Hypersaline Lake Research Articles

Thalassobacillus, a genus of extreme to moderate environmental halophiles with biotechnological potential.

Thalassobacillus is a moderately halophilic genus that has been isolated from several sites worldwide, such as hypersaline lakes, saline soils, salt flats, and volcanic mud. Halophilic bacteria have provided functional stable biomolecules in harsh conditions for industrial purposes. Despite its potential biotechnological applications, Thalassobacillus has not been fully characterized yet. This review describes the Thalassobacillus genus, with the few species reported, pointing out its possible applications in enzymes (amylases, cellulases, xylanases, and others), biosurfactants, bioactive compounds, biofuels production, bioremediation, and plant growth promotion. The Thalassobacillus genus represents a little-explored biological resource but with a high potential.

Effect of Salinity on Evaporation from Water Surface in Bench-Scale Testing

Freshwater and hypersaline lakes in arid and semi-arid environments are crucial from agricultural, industrial, and ecological perspectives. The purpose of this paper was to investigate the effect of salinity on evaporation from water surfaces. The main achievement of this research is the successful capture of simulated climate–surface interactions prevalent in the Canadian Prairies using a custom-built bench-scale atmospheric simulator. Test results indicated that the evaporative flux has a large variation during spring (water/brine: 1452/764 10−4 g·s−1·m−2 and 613/230 × 10−4 g·s−1·m−2 night) and summer (1856/1187 × 10−4 g·s−1·m−2 day and 1059/394 × 10−4g·s−1·m−2 night), and small variation in the fall (1591/915 × 10−4 g·s−1·m−2 and 1790/1048 × 10−4 g·s−1·m−2 night). The primary theoretical contribution of this research is that the evaporation rate from distilled water is twice that of saturated brine. The measured data for water correlated well with mathematical estimates; data scatter was evenly distributed and within one standard deviation of the equality line, whereas the brine data mostly plotted above the equality line. The newly developed 2:1 water–brine correlation for evaporation was found to follow the combination equations with the Monteith model best matching the measurements.

Chemical composition and Pb(II) binding of dissolved organic matter in a hypersaline lake in China

Chemical composition and Pb(II) binding of dissolved organic matter in a hypersaline lake in China

Salt to conserve: a review on the ecology and preservation of hypersaline ecosystems.

When it comes to the investigation of key ecosystems in the world, we often omit salt from the ecological recipe. In fact, despite occupying almost half of the volume of inland waters and providing crucial services to humanity and nature, inland saline ecosystems are often overlooked in discussions regarding the preservation of global aquatic resources of our planet. As a result, our knowledge of the biological and geochemical dynamics shaping these environments remains incomplete and we are hesitant in framing effective protective strategies against the increasing natural and anthropogenic threats faced by such habitats. Hypersaline lakes, water bodies where the concentration of salt exceeds 35g/l, occur mainly in arid and semiarid areas resulting from hydrological imbalances triggering the accumulation of salts over time. Often considered the 'exotic siblings' within the family of inland waters, these ecosystems host some of the most extremophile communities worldwide and provide essential habitats for waterbirds and many other organisms in already water-stressed regions. These systems are often highlighted as natural laboratories, ideal for addressing central ecological questions due to their relatively low complexity and simple food web structures. However, recent studies on the biogeochemical mechanisms framing hypersaline communities have challenged this archetype, arguing that newly discovered highly diverse communities are characterised by specific trophic interactions shaped by high levels of specialisation. The main goal of this review is to explore our current understanding of the ecological dynamics of hypersaline ecosystems by addressing four main research questions: (i) why are hypersaline lakes unique from a biological and geochemical perspective; (ii) which biota inhabit these ecosystems and how have they adapted to the high salt conditions; (iii) how do we protect biodiversity from increasing natural and anthropogenic threats; and (iv) which scientific tools will help us preserve hypersaline ecosystems in the future? First, we focus on the ecological characterisation of hypersaline ecosystems, illustrate hydrogeochemical dynamics regulating such environments, and outline key ecoregions supporting hypersaline systems across the globe. Second, we depict the diversity and functional aspects of key taxa found in hypersaline lakes, from microorganisms to plants, invertebrates, waterbirds and upper trophic levels. Next, we describe ecosystem services and discuss possible conservation guidelines. Finally, we outline how cutting-edge technologies can provide new insights into the study of hypersaline ecology. Overall, this review sheds further light onto these understudied ecosystems, largely unrecognised as important sources of unique biological and functional diversity. We provide perspectives for key future research avenues, and advocate that the conservation of hypersaline lakes should not be taken with 'a grain of salt'.

