Brackish Diatoms Research Articles

Optimization of Dissolved Silica Removal from Reverse Osmosis Concentrate by Gedaniella flavovirens for Enhanced Water Recovery

Photobiological treatment of reverse osmosis concentrate (ROC) using brackish diatoms is a green and sustainable technology that can enhance water recovery by removing dissolved silica from ROC while producing beneficial biomass. This study aimed to determine the optimum conditions for the photobiological treatment of ROC obtained from a full-scale advanced water purification facility using Gedaniella flavovirens Psetr3. While light color presented minor impacts on the silica uptake rate, the impact of color intensity was significant. The uptake rate improved from 28 ± 1 to 48 ± 7 mg/L/day by increasing photosynthetically active radiation (PAR) from 50 to 310 µmol m−2 s−1. Increasing the PAR further did not improve the performance. The optimum temperature was around 23–30 °C. While the silica uptake was slower at 10 °C, G. flavovirens Psetr3 was unable to survive at 40 °C. Experiments using sunlight as a light source verified the impact of temperature on the silica uptake and the detrimental effect of ultraviolet radiation on this diatom. The sunlight-based treatment effectively removed N-nitrosodimethylamine. The results of this study are being used in subsequent pilot-scale investigations and full-scale technoeconomic analysis and will contribute to the further development of this sustainable water technology.

Diatom community dynamics in a tropical brackish coastal ecosystem from an ecological and biogeochemical perspective: A size-fractionated approach

Diatoms are a major, ubiquitous photosynthetic group representing most aquatic ecosystem’s microalgal communities. The species composition encompasses a wide range of cell sizes. Although cell size is vital in aquatic ecology and biogeochemistry, size-based diatom community studies are sparse, especially in tropical ecosystems. This study assesses the size-fractionated brackish diatom community based on the microscopic cell abundance and carbon-biomass metrics. Despite sufficient nutrient availability, the seasonal and spatial relative proportion of abundance and biomass of the three diatom size fractions declined under high turbidity. It increased under higher light and nutrient availability with lower turbidity. Turbulence was a favorable factor irrespective of the size groups. Light availability, increased nutrients, and lower temperature resulted in a higher contribution from the larger size group to the total diatom carbon biomass. The smaller size group dominance during highly turbid conditions could be attributed to the higher surface-to-volume ratios. The intermediate-size groups thrived under reduced turbidity. Seasonal intra-species size variations reflected changes induced either due to life-cycle stages or environmental stress. The size-based metrics permitted an in-depth understanding of the diatom responses at the community and species level, which could have implications on their ecological and biogeochemical roles in aquatic ecosystems.

Озерные палеоархивы изменения природной среды полуострова Песчаный, Японское море (южное Приморье)

The stages of evolution of two barrier lakes and vegetation development of the Peschany Peninsula (South Primorye) have been reconstructed on the base of multi-proxy study of the sediment sequences, connected with hydroclimatic changes over the past 6300 years. Tephra of the caldera-forming eruption of Baitoushan volcano (946/947 AD) is one of the chronological markers. The Middle Holocene paleolake existed on the accumulative landform, and the lake on the isthmus connecting the paleoisland with the mainland, was formed at the beginning of the Late Holocene. Several periods of watering due to precipitation increase are distinguished in its development. Redeposited freshwater diatoms from subbasalt deposits are bioindicators of sheet wash activation during heavy rains associated with typhoons. Findings of valves of marine and brackish diatoms indicate the passage of extreme storms. Overgrowing of the paleolake began at the end of the Holocene thermal optimum (~5410 years ago). The periods of dryness are usually associated with cooling and a decrease in the intensity of the summer monsoon. The Little Ice Age is the exception: the flooding of the swamp with a relict lake on the isthmus increased sharply. A change of Korean pine/broad-leaved forests with the participation of fir, birches and polydominant broad-leaved forests was established. It is shown that since the Holocene Optimum there have been ecotopes with contrasting heat and moisture supply. Human impact to geosystems was recorded. Paleolimnological studies made possible to identify the Middle-Late Holocene short-period climatic rhythm on the coast of the Amur Bay. The manifestation of cold and warm events has been established, their correlation with regional data and global events has been carried out, and the connection with ocean anomalies and the intensity of the summer monsoon has been shown.

