated and massive limestones. Oxygen and carbon isotopes from authigenic carbonates support our interpretation in that the LPAH values strongly overlap those of the Oligocene-Miocene units. As a result, we interpret the Oligocene-Miocene RGF and HSF lacustrine carbonates as having been deposited in restricted, alkaline lake basins with high salinity. These basins were not conducive to the ecological success of animals and other, large multicellular organisms and, instead, fostered the growth of significant microbial communities. Lake margins, particularly during RGF deposition, were inhabited by reedy plants and salt tolerant shore grass much as is encountered in the LPAH today. These lakes were likely sourced by springs, but were nonetheless highly evaporative. Some unique aspects of both the LPAH and the Lake Mead region Oligocene-Miocene strata may shed light on the rarity of thick lacustrine carbonates in the rock record. Both of these systems are underlain by thick, Paleozoic carbonate sequences that host the principal aquifers that feed the lakes. [ABSTRACT FROM AUTHOR]

Acıgöl Lake is the second largest alkaline lake in the world and is in a region that is one of the most important sodium sulphate production fields in Turkey. The present study focuses on determination of sources of the Na 2 SO 4 deposits with main-trace element contents based on hydro-geochemical studies in the lake basin. The geological and hydrogeological properties of the study area were primarily determined. To identify the hydrogeochemical characteristics of spring/groundwater and lake water, chemical analyses results were evaluated with graphical plots such as Piper, Gibbs and Chadha diagrams and the conceptual hydrogeological model was prepared for the area. Mineral paragenesis of the lake sediments mainly consist of gypsum, aragonite, halite, calcite, dolomite, quartz, muscovite, smectite and illite besides tenardite, mirabilite and bloedite minerals. The dominant hydro geochemical facies are Na-SO 4 , Na-Cl, Ca-Mg-HCO 3 and Ca-Mg-SO 4 which are due to water-rock interaction. The mean Na, Ca, SO 4 , Cl and Mg concentrations in the spring waters are 221.27, 152.62, 374.81, 185.46 and 58.50 ppm respectively; whereas mean concentrations in the lake waters for Na, Ca, SO 4 , Cl and Mg ions are 22 507, 646, 16 186, 35 691 and 2399 ppm respectively. These major elements have very high concentrations in the lake waters due to the evaporation leading to enrichment. The main mechanism controlling water chemistry in the Acıgöl Lake basin is the process of water–rock interaction. The enrichment of these elements in the springs waters originate from lithological units such as sedimentary, ophiolitic and young magmatic rocks. [ABSTRACT FROM AUTHOR]

The in-situ data on the vertical structure and stability of the vertical stratification of saline Lake Shira over the past decade (2007-2015) are analyzed. Simplified mathematical models have shown that strong wind in the autumn of 2014 together with rather thick ice in the winter of 2015 caused a change in the circulation regime of this water reservoir from meromictic (incomplete mixing) to holomictic (compete mixing). Based on the results obtained, a circulation regime for deep saline lakes located in the continental climate zone, in particular, in the arid zones of Southern Siberia (Khakassia, Transbaikal, and Altai) can be predicted under various climate scenarios of the future. [ABSTRACT FROM AUTHOR]

Studies investigating the diversity of cyanobacteria from tropical environments are scarce, especially those devoted to the isolation and molecular characterization of the isolated strains. Among the Brazilian biomes, Pantanal has mainly been examined through microscopic observation of environmental samples, resulting in lists of morphotypes without any genetic information. Recently, two studies were conducted evaluating the morphologic and genetic diversity of cultured non-heterocytous cyanobacteria in this biome, which resulted in the separation and description of two novel genera. In order to complement the diversity of cultured cyanobacteria from saline-alkaline lakes in Pantanal, the present study is dedicated to the examination of cultured nitrogen-fixing heterocytous cyanobacteria from this extreme and underexplored environment. A total of fourteen cyanobacterial strains were isolated. According to morphological examination they belong to the order Nostocales and to the subsections IV.I and IV.II, according to the International Code of Nomenclature for Algae, Fungi and Plants and the Bergey’s Manual of Systematic Bacteriology, respectively. Phylogenetic evaluation of their 16S rRNA gene sequences resulted in the formation of five clusters. Among them, one is clearly related to the genus Anabaenopsis whilst the remaining clusters may represent new genetic lineages. These novel sequences aid in the delimitation of problematic groups, especially those containing sequences belonging to mixed genera. The application of both morphologic and phylogenetic studies has proven to be an important tool in resolving problematic groups in cyanobacteria systematics. This strategy is essential in order to detect novel cyanobacteria genera from other tropical environments. [ABSTRACT FROM AUTHOR]

Nhecolândia is a vast sub-region of the Pantanal wetland in Brazil with great diversity in surface water chemistry evolving in a sodic alkaline pathway under the influence of evaporation. In this region, more than 15,000 shallow lakes are likely to contribute an enormous quantity of greenhouse gas to the atmosphere, but the diversity of the biogeochemical scenarios and their variability in time and space is a major challenge to estimate the regional contribution. In this study, we compiled measurements of the physico-chemical characteristics of water and sediments, gas fluxes in floating chambers, and sedimentation rates to illustrate this diversity. Although these lakes have a similar chemical composition, the results confirm an opposition between the black-water and green-water alkaline lakes, corresponding to distinct biogeochemical functioning. Black-water lakes are CO2 and CH4 sources, with fairly constant emissions throughout the seasons. Annual carbon dioxide and methane emissions approach 790 mmol m-2 y-1 and 73 mmol m-2 y-1, respectively. By contrast, green-water lakes are CO2 sinks but significant CH4 sources with fluxes varying significantly throughout the seasons, depending on the development of the cyanobacterial bloom. The results highlight two hot moments for methane emissions. The first one is suspected after the disappearance of the cyanobacterial bloom, which is accompanied by a drop in pH of the upper part of the sediments. The second one is identified when the O2-supersaturation is reached under extreme bloom and sunny weather conditions, which provoke an abrupt O2 purging of the lakes. Taking into account the seasonal variability, annual methane emissions are around 8,850 mmol m-2 y-1, i.e., much higher than reported in previous studies for alkaline lakes in Nhecolândia. Carbon dioxide consumption is estimated about 1,140 mmol m-2 y-1. However, these balances must be better constrained with systematic and targeted measurements around these hot moments. [ABSTRACT FROM AUTHOR]