Ecology and biogeography of the 'marine Geitlerinema' cluster and a description of Sodalinema orleanskyi sp. nov., Sodalinema gerasimenkoae sp. nov., Sodalinema stali sp. nov. and Baaleninema simplex gen. et sp. nov. (Oscillatoriales, Cyanobacteria).

Filamentous cyanobacteria belonging to the 'marine Geitlerinema' cluster are spread worldwide in saline environments and considered to play an important ecological role. However, the taxonomy of this group remains unclear. Here, we analyzed the phylogeny, ecology and biogeography of the 'marine Geitlerinema' cluster representatives and revealed two subclusters: (1) an 'oceanic' subcluster containing PCC7105 clade and black band disease (BBD) clade with free-living and pathogenic strains distributed in Atlantic, Indian and Pacific Ocean-related localities, and (2) a Sodalinema subcluster containing free-living strains from marine, hypersaline, saline-alkaline and soda lake habitats from the Eurasian and African continents. Polyphasic analysis using genetic and phenotypic criteria demonstrated that these two groups represent separate genera. Representatives of Sodalinema subcluster were phylogenetically attributed to the genus Sodalinema. Our data expand the ecological and geographical distribution of this genus. We emended the description of the genus Sodalinema and proposed three new species differing in phylogenetic, geographic and ecological criteria: Sodalinema orleanskyi sp. nov., Sodalinema gerasimenkoae sp. nov. and Sodalinema stali sp. nov. Additionally, a new genus and species Baaleninema simplex gen. et sp. nov. was discribed within the PCC7105 clade. By this, we put in order the current confusion of the 'marine Geitlerinema' group and highlight its ecological diversity.

Metabarcoding under Brine: Microbial Ecology of Five Hypersaline Lakes at Rottnest Island (WA, Australia)

Hypersaline ecosystems—aquatic environments where concentration of salt exceeds 35 g L−1—host microbial communities that are highly specialised to cope with these extreme conditions. However, our knowledge on the taxonomic diversity and functional metabolisms characterising microbial communities in the water columns of hypersaline ecosystems is still limited, and this may compromise the future preservation of these unique environments. DNA metabarcoding provides a reliable and affordable tool to investigate environmental dynamics of aquatic ecosystems, and its use in brine can be highly informative. Here, we make use of bacterial 16S metabarcoding techniques combined with hydrochemical analyses to investigate the microbial patterns (diversity and functions) from five hypersaline lakes located at Rottnest Island (WA). Our results indicate lake-driven microbial aquatic assemblages that are characterised by taxonomically and functionally moderately to extremely halophilic groups, with TDS (total dissolved solids) and alkalinity amongst the most influential parameters driving the community patterns. Overall, our findings suggest that DNA metabarcoding allows rapid but reliable ecological assessment of the hypersaline aquatic microbial communities at Rottnest Island. Further studies involving different hypersaline lakes across multiple seasons will help elucidate the full extent of the potential of this tool in brine.

Analysis of Salt Lake Volume Dynamics Using Sentinel-1 Based SBAS Measurements: A Case Study of Lake Tuz, Turkey

As one of the largest hypersaline lakes, Lake Tuz, located in the middle of Turkey, is a key waterbird habitat and is classified as a Special Environmental Protection Area in the country. It is a dynamic lake, highly affected by evaporation due to its wide expanse and shallowness (water depth <40 cm), in addition to being externally exploited by salt companies. Monitoring the dynamics of its changes in volume, which cause ecological problems, is required to protect its saline lake functions. In this context, a spatially homogeneous distributed gauge could be critical for monitoring and rapid response; however, the number of gauge stations and their vicinity is insufficient for the entire lake. The present study focuses on assessing the feasibility of a time-series interferometric technique, namely the small baseline subset (SBAS), for monitoring volume dynamics, based on freely available Sentinel-1 data. A levelling observation was also performed to quantify the accuracy of the SBAS results. Regression analysis between water levels, which is one of the most important volume dynamics, derived by SBAS and levelling in February, April, July and October was 67%, 80%, 84%, and 95% respectively, for correlation in the range of 10–40 cm in water level, and was in line with levelling. Salt lake components such as water, vegetation, moist soil, dry soil, and salt, were also classified with Sentinel-2 multispectral images over time to understand the reliability of the SBAS measurements based on interferometric coherence over different surface types. The findings indicate that the SBAS method with Sentinel-1 is a good alternative for measuring lake volume dynamics, including the monitoring of water level and salt movement, especially for the dry season. Even though the number of coherent, measurable, samples (excluding water) decrease during the wet season, there are always sufficient coherent samples (>0.45) over the lake.