Holocene relative water level and storminess variation recorded in the coastal peat bogs of the Vistula Lagoon, southern Baltic Sea

The history of regional sea-level changes is critically important for building global environmental reconstruction models and identifying major driving forces. The coastal peatlands located on the terraces of the Vistula Lagoon (Gulf of Gdańsk, southern Baltic Sea) are one of the most valuable, and not yet fully explored, archives of the regional history of sea-level and storminess changes during the middle and late Holocene. The comprehensive analysis of peat and gyttja allowed establishing radiocarbon calibrated time series of stable carbon isotope composition (δ13C), pollen and diatom data. The results indicate that the sea-level increased from ∼20 to 8 m below present sea level between 9000 and 7000 yr b2k at an average rate of ∼6 mm/year. Around 5000 yr b2k, the sea-level was ∼2.5 m lower than at present, which indicates a decrease in the rate of sea-level rise to ∼2.75 mm/year between 7000 and 5000 yr b2k. During the last 5000 years, the sea-level had risen at ∼0.5 mm/year to the present position. Changes in brackish diatoms, Pediastrum sp. concentrations, and maxima of δ13C suggest ten periods of increased rates of sea-level rise and storminess between 7000 and 1500 yr b2k. Increased sea-levels and stormy surges on the peat surface occurred mainly during cold periods or the periods of transitions. These observations are in good agreement with climate fluctuations in the Northern Hemisphere related to the variations in total regional solar irradiation.

Isolation and evaluation of brackish diatoms for the photobiological treatment of reverse osmosis concentrate

Abstract Recently, the use of brackish diatoms has been proposed to remove various inorganic constituents, such as dissolved silica, nutrients, calcium, and bicarbonate, to enhance the freshwater recovery in reverse osmosis (RO). In this study, nine strains of brackish diatoms isolated from water and sediment samples from several evaporation ponds in California and Arizona were examined for their ability to assimilate silica and remove other constituents from RO concentrate. In addition to two previously reported strains, namely Gedaniella flavovirens PEWL001 and Nitzschia communis PEWL002, several new isolates including Halamphora sydowii PEWL004, Nitzschia sp. PEWL008, and Halamphora sp. PEWL011 were found to remove more than 95% of silica, 95% of ammonia and orthophosphate, and more than 50% of calcium and carbonate within 6 days. Two additional G. flavovirens strains (Psetr3 and Psetr7) collected from a brackish lake in Aomori, Japan, also showed rapid dissolved silica uptake (32 mg L−1 day−1) comparable to the one isolated from an agricultural drainage water evaporation pond in the Central Valley, California. This study demonstrated that the brackish diatoms isolated from the evaporation ponds could be useful for the treatment of RO concentrate, which would possibly enable more sustainable desalination processes.

Diatom diversity, distribution and ecology in Mediterranean ecosystems of Abrau Peninsula, north-western Caucasus.

The North Caucasus is an extensive region with a multitude of landscapes and high biological diversity. Amongst various ecosystems, the xerophytic sub-Mediterranean forests of the Abrau Peninsula (Utrish State Nature Reserve) and its vicinity are unique but have been poorly studied. The diversity of diatoms in North Caucasian ecosystems have been studied partially and only little information is available about their presence and distribution on the Abrau Peninsula. Here, we present a comprehensive check-list of diatoms sampled during a July 2021 field campaign. Samples were collected in 67 sites, including 39 permanent streams, 21 temporal (puddles) and seven permanent waterbodies. Results of the current study contribute to improving the knowledge about diatoms in the north-western Caucasus and its sub-Mediterranean ecosystems in particular. Here, we provide a detailed dataset that contains 215 freshwater and brackish diatom occurrences collected during a field campaign in July 2021. A total of 88 diatom (Bacillariophyta) taxa which belong to 12 orders, 25 families and 39 genera were collected. The genera with the highest number of occurrences per site were Gomphonema (26), Nitzschia (22), Navicula (20), Cocconeis (14), Amphora (14), Achnanthidium (14) and Planothidium (11). The genera with the highest number of infrageneric taxa were Nitzschia (8), Navicula (7), Gomphonema (6) and Mastogloia (5). Naviculablazencicae, known as the endemic of the Lake Prespa (Levkov 2007) is found from two sites in our study. Three specimens of the genus Mastogloia could not be assigned to a known species and may represent new diatom species. Distribution and ecology data are provided for each taxa. Occurrence data are given. Statistical analysis of diatom communities showed a significant dependence on habitat type and their ecological conditions.

