Diatom Community Structure Research Articles

Diatoms’ Diversity in the Assessment of the Impact of Diamond and Oil and Gas Mining on Aquatic Ecosystems of the Central Yakut Plain (Eastern Siberia, Yakutia) Using Bioindication and Statistical Mapping Methods

Diamond and oil and gas production carries risks to the aquatic ecosystem. In Eastern Siberia, on the territory of the Central Yakut Plain, mining development of the Yakut diamond-bearing province and Tas-Yuryakh oil and gas condensate field has been underway for several decades. But the problem of studying negative consequences in the region is covered only from the point of view of the impact on terrestrial ecosystems. The purpose of this study was to assess the impact of diamond and oil and gas production on the aquatic ecosystems of the region using the bioindicative properties of diatoms. The work used previously widely tested methods of ecological mapping, JASP, and species–environments relationship analysis. The results of chemical analysis of water showed that in oil and gas production areas, there is no pollution with petroleum products, but the concentration of silicon and zinc is increased. The study identified key pollutants in the Central Yakut Plain and demonstrated the effectiveness of diatoms as bioindicators. Elevated chloride levels were found in diamond mining areas, and increased copper levels were noted in oil production regions. In the diatom flora of the region, 144 species were identified, of which 137 are indicator species. Natural and anthropogenic clusters of environmental factors are identified, characterized by a specific effect on the species composition and taxonomic structure of diatom communities. The results obtained are suitable for assessing the level of anthropogenic impact on aquatic communities of photosynthetic microorganisms in permafrost conditions.

Benthic diatom diversity in microtidal mangrove estuaries

Mangrove habitats support taxonomically diverse benthic communities, yet their effects on microphytobenthos remain understudied. This study investigated the benthic diatom community structure of 17 microtidal mangrove estuaries situated along the east coast of South Africa. High sediment organic content (≤ 18.1 %) and clay fraction (≤ 17.5 %) measured in the Avicennia marina and Rhizophora mucronata habitats favoured diverse communities (H′ > 3) and the presence of unique benthic diatom species such as Gyrosigma balticum. The habitat complexity and stabilisation provided by the mangrove forests served as microrefugia for colonisation of benthic diatoms. Taxa displayed a broad range of nutrient tolerance, with some nutrient tolerant species (e.g., Halamphora acutiuscula, Navicula clausii, Navicula gregaria, and Navicula radiosa) dominating the communities in the Mbashe and Mnyameni estuaries. The presence of these nutrient tolerant taxa in relatively pristine systems serves as an early warning for possible anthropogenic nutrient enrichment.

HSP70A promotes the photosynthetic activity of marine diatom Phaeodactylum tricornutum under high temperature.

With global climate change, the high-temperature environment has severely impacted the community structure and phenotype of marine diatoms. Phaeodactylum tricornutum, a model species of marine diatom, is sensitive to high temperature, which grow slowly under high temperature. However, the regulatory mechanism of P. tricornutum in response to high-temperature is still unclear. In this study, we found that the expression level of the HSP70A in the wild type (WT) increased 28 times when exposed to high temperature (26°C) for 1 h, indicating that HSP70A plays a role in high temperature in P. tricornutum. Furthermore, overexpression and interferenceof HSP70A have great impact on the exponential growth phase of P. tricornutum under 26°C. Moreover, the results of Co-immunoprecipitation (Co-IP) suggested that HSP70A potentially involved in the correct folding of the photosynthetic system-related proteins (D1/D2), preventing aggregation. The photosynthetic activity results demonstrated that overexpression of HSP70A improves non-photochemical quenching (NPQ) activity under high-temperature stress. These results reveal that HSP70A regulates the photosynthetic activity of P. tricornutum under high temperatures. This study not only helps us to understand the photosynthetic activity of marine diatoms to high temperature but also provides a molecular mechanism for HSP70A in P. tricornutum under high-temperature stress.

Deviation from neutral species abundance distributions unveils geographical differences in the structure of diatom communities.