Filamentous anoxygenic phototrophic bacteria in water bodies of Middle and Lower Volga basin (European Russia): an overview

“Filamentous anoxygenic phototrophs” or “green non-sulfur bacteria” form a distinct lineage, order Chloroflexales (Chloroflexia: Chloroflexi) in broad polyphyletic group of anoxygenic phototrophic bacteria. Filamentous anoxygenic phototrophic bacteria have apparently important, though not fully understood functions in contemporary ecosystems and perhaps were much more significant in the Archaean. However, since their discovery in hot spring mats in the late 1960s, the extremophilic species of thermal, hypersaline and/or hyperalcaline habitats remain the most studied representatives of the lineage. In this overview, we show our representation of the history of finding and research of filamentous anoxygenic phototrophs, and current situation with their taxonomy, phylogeny and diversity. Some problems and uncertainties in these fields are also discussed. The special section is dedicated to the discovery and research of this group in the Volga River basin. Due to the small number of studies, the exact distribution of filamentous anoxygenic phototrophic bacteria in the region is unknown. For example, in small stratified lakes with high humic and/or ferruginous water in the basins of the Oka and the Upper Volga the development of planktonic filamentous anoxygenic phototrophs is very likely. Besides, the development of Chloroflexales, including new species, is quite expected in the microbial mats of saline rivers and hypersaline lakes of the Lower Volga region. Further progress in the field will be possible only with the use of molecular methods along or preferably in combination with traditional methods (polyphasic approach). Since their role in communities is far from elucidated, further studies of FAP may also provide new opportunities in the field of microbial biotechnology.

Evaluation of UV-B protection efficiency of mycosporine like amino acid extracted from the cyanobacteria Anabaenopsis sp. SLCyA isolated from a hypersaline lake

MAAs are natural UV-protectant molecules produced by many marine organisms including cyanobacteria. In the present study five different cyanobacterial strains were isolated from hypersaline Sambhar Lake, India. The isolated cyanobacterium Anabaenopsis sp. SLCyA was able to produce large quantity of MAA (0.1 mg/g dry weight) when exposed to photosynthetically active radiation (PAR) and ultraviolet radiation-B (UV-B) until 48 h. The produced MAA was identified as Shinorine showed the absorption maximum at 334 nm. This MAA was able to provide significant protection to E. coli ATCC 25922 against UV-B radiation and 83.5% of the cells survived even after 20 min of exposure.

Temporal Microbial Community Dynamics Within a Unique Acid Saline Lake.

Lake Magic is an extremely acidic, hypersaline lake found in Western Australia, with the highest concentrations of aluminum and silica in the world. Previous studies of Lake Magic diversity have revealed that the lake hosts acid- and halotolerant bacterial and fungal species. However, they have not canvassed microbial population dynamics across flooding, evapo-concentration and desiccation stages. In this study, we used amplicon sequencing and potential function prediction on sediment and salt mat samples. We observed that the bacterial and fungal diversity in Lake Magic is strongly driven by carbon, temperature, pH and salt concentrations at the different stages of the lake. We also saw that the fungal diversity decreased as the environmental conditions became more extreme. However, prokaryotic diversity was very dynamic and bacteria dominated archaeal species, both in abundance and diversity, perhaps because bacteria better tolerate the extreme variation in conditions. Bacterial species diversity was the highest during early flooding stage and decreased during more stressful conditions. We observed an increase in acid tolerant and halotolerant species in the sediment, involved in functions such as sulfur and iron metabolism, i.e., species involved in buffering the external environment. Thus, due to activity within the microbial community, the environmental conditions in the sediment do not change to the same degree as conditions in the salt mat, resulting in the sediment becoming a safe haven for microbes, which are able to thrive during the extreme conditions of the evapo-concentration and desiccation stages.