Artificial sandpit lake as a habitat of brackish diatom species

ABSTRACT During a survey of diatoms in the artificial sandpit lake “Peskara” in the protected zone of the Rusanda Nature Park, a large number of brackish taxa at epipsamic and epiphytic communities were recorded (e.g. Bacillaria paxillifera, Caloneis permagna, Ctenophora pulchella, Entomoneis costata. Haslea duerrenbergiana, Navicula salinarum, Nitzschia agnita, N. filiformis, Staurophora brantii, Seminavis strigosa, Tryblionella apiculata). One new genus Seminavis and 15 diatom species were noted for the first time for the diatom flora of Serbia. Dominant taxa changed over seasons without any regularity. In spring 2021, we have observed an increased abundance of centric species Thalassiosira pseudonana and Stephanodiscus parvus while in other seasons it was difficult to discern a pattern of dominance among benthic diatoms. Metabarcoding analysis of the same sample using 18S rRNA as a gene marker confirmed the dominance of centric diatoms. This study contributes to a better understanding of brackish diatom taxa found in inland habitats, many of which can be utilized as useful tools for the ecological status assessment.

Brackish diatom species (Bacillariophyta) from rivers of Rhin-Meuse basin in France

ABSTRACT The French part of the Rhin-Meuse basin is quite heterogeneous due to the broad variability in pH and conductivity ranges of its rivers and streams. Parts of the basin are characterized by the presence of typical natural or anthropogenically induced brackish environments, showing a typical diatom flora. Since many brackish diatom species observed in these particular environments are often only poorly illustrated in literature used for biomonitoring, the present paper tends to fill this gap in our knowledge. Therefore, we illustrate in this work a large number of brackish taxa such as Cyclotella scaldensis, Skeletonema potamos, Thalassiosira gessneri, T. lacustris, T. weissflogii, Achnanthes secretitaeniata, Bacillaria paxillifera, Berkeleya rutilans, Entomoneis paludosa, Halamphora coffeaeformis, Haslea spicula, Nitzschia amplectens, N. aurariae, N. frequens, N. inconspicua and N. thermaloides. Additionally, one new species, Tabularia massenana sp. nov. is described based on detailed LM and SEM observations.

Nitzschia taikiensis sp. nov. (Bacillariophyta) – a new brackish diatom from the Toberi River marsh in the eastern Hokkaido, Japan

Abstract Nitzschia taikiensis sp. nov. is a brackish diatom species found in the Toberi River marsh, eastern Hokkaido, Japan. This species has characteristics similar to Nitzschia subamphioxoides Hustedt, which was originally described by Hustedt in 1959. In the present study, we conducted a comparative morphological analysis of N. taikiensis and N. subamphioxoides. The obtained results showed that they are different species. Sampling sites of N. taikiensis were located in salt marsh environments with very low salinity (1-5‰), acidic pH (5.2-5.9) and high mud content (95.0-97.5%). Identification of this species was relatively easy based on LM and SEM image analysis of its frustule features, such as the external form and stria density. This species has not been previously reported in Japan, which could be attributed to the reduction or loss of Japanese freshwater and salt marsh environments in the coastal areas, resulting from urban and industrial development.

The Senegal River during the last millennium

The diatom and pollen assemblages of the upper 4.5 m of a core recovered from the bank of the Senegal River upstream of St Louis (16.03 N, 16.48 W) reveal an exceptional diversity (39 diatom taxa from which 5 mentioned for the first time in Senegambia and 147 pollen taxa), allowing reconstruction of the environmental history of the northern Sahel over the last millennium. Our study confirms that the Little Ice Age was a period of increased dryness. This resulted in the disappearance of tropical trees that were developed in gallery forests during the Holocene humid period. However, freshwater inputs from the Senegal River remained constant during the whole millennium while being strongly impacted by sea level variations: An episode of sea level rise, already recorded in the Ferlo River valley, led to a supply of salt waters up to 1250 CE. It was only after 1720 CE that a dramatic event occurred with the massive development of marine to brackish diatoms at the expense of freshwater forms as a result of the weakening of the Senegal River inputs. Increased dry conditions during the second half of the 18th and the 19th centuries culminating 1826 CE led to the salinization of the core site with the development of Avicennia populations and halophilic plant species from the rear mangrove.