Desulfurivibrio alkaliphilus strain AHT2T is a strictly anaerobic sulfidogenic haloalkaliphile isolated from a composite sediment sample of eight hypersaline alkaline lakes in the Wadi al Natrun valley in the Egyptian Libyan Desert. D. alkaliphilus AHT2T is Gram-negative and belongs to the family Desulfobulbaceae within the Deltaproteobacteria. Here we report its genome sequence, which contains a 3.10 Mbp chromosome. D. alkaliphilus AHT2T is adapted to survive under highly alkaline and moderately saline conditions and therefore, is relevant to the biotechnology industry and life under extreme conditions. For these reasons, D. alkaliphilus AHT2T was sequenced by the DOE Joint Genome Institute as part of the Community Science Program. [ABSTRACT FROM AUTHOR]

Lake Salda, located in south-western Anatolia, is characterized by the presence of living stromatolites and by a low diversity of both phytoplankton and zooplankton due to high pH and magnesium concentration. The most abundant, free sedimentary lipids of the uppermost five centimetres of the lake sediments were studied as potential environmental biomarkers, and proxies based on glycerol dialkyl glycerol tetraethers (GDGT) were tested in this extreme environment. Dinosterol and tetrahymanol are potentially relevant biomarkers for the dinoflagellate Peridinium cinctum and ciliates, respectively. C20:1 and C25:2 highly branched isoprenoid (HBI) alkenes, and n-C17 alkane and n-C17:1 alkene are considered to represent, respectively, diatoms and Cyanobacteria, that are involved in the formation of stromatolites. Crenarchaeol is assumed to be derived mainly from Thaumarchaeota thriving in the lake. Allochthonous organic material is represented by long-chain n-alkanes and n-alkanols derived from land plant leaf waxes, as well as branched GDGTs produced by soil bacteria. The latter may also be produced partly in the water column and/or the surface sediment of the lake. Branched GDGT-derived lake calibrations for water pH provide estimates close to observations, but estimated lake water/air temperature are lower than observed values. TEX86 (tetraether index of tetraethers consisting of 86 carbons), a proxy based on isoprenoid GDGTs, potentially allows estimating mean annual lake surface temperature. Interestingly, C22 to C25 1,2 diols, which have a yet unknown origin, were found for the first time in lake sediments. This study represents the first investigation of sedimentary lipid distribution in an alkaline and magnesium-rich lake in Anatolia, and provides a basis for future biomarker-based paleoenvironmental reconstruction of Lake Salda. [ABSTRACT FROM AUTHOR]

The Sambhar Soda Lake situated in Rajasthan, is the largest inland salt lake. The chemical assessment of this lake water is studied with respect to its abiotic characters. Monsoon and winter water sample analyses revealed that the lake water is hypersaline and highly alkaline in nature. The average maximum pH is 9.5 and salinity 30%, which is one of the unique features of this lake. As compared to monsoon water sample the winter sample contains remarkable concentration of various ions like sodium (9930 mg/L), chloride (7356 mg/L), bicarbonates (6080 mg/L), sulfate (9152 mg/L). Various metals were recorded from this sample analysis. The considerable amount of lead (1359 μg/L), cadmium (1416 μg/L), copper (2099 μg/L), and cobalt (2453 μg/L) metals were found from winter 2010 sample. As compare of to other saline lake and sea water the Sambhar Lake water chemistry is different, and require continuous monitoring. [ABSTRACT FROM AUTHOR]

The origin of spherical-radial calcite bodies – spherulites – in sublacustrine, hyperalkaline and saline systems is unclear, and therefore their palaeoenvironmental significance as allochems is disputed. Here, we experimentally investigate two hypotheses concerning the origin of spherulites. The first is that spherulites precipitate from solutions super-saturated with respect to magnesium-silicate clays, such as stevensite. The second is that spherulite precipitation happens in the presence of dissolved, organic acid molecules. In both cases, experiments were performed under sterile conditions using large batches of a synthetic and cell-free solution replicating waters found in hyperalkaline, saline lakes (such as Mono Lake, California). Our experimental results show that a highly alkaline and highly saline solution supersaturated with respect to calcite (control solution) will precipitate euhedral to subhedral rhombic and trigonal bladed calcite crystals. The same solution supersaturated with respect to stevensite precipitates sheet-like stevensite crystals rather than a gel, and calcite precipitation is reduced by ~ 50% compared to the control solution, producing a mixture of patchy prismatic subhedral to euhedral, and minor needle-like, calcite crystals. Enhanced magnesium concentration in solution is the likely the cause of decreased volumes of calcite precipitation, as this raised equilibrium ion activity ratio in the solution. On the other hand, when alginic acid was present then the result was widespread development of micron-size calcium carbonate spherulite bodies. With further growth time, but falling supersaturation, these spherules fused into botryoidal-topped crusts made of micron-size fibro-radial calcite crystals. We conclude that the simplest tested mechanism to deposit significant spherical-radial calcite bodies is to begin with a strongly supersaturated solution that contains specific but environmentally-common organic acids. Furthermore, we found that this morphology is not a universal consequence of having organic acids dissolved in the solution, but rather spherulite development requires specific binding behaviour. Finally, we found that the location of calcite precipitation was altered from the air:water interface to the surface of the glassware when organic acids were present, implying that attached calcite precipitates reflect precipitation via metal–organic intermediaries, rather than direct forcing via gas exchange. [ABSTRACT FROM AUTHOR]

