Asterionella Formosa Research Articles

Diatom dynamics during the last six centuries in Lake Odensjön: a new varved sediment record from southern Sweden

AbstractVarved lake sediments offer valuable insight into past environmental conditions with high temporal resolution and precise chronological control. A combination of diatom and geochemical analyses of the recently deposited sediments of Odensjön, a small dimictic lake in southern Sweden, shows alternating light and dark laminae composed of greater amounts of biogenic silica and organic matter, respectively. As confirmed by independent radiometric dating and Pb pollution data, and supported by scanning electron microscopy of individual laminae, these features represent ongoing deposition of biogenic varves. Corresponding diatom and geochemical data obtained from a 92-cm long freeze core provide evidence of substantial lake-ecosystem dynamics during the last six centuries, related mainly to variations in light penetration and wind shear driven by human-induced changes in catchment vegetation. The diatom assemblage of Odensjön’s varved sediments is dominated by planktonic species, primarily Asterionella formosa, Fragilaria saxoplanktonica and Discostella lacuskarluki during periods of forest cover, while increased catchment openness from the mid-1500s to the late 1800s led to increased abundance of Lindavia comensis. Long-term variations in climate and land use, mediated through changing length of the ice-cover season and nutrient input, respectively, probably contributed to the observed trends, as well as to variations in the appearance and visibility of the varve record across the sampled sediment sequence. Odensjön represents the southernmost varved sediment record in Fennoscandia documented to date, offering potential to study the effects of various types of external forcing on its sensitive lacustrine ecosystem since the Late Weichselian deglaciation. In the present study, we investigated the possibility of assessing the local impacts of two major, historically documented volcanic events, Laki 1783–84 and Tambora 1815, which are known to have affected European societies. Although the mildly alkaline waters of the lake are well buffered and hence relatively resilient to volcanic acid deposition, a minor response to the Laki eruption may be recorded in the diatom stratigraphy.

SPECIES COMPOSITION OF PHYTOPLANKTON OF THE BLAGODATNOYE LAKE (ITURUP ISLAND, KURIL ISLANDS, RUSSIA)

Algological studies conducted in June–August 2021 on the lagoon Blagodatnoye Lake (Iturup Island) and showed a high diversity of species composition of cyanobacteria and algae (274 species and intraspecifi c taxa from eight divisions: Cyanobacteria, Miozoa, Bacillariophyta, Chlorophyta, Charophyta, Criptista, Ochrophyta, Euglenozoa). Diatoms make up a signifi cant share in the formation of algofl ora (73,2 % of the total number of species). Complexes of dominant species in lake plankton are represented by cyanobacteria and diatoms: Aulacoseira granulata and it’s variation A. granulata var. angustissima Aphanizomenon fl os-aquae (August). The maximum values of quantitative indicators of the main dominants reached: N = 1323,3 thousand cells/l, B = 685,5 mg/l for Asterionella formosa, and N = 3646 thousand cells/l, B = 4579,4 mg/l for Aulacoseira granulata. The ecological and geographical characteristics of the algal fl ora of Blagodatnoe Lake were carried out: benthic species (48,2 % of the total number of taxa), indiff erent to salinity change (68,6 %), alkaliphilic (42,3 %), cosmopolitan (70,1 %) species were predominance, and oligosaprobionts and betamesosaprobionts were 35,4 and 33,9 %, respectively.

Flora of Lake Shirokoe and its environs of the Birsky district of the Republic of Bashkortostan

The article presents an analysis of the flora of Lake Shirokoe and its surroundings of the Birsky district of the Republic of Bashkortostan. It is shown that the flora is represented by 72 species of plants, of which: 8 species of trees, 1 species of shrubs, 2 species of semi-shrubs, 64 species of herbaceous plants. A total of 32 families, 64 genera and 72 species are represented. The most representative family is the Asteraceae, which includes 14 species. Of the small ones, 19 families with 1 species have been registered. Analysis of the flora of Lake Shirokoe shows that its composition is characterized by the predominance of hemicroptophytes - 25 species (34.7%) and cryptophytes - 17 species (23.6%). The least represented are therophytes (9.72%). Phanerophytes are also present in the flora (12.5%). These spectra of life forms belong to the moderately cold zone. The analysis of algae of the lake is carried out. It is represented by 14 species from two divisions (Diatomeae and Chlorophyta). The analysis of phytoplankton of the lake was carried out. It is represented by such species as: Navicula oblonga Kutz, Navicula menisculus Schum, Navicula viridula Kutz, Navicula elegans Schum, Cocconeis pediculus Ehrenberg, Nitzschia sigmoidea Nitzsch, Melosira varians C.Agardh, Pinnularia gibba Ehrenb, Surirella bifida Kütz, Asterionella formosa Hassall. An indicator species of pure water (Melosira varians C.Agardh) was found in water samples.