In recent years, the application of metagenomics techniques has advanced our understanding of plankton communities and their global distribution. Despite this progress, the relationship between the abundance distribution of diatom species and varying marine environmental conditions remains poorly understood. This study, leveraging data from the Tara Oceans expedition, tests the hypothesis that diatoms in sampled stations display a consistent species abundance distribution structure, as though they were sampled from a single ocean-wide metacommunity. Using a neutral sampling theory, we thus develop a framework to estimate the structure and diversity of diatom communities at each sampling station given the shape of the species abundance distribution of the metacommunity and the information of a reference station. Our analysis reveals a substantial temperature gradient in the discrepancies between predicted and observed biodiversity across the sampled stations. These findings challenge the hypothesis of a single neutral metacommunity, indicating that environmental differences substantially influence both the composition and structure of diatom communities.

Influence of the industrial pollutant on water quality, radioactivity levels, and biological communities in Ismailia Canal, Nile River, Egypt

In the twenty-first century, numerous forms of pollution have adversely impacted freshwater and the entire aquatic ecosystem. The higher population density in urban areas also contributes to increased releases of substances and thermal contaminants, significantly stressing the ecosystem of industrial companies. This study aimed to assess the potential pressure of industrial and municipal activities on water quality, radioactivity levels, and biological diversity, focusing on the consequences of radionuclides on periphytic diatom communities. Furthermore, the environmental impact of pollutants will be evaluated to monitor the ecological condition of the Ismailia Canal. Chemical analyses employed various instruments and methods to identify and quantify matter, with radionuclide elements measured by gamma spectrometry and diatoms counted and identified by inverted microscopy. Our results revealed that the canal was classified as excellent for irrigation, aquatic life, and drinking water based on FAO, CCME, and EWQS water quality indices, with high nutrient levels at Abu Za’baal fertilizer company. The activity concentration of 226Ra-series, 232Th-series, and 40K in the water and sediment samples for two seasons was within the guideline values, except for a few stations in the zone [B] (the industrial zone). Fertilizer samples (raw material) showed a high value of the 226Ra-series activity. Diatom community structure significantly varied across the different canal locations regarding the presence or absence of industrial activities, with no discernible variations between the study seasons. A specific variety of algal species was found to be predominant at the highest radioactive sites. Redundancy analysis (RDA) showed a significant correlation between parameters (pH, Na, TDS, PO4, SO4, SiO2, K, and CO3), radionuclides, environmental conditions, and the composition of the diatom community, especially in the area affected by industrial discharges. Moreover, the radiological hazard index in water and sediment remained below the maximum for two seasons. This research provides valuable data and information for communities and decision-makers, suggesting the strategic use of phycoremediation as a water biotreatment process to protect the valuable economic resources of the Ismailia Canal.

The impact of polyphenols on the structure of diatom communities inhabiting Cladophora glomerata mats during the vegetation cycle

Cladophora glomerata is the main macroalgae species responsible for the appearance of large mass compact algae formations, known as mats, in the fresh water of Lake Oporzynskie and the river Nielba, in western Poland. The mats are usually created by single species. In order to achieve seasonal domination, the algae secrete to the environment the allelopathic substances, which are phenolic compounds. In the period of intensive population growth, the thread-like thalli of these algae are richly incrusted with epiphytic diatoms. The amount of the secreted phenolic compounds changes in time within the vegetation period and depends on the weather conditions. The most abundant secretion of phenolic compounds takes place in July when, with increasing concentration of phenolic compounds in water, their content in the cells decreases.The main aim of the study was to establish the effect of the phenolic compounds secreted by C. glomerata thalli on the diatoms growing on them. According to our results, polyphenolic compounds have an impact not only on the abundance of diatom communities, but also on the structure of their communities. With increasing concentration of polyphenols, the abundance of Achnathidium minutissimum, Gomphonema olivaceum, Cocconeis pediculus, Navicula tripunctata decreased, while that of Amphora ovalis, Navicula rostellata, Staurosira construens, Cymbella lange-bartelotti increased. The species Cocconeis placentula reached domination thanks to the favorable influence of the environment and the effect of polyphenols secreted by the macroalgae. The variation in the diatom communities' structure was proved to also depend on the habitat parameters, mainly: EC, Turbidity, N-NH4, N-NO3, TDS.