The Mesoproterozoic (1.1 Ga) Borden Basin contains extremely large, deep-water dolostone seep mounds (Ikpiarjuk Formation) whose distribution is controlled by faults. Four mounds were investigated along measured stratigraphic sections. Petrographic study revealed several depositional components, and a mixture of at least two distinct carbonate sources. Stable isotope data showed no significant methane contribution to the carbonate phases. Detritus-corrected REE+Y patterns, obtained using solution ICP-MS, depict binary mixtures between basin-water-derived precipitates and seep-fluid-derived carbonate. The purest pelagic REE+Y signal is from mound tops, suggesting that mound accumulation ceased when the seep fluid waned. The REE+Y pattern of the pelagic precipitates resembles that of modern alkaline lake water. The shale-normalised pattern of the basin water is LREE-depleted, has a positive Ce anomaly and pronounced Y-excess, but lacks the La and Gd anomalies typical of seawater. The seep-fluid-related dolomite has flat shale-normalised REE+Y patterns, no Ce anomaly, and a negative Eu anomaly. This combination of characteristics points to circum-neutral (Ca and Mg-bearing?) fluids that interacted with the underlying basement before seeping into the lake bottom through faults. The chemostratigraphic patterns of the mounds result from the relative contribution of elements from the basin water vs. seep fluids. When combined with published geochemical data for coeval black shale surrounding the mounds, the new data suggest a lacustrine setting, surrounded by catchments with a preponderance of moderately to strongly weathered alkali basalt whose runoff drove the lake to alkalinity. Seep fluid was probably evaporatively concentrated basin water that acquired new geochemical characteristics both during evaporation and through water-rock interaction in the subsurface. The new understanding of this depositional stage of the Borden Basin highlights the importance of lacustrine deposits in the Mesoproterozoic, and presents an obvious impediment to using carbonate stable isotope or trace element geochemistry to reconstruct global atmosphere-hydrosphere conditions for this time for any units that cannot be demonstrated conclusively to be of marine origin. [ABSTRACT FROM AUTHOR]

The novel, cream coloured, Gram-negative-staining, rod-shaped, motile bacteria, designated strains AK23 T and AK28, were isolated from sediment samples collected from Lonar Lake, Buldhana district, India. The predominant fatty acids were C 18:1 ω7c , C 16:0 , C 10:0 3OH and C 16:1 ω7c and/or iso-C 15:0 2OH (summed feature 3). Polar lipid content of strains AK23 T and AK28 were found to be phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphotidylserine (PS), one unidentified phospholipid (PL) and two unidentified lipids (L1 and L2). The 16S rRNA gene sequence analysis indicated strains AK23 T and AK28 as the members of the genus Nitrincola and closely related to the type strain Nitrincola lacisaponensis with pair-wise sequence similarity of 97.67% and 97.62% respectively. DNA–DNA hybridization between strain AK23 T and AK28 showed a relatedness of 91%. Genome of strains AK23 T and N. lacisaponensis DSM 16316 T were sequenced. A comparative genomics approach was used to study strains AK23 T , N. lacisaponensis DSM 16316 T and five other phylogenetic neighbours. The genome size of N. lacisaponensis DSM 16316 T was found to be 614,784 bp smaller than that of the strain AK23 T . This variation could be due to multiple reasons, gene uptake, evolution, mutation, genome reduction phenomenon and draft nature of sequencing. Based on data from the current polyphasic study, strains AK23 T and AK28 are proposed as novel species of the genus Nitrincola , for which the name Nitrincola nitratireducens sp. nov. is proposed. The type strain of N. nitratireducens is AK23 T (= JCM 18788 T = MTCC 11628 T ). [ABSTRACT FROM AUTHOR]

A striking feature of the Mongolian plateau is the wide range of air temperatures during a year, -30 to 30°C. High summer temperatures, atmospheric weathering and the arid climate lead to formation of numerous alkaline soda lakes that are covered by ice during 6-7 months per year. During the study period, the lakes had pH values between 8.1 to 10.4 and salinity between 1.8 and 360 g/L. According to chemical composition, the lakes belong to sodium carbonate, sodium chloride-carbonate and sodium sulfate-carbonate types. This paper presents the data on the water chemical composition, results of the determination of the rates of microbial processes in microbial mats and sediments in the lakes studied, and the results of a Principal Component Analysis of environmental variables and microbial activity data. Temperature was the most important factor that influenced both chemical composition and microbial activity. pH and salinity are also important factors for the microbial processes. Dark CO fixation is impacted mostly by salinity and the chemical composition of the lake water. Total photosynthesis and sulfate-reduction are impacted mostly by pH. Photosynthesis is the dominant process of primary production, but the highest rate (386 mg C/(L∙d)) determined in the lakes studied were 2-3 times lower than in microbial mats of lakes located in tropical zones. This can be explained by the relatively short warm period that lasts only 3-4 months per year. The highest measured rate of dark CO assimilation (59.8 mg C/(L∙d)) was much lower than photosynthesis. The highest rate of sulfate reduction was 60 mg S/(L∙d), while that of methanogenesis was 75.6 μL СН/(L∙d) in the alkaline lakes of Mongolian plateau. The rate of organic matter consumption during sulfate reduction was 3-4 orders of magnitude higher than that associated with methanogenesis. [ABSTRACT FROM AUTHOR]