Production of Fluorescent Dissolved Organic Matter by Microalgae Strains from the Ob and Yenisei Gulfs (Siberia).

Dissolved organic matter (DOM) is an important component of aquatic environments; it plays a key role in the biogeochemical cycles of many chemical elements. Using excitation-emission matrix fluorescence spectroscopy, we examined the fluorescent fraction of DOM (FDOM) produced at the stationary phase of growth of five strains of microalgae sampled and isolated from the Ob and Yenisei gulfs. Based on the morphological and molecular descriptions, the strains were identified as diatoms (Asterionella formosa, Fragilaria cf. crotonensis, and Stephanodiscus hantzschii), green microalgae (Desmodesmus armatus), and yellow-green microalgae (Tribonema cf. minus). Three fluorescent components were validated in parallel factor analysis (PARAFAC): one of them was characterized by protein-like fluorescence (similar to peak T), two others, by humic-like fluorescence (peaks A and C). The portion of fluorescence intensity of humic compounds (peak A) to the total fluorescence intensity was the lowest (27 ± 5%) and showed little variation between species. Protein-like fluorescence was most intense (45 ± 16%), but along with humic-like fluorescence with emission maximum at 470 nm (28 ± 14%), varied considerably for different algae strains. The direct optical investigation of FDOM produced during the cultivation of the studied algae strains confirms the possibility of autochthonous production of humic-like FDOM in the Arctic shelf regions.

Cover Image

The cover image is based on the Original Article A trophic cascade triggers blooms of Asterionella formosa in subtropical eutrophic Lake Taihu, China, by Xia Liu et al. https://doi.org/10.1111/fwb.13986.

A trophic cascade triggers blooms of Asterionella formosa in subtropical eutrophic Lake Taihu, China

Abstract The importance of trophic interactions for determining the distributions, abundances, and taxonomic compositions of organisms in ecosystems has long been studied and debated. Here we test the effect of a trophic cascade on diatom (Asterionella formosa) blooms in subtropical, eutrophic Lake Taihu, China. A long‐term data series (2005–2015) on planktivorous fish, zooplankton and diatoms has been analysed. Structural equation modelling is used to test our hypotheses about the influences of top‐down and bottom‐up forces on A. formosa. Since 2009, a spring bloom of A. formosa has occurred in the lake, coinciding with a reduction of Daphnia galeata biomass and of total cladoceran biomass following a marked increase in the stock of planktivorous fish (bighead carp and silver carp). Light, phosphorus (total and soluble reactive phosphate) and silica did not act as limiting factors for the growth of A. formosa. Structural equation modelling analysis showed that top‐down effects of cladocerans on A. formosa biomass were more important than bottom‐up effects (wind speed and soluble reactive phosphate). Although A. formosa was negatively correlated with total nitrogen, total with other inorganic nitrogen (NO3 and NH4) did not restrict the proliferation of diatom blooms after 2007. These results suggested that the substantial reduction of the Daphnia population caused a diatom bloom through a trophic cascade by planktivorous fish. Our study provides new insight into the effects of trophic interactions on diatom bloom formation in natural freshwater ecosystems.

Planktonic diatom communities in temperate South-Central Chilean lakes with a focus on Asterionella formosa and the genus Aulacoseira

Planktonic diatom communities in temperate South-Central Chilean lakes with a focus on Asterionella formosa and the genus Aulacoseira

Species diversity of phyto- and zooplankton in the water bodies of Kharanorskaya State District Power Plant, Transbaikalia (according to 2019 data)

We described the taxonomic structure of planktonic associations in the water bodies of Kharanor State District Power Plant (cooling pond, water supply, drainage, and water intake channels of Kharanor reservoir located in the arid zone of the south-eastern Transbaikalia in a highly continental climate). Hydrobiological researches were conducted in April, July, and October 2019. We identified 141 algal taxa ranked below the genus, representing the divisions of Cyanobacteria (15 taxa), Bacillariophyta (41), Chrysophyta (10), Cryptophyta (3), Dinophyta (4), Charophyta (8), Chlorophyta (56), and Euglenophyta (4), and 52 zooplankton taxa, including 28 species and subspecies of Rotifera, 15 species of Cladocera, and 9 species of Copepoda. In the cooling reservoir, the plankton community included 135 phytoplankton taxa and 38 zooplankton species; 58 algal taxa and 27 invertebrate species were sampled in the water supply channel, 50 taxa and 26 species were sampled in the drainage channel, and 94 taxa and 24 species were collected from water intake channel respectively. Six diatom species (Stephanodiscus hantzschii, Nitzschia sigmoidea, Fragilaria radians, Asterionella formosa, Ulnaria ulna) and four zooplankton species (rotifers Asplanchna priodonta and crustaceans Daphnia galeata, Bosmina longirostris, Thermocyclops crassus) occurred in all water bodies during the entire study period.