Improvement of the knowledge of diatom ecology by coupling geochemistry, radioactivity and taxa inventory in thermo-mineral springs of a volcanic and upland area in south-central France, the Massif Central

ABSTRACT In connection with its geological history, many thermo-mineral springs are present in the Massif Central (France). The physicochemical characteristics of these springs (temperature, mineralization, gas content) result both from their deep circulation and from the geological formations or surface waters with which they interact during their ascent. In mineral springs, diatoms are well represented. To date, no study has focused on coupling the origin of water with diatom communities, whether in the Massif Central or in other parts of the world. The purpose of this study is to cross the information obtained on the water and the diatoms in order to analyse the biodiversity and improve knowledge of the species autecology. Twelve mineral springs with some of which have high levels of radioactivity were studied in the Massif Central. As results, the geochemical facies, the origin of the water and the Total Dissolved Solids influence the taxonomic composition but not the specific richness, Shannon index and Evenness. Furthermore, 222Rn influences diatom richness and community structure. Planothidium frequentissimum, Crenotia angustior and Sellaphora labernardierei were associated with high values of 222Rn activity. The water temperature was a factor that influences diatom species distribution. Some species appears to be more sensitive to the composition of water, such as Planothidium frequentissimum which attests to a mixing between deep and surface waters.

Spatial patterns of benthic diatom community structure in the largest northwestern river of Cambodia (Sangker River)

To date, very little is known about the relative importance of physicochemical factors structuring the benthic diatom community in the flood-pulse tropical ecosystems. This paper aims to investigate the spatial distribution of the benthic diatom community in a poorly studied river catchment of the Tonle Sap Basin in Cambodia. Diatom samples were collected at nineteen (19) monitoring sites from 2018 to 2023 along the Sangker River, and the hierarchical clustering technique was applied to characterize the variation in diatom community structure based on the similarity of diatom genera composition. Seventy-eight (78) diatom genera belonging to 36 families, 18 orders, and 5 classes of diatom flora were recorded. Gomphonema Ehrenberg, Nitzschia Hassall, and Navicula Bory were the most dominant diatom genera in the catchment area. Accordingly, three main diatom assemblages (Ia, Ib, and II) were classified, and 11 indicator genera were identified. Indeed, the identified assemblages reflect the change of diatiom community composition from the upstream assemblage (Ia), middle course (Ib), and floodplain assemblage (II). Dissolved oxygen (DO), pH, conductivity (EC), total phosphorus (TP), and silicon dioxide (SiO2) were the physico-chemical determinants of benthic diatom communities, while physical factors (DO, pH, and nutrients) seemed to be more important than chemical factors. Consequently, any disturbances to the physical condition of the river would drive an abrupt shift in the diatom community’s diversity and structure. These findings pave an essential step towards the establishment of sustainable biomonitoring programs in developing countries such as Cambodia to protect aquatic ecosystems from global change.

The distribution of diatom assemblages with the effects of environmental parameters and ecological status assessment based on diatom indices in the lentic systems of the Akarçay and Asi Basins (Türkiye).

In order to detect the effects of different stressors on the littoral diatom assemblages and biodiversity of the lentic systems in two different basins in Türkiye, 15 lentic systems in the Akarçay and Asi basins were sampled three times (spring, summer, and fall) for littoral diatoms and environmental variables. The biological assessment of these sites was also evaluated using 9 different river and lake diatom indices. Based on the total phosphorus (TP), total nitrogen (TN), electrical conductivity (EC), salinity (SAL) values, and dominant diatom species, three lentic systems in Akarçay Basin (Lake Eber, 26 Ağustos Pond, and Lake Karamık) were more eutrophic and under the pressure of anthropogenic and climatic (precipitation) stressors. Trophic diatom index for lakes (TDIL) showed a higher correlation with TN and TP and was the most effective index in explaining ecological quality in 15 lentic systems. The species richness of diatoms was also negatively affected by EC and SAL values. The lentic systems of the two basins were separated from each other based on the species composition and the distribution of the dominant species with the effect of altitude (ALT). Considering the distribution of diatom assemblage of the lentic systems in these two basins, anthropogenic, climatic, and geographical factors have become prominent to shape the diatom community structure.

Assessing diatom distribution in Cambay Basin, Western Arabian Sea: impacts of oil spillage and chemical variables.