Microbially induced sedimentary structures (MISS) were studied in detail in the alkaline hypersaline El Beida Lake of Wadi El Natrun in the western desert sector of Egypt, based on field observations and sampling performed in 2013 and 2014. Geomorphologically, the lake can be subdivided into three zones, each with characteristic sedimentary and biosedimentary structures. The marginal elevated zone that borders the lake is characterized by thick blocky crusts devoid of microbial mats. The middle-lower supratidal zone has luxuriant microbial mats associated with knotty surfaces, mat cracks and wrinkle structures. A zone of ephemeral shallow pools and channels is characterized by reticulate surfaces, pinnacle mats, sieve-like surfaces, gas domes and mat chips. In the microbial mats, authigenic minerals include thenardite NaSO, trona Na(CO)(HCO)•2HO and halite NaCl. Scanning electron microscopy (SEM) analyses revealed that the minerals are closely associated with the MISS, suggesting some influence of microorganisms on mineral precipitation. Complex interactions between regional hydrological cycles and diagenetic processes imply low preservation potential. MISS signatures of such saline lakes can serve as key analogues for interpreting the geologic record. [ABSTRACT FROM AUTHOR]

The inland Lonar Lake, encompassing a circular area of about 1 sq. km is situated in Buldhana district, Maharashtra state, India. The lake is part of the Lonar crater believed to have formed due to meteoric impact. It is third largest natural salt-water lake in the world. The lake water is not only saline, but also highly alkaline. In recent years, it is believed that the alkalinity and salinity of the lake water is being diluted with increased lake water level due to external inputs like seepage of water into the lake from nearby surface reservoirs. Studies on hydrochemical and isotopic signatures of lake water, and also lake water levels were carried out for one year to understand the lake dynamics. The generated data were compared with those available in the literature. This comparison showed that the water level and hydrochemistry of lake water are controlled by the local rainfall and evaporation, and that there are no other external water inputs to the lake. [ABSTRACT FROM AUTHOR]

Adsorption properties of Cu, Ni, and Zn in alkaline sediments of Lake Fehér at Szeged (Hungary) were investigated. The effects of pollution of these three chosen phytotoxic elements in sodic sediments were primarily examined. These elements are strongly adsorbed in the soils and sediments with relatively high pH values for a long time without any influence on the geochemical processes. However, the salinization (indicated by the global climate change) of soils and sediments can strongly change the original geochemical status. For the adsorption experiments, the horizons with the highest organic matter contents were selected from two profiles. The pH, electrical conductivity (EC), particle size distribution, carbonate content, quality and quantity of organic matter, and clay mineral content of the selected samples were also determined. Efficiency of the adsorption is reduced in Cu >> Zn > Ni and Cu > Ni >> Zn order based on the calculated maximum and specific adsorption values. The adsorption properties of heavy metals are dependent on the content of soil constituents. The results showed that Cu has the highest but not the same affinity to each of the sorbent materials. Ni is strongly while Zn is less bounded to the organic matter. In most cases the results showed that the most effective fixative soil constituent is carbonate, followed by clay minerals and, last, organic matter regarding to the investigated elements. [ABSTRACT FROM AUTHOR]

We examined the distribution of submerged and emergent macrophyte species and the entire macrophyte community within and between five lake types (highland reservoirs, alkali lakes, large shallow lakes, small to medium sized shallow lakes, marshes) in the Pannon Ecoregion, Hungary. The lowest submerged, emergent and total species richness was found in alkali lakes. The highest submerged macrophyte richness was in small to medium sized lakes, while the highest emergent macrophyte species richness was in reservoirs, small to medium sized lakes, and marshes. The values of within-lake type beta diversity were generally lower than the values of alpha diversity, especially for submerged macrophytes, indicating between site homogeneity in species composition within the lake types. Emergent macrophyte communities contributed the most to within and between lake type diversity and total (gamma) diversity. Canonical correspondence analyses showed that the main environmental variables which influenced the distribution of submerged macrophytes were conductivity, Secchi transparency and water nitrogen contents. For emergent macrophytes conductivity, lake width, altitude and water depth proved to be the most influential variables. Our results contribute to the knowledge of large-scale distribution of macrophytes in the Pannon Ecoregion and to the identification of conservation value of lakes using macrophytes. The results support the importance of small lakes and artificial lakes in the conservation of macrophyte diversity compared to large and natural lakes in the Pannon Ecoregion. [ABSTRACT FROM AUTHOR]

Cletocamptus gomezi Suárez-Morales, Barrera-Moreno & Ciros-Pérez (2013) is a recently described new species of meiobenthic Harpacticoida copepod, micro-endemic to Lake Alchichica, Puebla, Central Mexico. Cletocamptus gomezi lives in saline water (K25=12.6 mS cm--1) dominated by sodium, magnesium, chloride, and bicarbonate ions and markedly alkaline (pH 9.0±0.1). Cletocamptus gomezi occurs in a depth range of surface to 10 m with preference to shallow (<3 m), well oxygenated (above saturation) and warm (>20°C) waters; fine sandy sediments (2.3 ϕ), rich in organic matter (8.4%) and carbonate concentrations (29%), and abundant aquatic vegetation coverage. In the littoral zone the average density and biomass of Cletocamptus gomezi reaches 4106±10,962 ind m-2 and 3.66±9.75 mg C m-2. Below 3 m, along the lake's slope, the density reduces dramatically down to 265±593 ind m-2 and 0.23±0.51 mg C m-2 at 10 m. Cletocamptus gomezi is absent below 10 m down to 62 m, the maximum depth of the lake. Spatially, except L3 (whose density and biomass values are the lowest) that differs (P<0.05) from L4 (whose density and biomass values are the highest), the littoral sampling stations are statistically similar in density and biomass (P>0.5). Temporally, there are no statistical differences (P>0.5) in density or biomass. The fact of finding Cletocamptus gomezi far away from the coast line (>100 km) and at high altitude (2335 m asl) is uncommon since most reports of Cletocamptus are from coastal brackish waters, and consequently, at sea level. Migrating waterbirds, as dispersal agents could be the explanation of Cletocamptus gomezi successfully inhabiting Lake Alchichica. Cletocamptus gomezi shares the same habitat with dense populations of tubificid oligochaetes, amphipods, leeches, chironomids, and nematodes. The disappearance of Cletocamptus gomezi habitat by the lake's -natural and mostly anthropogenic- desiccation process, seriously threatens the survival of this and the other numerous micro-endemic species of Lake Alchichica. [ABSTRACT FROM AUTHOR]