Improved lipid production in oleaginous brackish diatom Navicula phyllepta MACC8 using two-stage cultivation approach.

A two-stage cultivation method involving the initial growth in optimized conditions for biomass production followed by those for lipid production in oleaginous brackish diatom Navicula phyllepta MACC8 resulted in a proportional increase of lipid concentration along with biomass production. The diatom was further subjected to stress conditions by altering the nutrient components such as nitrate, phosphate, silicate, and temperature. Silicon deprivation resulted in the highest lipid percentage of 28.78% of weight at the end of the 18th day of the second stage. A significant increase in lipid content was observed on the complete removal of the nutrients silicon and urea one at a time, while the biomass showed a considerable reduction. The application of multiple nutrient stress conditions had a profound influence on the increased rate of lipid production. A combination of phosphate deprivation, silicate limitation and temperature reduction resulted in a significant increase in lipid percentage of 32.13% at the cost of reduced biomass (1.1g L-1), whereas phosphate deprivation, urea limitation, and temperature reduction resulted in lipid percentage of 27.58% with a biomass of 1.44g L-1 at the end of the second stage. Further, the results were supported by Nile red staining, FTIR, fatty acid profile and oxidative stress marker analyses. The changes in biochemical composition and oxidative stress parameters within the various stress conditions demonstrated the profound influence of the selected stress factors on the biodiesel productivity of the diatom, besides its stress tolerance. A two-phase culturing system, with multifactor stress application, especially nitrogen limitation along with phosphate starvation and temperature stress, would be the suitable method for gaining maximum biomass productivity and lipid content in diatom Navicula phyllepta MACC8 towards biofuel production.

Sediment distribution pattern and environmental implications of physico-chemical characteristics of the Akkulam-Veli Lake, South India

This study reports the spatial distributions of diatom assemblages and potential relationships between diatom diversity and environmental variables (C/N ratio, CaCO3%, clay mineralogy) using multivariate analyses in surface sediments of the Akkulam-Veli Lake. Surface sediment samples were collected at 19 sites throughout the lake to analyse diatom distribution, TOC, N, CaCO3%, clay mineralogy and sediment texture. The results suggest that the clay fraction is predominant in the eastern flank, whereas sand fraction is more in the western flank. TOC% and CaCO3% in the lake floor sediments are attributed to high organic activity within the lake and contributions from the vegetation around the lake margins. The results suggest that N is being added to the lake from secondary sources from catchment area leading to eutrophication of the lake. Further, clay mineralogy of the sediment samples reveals that kaolinite mineralogy dominates in clay fractions. Diatom studies show rich diversity of freshwater, marine and brackish diatoms and abundance of pollution-reflecting species such as Cyclotella sp. and Navicula sp.

Benthic Diatom Composition of Iztuzu Coastal Lake, Dalyan (Aegean Sea, Turkey)

<div><!--block-->Coastal lakes are shallow lakes that have variable characteristics through fluctuations and marine winds. In this study, benthic diatom composition in the coastal lake of Iztuzu, Dalyan of Muğla was investigated from the material collected in 2011 and 2015. Little research has been done on coastal lakes and lagoon diatom flora in Turkey; this study contributes a total of 49 taxa identified to species level and 9 of the taxa for the first time recorded for diatom flora of Turkey. The most abundant taxa were; Cocconeis placentula Ehrenberg, Diploneis bombus (Ehrenberg) Ehrenberg, Mastogloia sp. and Chamaepinnularia alexandrowiczii Witkowski, Lange-Bertalot and Metzeltin. The results reveal a habitat-specific flora for Iztuzu Lake and give an aspect of understanding the marine-brackish distribution of diatoms in coastal lakes and lagoons. The results extend the knowledge of marine and brackish diatoms in Turkey and could provide data for similar lagoon and lakes which are under protection.</div>

The impact of climate change and human activity on the ecological status of Bosten Lake, NW China, revealed by a diatom record for the last 2000 years

