Saline-alkaline Lake Research Articles

Opaline silica precipitations in the Permian Fengcheng Formation indicate hot spring environments in north Mahu Sag, NW China

The Permian Fengcheng Formation represents a series of deposits formed in an alkaline saline lake, characterized by high proportions of cherts, located in the Northwestern Junggar Basin in China. While discussions on silica-rich hot springs as sources of silica for brine and subsequent chert deposition have been extensively conducted for Quaternary and Mesozoic-Cenozoic alkaline saline lakes worldwide, investigations into Paleozoic alkaline saline lakes are scarce due to challenges associated with identifying evidences of hot spring environments. In this study, we present detailed SEM-EDS analyses and examine silica isotope compositions as well as oxygen isotope compositions to discuss hydrothermal-associated silica precipitation processes. Our findings suggest that migrating silica-rich hot springs along deep-rooted faults released silica into the brine, leading to chert deposition during cooling periods and induction of thermophilic microorganism degradation. Microorganism-associated siliceous precipitates primarily consist of opal-A spheres adhered by extracellular polymeric substances (EPS), while numerous microorganism spheres have undergone silicification. Opal-A spheres within these structures were partially transformed into well-crystallized quartz through multiple stages of dissolution-precipitation processes during prolonged burial history. Furthermore, our results indicate that deep-rooted fault-related hot springs can occur both in marginal and subaqueous areas within alkaline saline lakes, with chert formations observed in shallow-marginal saline lake settings as well as deeper regions. The findings of this study provide valuable insights into the paleoenvironmental conditions, which can be further explored in investigating the accumulation of organic matter in chert-rich successions formed within an alkaline saline lake.

Distribution characterization of MPs and DOM in ice-covered season in a saline-alkaline Lake in Daihai with an innovative analysis using 2DCOS and structural equation modelling

Due to the characteristics of low density, light weight, and strong hydrophobicity, microplastics (MPs) can adsorb dissolved organic matter (DOM) in lake water to jointly accomplish migration and transformation in the ice/water medium, which causes serious pollution to the lake during the ice period through accumulation. In this study, the distribution of Daihai Lake MPs and DOM was studied by fluorescence excited emission matrix (EEM) and micro-infrared spectroscopy, and the relationship between them was examined by two-dimensional correlation spectroscopy (2DCOS) and structural equation modelling (SEM) to obtain the influencing factors of pollution. The results indicate that the concentration of MPs in the surface ice layer is 1.35 times more than in the water and in the surface and bottom ice layers 1–2 times more than the middle layer. DOM in the ice cover is mainly protein-like (73.33%), and humus-like DOM (44.8%) is dominant in the water under the ice that is consistent with the distribution of MPs in the ice and water layer. As a result, MPs are more prospective to adsorb humus-like substances into the ice during migration. Through SEM analysis, it was concluded that human activities and the degree of economic development seriously affect the pollution level and the type of MPs and DOM in lakes. One of the most important factors in winter is the ice cover, and there is a strong correlation between the MPs and DOM in different ice layers. Combined with experimental data, it was concluded that the ice layer influences the distribution characteristics of the pollutants in lakes as well as the direction of migration. However, the adsorption mechanism of the ice is not clear, which will be a key direction for future research on microplastics in ice-covered lakes.

Diversity of Freshwater Calanoid Copepods (Crustacea: Copepoda: Calanoida) in North-Eastern China

The distribution and diversity of calanoid copepods were investigated using samples collected from 37 lakes in North-eastern (NE) China in 2019. A total of 10 calanoid copepods belonging to eight genera and three families were identified. Among them, Heterocope soldatovi Rylov, 1922 was recorded for the first time in China. Species from the family Centropagidae were more widespread than those from the families Temoridae and Diaptomidae. Sinocalanus doerrii (Brehm, 1909), previously not recorded in NE China, is now widespread alongside Boeckella triarticulata (Thomson G.M., 1883), and the latter species is also prevalent in that region. Canonical correspondence analysis (CCA) and redundancy analysis (RDA) revealed that calanoid copepods were significantly correlated with total phosphorus (TP), total nitrogen, conductivity, nitrate nitrogen, altitude, and dissolved organic carbon. TP was the most important environmental variable that impacted the distribution of calanoid copepods, including both fresh and saline–alkaline lakes. Integrating historical records, a total of 21 calanoid copepods were distributed in NE China, and we also gave comments on the ecology and distribution of these species.