Species of the genus Halomonas are halophilic and their flexible adaption to changes of salinity and temperature brings considerable potential biotechnology applications, such as degradation of organic pollutants and enzyme production. The type strain Halomonas lutea YIM 91125T was isolated from a hypersaline lake in China. The genome of strain YIM 91125T becomes the twelfth species sequenced in Halomonas, and the thirteenth species sequenced in Halomonadaceae. We described the features of H. lutea YIM 91125T, together with the high quality draft genome sequence and annotation of its type strain. The 4,533,090 bp long genome of strain YIM 91125T with its 4,284 protein-coding and 84 RNA genes is a part of Genomic Encyclopedia of Type Strains, Phase I: the one thousand microbial genomes (KMG-I) project. From the viewpoint of comparative genomics, H. lutea has a larger genome size and more specific genes, which indicated acquisition of function bringing better adaption to its environment. DDH analysis demonstrated that H. lutea is a distinctive species, and halophilic features and nitrogen metabolism related genes were discovered in its genome. [ABSTRACT FROM AUTHOR]

Haloalkaliphiles are double extremophilic organisms thriving both at high salinity and alkaline pH. Although numerous haloalkaliphilic representatives have been identified among Archaea and Bacteria over the past 15 years, the adaptations underlying their prosperity at haloalkaline conditions are scarcely known. A multi-level adaptive strategy was proposed to occur in haloalkaliphilic organisms isolated from saline alkaline and soda environments including adjustments in the cell wall structure, plasma membrane lipid composition, membrane transport systems, bioenergetics, and osmoregulation. Isolation of chemolithoautotrophic sulfur-oxidizing γ-Proteobacteria from soda lakes allowed the elucidation of the structural and physiological differences between haloalkaliphilic (prefer NaCl) and natronophilic (prefer NaHCO 3 /Na 2 CO 3 , i.e. soda) microbes. [ABSTRACT FROM AUTHOR]

Soda lakes represent unique permanently haloalkaline system. Despite the harsh conditions, they are inhabited by abundant, mostly prokaryotic, microbial communities. This review summarizes results of studies of main functional groups of the soda lake prokaryotes responsible for carbon, nitrogen and sulfur cycling, including oxygenic and anoxygenic phototrophs, aerobic chemolithotrophs, fermenting and respiring anaerobes. The main conclusion from this work is that the soda lakes are very different from other high-salt systems in respect to microbial richness and activity. The reason for this difference is determined by the major physico-chemical features of two dominant salts — NaCl in neutral saline systems and sodium carbonates in soda lakes, that are influencing the amount of energy required for osmotic adaptation. [ABSTRACT FROM AUTHOR]

The aim of this study was to isolate the alkaliphilic and salt tolerant, protease inhibitor (PI) producing actinomycetes The screening of water-soil sediment sample collected from Soda lake (Lonar, Dist. Buldhana) resulted into isolation of 80 actinomycetes on starch casein agar and glycerol aspargine agar (pH 9.4, 1M salinity). Ten strains were separated as their cell free extracts showed PI activity in skimmed milk agar. From these potential 10 actinomycetes, five strains designated as VL18, VL24, VL50, VL61 and VLJ2 showing 50 to 100 % inhibition of standard trypsin, on the basis of zone of inhibition of hydrolysis on skimmed milk agar were shortlisted. The secondary screening revealed that all the five isolates VL J2, VL 18, VL 24, VL 50 and VL 61 produce the extracellular protease inhibitor in the range of 26.90 to 30.72 Units. All five strains were able to grow and secrete protease inhibitor at 0.2 to 5% (w/v) NaCl but the maximum PI production was observed at 0.2 % NaCl (w/v). Growth and PI production were optimum at pH 9.5 with gradual decline at neutral pH. The results are valuable, as only few actinomycetes, particularly salt tolerant alkaliphilic ones, have so far been explored for protease inhibitor activity. [ABSTRACT FROM AUTHOR]

Plankton fractions from a saline lake in Argentina were studied using a combined trophic marker approach. A strong seasonality of biomarkers was characteristic for the different fractions, particularly the variations in the 18:4(n - 3) and 20:4(n - 3) fatty acids and the δ13C values. The primary production in the lake was mainly driven by diatoms, reflected by the close relation of δ13C, chlorophyll a and diatom fatty acid markers. The combined approach of δ13C and 20:4(n - 3) enabled processes in the lipid metabolism of the copepod Boeckella poopoensis to be inferred. The polyunsaturated fatty acid 22:6(n - 3) and the δ15N separated the trophic levels in this food web with copepods at higher trophic level. Nutritional stress and omnivory of B. poopoensis partially explained the δ15N variations in mesozooplankton. The δ15N signature was probably driven by cyanobacteria in the microplankton and by microbial processes in the nanoplankton fraction. Warmer temperatures may favour the saturation of microalgae fatty acids and the abundance of plankton groups richer in saturated fatty acids. The tendency to unsaturation in mesozooplankton at colder temperatures was probably influenced by diet and metabolic requirements. Future temperature increase and eutrophication-like processes may increase the importance of cyanobacterial and bacterial markers under climate change scenarios. [ABSTRACT FROM AUTHOR]