Explaining Variation in Abundance and Species Diversity of Avian Cestodes in Brine Shrimps in the Salar de Atacama and Other Chilean Wetlands

Further biogeographical studies of parasites are vital to improve our understanding of biodiversity distribution and predict the impacts of global change. Hypersaline lakes are good laboratories to investigate the avian cestode abundance and species diversity given the abundance of hosts (waterbirds and Artemia) and their broad latitudinal distribution. We analysed cestode infection in brine shrimp Artemia franciscana in northern (Atacama) and central Chile and compared them to results from A. persimilis in southern Chile (Patagonia). Thus, we covered a broad latitudinal gradient from 23° to 53° S. Five cestode taxa including two species of the genus Flamingolepis, Gynandrotaenia stammeri, Eurycestus avoceti, and Fuhrmannolepis averini were recorded from A. franciscana in Atacama lagoons (prevalence = 4.1%). In contrast, no cestode infection was detected in central Chile, likely because they are temporary wetlands. Parasites of flamingos and shorebirds were associated with Atacama lagoons (arid and higher salinity), while Confluaria podicipina and Fimbriarioides sp. (parasites of grebes and ducks, respectively) were dominant in Patagonian lagoons (sub-antarctic and of lower salinity). These differences mirror changes in the relative abundance of the respective final hosts. The flamingo parasite Flamingolepis sp. 1 was the most prevalent and abundant cestode in Atacama, where it was recorded only in autumn. Seasonality and habitat effects (especially abundance and phenology of different bird species) appear to override any latitudinal trends in the prevalence, diversity, and distribution of cestodes. Cestode prevalence was higher in larger wetlands but was not related to the sex of either intermediate host. We recorded a greater taxonomic richness at the cestode family level in Atacama, but a greater dominance of a single family of avian hosts (the flamingos). Ours is the first spatio–temporal study of Artemia cestodes at local and regional scales in the southern hemisphere.

Both pH and salinity shape the microbial communities of the lakes in Badain Jaran Desert, NW China

Badain Jaran Desert (BJD), characterized by extremely arid climate and tallest sand dunes in the world, is the second largest desert in China. Surprisingly, there are a large number of permanent lakes in this desert. At present, little is known about the composition and distribution of microbial communities in these desert lakes, which are an important bioresource and play a fundamental role in the elemental cycles of the lakes. In this study, the physicochemical characteristics and microbial communities of water samples from 15 lakes in BJD were comparatively investigated. The results showed that the lakes were rich in Na+, Cl−, CO32− and HCO3− while Ca2+ and Mg2+ were scarce, with pH 8.52–10.27 and salinity 1.05–478.70 g/L. Bacteria dominated exclusively in low saline lakes (salinity < 50 g/L) while archaea were predominant in hypersaline lakes (salinity > 250 g/L), which abundance increased along salinity gradient linearly. Genera Flavobacterium, Synechocystis and Roseobacter from phyla Bacteroidetes, Cyanobacteria, Alphaproteobacteria were the major members in low saline lakes whereas Halomonas, Aliidiomarina and Halopelagius from Gammaproteobacteria and Euryarchaeota were abundant in moderately saline lakes (salinity 50–250 g/L). The hypersaline lakes were predominated by extreme halophiles such as Halorubrum, Halohasta and Natronomonas from Euryarchaeota. The correlation among the microbes in the lakes was mainly positive, suggesting they can survive in the harsh environments through synergistic interactions. Statistical analyses indicated that physicochemical characteristics rather than spatial factors shaped the microbial communities in the desert lakes. The pH was the most important environmental factor controlling alpha diversity, while salinity was the major driver determining microbial community structure in BJD lakes. In contrast, geographic factors had no significant impact on the microbial community compositions.

Isolation of a novel halothermophilic strain of the genus Gracilibacillus from Howz-e Sultan hypersaline lake in Iran.