Transcriptomic insights into the dominance of two phototrophs throughout the water column of a tropical hypersaline-alkaline crater lake (Dziani Dzaha, Mayotte).

Saline-alkaline lakes often shelter high biomasses despite challenging conditions, owing to the occurrence of highly adapted phototrophs. Dziani Dzaha (Mayotte) is one such lake characterized by the stable co-dominance of the cyanobacterium Limnospira platensis and the picoeukaryote Picocystis salinarum throughout its water column. Despite light penetrating only into the uppermost meter, the prevailing co-dominance of these species persists even in light- and oxygen-deprived zones. Here, a depth profile of phototrophs metatranscriptomes, annotated using genomic data from isolated strains, is employed to identify expression patterns of genes related to carbon processing pathways including photosynthesis, transporters and fermentation. The findings indicate a prominence of gene expression associated with photosynthesis, with a peak of expression around 1 m below the surface, although the light intensity is very low and only red and dark red wavelengths can reach it, given the very high turbidity linked to the high biomass of L. platensis. Experiments on strains confirmed that both species do grow under these wavelengths, at rates comparable to those obtained under white light. A decrease in the expression of photosynthesis-related genes was observed in L. platensis with increasing depth, whereas P. salinarum maintained a very high pool of psbA transcripts down to the deepest point as a possible adaptation against photodamage, in the absence and/or very low levels of expression of genes involved in protection. In the aphotic/anoxic zone, expression of genes involved in fermentation pathways suggests active metabolism of reserve or available dissolved carbon compounds. Overall, L. platensis seems to be adapted to the uppermost water layer, where it is probably maintained thanks to gas vesicles, as evidenced by high expression of the gvpA gene. In contrast, P. salinarum occurs at similar densities throughout the water column, with a peak in abundance and gene expression levels which suggests a better adaptation to lower light intensities. These slight differences may contribute to limited inter-specific competition, favoring stable co-dominance of these two phototrophs.

Fungal endophytes from saline-adapted shrubs induce salinity stress tolerance in tomato seedlings.

To meet the food and feed demands of the growing population, global food production needs to double by 2050. Climate change-induced challenges to food crops, especially soil salinization, remain a major threat to food production. We hypothesize that endophytic fungi isolated from salt-adapted host plants can confer salinity stress tolerance to salt-sensitive crops. Therefore, we isolated fungal endophytes from shrubs along the shores of saline alkaline Lake Magadi and evaluated their ability to induce salinity stress tolerance in tomato seeds and seedlings. Of 60 endophytic fungal isolates, 95% and 5% were from Ascomycetes and Basidiomycetes phyla, respectively. The highest number of isolates (48.3%) were from the roots. Amylase, protease and cellulase were produced by 25, 30 and 27 isolates, respectively; and 32 isolates solubilized phosphate. Only eight isolates grew at 1.5M NaCl. Four fungal endophytes (Cephalotrichum cylindricum, Fusarium equiseti, Fusarium falciforme and Aspergilus puniceus) were tested under greenhouse conditions for their ability to induce salinity tolerance in tomato seedlings. All four endophytes successfully colonized tomato seedlings and grew in 1.5M NaCl. The germination of endophyte-inoculated seeds was enhanced by 23%, whereas seedlings showed increased chlorophyll and biomass content and decreased hydrogen peroxide content under salinity stress, compared with controls. The results suggest that the the four isolates can potentially be used to mitigate salinity stress in tomato plants in salt-affected soils.