Response of Aquatic Organisms Communities to Global Climate Changes and Anthropogenic Impact: Evidence from Listvennichny Bay of Lake Baikal

Simple SummaryLake Baikal is ranked first among the world’s lakes in terms of freshwater reserves (23,000 km3). It is a UNESCO World Heritage Site, and its biota is represented by unique fauna and flora, with endemics accounting for more than 60%. What is happening in the Baikal ecosystem in recent decades due to global climate change and anthropogenic impacts? In this paper, we studied this issue on the example of one of the few open bays on the western shore of Lake Baikal, as well as of some remote areas. It has been found that the plankton composition is dominated by thermophilic species; the role of endemic species in the formation of total biomass is decreasing, which confirms the ecosystem’s response to climate warming. As a result of human activity, filamentous algae bloom suppresses endemic algae species and reduces mollusk proportion. The coastal zone of Lake Baikal is taking on the features of common shallow freshwater lakes due to the predominance of cosmopolitan and widespread Palearctic species. It is necessary to monitor the Baikal ecosystem in the changing climate and to strengthen control over human activities on the shores of the lake.Recent studies have revealed how the freshwater biota of Lake Baikal responds to climate change and anthropogenic impacts. We studied phyto- and zooplankton, as well as phyto- and zoobenthos, in the open coastal waters of the southern basin of the lake and of Listvennichny Bay. A total of 180 aquatic organism taxa were recorded. The response of the Baikal ecosystem to climate change can be traced by changes in the species composition of planktonic communities of the lake’s open coasts in summer. The key species were thermophilic the Anabaena lemmermannii P. Richt. (Fij = +0.7) blue-green algae, the Asplanchna priodonta Gosse (Fij = +0.6) rotifers in 2016, the Rhodomonas pusilla (Bachm.) Javorn. (Fij = +0.5) cold-loving algae, and the Cyclops kolensis Lilljeborg (Fij = +0.9) copepods in the past century. The proportion of Chlorophyta decreased from 63% to 17%; the Cyanophyta increased from 3% to 11% in the total biomass of phytoplankton; and the proportion of Cladocera and Rotifera increased to 26% and 11% in the biomass of zooplankton, respectively. Human activity makes an additional contribution to the eutrophication of coastal waters. The Dinobryon species, the cosmopolitan Asterionella formosa Hass. and Fragilaria radians Kütz., dominated phytoplankton, and filamentous algae, Spirogyra, dominated at the bottom in the area with anthropogenic impact. The trophic level was higher than at the unaffected background site: the saprobity index varied from 1.45 to 2.17; the ratio of eutrophic species to oligotrophic species ranged from 1:2 to 3:1, and the ratio of mesosaprobiont biomass to endemics biomass ranged from 2:1 to 7:1. Currently, the boundaries of eutrophication zones of shallow waters in Lake Baikal are expanding, and its coastal zone has acquired features typical of freshwater bodies of the eutrophic type.

Inorganic carbon uptake in a freshwater diatom, Asterionella formosa (Bacillariophyceae): from ecology to genomics

ABSTRACT Inorganic carbon availability can limit primary productivity and control species composition of freshwater phytoplankton. This is despite the presence of CO2-concentrating mechanisms (CCMs) in some species that maximize inorganic carbon uptake. We investigated the effects of inorganic carbon on the seasonal distribution, growth rates and photosynthesis of a freshwater diatom, Asterionella formosa, and the nature of its CCM using genomics. In a productive lake, the frequency of A. formosa declined with CO2 concentration below air-equilibrium. In contrast, CO2 concentrations at 2.5-times air-equilibrium did not increase growth rate, cell C-quota or the ability to remove inorganic carbon. A pH-drift experiment strongly suggested that HCO3 − as well as CO2 could be used. Calculations combining hourly inorganic carbon concentrations in a lake with known CO2 and HCO3 − uptake kinetics suggested that rates of photosynthesis of A. formosa would be approximately carbon saturated and largely dependent on CO2 uptake when CO2 was at or above air-equilibrium. However, during summer carbon depletion, HCO3 − would be the major form of carbon taken up and carbon saturation will fall to around 30%. Genes encoding proteins involved in CCMs were identified in the nuclear genome of A. formosa. We found carbonic anhydrases from subclasses α, β, γ and θ, as well as solute carriers from families 4 and 26 involved in HCO3 − transport, but no periplasmic carbonic anhydrase. A model of the components of the CCM and their location in A. formosa showed that they are more similar to Phaeodactylum tricornutum than to Thalassiosira pseudonana, two marine diatoms.