Freshwater and marine diatoms produce the majority of the oxygen in aquatic systems. Estimates range from 12,000 to 30,000 species, and spatial distribution varies globally. There is significant variation in diatom diversity based on geographical and environmental conditions as well as the physicochemical characteristics of the habitat. Therefore, understanding the underlying factors that contribute to changes in diatom community structures requires a comprehensive understanding of taxons. A study of diatom assemblages from the Cambay Basin, Western Arabian Sea, was conducted, particularly on oil fields. A total of 37 samples were collected; nine were from oil fields. We evaluated micro-oil spills using Fourier transform infrared (FTIR) analysis and microscopic techniques. Correlations were established through the ordination analysis of pernicious physical and chemical water variables (BOD, COD, TDS, pH, temperature, and DO), including principal component analysis (PCA). The oil field sites showed more total dissolved solids (TDS) and chemical oxygen demand (COD) than the respective marine control sites. The study does not display a cause-and-effect relationship, but we observed a positive correlation between increasing silica concentrations and diatom growth in oil fields. In contrast, high aluminium concentrations in oil fields negatively impacted the growth of diatom assemblage and abundance. When surveyed in nine oil fields, we found that Gomphonella pseudosphaerophorum and Nitzschia palea are well adapted to oil concentrations up to 40 ppm.

Effects of mesohabitat, grazing and substratum roughness on locally common and rare diatom species

Abstract Habitat type and grazing are key factors controlling benthic diatom communities. Nonetheless, the strength of grazing may depend on the habitat complexity at fine (substratum roughness) and meso scales (mesohabitat type). The interaction between grazers and physical conditions may thus be an important factor shaping benthic diatom communities. Several investigations have evaluated how habitat type, grazing and substratum roughness separately affect the biomass, species richness and community structure of algal communities. However, how these factors act together remains poorly understood, particularly for sets of common and rare species. The latter is important for understanding whether common and rare species are affected differently by environmental filters at the local scale. We investigated the effects of mesohabitat type, grazer occurrence and substratum roughness as well as their interactions on benthic diatom communities in a split‐split‐plot field experiment consisting of hierarchical treatments: (i) mesohabitat (pools and riffles); (ii) grazer occurrence (presence or absence of grazers >1 cm in size); and (iii) substratum roughness (smooth and rough substrata). We analysed the entire community and also datasets of common and rare species. Here, we define common and rare species based on their abundance–occupancy relationships, with rare species presenting low mean abundance per experimental unit (between 0.025 and 8.2) and low occupancy (between 2.5% and 25%). Substratum roughness was the main factor explaining differences in species richness, with higher species richness found on rough than on smooth substrata for both the complete dataset and for common and rare species. There was evidence that the interactions between mesohabitat and grazer occurrence and between mesohabitat and substratum roughness affected community structure (relative abundances) for the complete dataset and for common species, whereas the three‐way interaction between mesohabitat, grazer and substratum roughness affected community structure of rare species. Our findings emphasise that crevices are important microhabitats that allow the establishment of both common and rare species. Furthermore, our results suggest that physical differences between mesohabitats influenced the effect of grazers on the community structure of common and rare species. For common species, the effects of this interaction were difficult to depict, but we found a change in the second‐most‐common species between mesohabitats and depending on the occurrence of grazers. For rare species, grazers more clearly affected community structure on smooth substrata in riffles than in pools. Our results demonstrate that local patterns of common and rare diatom species resulted from distinct combinations of the evaluated environmental filters. Together, our results highlight how multifactorial field experiments are key to understanding the main environmental filters driving the species richness and community structure of benthic diatom communities.

Unveiling relationships between ecosystem services and aquatic communities in urban streams

River and stream ecosystems within cities can provide important Ecosystem Services (ES) to urban population along with the maintenance of biodiversity. Increasing urbanization with land use change can affect biodiversity, impacting ES provision, but the relationships between biota and ES are complex and poorly understood. This study aims to explore relationships between aquatic biodiversity (communities’ composition and structure), urbanization and ES provided by urban streams. Nine streams were surveyed within a city area (up to 8 km of the city centre) focusing on common biological indicators (i.e., macroinvertebrates and diatoms), as well as several indicators of Provisioning (N = 7), Regulation (N = 14) and Cultural (N = 23) services for this type of ecosystem. Urban stream sampling sites were also assessed in terms of their urbanization degree, according to the surrounding imperviousness area (IMD). Pearson correlations showed trends of negative relationships between IMD and both Provisioning and Regulating services. Yet, urbanization effects on the biota seemed to be mitigated due to enhanced hidromorphological site features. The community structure and composition of invertebrates and diatoms was differently associated to ES (BIOENV analysis). Whereas macroinvertebrate communities related specifically with Provisioning and Regulating indicators, the diatom responded just to regulating indicators. Overall, this study showed that aquatic biodiversity is linkable with ES provided by urban streams, and such relationship depends on specific ES indicators mainly for Provisioning and Regulating services. Additionally, macroinvertebrate communities can be used as a suitable indicator for the potential of streams in supplying Provisioning and Regulating ecosystem services. This shows that their indicator value goes beyond their known potential as indicators of structural and functional integrity of river ecosystems. These results also reinforce the need to protect nature associated to running water ecosystems in urbanized areas, as they provide green and blue solutions for the sustainability of cities.