Review of secondary phases formed under natural alkaline conditions at low temperatures and implications for cement–bentonite interactions in radioactive waste repositories

Abstract The alteration of bentonite under alkaline conditions and the subsequent changes in properties such as permeability and self-sealing ability should be evaluated for the performance assessment of radioactive waste repositories. As the period of evaluation for alterations is extremely long, natural analog (NA) studies that can observe long-term phenomena similar to the system of radioactive waste repositories have significant advantages. However, locations that can be set up as NA study sites with significant similarity are limited and should be pursued by localizing analog systems. This literature review summarized studies reporting secondary phases formed at low temperatures (<100°C) under a broader range of natural sites which are chemically similar to the alkaline conditions expected at bentonite in radioactive waste repositories, including near pyrometamorphic rocks, near ophiolites, and in alkaline saline lakes. This review provides insights into the species, formation conditions, and stability of secondary phases that could be formed during cement–bentonite interactions and the timescale for mineralogical transitions from a metastable to a stable phase. The findings could be useful for selecting secondary phases to be considered in reactive transport modeling for predicting cement–bentonite interactions in radioactive waste repositories.

Soils surrounding saline-alkaline lakes of Nhecolândia, Pantanal, Brazil: Toposequences, mineralogy and chemistry

The Nhecolândia subregion of the Brazilian Pantanal, subject to a highly seasonal climate, hosts a diverse range of freshwater and saline-alkaline lakes. The latter can be green due to cyanobacterial bloom, black due to dissolved organic matter, or crystalline. Over the past two decades, numerous studies in the region have explored the connections between the lake type, the surrounding soils, and water table dynamics. However, these insights emerged from independent studies conducted at multiple sites, making their synthesis challenging and leaving questions about the differences between lake types. Our research focuses on a representative Nhecolândia site, aiming to comprehensively understand soil and lake genesis and dynamics. For each lake type, we conducted detailed toposequence soil studies, assessing particle size distribution, chemistry and mineralogy of the <2 mm fraction of identified horizons. A 49-month temporal study utilizing PlanetScope satellite data examined lake connections to the hydrographic network affected by seasonal flooding. Our findings confirmed the general organization and mineralogy of soils around saline-alkaline lakes. Notably, we identified variations in soil toposequences corresponding to different lake type. Two types of silcrete were observed: one acidic, found at the upper slopes, and the other alkaline, located at the lower slopes. We determined that, for endorheism and lake alkalinization, the presence of a ridge around a lake is insufficient. Instead, deep impermeable horizons in the lower portion of the toposequences are essential. Additionally, crystalline lakes differentiate from black and green ones due to less efficient hydraulic isolation. Our comprehensive dataset from a single site provides a valuable resource for guiding and developing more specific studies on these alkaline systems.

Effects of lakeshore landcover types and environmental factors on microplastic distribution in lakes on the Inner Mongolia Plateau, China

Microplastic pollution in freshwater environments has received increasing attention. However, limited research on the occurrence and distribution of microplastics in plateau lakes. This study investigated the microplastic characteristics and influencing factors in lakes with different land cover types on the Inner Mongolia Plateau. Results showed that microplastic abundance ranged from 0.5 to 12.6 items/L in water and 50–325 items/kg in sediments. Microplastics in water were predominantly polypropylene (50.5%), fragments (40.5%), and 50–200 µm (66.7%). High-density (27.9%), fibrous (69.3%), and large-sized microplastics (47.7%) were retained primarily in lake sediments. The highest microplastic abundance in water was found in cropland lakes and grassland lakes, while that in sediments was in descending order of desert lakes > cropland lakes > grassland lakes > forest-grassland lakes. Differences among lake types suggest that agriculture, tourism, and atmospheric transport may be critical microplastic sources. Microplastic distribution was positively correlated with farmland and artificial surface coverage, showing that land cover types related to human activities could exacerbate microplastic pollution in lakes. Redundancy analysis showed that ammonia nitrogen and pH were the key physicochemical factors affecting microplastic distribution in lakes, indicating the potential sources of microplastics in lakes and the uniqueness of microplastic occurrence characteristics in desert saline-alkaline lakes, respectively.