Carbon (C) and nitrogen (N) stable isotope analysis (SIA) has been used to identify the terrestrial subsidy of freshwater food webs. However, SIA fails to differentiate between the contributions of old and recently fixed terrestrial C and consequently cannot fully determine the source, age, and biochemical quality of terrestrial carbon. Natural abundance radiocarbon (Δ14C) was used to examine the age and origin of carbon in Lower Lough Erne, Northern Ireland. 14C and stable isotope values were obtained from invertebrate, algae, and fish samples, and the results indicate that terrestrial organic C is evident at all trophic levels. High winter δ15N values in calanoid Zooplankton (δ15N = 24%o) relative to phytoplankton and particulate organic matter δ15N = 6%o and 12%o, respectively) may reflect several microbial trophic levels between terrestrial C and calanoid invertebrates. Winter and summer calanoid Δ14C values show a seasonal switch between autochthonous and terrestrial carbon sources. Fish Δ14C values indicate terrestrial support at the highest trophic levels in littoral and pelagic food webs. 14C therefore is useful in attributing the source of carbon in freshwater in addition to tracing the pathway of terrestrial carbon through the food web. [ABSTRACT FROM AUTHOR]

This article presents a case study of Lower Lough Erne, a humic, alkaline lake in northwest Ireland, and uses the radiocarbon method to determine the source and age of carbon to establish whether terrestrial carbon is utilized by heterotrophic organisms or buried in sediment. Stepped combustion was used to estimate the degree of the burial of terrestrial carbon in surface sediment. Δ14C, δ13C, and δ15N values were measured for phytoplankton, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and particulate organic carbon (POC). Δ14C values were used to indicate the presence of different sources of carbon, including bedrock-derived inorganic carbon, "modern," "recent," "subsurface," and "subfossil" terrestrial carbon in the lake. The use of 14C in conjunction with novel methods (e.g. stepped combustion) allows the determination of the pathway of terrestrial carbon in the system, which has implications for regional and global carbon cycling. [ABSTRACT FROM AUTHOR]

Nitrogen isotope ratios in ancient sedimentary rocks are generally interpreted as a proxy for metabolic nitrogen pathways and the redox state of the water column. Fractionation processes occurring under anoxic, alkaline conditions during the dissociation of NH 4 + to H + and volatile NH 3 are frequently overlooked, although this mechanism imparts large isotopic fractionations. Here we propose that NH 3 volatilization is largely responsible for δ 15 N values of up to + 50 ‰ at high C/N ratios in the late Archean Tumbiana Formation. This sequence of sedimentary rocks represents a system of lakes that formed on subaerial flood basalts and were partly filled by basaltic volcanic ash. Aqueous alteration of volcanic glass followed by evaporative concentration of ions should have led to the development of high alkalinity with a pH of 9 or higher, as in modern analogues. In this sedimentologically unusual setting, nitrogen isotope ratios thus provide indirect evidence for the oldest alkaline lake system in the rock record. These very heavy lacustrine δ 15 N values contrast markedly with those of Archean marine sedimentary rocks, making a Precambrian “soda ocean” unlikely. Today, alkaline lakes are among the most productive ecosystems on Earth. Some nutrients, in particular molybdenum, are more soluble at high pH, and certain prebiotic reactions would likely have been favored under alkaline conditions in similar settings earlier in Earth's history. Hence alkaline lakes in the Archean could have been significant for the origin and early evolution of life. [ABSTRACT FROM AUTHOR]

To test the paradigm that large-bodied zooplankton species dominate in fishless lakes, we evaluated crustacean zooplankton composition of 53 fishless boreal lakes across a broad geographic scale (north-west Saskatchewan, Canada) in relation to contemporary environmental factors. Lake productivity, acid–base status and intensity of invertebrate predation were the three major environmental filters of crustacean zooplankton composition of the survey lakes, while lake morphometry and drainage basin characteristics likely had indirect effects by influencing the variations in above environmental factors. The traditionally expected dominance of large-bodied zooplankton species in fishless conditions only occurred in well-buffered shallow lakes with higher productivity and intense invertebrate predation. Daphnia pulex was dominant in more eutrophic lakes, while higher abundances of Holopedium gibberum were favored by relatively mesotrophic conditions. In exception to the traditional view, small-bodied species dominated in 57% of survey lakes as influenced by interactions of biotic and abiotic factors. Bosmina longirostris and cyclopoid copepods dominated less productive, deeper lakes with low invertebrate predation. Predominance of Leptodiaptomus minutus was supported under unfavorable environmental conditions for other species, i.e. poor buffering capacity and/or low calcium concentration. The present study demonstrates that exceptions to the generally expected species composition in fishless lakes can be caused by interactions among abiotic and biotic factors. [ABSTRACT FROM PUBLISHER]

The phylogenetic diversity of picocyanobacteria in seven alkaline lakes on the Tibetan Plateau was analyzed using the molecular marker 16S-23S rRNA internal transcribed spacer sequence. A total of 1,077 environmental sequences retrieved from the seven lakes were grouped into seven picocyanobacterial clusters, with two clusters newly described here. Each of the lakes was dominated by only one or two clusters, while different lakes could have disparate communities, suggesting low alpha diversity but high beta diversity of picocyanobacteria in these high-altitude freshwater and saline lakes. Several globally distributed clusters were found in these Tibetan lakes, such as subalpine cluster I and the Cyanobium gracile cluster. Although other clusters likely exhibit geographic restriction to the plateau temporally, reflecting endemicity, they can indeed be distributed widely on the plateau. Lakes with similar salinities may have similar genetic populations despite a large geographic distance. Canonical correspondence analysis identified salinity as the only environmental factor that may in part explain the diversity variations among lakes. Mantel tests suggested that the community similarities among lakes are independent of geographic distance. A portion of the picocyanobacterial clusters appear to be restricted to a narrow salinity range, while others are likely adapted to a broad range. A seasonal survey of Lake Namucuo across 3 years did not show season-related variations in diversity, and depth-related population partitioning was observed along a vertical profile of the lake. Our study emphasizes the high dispersive potential of picocyanobacteria and suggests that the regional distribution may result from adaptation to specified environments. [ABSTRACT FROM AUTHOR]