Differences in Phytobenthic Diatom Community between Natural and Channelized River Sections.

The structure of phytobenthic diatom communities was studied to reveal differences between natural and channelized river sections in Slovenia. As part of the national monitoring of surface waters, samples of phytobenthos were collected at 85 sites throughout the country according to standard protocols. At the same time, basic environmental parameters were also assessed. Trophic (TI) and saprobic (SI) indices were calculated based on diatoms and other algae, while diversity indices and gradient analyses were performed only for the diatom community. The results showed that channelized rivers harbor significantly more diverse benthic diatom communities than natural sections, mainly due to the significantly higher number of motile diatom taxa that are able to take advantage of more nutrient-rich and less-shaded river sections because of their high adaptability. Selected environmental parameters explained 34% of the variability in diatom community structure when taxa were classified into ecological types. The removal of Achnanthidium minutissimum yielded clearer results (24.1%) than the total species matrix (22.6%). Therefore, we suggest excluding this taxon from calculations of TI, SI, or other indices when it is determined as A. minutissimum complex, because A. minutissimum complex was most abundant in both types of reaches in our study and has a wide ecological amplitude, which reduces the indicative power of the diatom community in the evaluation of environmental conditions and ecological status.

Long-term functional recovery and associated microbial community structure after sediment drying and bedform migration

Climate change and erosion from agricultural areas cause increased drying periods and bedform migration of riverbeds, respectively, worldwide. Both sediment drying and bedform migration can independently stress the microbial community residing in the riverbed. Here, we investigated the microbial response after exposure to these stressors with a focus on long-term recovery. We conducted an in situ experiment to investigate the long-term (8 months) functional and structural recovery of benthic microbial communities from either sediment drying (episodic severe stressor) or bedform migration (frequent moderate stressor). Stressed sediment associated communities were rewetted (dried sediments) and immobilized (migrated sediments) and exposed in the River Spree (north-eastern Germany) to initiate the recovery process. We then evaluated the microbial function (community respiration, net community production and extracellular enzymatic activities) as well as the bacterial, fungal and diatom community structure (16S rRNA gene and ITS region metabarcoding, and microscopic diatom morphotype classification). We observed different recovery times for community respiration (less than 7 days) and gross primary production (more than 5 months), implying a shift toward net heterotrophy in the first few months after stress exposure. Similarly, we observed a strong autotrophic community response (particularly associated with the diatoms Navicula and Fragilaria), especially in migrated sediments. The bacterial and fungal community response to sediment drying was stronger than to bedform migration (particularly associated with the bacterium Flavobacterium and the fungi Alternaria sp. and Aureobasidium pullulans). Our results show that sediment drying and bedform migration had a significant impact on the microbial community function and structure, which persisted for several months after the stress. Due to the surprising long period of recovery, successive stress events combined with seasonal effects will likely hamper the ongoing recovery process with severe alterations to the microbial function and structure. These findings extend the concept of ecosystem resilience and stability on the dimensions of timescale and seasonal environmental variations. Legacy effects are expected to play a key role when facing future stress.

High-resolution history of oxygen depletion in the SW Baltic Sea since the mid-19th century as revealed by bivalve shells