Silicified unicellular green microalga as a significant oil source in the Late Paleozoic alkaline lake-playa deposit, Junggar Basin, NW China

Siliceous mudstones and chert-shale couplets are primary source rocks for many large paleo-oil reservoirs over the world. It is well established that photosynthetic organisms can be exceptionally well preserved in silica precipitates, but the fate of the trapped organic matter (OM) during burial remains poorly studied. Here, dense unicellular microbial fossils have been recently discovered in the cherts of the Late Paleozoic alkaline saline lake deposit in NW Junggar Basin, NW China. We use petrographic observations and organic geochemical analysis to study the origin of unicellular microbes and how silicified organic matter generate and expel hydrocarbons. A 300-m-long oil shale core shows overall low levels of porosity, permeability and total organic carbon contents (generally <0.5 wt%), but very high extracts (on average 0.26 wt%), suggesting that the rich extracts were mostly indigenous and the original organic matter had a high hydrocarbon conversion. Analysis of biomarkers and silicified fossils both suggest that the bio-precursor for the organic matter is a special green alga. Reconstruction of silica diagenesis of cherts indicates that both the trapped lipids and hydrocarbons in silicified microbial cells and extracellular polymeric substances had been effectively expelled out during the transformations of Opal-A to microcrystalline quartz and during OM thermal maturation. Exceptional OM preservation and effective oil expelling ways render siliceous source rocks as excellent unconventional hydrocarbon reservoirs.

Comprehensive analyses of annexins in naked carp (Gymnocypris przewalskii) unveil their roles in saline-alkaline stress

Naked carp (Gymnocypris przewalskii) is a migratory fish endemic to the Qinghai Lake, the largest inland saline-alkaline lake in China. Based on our previous results of comparative transcriptome sequencing, we found that pathways related to regulation of actin cytoskeleton, plasma membrane damage, and inflammation-related signaling were significantly enriched during saline-alkaline stress, suggesting involvement of annexin (ANN) family proteins in stress adaption in naked carp. Herein, to explore the role of annexin family in naked carp under saline-alkaline stress, twenty GpANNs family members were identified at the genome-wide scale, and bioinformatics and expression analysis under saline-alkaline stress were performed. The predicted subcellular localization showed that most members of GpANNs were distributed in the cytoplasm, and the rest were localized in the cytoskeleton, nucleus, or mitochondria, respectively. GpANNs family proteins contained specific type II Ca2+-binding motifs, actin-binding motifs, GTP-binding motifs, etc. Phylogenetic tree analysis showed that the annexin homologues from naked carp, carp (Cyprinus carpio), zebrafish (Danio rerio), and chinese cavefish (Sinocyclocheilus rhinocerous) were divided into eight groups, i.e. ANN1 ∼ 6, ANN11 and ANN13. But homologues of ANN7 ∼ 10 groups were not found in these three fish species. Twenty-eight, nineteen and twenty-nine orthologous gene pairs were identified between naked carp and carp, zebrafish and chinese cavefish, respectively. Six paralogous gene pairs were identified in naked carp, all of which had a Ka/Ks ratio less than one, suggesting that the GpANNs family may have undergone purifying selection pressure during evolution. Expression of GpANN3 was significantly up-regulated in the kidney tissue under saline-alkaline stress, while GpANN2 was significantly down-regulated. Similar trends of protein expression were also observed by Western blot, suggesting involvement of GpANN3 and GpANN2 in stress response. Confocal microscopy revealed that GpANN2 was localized in both cytoplasm and nucleus, but GpANN3 was preferentially localized in the cytoplasm. Our study demonstrated the role of annexins in stress adaption, and provided the basic information required for further function analyses in naked carp.