We present a 2000-year high-resolution diatom record from Bosten Lake (Yanqi Basin, Xinjiang), which is the largest inland freshwater lake in China. Our aims were to investigate the influence of climate change and human activity on its aquatic ecology during the late Holocene. During AD 280–480, a low water level and high salinity occurred, based on the dominance of epipelic and brackish diatoms. In addition, the diatom stratigraphy, combined with records of mean grain size and carbonate content, suggests that the lake experienced a high level of eolian input from the surrounding dunes. We hypothesize that during this interval, Loulan Kingdom, an important city of the Han Dynasty, located downstream of Bosten Lake, was abandoned due to the increasing scarcity of water resources and related harsh environmental conditions, including stronger eolian activity, which were the consequences of climate change. The dominance of meso-eutrophic small fragilarioid diatoms coincides with warm and arid intervals which also correspond to intensified human activity. These intervals correspond to the development of the Tang Dynasty (from ~AD 600), the ‘Medieval Warm Period’ (AD 1000–1200), and the last ~200 years. A shift from meso-eutrophic/benthic diatoms to oligotrophic/planktonic diatoms occurred during an interval of enhanced precipitation throughout the humid ‘Little Ice Age’ (AD 1600–1800). A return to markedly eutrophic conditions and a decreasing lake level occurred after the ‘Little Ice Age’, reflecting the more arid regional environment of the last 200 years. The high variability of the proxies suggests that both climate change and human activity were the major drivers of the ecological status of Bosten Lake during the late Holocene. We suggest that both the continuous increase of human activity and ongoing global warming will cause the major eutrophication or salinization of the freshwater lakes in the arid zone of northwest China.

Redeposition of volcaniclastic sediments by a tsunami 4600 years ago at Kushima City, south‐eastern Kyushu, Japan

AbstractThe Hyuga‐nada Sea, south‐eastern Kyushu, Japan, is located between a strong (Nankai Trough) and a weak interplate coupling zone (Ryukyu Trench). Over the past 400 years this area has only experienced Magnitude 7·5 earthquakes or smaller and associated small‐scale tsunamis. However, this short historical record most likely does not include the full range of high magnitude, low frequency giant earthquakes that might have occurred in the region. Thus, it is still unclear whether giant earthquakes and their associated tsunamis have occurred in this region. This paper reports on a prehistoric tsunami deposit discovered in a coastal lowland in south‐eastern Kyushu facing the Hyuga‐nada Sea. There is a reddish‐brown pumiceous layer preserved in a non‐marine, organic‐rich mud sequence obtained from onshore sediment cores. This layer is recognized as the ca 4600 year old Kirishima‐Miike tephra (that is now placed around 4500 years ago) sourced from Mount Kirishima, southern Kyushu. Another whitish pumiceous layer is evident below the Kirishima‐Miike tephra in almost all of the sediment cores. A relatively high percentage of marine and brackish diatoms is recorded within this lower pumiceous layer (but not in the surrounding muds or in the overlying Kirishima‐Miike tephra), indicating a marine or beach sediment source. Plant material obtained from organic‐rich mud immediately below the event layer was dated to ca 4430 to 4710 cal yr bp, providing a limiting‐maximum age for this marine incursion event. The presence of marine diatoms below the event layer is probably explained by pre‐seismic subsidence. An absence of the resting spore of the planktonic brackish diatom Cheatoceros and the appearance of the freshwater diatom Eunotia serra immediately above the event layer probably represents a marked change to a relatively low‐salinity environment. Assuming that there were no significant local geomorphological changes, such as drainage obstruction caused by formation of a new barrier spit, it is considered that co‐seismic or immediate post‐seismic uplift are the most likely explanations for this notable environmental change. Based on the crustal movements noted before and after the marine incursion, this event is interpreted here as an earthquake‐generated tsunami. Moreover, because of these notable seismic crustal movements the tsunamigenic earthquake probably occurred immediately offshore of the study site.

Navicula amoyensis sp. nov. (Bacillariophyceae), a new benthic brackish diatom species from the Jiulong River estuary, Southern China

Based on the light and scanning electron microscopy observations, we present a detailed description of a new brackish diatom Navicula amoyensis sp. nov. Samples were collected from an intertidal sand flat in the Jiulong River estuary, Southern China. The key diagnostic features of this species include the simple terminal raphe endings, broad terminal area, two rows of perpendicular apical pores, a wide contracted girdle region with pectinate margin and internal proximal raphe endings with a raised siliceous rib and accessory rib. Furthermore, the main taxonomic features of N. amoyensis sp. nov. and the genera Hippodonta and Navicula are also discussed in detail.