The Baltic Sea serves as a model region to study processes leading to oxygen depletion. Reconstructing past low-oxygen occurrences, specifically hypoxia, is crucial to understand current ecological disturbances and developing future mitigation strategies. The history of dissolved oxygen (DO) concentration in some Baltic Sea basins has been investigated in previous studies, but temporally well-constrained, inter-annual and better resolved DO reconstructions are still scarce. Here, we present precisely dated, high-resolution DO record since the mid-19th century reconstructed from Mn/Cashell values of Arctica islandica (Bivalvia) collected in the Mecklenburg Bight. According to the data, this area experienced similar low oxygenation during the second half of the 19th century and the late 20th century, but DO variability increased: A 12–15-yr oscillation prevailed in the 19th century, but a 4–6-year period dominated in the late 20th century. Shortly after the onset of the Industrial Revolution around 1850, Mn/Cashell values increased, indicating a DO decrease, probably caused by strong anthropogenic nutrient input. More recently, phosphate levels and inflows of oxygen-rich North Sea water have been identified as major factors controlling the bottom water oxygenation. For example, the increase in DO in the mid-1990s was linked to the decrease in phosphate content and several Major Baltic Inflows. The strong Ba/Cashell rise between the 1860s and the turn of the century most likely reflects changes in diatom community structure rather than a bloom of mass phytoplankton. This is supported by largely unchanged Mn/Cashell and shell growth. Decadal and multi-decadal cycles of shell growth rate correlated strongly with the Atlantic Multidecadal Variability, likely reflecting changes in atmospheric circulation patterns, precipitation rate and riverine nutrient supply. To further improve the management and protection of ecosystems in the Baltic Sea, a larger number of such high-resolution retrospective studies covering long periods of time and large regions are needed.

Influence and Driving of Environmental Heterogeneity on the Epilithic Diatom Community in Xiangxi River, a Tributary of the Three Gorges Reservoir Area

Environmental heterogeneity can not only increase species diversity to some extent but also affect the stability of terrestrial communities. However, how environmental heterogeneity affects species diversity of epilithic diatom communities in aquatic ecosystems is rarely reported. In this study, therefore, epilithic diatoms and their roles in driving species diversity were explored by quantifying and comparing the environmental heterogeneity in Xiangxi River, a tributary of the Three Gorges Reservoir Area (TGR), on a time scale. The results showed that environmental heterogeneity, taxonomic β-diversity, and functional β-diversity in non-impoundment periods were significantly higher than those in impoundment periods. Moreover, the turnover components in the two hydrological periods showed the highest contribution to β-diversity. However, the taxonomic α-diversity in impoundment periods was significantly higher than that in non-impoundment periods. In addition, functional richness in functional α-diversity was significantly higher in non-impoundment periods than that in impoundment periods, whereas there was no significant difference in other functional α-diversity, i.e., functional dispersion and functional evenness, found between the two periods. Multiple regression on (dis)similarity matrices (MRM) analysis indicated that ammonium nitrogen (NH4+-N) and silicate (SiO32--Si) were the key environmental heterogeneous factors affecting the epilithic diatom community in Xiangxi River during the non-impoundment periods, whereas the key heterogeneous factors were ammonium nitrogen (NH4+-N), silicate (SiO32--Si), and total phosphorus (TP) during the impoundment periods. These results suggested that the environmental heterogeneity during different hydrological periods in TGR can significantly affect the community structure of epilithic diatoms, resulting in the differentiation of species within the community and even affecting the stability of aquatic ecosystems.

Analysis of the Community Structure of Diatoms (Bacillariophyta) in Roraima Fluvial Systems, Amazon – Brazil

The State of Roraima (Amazon - Brazil) is considered well-preserved from an environmental point of view, sheltering a great variety of rivers and forest and “cerrado” streams, with white (muddy), black and clear waters. From the identification of the planktonic community of diatoms, ecological indices and statistical analyzes were applied in order to determine the degree of abundance and species richness among the different ecosystems in the region. Qualitative and quantitative samples of phytoplankton were obtained during periods of low water (December to March), as well as measurements and analyzes of limnological parameters: water temperature (ºC), pH, dissolved oxygen (mg/L), oxygen saturation (%), transparency (m), total dissolved ions Na+, K+, Ca2+, Mg2+, Fe2+, Fe3+ and Cl-, total P and N (mg/L) and Chlorophyll-a (µg/L). A total of 172 plankton samples from 43 sampling points (20 in rivers and 23 in streams) were carried out. The low water period was characterized by slightly acidic to neutral pH, with low transparency and variations in conductivity and concentration of the ionic composition. The results indicated similarity in diatom composition between rivers and streams, with little heterogeneity in “cerrado” streams. Considering climate oscillation and spatial distribution, the PCA highlighted the parameters conductivity, dissolved ions, total P and chlorophyll-a as preponderant to explain the behavior observed in the distribution of communities. For three components, the cumulative explanation was 68.6%. The ecological indices of richness and diversity indicated high similarity between rivers and streams, with good stability, homogeneity and ecological diversity for bacillariophytic diatoms. There were, however, some areas that, depending on the type of water and ionic concentration, showed some divergence in the composition of the diatom community. As environmental indicators, the diatoms showed that the water quality in the region is well-preserved, without eutrophication signals.