Constraints on dolomite formation in a Late Palaeozoic saline alkaline lake deposit, Junggar Basin, north‐west China

ABSTRACTAlkaline lakes (pH &gt; 9) are among the few modern sedimentary environments that are hydrochemically favourable for low‐temperature dolomite formation. While Mg‐clays and Mg‐evaporites also form more easily in alkaline environments, few studies have focused on how the kinetically inhibited dolomite wins the competition for Mg2+. Here, a basin‐wide survey of the distribution, paragenesis and stable C, O and Mg isotopes of main Mg‐rich minerals in the Late Palaeozoic saline alkaline lake deposit of the north‐west Junggar Basin, north‐west China, is conducted to study the influence of the formation and diagenesis of eitelite, northupite and Mg‐clays on dolomite formation. Large, isolated dolomite crystals (20 to 70 μm in diameter), show positive δ13C values (ranging from +1 to +7‰) and a restricted distribution in the mudstones of the lake‐transitional zone. These crystals have been interpreted as organogenic dolomite driven by methanogenesis via fermentation of organic substrates. The δ18O values of dolomitic mudstones (from −7.4 to +3.4‰), calcitic mudstones (from −15.1 to −3.3‰) and bedded Na‐carbonate evaporites (from +0.08 to +3.7‰), together with their Mg isotopic compositions, suggest that dolomite was not enriched in the most concentrated environments or during stages with most Mg sources, but in the organic‐rich deposits containing few other authigenic Mg‐rich minerals. Dolomite is at a competitive disadvantage for Mg2+ ions compared to Mg‐evaporite and Mg‐clay minerals due to its slow crystallization rates and the deficiency of micritic calcium carbonate precursors. However, it can nucleate and progressively grow into large crystals (&gt;20 μm) if bacterial methanogenesis could effectively lower porewater pH (&lt;8.5) and induce the dissolution of generated eitelite, northupite or Mg‐clays. These findings suggest that high salinity and/or high alkalinity are not always favourable conditions for dolomite formation and highlight the active role of pH fluctuations in inducing low‐temperature dolomite formation.

Solubility of Amorphous Magnesium Carbonate at Low Temperatures: Implications for Carbonate Mineral Formation in Alkaline Lakes

Amorphous magnesium carbonate (AMC: MgCO3·nH2O) is a metastable phase with respect to crystalline magnesium carbonate. AMC has been suggested to be an important mineral, a major process of CO2 fixation in alkaline saline lakes. Understanding the role of AMC for carbon fixation in alkaline lakes requires knowledge of the solubility of AMC under the full range of relevant environmental conditions, but its solubility is poorly known for low water temperatures. In this study, the solubility of AMC at 7 °C was measured in laboratory experiments and compared with chemical analyses of water samples from Olgoy Lake, a natural alkaline saline lake in Mongolia. Laboratory measurements using both supersaturation and undersaturation methods provided very similar solubility products of AMC (log Ksp = −5.20 ± 0.02) at 7 °C, which was markedly higher than the solubility product at 25 °C (log Ksp = −5.59). The temperature dependence of the solubility of AMC is much greater than that of monohydrocalcite, another important authigenic calcium carbonate in alkaline lakes. Analyses of water from Olgoy Lake consistently showed a significant temperature dependency of ion activity products with respect to magnesium carbonate. The relatively high solubility of AMC at low temperatures implies that the formation of AMC requires relatively high concentrations of dissolved components in lakes. Our results suggest that the formation of AMC is favored more in summer than in winter.