Background and Objectives:Halothermophilic bacteria are adapted to high osmolarity and can grow in high saline environments and high temperatures. This study was aimed at the isolation of halothermophilic bacteria from Howz-e Sultan hypersaline lake in the central desert zone in Iran.Materials and Methods:Samples were collected and after preparing dilutions, the samples were cultured on Molten haloid agar with different salt concentrations (5–35%), then the plates were incubated at 35–70ºC in both aerobic and anaerobic conditions. Biochemical characterizations, utilization of carbon sources, production of exoenzymes and antibiotic susceptibility were investigated. Taxonomic and phylogenetic analyses were performed using 16S rRNA gene sequences.Results:One of the isolated bacteria was found to be Gram-positive, hyperhalophilic, thermophilic, endospore-forming, and was named as 1–9 h isolate. The bacterial cells were bacilli-shaped, which produced endospores at a subterminal position. This isolate was an aerobe and facultative anaerobe and grew between pH 5.0 and 10.0 (optimal growth at pH 7.0–7.5), at temperature between 15°C and 65°C (optimal growth at 40–45°C) and at salinity of 9–32% (w/v) NaCl, growing optimally at 18% (w/v) NaCl. On the basis of 16S rRNA gene sequence analysis, isolate 1–9 h belongs to the genus Bacillus within the phylum Firmicutes and showed the closest phylogenetic similarity to Gracilibacillus sp. IBP-V003 (99.0%).Conclusion:Based on the results of its phenotypic and genotypic properties, strain 1–9 h represents a novel strain of the genus Gracilibacillus. It can be used in various fields of industry and biotechnology.

Investigation of climate, land cover and lake level pattern changes and interactions using remotely sensed data and wavelet analysis

Lake Urmia –a hypersaline lake in northwest of Iran- has lost perceptible amount of its waterbody since mid ‘90s. Reasons behind this catastrophe could be categorized as climatic factors and anthropogenic activities. To investigate pattern changes and interactions of the components involved in this dramatic water loss, precipitation (P), discharge (Q), temperature (T), sea surface temperature (SST) alongside satellite images of vegetation cover (VC) from 1990 to 2019 were used for pattern and interaction analysis, including trend and seasonality detection. Owing to the fact that this endorheic lake in extremis is located between East Azerbaijan (EA) and West Azerbaijan (WA) provinces, additionally it was aimed to juxtapose changes in the aforementioned variables assembled from these two provinces. To monitor changes in VC, normalized difference vegetation index (NDVI) time series for two pilot sub-watersheds from EA and WA provinces were calculated using remotely sensed images. Mann-Kendall (MK) trend test revealed that amongst all variables, Q in both sub-watersheds has been intensely decreased in 99% confidence level. Moreover, continuous wavelet transform (CWT) of Q exhibited drastic de-escalations in terms of annual and semi-annual periodicities. VC and urbanization in both sub-watersheds showed significant increasing trends, whereas VC in WA province showed a higher level of trend. Fairly stable P in terms of trend and periodicity alongside intensification in VC concluded intense exploitations of Q which is the other main inflow into this lake. Wavelet coherence transformation (WTC) between all considered variables and Lake Urmia's WL revealed the great impacts of Q, T and SST variables on the lake's WL fluctuations and seasonality. The impact of T and SST on WL fluctuations did not illustrate perceptible changes throughout the study period (i.e., before and after lake's desiccation). The impact of Q on the lake's WL, however, has moved to larger frequency bands with increased phase-lags, and thus, it could be concluded that the intense reduction of the lake's WL is in proportion to intense reduction of rivers discharge to this lake; leaving transparent traces of anthropogenic impacts on Lake Urmia's tragedy.

Evaluating the long-term resilience of water resources systems: Application of a generalized grade-based combination approach

This paper introduces a new methodology for evaluating water resource systems' resilience under extreme events by taking advantage of a generalized grade-based technique to combine criteria. To determine extreme events, we evaluate the impacts of climate change scenarios using the Soil and Water Assessment Tool (SWAT). The proposed framework for evaluating the long-term resilience of water resources systems has three main steps. At first, three performance criteria (i.e., reliability, traditional resiliency, and vulnerability (RRV)), which show the resilience against crossing a performance threshold, are calculated considering the optimal allocated water to demand nodes. In the second step, a new resilience-based criterion is proposed considering five sub-criteria: robustness, redundancy, resourcefulness, rapidity, and durability (4R-D). In addition, a new social resilience-based criterion (i.e., SR) is proposed, and these two criteria are considered to evaluate the total resilience of the system. In the third step, some adaptive management scenarios are defined to improve the resilience of the system. The proposed methodology has been applied to the Zarrinehrud river basin, the main water supplier of the largest hypersaline lake in the Middle East, Lake Urmia.Regarding the qualitative and quantitative nature of the criteria, the generalized combination (GC) rule for the evidential reasoning approach (ER) is used to evaluate and integrate the criteria under uncertainty. The results show that the traditional RRV criteria do not accurately evaluate the temporal resilience of the system under extreme events. Therefore, 4R-D and SR criteria are taken into account to evaluate the long-term resilience of the water supply and demand system under extreme events with known and unknown probabilities of occurrence. According to the results, the RRV criteria are not sensitive to water resources management scenarios, but the scenarios improve 4R-D and SR criteria up to 0.6–0.8 and 0.76, respectively.