Soda lakes contain high concentrations of sodium carbonates resulting in a stable elevated pH, which provide a unique habitat to a rich diversity of haloalkaliphilic bacteria and archaea. Both cultivation-dependent and -independent methods have aided the identification of key processes and genes in the microbially mediated carbon, nitrogen, and sulfur biogeochemical cycles in soda lakes. In order to survive in this extreme environment, haloalkaliphiles have developed various bioenergetic and structural adaptations to maintain pH homeostasis and intracellular osmotic pressure. The cultivation of a handful of strains has led to the isolation of a number of extremozymes, which allow the cell to perform enzymatic reactions at these extreme conditions. These enzymes potentially contribute to biotechnological applications. In addition, microbial species active in the sulfur cycle can be used for sulfur remediation purposes. Future research should combine both innovative culture methods and state-of-the-art 'meta-omic' techniques to gain a comprehensive understanding of the microbes that flourish in these extreme environments and the processes they mediate. Coupling the biogeochemical C, N, and S cycles and identifying where each process takes place on a spatial and temporal scale could unravel the interspecies relationships and thereby reveal more about the ecosystem dynamics of these enigmatic extreme environments. [ABSTRACT FROM AUTHOR]

Saline-alkaline lakes are extreme environments that limit the establishment and development of life. The Nhecolândia, a subregion of the Pantanal wetland in Brazil, is characterized by the existence of ~500 saline-alkaline lakes, which support an underexplored and rich diversity of microorganisms. In this study, unicellular and homocytous cyanobacteria from five saline-alkaline lakes were accessed by culture-dependent approaches. Morphological evaluation and analyses of near complete sequences (~1400 nt) of the 16S r RNA genes were applied for phylogenetic and taxonomic placement. This polyphasic approach allowed for the determination of the taxonomic position of the isolated strains into the following genera: Cyanobacterium, Geminocystis, Phormidium, Leptolyngbya, Limnothrix, and Nodosilinea. In addition, fourteen Pseudanabaenales and Oscillatoriales representatives of putative novel taxa were found. These sequences fell into five new clades that could correspond to new generic units of the Pseudanabaenaceae and Phormidiaceae families. [ABSTRACT FROM AUTHOR]

The work presents the morphology of cells and trichomes of Glaucospira laxissima (G.S. West) comb, nova analyzed by light microscopy, confocal laser microscopy (CLM) and transmission electron microscopy (TEM). Cyanobacterial characteristics are confirmed for the first time. It also contains the data on the ecology of this species, found for the first time in Serbia, in a small alkaline lake in a planktic community with the species Cylindrospermopsis raciborskii (Wołoszyńska) Seenayya & Subba Raju, Anabaenopsis elenkinii V.V. Miller and Chrysosporum bergii ( Ostenfeld) Zapomělová et al. [ABSTRACT FROM AUTHOR]

This study aimed to explain the seasonal and vertical distribution of phytoplankton in the pelagic zone of a deep alkaline lake that is characterized by low phytoplankton abundance. Phytoplankton and water samples were collected seasonally from 9 points and 7 depths between the surface and 20 m from December 2004 to September 2005. Planktolyngbya contorta was the dominant or subdominant species in all seasons and depths. The dominance of Gomphonema species was observed in December, but they were subdominant in September. Cyclotella meneghiniana was dominant at 20 m and subdominant in the upper depths during March, June, and September. Melosira sp. and Meridion circulare were the dominant taxa of the surface phytoplankton in March and June, respectively. A nonparametric test showed the prevalence of cyanobacteria and green algae at a depth of 10 m. Principal component analysis showed the effect of temperature, pH, dissolved solids, nitrate, and silica on the abundance and distribution of phytoplankton. The generalized linear model revealed that high pH and high dissolved solids content seemed to affect the abundance of phytoplankton via limiting nutrient availability. [ABSTRACT FROM AUTHOR]

The pelagic phytoflagellate Phacotus lenticularis creates a shell of highly symmetrical calcite crystals at its outer extracellular layer and thereby constitutes a significant source of calcite in temperate alkaline lakes worldwide. Responses of P. lenticularis to a changing lake environment therefore have potential implications for the calcium carbonate flux in lakes. How meteorological variability in interaction with the CaCO3 saturation state may influence the abundance and phenology of P. lenticularis has not been investigated so far. We measured, biweekly to daily, algal abundance, CaCO3 saturation, pH, water temperature and nutrient status in three hard-water lakes that varied in lake morphology and wind exposure. Our data provide evidence that increasing supersaturation of CaCO3 mediates the onset of P. lenticularis exponential growth and stimulates seasonal peak development. However, total cell concentration in the lake water appears to be independent of the CaCO3 saturation state and was the highest in the most wind exposed lake. Phacotus lenticularis abundance and epilimnetic CaCO3 supersaturation were significantly positively correlated at a time lag of about 1 day. Wind caused an immediate decline in epilimnetic pH followed by a decline in CaCO3 saturation about 2 days later. Solar irradiance positively affected both pH and water temperature, but water temperature changes were insufficient to produce a significant CaCO3 saturation response. We conclude that the CaCO3 saturation state is a determinant factor driving the timing of P. lenticularis peaks in alkaline lakes. [ABSTRACT FROM AUTHOR]

Abstract: The many lakes present among the inactive dunes of the Nebraska Sand Hills are unique ecosystems that formed under particular conditions of local and regional geomorphology, hydrology and climate. They offer an exceptional opportunity to study the inter-relations between hydrology, microbial diversity, and biogeochemistry in comparatively closely-spaced bodies of water ranging in pH from neutral to alkaline. We analyzed for lipid biomarkers in the surficial sediments of six Sand Hills lakes, including alkanes, alkenes, alkanols, phytol, sterols, hopanoids, tetrahymanol, and phospholipid fatty acids. Overall, these biomarkers exist in significantly lower concentrations in the alkaline lakes of the Sand Hills than in ordinary neutral lakes. More specifically, microbial functional groups can be identified in the lake sediments on the basis of the biomarkers for which we analyzed. The presence of eukaryotic phototrophs is indicated by the detection of phytadienes, phytol, phytanol, diatomsterol, dinosterol, and polyunsaturated fatty acids. The detection of short-chain wax esters suggests the presence of anoxygenic autotrophic sulfur bacteria (purple and green sulfur bacteria). The phospholipid fatty acid (PLFA) profiles indicate the presence of sulfate-reducing bacteria in the sediment. Tetrahymanol and polyunsaturated fatty acids in the sediments suggest the presence of bacterivorous ciliates and phototrophic sulfur bacteria, which probably live at the chemocline. Our results reveal that there are unique and integrated ecosystems within the Sand Hills lakes that are defined by the close interactions between regional hydrology, geochemistry, and microbiology. [Copyright &y& Elsevier]