Lithofacies classification and itssignificance on oil and gas exploration of the Permain Fengcheng mixed shale in the Hashan area, northwestern Junggar Basin, China

The Fengcheng Formation in the Hashan area of the northwestern Junggar Basin is a complex fine-grained sedimentary rock deposited in a saline-alkaline lake basin and influenced by mechanical, volcanic, chemical, and biological processes. The Fengcheng Formation, influenced by synsedimentary volcanism, has a complex mineral composition, abundant organic matter, and frequent sedimentary structure. As a result, the commonly used lithofacies classification scheme based on rock composition and grain size is difficult to characterize accurately, hampering the evaluation of the Fengcheng Formation's hydrocarbon exploration potential. Therefore, the shale lithofacies classification scheme of Fengcheng Formation was proposed. This scheme classifies the Fengcheng Formation shales into four categories and eight sub-categories based on terrigenous clasts, carbonate minerals, and volcanic clasts, as well as organic matter content and sedimentary structure. Furthermore, this scheme considers the organic and tuffaceous matter, which is essential for evaluating hydrocarbon generation properties, reservoir properties, and the brittleness of fine-grained sedimentary rocks.

Rapid nitrification involving comammox and canonical Nitrospira at extreme pH in saline-alkaline lakes.

Nitrite-oxidizing bacteria (NOB) catalyse the second nitrification step and are the main biological source of nitrate. The most diverse and widespread NOB genus is Nitrospira, which also contains complete ammonia oxidizers (comammox) that oxidize ammonia to nitrate. To date, little is known about the occurrence and biology of comammox and canonical nitrite oxidizing Nitrospira in extremely alkaline environments. Here, we studied the seasonal distribution and diversity, and the effect of short-term pH changes on comammox and canonical Nitrospira in sediments of two saline, highly alkaline lakes. We identified diverse canonical and comammox Nitrospira clade A-like phylotypes as the only detectable NOB during more than a year, suggesting their major importance for nitrification in these habitats. Gross nitrification rates measured in microcosm incubations were highest at pH10 and considerably faster than reported for other natural, aquatic environments. Nitrification could be attributed to canonical and comammox Nitrospira and to Nitrososphaerales ammonia-oxidizing archaea. Furthermore, our data suggested that comammox Nitrospira contributed to ammonia oxidation at an extremely alkaline pH of 11. These results identify saline, highly alkaline lake sediments as environments of uniquely strong nitrification with novel comammox Nitrospira as key microbial players.

Transcriptomic and proteomic analyses provide insights into the adaptive responses to the combined impact of salinity and alkalinity in Gymnocypris przewalskii

Gymnocypris przewalskii is the only high-land endemic teleost living in Qinghai Lake, the largest saline–alkaline lake in China. Its osmoregulatory physiology remains elusive due to a lack of precise identification of the response proteins. In the present study, DIA/SWATH was used to identify differentially expressed proteins (DEPs) under alkaline (pH = 10.1, carbonate buffer), saline (12‰, sodium chloride), and saline–alkaline [carbonate buffer (pH = 10.1) plus 11‰ sodium chloride] stresses. A total of 66,056 unique peptides representing 7,150 proteins and 230 DEPs [the false discovery rate (FDR) ≤ 0.05, fold change (FC) ≥ 1.5] were identified under different stresses. Comparative analyses of the proteome and transcriptome indicated that over 86% of DEPs did not show consistent trends with mRNA. In addition to consistent enrichment results under different stresses, the specific DEPs involved in saline–alkaline adaptation were primarily enriched in functions of homeostasis, hormone synthesis and reactions of defense response, complement activation and reproductive development. Meanwhile, a protein–protein interaction (PPI) network analysis of these specific DEPs indicated that the hub genes were ITGAX, MMP9, C3, F2, CD74, BTK, ANXA1, NCKAP1L, and CASP8. This study accurately isolated the genes that respond to stress, and the results could be helpful for understanding the physiological regulation mechanisms regarding salinity, alkalinity, and salinity–alkalinity interactions.Graphical