Entomofauna in Egyptian saltwater habitats

The entomofaunas of salty Egyptian environments are reviewed in the present paper according to the available data. Most saltwater habitats were poor with insect fauna. Class Insecta was represented in seven lakes and completely disappeared in two hypersaline lakes, Bitter and Temsah. Chironomid larvae were the most abundant insects in the seven lakes followed by the mosquito larvae, especially in Suez Canal and Wadi El-Rayan. Other aquatic insects include Odonata, Hemiptera, Coleoptera, Trichoptera, and Collembola were represented as extremely low or completely absent. The richness of insect diversity was observed in Burullus and Wadi El-Rayan Lakes as well as the Red Sea coast (swamps and mangroves). It has also been observed that the physical and chemical characteristics of these habitats were changed due to the environmental and climatic changes. Consequently, led to changes in the insect species and other communities. Generally, the data and the studies of insect fauna in Egyptian saltwater are very poor. Also, the taxonomic identification to the level of genus and species is almost non-existent. This paper recommended more studies of insect fauna in these environments with more precise classification.

Managing Lake Urmia, Iran for diverse restoration objectives: Moving beyond a uniform target lake level

Study RegionLake Urmia, Iran. Study focusThere is widespread interest in restoring drying saline lakes. At Iran’s hypersaline Lake Urmia, managers have sought a uniform target lake level of 1274.1 m above sea level to lower salinity below 263 g L−1 and recover Artemia to sufficient densities to support flamingos. We suggest that addressing a broader range of objectives will allow more flexibility for managing the lake. We define eight restoration objectives to lower salinity, sustain Artemia and flamingo populations, separate islands from each other and the mainland, reduce lakebed dust, maintain commercially valuable ions, and improve recreational access from resort beaches. We use 40 years of experimental, field, satellite, and model data to relate each objective to lake level. We describe variations through time and associated uncertainties for meeting each objective. New hydrological insightsWe show that:1) Lake variations prevent setting a precise target restoration level; 2) The current target may not sufficiently lower salinity to recover Artemia to sufficient densities to support flamingos; 3) Restoration objectives do not converge to a single lake level; tradeoffs are murky; 4) Lake Urmia managers should focus on multiple ecosystem services and track how they are met as lake level varies over time; and 5) As information about the lake improves, managers should adapt their management strategies to meet the most attainable objectives.

Lake Urmia restoration success story: A natural trend or a planned remedy?

Lake Urmia is the second-largest hypersaline lake in the world. There has been a drastic water level drop of 7.2 m from 1995 to 2016. Beginning in October 2013, the Lake Urmia Restoration Plan (LURP) launched a 10-year program. An increase in water level and a relative improvement in Lake Urmia condition has been observed since 2017. It is an undecided and controversial issue whether the recent positive trend of Lake Urmia has been due to the LURP activities or it is a natural contribution of climate factors variations. To shed some light on this issue, we examine three other lakes, adjacent to the Lake Urmia basin, with similar rainfall variability to investigate their status during the same period. Van (Turkey), Mosul, and Tharthar (both in Iraq), are evaluated as well as Lake Urmia. Three decades of remotely sensed data including precipitation (P), water level (WL), and lake extent (A) were considered for the mentioned lakes. A significant correlation was observed between standardized WL-P, and A-P over the long-term period, especially for the recent three years (R2 = 0.63–0.87). We show that the cumulative precipitation in the antecedent months played a major role in the improvement of these lakes' situation but with different time lags (up to 6 months for Van and Mosul lakes and up to 36 months for Lake Urmia and Tharthar lake). These findings could inform the planners of LURP to adopt strategies for achieving a sustainable state of Lake Urmia based on a more realistic outlook.