Spirochaeta africana Zhilina et al. 1996 is an anaerobic, aerotolerant, spiral-shaped bacterium that is motile via periplasmic flagella. The type strain of the species, Z-7692, was isolated in 1993 or earlier from a bacterial bloom in the brine under the trona layer in a shallow lagoon of the alkaline equatorial Lake Magadi in Kenya. Here we describe the features of this organism, together with the complete genome sequence, and annotation. Considering the pending reclassification of S. caldaria to the genus Treponema, S. africana is only the second 'true' member of the genus Spirochaeta with a genome-sequenced type strain to be published. The 3,285,855 bp long genome of strain Z-7692 with its 2,817 protein-coding and 57 RNA genes is a part of the G enomic E ncyclopedia of B acteria and A rchaea project. [ABSTRACT FROM AUTHOR]

Abstract: Moderately haloalkaliphilic Halomonas campisallis MCM B-1027 isolated from the alkaline lake of Lonar, India was found to produce a biodegradable polymer, polyhydroxyalkanoate (PHA). Scale up production of PHA from H. campisalis MCM B-1027 was carried out in 120L stainless steel (SS) fermenter using 85L production medium with a yield of 51.56% PHA on dry cell weight basis. The recovery of PHA was studied by several methods such as solvent extraction of the polymer, chemical digestion of the non-PHA biomass and mechanical disruption of the cells. Highest rate of PHA recovery obtained was 63mg/h with solvent extraction using rotary film evaporator. Further optimization of extraction of PHA from dry cells in chloroform using 10L rotavapor was carried out. L9 orthogonal array was chosen to study the influence of time, rotation and temperature at three levels along with their interactive effects on extraction process. Maximum PHA recovery of 84.47% was obtained at 25rpm, 60°C, within 3h. Time factor had highest 84.11% contribution in the extraction process. This study is the first report on model for batch extraction of PHA and its validation based on second-order mechanism developed to predict the saturation capacity of the solvent, initial rate of extraction at different temperatures and activation energy of the process. [Copyright &y& Elsevier]

Abstract: Early to Mid-Miocene extension in western Anatolia, related to plate tectonic motions, resulted in the development of a number of normal fault-bounded sedimentary basins as well as different styles and compositions of volcanic activity. The Uşak and Güre basins accumulated a thick fluvio-lacustrine fill in which three distinct volcanic edifices (Elmadağ, İtecektepe and Beydağı) and their deposits can overlap with each other and with the sediments produced by the background sedimentation. In addition, complete facies architectures of small-volume (monogenetic) volcanoes have been recognised in association with the three large complex (polygenetic) volcanoes providing a complex mixed siliciclastic and volcaniclastic basin infill in the respective basins where volcanism took place. All three volcanic centres display a complex succession of effusive and explosive volcanisms and their reworked deposits, with abundant evidences of magma–water interaction such as peperites for non-explosive magma-water interaction with the lacustrine water-saturated sediment and standing water body in a large alkaline lake. During the constructive phase, proximal successions of pyroclastic flows, pyroclastic falls, and rarely surge deposits are associated with distally-emplaced debris flow deposits, sometimes of mixed volcanogenic and terrestrial origins, and are interbedded with lacustrine sediments of the Inay Group. All three volcanic centres then experienced a phase of volcano growth and degradation between 17 and 15Ma ago, most likely related to a combination of tectonic movements on NE–SW-trending basement faults, which triggered multiple flank collapses and volcanic debris avalanches (Elmadağ), and voluminous ignimbrite eruptions that triggered caldera formation (İtecektepe and Beydağı volcanic centres). Lacustrine conditions persisted during the destruction and post-destruction stages of the volcano''s evolution, as evidenced by indications of magma–water interactions within the central collapse structures, which also contain uplifted basement metamorphic rocks now exhumed in their eroded cores. [Copyright &y& Elsevier]

The facies architecture in hot spring systems tends to become more varied and complicated as the degrees of freedom in the system increase. Discharge aprons fed by waters from a single vent will, for example, be characterized by predictable downslope facies changes that reflect downslope changes in water chemistry and temperature. The facies architecture, however, becomes exponentially more intricate when more factors start to impact the system. This phenomenon is readily apparent in the geothermal area around Lake Roto-a-Tamaheke (located in the Whakarewarewa Thermal Village, Rotorua, New Zealand) where the facies architecture developed in response to the interactions between acid lake, acid hot spring, and alkaline hot spring depositional regimes, with additional extraneous sediment being brought into the area by volcanic ash clouds, wind-blown pollen, and surface run-off from the surrounding drainage basin. Much of the complexity in the facies architecture of this system stems from the temporal variance in the lake level and the variable life cycles of the acid and alkaline hot springs. Fluctuations in lake level controlled the extent of lacustrine deposits, and flooding commonly quenched spring activity. During some periods various minerals precipitated around the acidic springs, whereas during other periods silica precipitated around the hot alkaline springs that are preferentially located along faults that transect the area. The interaction of all of these variables produces depositional regimes with largely unpredictable and highly variable facies architectures. As such, they contrast sharply with the more organized spring systems that develop when one type of water flows from a single vent. [ABSTRACT FROM AUTHOR]