Possible formation pathways for zeolites in closed-basin lakes on noachian Mars: Insights from geochemical modeling

Zeolites are among the most common and widespread authigenic silicate minerals found in saline-alkaline paleolacustrine environments on Earth. Analcime, a Na-zeolite, has been detected on crustal outcrops on Mars using orbital spectral image data. Identifying other zeolite species is complicated by the lack of diagnostic absorption features in spectral data and spectral similarity to some polyhydrated sulfates. Therefore, analcime is the only zeolite species so far unambiguously identified as present on Mars. The presence of certain zeolite mineral species or assemblages in a closed basin paleolake can be used to track hydrological changes in that basin. This paper discusses the application of geochemical modeling to identify zeolite phases that could have formed in closed lake basins of late Noachian Mars. The composition of the high-silica Buckskin sample from Gale crater is used as a starting material because 1) most zeolite-rich assemblages in closed hydrologic systems on Earth originate from the decomposition of high-silica volcanic glass, and 2) geochemical modeling studies are already available for the more common lower silica basalts on Mars. This study, along with previous studies involving basaltic starting materials, allow a comparison between terrestrial and Martian data and an exploration of the differences in secondary mineral precipitation with substrates of different silica contents. The EQ3/6 geochemical modeling code was adopted, and Late Noachian Mars was assumed to be warm and semi-arid, with an atmosphere with 1.3 bars of PCO2 and current Mars PO2 (14.7 μbar). The Buckskin sample was reacted with three different starting solutions including two different rainfall chemistries and an acidic H2SO4 − HCl solution, which could have formed through volcanic degassing. The mineral formation and re-dissolution patterns under different Water/Rock (W/R) ratios are also explored.The results show that near neutral and acidic solutions in closed-basin lakes filled with high-silica volcaniclastic materials could eventually produce zeolite minerals like those in saline-alkaline lakes on Earth. Analcime forms only in water-limited environments (low W/R ratio), while chabazite is present even at relatively high W/R ratio. Clinoptilolite transforms to analcime with an increase in pH, with decreased W/R ratio, and with time. Analcime was found to be the most stable zeolite mineral over the greatest range of conditions in this environment, associated with increased pH, consistent with its presence as a very common constituent of saline-alkaline lake deposits on Earth. The study shows that the mineral precipitation patterns associated with the dissolution of high-silica materials through acid weathering are comparable to the mineral precipitation patterns following the dissolution of basaltic rocks by acid weathering under 0 − 25oC conditions or hydrothermal conditions as described in previous laboratory, field, and geochemical modeling studies.

A Pennsylvanian saline-alkaline lake in Gondwana mid-latitude: Evidence from the Piauí Formation chert deposits, Parnaíba Basin, Brazil

The Pangaea assemblage resulted in significant tectonic and eustatic changes, but also in a well-known desertification triggered by the increasing continentalization. While the northern hemisphere basins have been thoroughly studied, several recent studies on southern hemisphere basins bring new insight on how these events affected the Gondwana hinterlands. In this study, sedimentological and geochemical analyses of chert deposits from the Pennsylvanian Piauí Formation of the Parnaíba Basin are examined as new evidence for the onset of continentalization and aridification in the northwestern Gondwana mid-latitudes. The chert deposits correspond to three facies (stromatolites, ooidal arenites and breccias) that together suggest deposition in a shallow water environment and biomarkers analysis of stromatolites indicated predominance of organic matter produced by cyanobacteria in an environment characterized by high salinity and elevated pH. Such evidence suggests that the Piauí Formation cherts deposited in a shallow, saline-alkaline lacustrine environment during a period marked by increasing arid climate conditions.

Genome Sequence of Salipaludibacillus sp. Strain CUR1, Isolated from an Alkaline-Saline Lake in Rajasthan, India.