Diatom (Bacillariophyceae) assemblages in salt marshes of south‐central Chile: Relations with tidal inundation time and salinity

SUMMARYTo reconstruct sea‐level history from changes in tidal environments using diatom assemblages, we need to better understand the relations among brackish diatom assemblages and changing environments along elevational gradients from diverse coastal sites. Our statistical analysis reveals relations between environmental variables and brackish benthic diatom assemblages in the little studied region of south‐central Chile. Along four transects across salt marshes at two sites, we identified 224 diatom taxa in 112 samples. Detrended canonical correspondence analysis showed that tidal exposure time index and salinity were appropriately regressed against the abundance of diatom species using unimodal‐based methods. Our tests of classical and inverse regressions of weighted average and weighted averaging partial least squares (WA‐PLS) showed that WA‐PLS resulted in the highest coefficient of determination and the lowest root‐mean square of the error of prediction. Our regression will be useful in reconstructing environmental variables from fossil diatom assemblages in Chile.

A brackish diatom, Pseudofrustulia lancea gen. et sp. nov. (Bacillariophyceae), from the Pacific coast of Oregon (USA)

Light and electron microscope observations show that a brackish diatom taxon should be classified as a new species of a new genus; Pseudofrustulia lancea gen. et sp. nov. We propose separating Pseudofrustulia from other similar genera such as Frickea, Frustulia, Amphipleura, Muelleria, and Envekadea on the basis of its thickened axial ribs, raphe endings, axial costae, morphology of helictoglossa, size of striae on valve surfaces, and areolae on the inner side between its axial ribs and raphe. Girdle bands may be another diagnostic feature for the separation of Pseudofrustulia from related taxa, but more detailed observations using SEM images are required to determine if bands are diagnostic.

Molecular and morphological analyses of solitary forms of brackish Thalassiosiroid diatoms (Coscinodiscophyceae), with emphasis on their phenotypic plasticity

Blooms of centric diatoms are a common feature in the Bilbao estuary during summer when river flow is at its lowest and water temperature is above 20ºC. To gain insight into the specific composition of these diatom blooms, net samples and cultures of estuarine isolates were analysed under the scanning electron microscope (SEM) and by molecular analyses of the Internal Transcribed Spacers 1 and 2 plus the coding region 5.8S (ITS region) and the 28S rRNA gene. Seven species of solitary centric diatoms belonging to four genera were found in the estuary including: Conticribra weissflogii, Cyclotella atomus var. atomus, Cyclotella cryptica, Cyclotella marina, Cyclotella meneghiniana, Discostella pseudostelligera and Thalassiosira pseudonana. Dominant species during blooms were C. meneghiniana and Co. weissflogii in the upper estuary and D. pseudostelligera and T. pseudonana in the middle estuary. The morphological traits used to differentiate between species pairs of similar morphology (C. meneghiniana/C. cryptica or D. pseudostelligera/D. woltereckii) were observed to vary with environmental conditions, denoting a great deal of phenotypic plasticity which would hinder accurate identification of the species when using morphological approaches alone.

Shorter intervals between great earthquakes near Sendai: Scour ponds and a sand layer attributable to A.D. 1454 overwash

AbstractA sparsely documented tsunami in 1454 may subdivide the recurrence interval between the 869 and 2011 tsunamis near Sendai, as judged from geomorphic, stratigraphic, and archival evidence. Pond‐filled breaches cut across beach ridges on century‐old topographic maps. The basal pond deposit in one of these breaches postdates 1454. Stratigraphy on Sendai Plain includes a sand sheet that contains marine and brackish diatoms. Radiocarbon ages suggest that the sheet dates to 1406–1615 (2σ), and written records for this interval in Tohoku mention a tsunami in 1454. The inferred inundation extended 1.0–2.5 km inland from an approximate medieval shoreline. Simulated tsunamis that best account for the sand sheet require a thrust earthquake of moment magnitude 8.4 or larger. If the sand sheet represents the 1454 tsunami, the two most recent intervals between great thrust earthquakes in Sendai region spanned 585 and 557 years.