Depositional environments and salt-thickness variations in Urmia Lake (NW Iran): Insight from sediment-core studies

ABSTRACT Urmia Lake is a large-scale hypersaline lake that experienced a drastic water-level fall due to natural and anthropogenic forces during the last two decades. Construction of a causeway in the central part of the lake after 1989 has divided the lake into northern and southern parts and caused an extreme change of the lake hydrochemical system. Precipitation of evaporite minerals as crust on the lake floor was caused by the combination of lake level fall and increasing water salinity. However, some parameters controlling rates of salt deposition and dissolution and temporal and spatial variation in salt thickness in Lake Urmia are poorly understood. This study reviews 90 sediment cores from various parts of the lake to put forward a better understanding of the salt depositional system and salt thickness variations in the basin for the last 40 years (1977–2017). Our results indicate that the sedimentary system of Urmia Lake changed rapidly during the last two decades from a permanent hypersaline lake with predominantly fast terrigenous–biochemical sedimentation to a seasonally changing playa sedimentary environment with predominance of evaporite minerals. These changes are responsible for rapid salt deposition that generated a salt-crust with a maximum thickness of 2.95 m overlying Holocene terrigenous sediments. The salt-crust thickness and the water depth have a positive correlation for water depth greater than 1 meter, which means that salt-crust thickness increases where water depth increases. While the thickness of shallow deposits are affected by fresh-water dissolution. In addition, the average salt precipitation rate in the northern and the southern parts of the lake is 466 and 266 times higher, respectively, than the average (0.3 mm/y) sedimentation rate before the lake shrinkage. Similar to other large hypersaline lakes such as the Great Salt Lake (USA) and the Aral Sea (Central Asia), the manmade intervention at Urmia Lake (damming of the catchment, extension of agricultural fields, and causeway construction in the middle part of the lake) threatens its further hydrologic existence.

Mechanisms of sedimentation in lacustrine environment of Babouri-Figuil and Mayo Oulo-Lere basins deposits (North Cameroon) during the Southern Atlantic opening: sedimentary structures and geochemistry constraints

Sedimentary structures are very useful to characterize sedimentation environments. In this study, sedimentary structures are documented in the Lower Cretaceous Babouri-Figuil and Mayo Oulo-Lere intracontinental Basins whose genesis is linked to the opening of the Southern Atlantic Ocean. Geochemical data is also presented with the aim to discriminate the paleoenvironment. Field investigations and facies analyses revealed synsedimentary and postsedimentary structures related or not to tectonic. Synsedimentary structures not affected by tectonic are lamination or bedding (rhythmic), graded bedding, cross-stratification, loads casts, channels, and ripple marks. Those affected by tectonic are convolute bedding, slump (Slump sensus stricto and olistolith). Desiccation cracks and print marks are postsedimentary structures not related to tectonic; others are stratigraphic unconformity, oblique bedding, clastic injection, and volcanic veins. The bottom of the sequence in the two basins is fluvio-lacustrine deposits with oblique stratification and global positive graded bedding; sometimes there is alternation of positive and negative graded beddings related to progressive variation of energy of sedimentation from high to low and low to high. The intermediate level is lacustrine dominated by lamination or bedding that characterizes a calm sedimentation environment marked by regular seasonal fluctuation. The ripple marks, desiccation cracks, and dinosaur footprints indicate the emersion period, and their fossilization indicates slow phases of sedimentation. Channels and load casts correspond to a rapid sedimentation phase. Seismic shocks at time break the fragile stability of deposited materials causing gravitational flows of the sublacustrine avalanche type and give olistolith and convolute bedding to slumps. The clastic or chemical injections and volcanic veins are related to brittle tectonic that affects consolidated deposits. From the geochemical data, the high accumulation of LREE (average: 142.93 ppm) over HREE (average: 13.10 ppm); La/La* generally 2) and the slight to very slight negative Ce/Ce* (0.87–0.99) suggest the nonmarine deposition, and the Y/Ho ratios (< 45) and ratios indicate river condition or transportation. The Sr/Ba ratios, ranging from 0.55 to 6.41, suggest a freshwater environment with fluctuant salinity and sometimes hypersaline (Hypersaline Lake). Thus the synsedimentary structures were essentially formed in lacustrine milieu, and some structures such as graded bedding and cross-stratification affecting the basal deposit indicate a fluviatile to fluvio-lacustrine environment.