ABSTRACTWe report the complete genome sequence of Salipaludibacillus sp. strain CUR1, which was isolated from Sambhar Lake (a soda lake) in Rajasthan, India. The whole-genome sequencing of this strain has been done to explore the industrially important hydrolytic and extracellular enzymes that can be active under high-salt and high-pH conditions.

Microbial Community Structure Is Most Strongly Associated With Geographical Distance and pH in Salt Lake Sediments.

Salt lakes are globally significant microbial habitats, hosting substantial novel microbial diversity and functional capacity. Extremes of salinity and pH both pose major challenges for survival of microbial life in terrestrial and aquatic environments, and are frequently cited as primary influences on microbial diversity across a wide variety of environments. However, few studies have attempted to identify spatial and geochemical contributions to microbial community composition, functional capacity, and environmental tolerances in salt lakes, limiting exploration of novel halophilic and halotolerant microbial species and their potential biotechnological applications. Here, we collected sediment samples from 16 salt lakes at pH values that ranged from pH 4 to 9, distributed across 48,000 km2 of the Archaean Yilgarn Craton in southwestern Australia to identify associations between environmental factors and microbial community composition, and used a high throughput culturing approach to identify the limits of salt and pH tolerance during iron and sulfur oxidation in these microbial communities. Geographical distance between lakes was the primary contributor to variation in microbial community composition, with pH identified as the most important geochemical contributor to variation in microbial community composition. Microbial community composition split into two clear groups by pH: Bacillota dominated microbial communities in acidic saline lakes, whereas Euryarchaeota dominated microbial communities in alkaline saline lakes. Iron oxidation was observed at salinities up to 160 g L–1 NaCl at pH values as low as pH 1.5, and sulfur oxidation was observed at salinities up to 160 g L–1 NaCl between pH values 2–10, more than doubling previously observed tolerances to NaCl salinity amongst cultivable iron and sulfur oxidizers at these extreme pH values. OTU level diversity in the salt lake microbial communities emerged as the major indicator of iron- and sulfur-oxidizing capacity and environmental tolerances to extremes of pH and salinity. Overall, when bioprospecting for novel microbial functional capacity and environmental tolerances, our study supports sampling from remote, previously unexplored, and maximally distant locations, and prioritizing for OTU level diversity rather than present geochemical conditions.

Diatom evidence for a groundwater divide that limited the extent of Lake Estancia, New Mexico, USA, highstands during the Last Glacial Maximum

Abstract A high-resolution time series of diatoms from the Estancia Basin of central New Mexico, USA, reveals decadal to millennial changes in water chemistry during the Last Glacial Maximum (LGM) and suggests that groundwater leakage limited the size of Lake Estancia highstands. Previous work showed that the lake expanded at least five times during the LGM, with each highstand reaching the same elevation; numerical modeling experiments showed that highstands required increases in precipitation of 1.5–2 times that of modern times but also demonstrated that these conditions could have lasted for only a few decades or the lake would have overflowed the basin’s sill. The fact that the lake returned to the same elevation suggests that highstands were climatologically similar. Here we present an alternative scenario, that once the lake reached a particular threshold volume, groundwater leakage prevented further expansion, which means that precipitation increases may have been larger than previously thought. The LGM diatom sequence is dominated by freshwater planktonic species in the Lindavia ocellata complex, the freshwater to brackish littoral species Pseudostaurosira brevistriata, and the brackish to saline benthic species Diploneis cf. smithii, all of which show decadal to centennial oscillations that were likely driven by solar cycles. Canonical correspondence analyses using mineralogical time series as proxies for wetter and drier conditions reveal that diatom assemblages varied with salinity and pH/alkalinity and suggest that groundwater outflow led to variable water chemistry for different highstands of the same magnitude. Nonmetric multidimensional scaling confirms the uniqueness of each highstand in terms of the diatom assemblages. The diatom data presented here are among only a handful of such records for Pleistocene pluvial lakes in the American West and reveal that saline alkaline lakes can yield important information despite valve preservation issues.