Annual-scale assessment of mid-20th century anthropogenic impacts on the algal ecology of Crawford Lake, Ontario, Canada.

Meromictic Crawford Lake, located in SW Ontario, Canada is characterized by varved sediments, making it suitable for high-resolution paleoecological studies. Freeze cores, the only coring method available that reliably preserves the fragile laminations representative of seasonal deposition in the lake, were used to document siliceous diatom and chrysophyte community structure at an annual resolution from 1930-1990CE. Stratigraphically constrained cluster analysis identified major assemblage changes that are believed to have been caused by local, regional and possibly global anthropogenic impacts. The assemblage changes within the siliceous algae are attributed to regional weather and increased industrial emissions and related effects of acid deposition on the lake's catchment associated with the Great Acceleration -the massive economic, industrial, and demographic expansion beginning in the mid-20th century. Observed increases in spheroidal carbonaceous particles (SCPs) in varved lake sediment dating to the early 1950s record rapidly expanding steel production without emission controls around 30 km upwind of the lake. The findings reported here reflect major changes in earth systems that the Anthropocene Working Group recommends for a proposed epoch to be termed the Anthropocene, providing support for the laminated sediments from Crawford Lake as a potential Global boundary Stratotype Section and Point (GSSP).

Characteristics of Benthic Diatom Community Structure and Water Ecological Health Evaluation in the Lalin River Basin

With the improvement of public requirements for the health status of aquatic ecosystems, there have been innovative assessment methods developed for aquatic ecosystems. In this study, benthic algae assemblages and water quality variables were analyzed to develop a benthic diatom-based index of biotic integrity (D-IBI) for the assessment of the aquatic environment in the Lalin River. In addition, using redundancy analysis (RDA) based on dominant species and physicochemical indexes, the ecological distribution characteristics of the benthic diatom community were revealed, and the key influencing factors were identified. The results showed that the benthic diatom community structure in the Lalin River basin had obvious spatial differences. The application of the index revealed that the water quality could be described as excellent condition in the upper reaches of the Lalin River, good to common condition in the middle of the sites, and moderate to poor condition in the downstream. The assessment further revealed that the main reason for the degradation of the Lalin River ecosystem was nutrient enrichment through agricultural land use.

Diatom DNA metabarcoding to assess the effect of natural radioactivity in mineral springs on ASV of benthic diatom communities

Little is still known about the low dose effects of radiation on the microbial communities in the environment. Mineral springs are ecosystems than can be affected by natural radioactivity. These extreme environments are, therefore, observatories for studying the influence of chronic radioactivity on the natural biota. In these ecosystems we find diatoms, unicellular microalgae, playing an essential role in the food chain. The present study aimed to investigate, using DNA metabarcoding, the effect of natural radioactivity in two environmental compartments (i.e. spring sediments and water) on the genetic richness, diversity and structure of diatom communities in 16 mineral springs in the Massif Central, France. Diatom biofilms were collected during October 2019, and a 312 bp region of the chloroplast gene rbcL (coding for the Ribulose Bisphosphate Carboxylase) used as a barcode for taxonomic assignation. A total of 565 amplicon sequence variants (ASV) were found. The dominant ASV were associated with Navicula sanctamargaritae, Gedaniella sp., Planothidium frequentissimum, Navicula veneta, Diploneis vacillans, Amphora copulata, Pinnularia brebissonii, Halamphora coffeaeformis, Gomphonema saprophilum, and Nitzschia vitrea, but some of the ASVs could not be assigned at the species level. Pearson correlation failed to show a correlation between ASV’ richness and radioactivity parameters. Non-parametric MANOVA analysis based on ASVs occurrence or abundances revealed that geographical location was the main factor influencing ASVs distribution. Interestingly, 238U was the second factor that explained diatom ASV structure. Among the ASVs in the mineral springs monitored, ASV associated with one of the genetic variants of Planothidium frequentissimum was well represented in the springs and with higher levels of 238U, suggesting its high tolerance to this particular radionuclide. This diatom species may therefore represent a bio-indicator of high natural levels of uranium.