Seasonal variation of phytoplankton community structure in the Tianhe Reservoir of the Daluoshan Mountain in southern Zhejiang Province, China and its indication to water quality

To explore the association between phytoplankton community structure and water quality of the Tianhe Reservoir in Wenzhou, Zhejiang, we examined the phytoplankton and physico-chemical factors in the Tianhe Reservoir from February 2019 to January 2020. A total of 89 phytoplankton species belonging to 60 genera and 7 phyla were identified. The annual average abundance and biomass of phytoplankton were 2.02×105 cells·L-1 and 0.26 mg·L-1 respectively. Bacillariophyta was dominant in the whole year. Chlorophyta was dominant in spring and autumn. Cyanophyta was dominant in summer. Both Euglenophyta and Pyrrophyta appeared in the whole year. Cryptophyta appeared in autumn and winter. However, none of them was dominant due to their low abundance. The dominant species throughout the year were Melosira granulata, Synedra acus, Navicula cryptocephala, Asterionella formosa, Pseudoanabaena, Closterlum venus, Pediastrum duplex, Peridinium bipes, Dinobryon cylindricum and Cryptomonas ovata. Results of redundancy analysis (RDA) showed that water temperature, total nitrogen, CODMn and pH value were the main factors driving phytoplankton community structure in the whole year. According to the evaluation based on diversity indices, including Shannon index, Pielou evenness index, Margalef richness index and comprehensive trophic status index (TLI), water quality of Tianhe Reservoir is between oligotrophication and mesotrophication.

Community structure and spatial distribution of phytoplankton in relation to hydrography in the Laptev Sea and the East Siberian Sea (autumn 2008)

The Laptev Sea and the East Siberian Sea are remote areas of the Arctic region where detailed data on phytoplankton composition and spatial distribution remain limited. In the context of the ongoing environmental changes (increasing warming and ice melting) and prospective exploration activities (oil and gas production) on the Arctic shelves, understanding of the seasonal and interannual phytoplankton community dynamics is of critical importance. Our study provides new specifying data on species composition of phytoplankton over the vast area of the Laptev Sea shelf and the East Siberian Sea shelf. We found that the outer shelf of the Laptev and East Siberian seas was characterized by typical late spring diatom species (Chaetoceros furcellatus, Chaetoceros diadema, Chaetoceros debilis, Chaetoceros constrictus). On the inner shelf of the Laptev Sea, which is strongly affected by the Lena River water masses, the phytoplankton were characterized by the transition from the summer to an autumn stage of development. Local algal assemblages were composed by mixo- and heterotrophic dinoflagellates (Dinophysis and Protoperidinium genera) together with marine and brackish water-marine diatoms (Thalassiosira hyperborea, Thalassiosira baltica, Thalassiosira gravida, Thalassiosira nordenskioeldii) accompanied by sporadically occurring freshwater riverine planktonic diatom species (Aulacoseira granulata, Aulacoseira italica, Asterionella formosa). These variations in species composition over the Laptev Sea shelf were attributed to differences in the hydrography, marine chemical conditions, and the sea-ice regime.

Temporal variation in community structure of zoosporic fungi in Lake Biwa, Japan

Zoosporic fungi play an important role in aquatic environments, but their diversity, especially that of parasitic fungi of phytoplankton, has still not been fully revealed. We conducted monthly analyses of the community structure of zoosporic fungi at a pelagic site in Lake Biwa, Japan, from May to December 2016. Metabarcoding analysis, targeted to a large subunit region of ribosomal DNA in the nano-size fraction of particles (2-20 µm), was carried out on the samples. We also counted large phytoplankton and chytrid sporangia attached to the hosts. We detected 3 zoosporic fungal phyla (Blastocladiomycota, Chytridiomycota and Cryptomycota) within 107 operational taxonomic units (OTUs), in which Chytridiomycota was the most diverse and abundant phylum. Few fungal OTUs overlapped between months, and specific communities were detected in each month. These results showed that diverse zoosporic fungi with high temporal variability inhabited the lake. Five large phytoplankton species were found to be infected by chytrids: Staurastrum dorsidentiferum, S. rotula, Closterium aciculare, Asterionella formosa and Aulacoseira granulata. Some chytrids were detected by metabarcoding analysis: Zygophlyctis asterionellae infecting A. formosa, Staurastromyces oculus infecting S. dorsidentiferum and Pendulichytrium sphaericum infecting A. granulata. One OTU detected in association with infected C. aciculare by microscopic counting might have been an obligate parasitic chytrid of C. aciculare. The results indicated that a combination of metabarcoding and microscopic analysis revealed more information on zoosporic fungi, including those that are parasitic.

Seasonal and interannual variation in lower Columbia River phytoplankton (2005-2018): environmental variability and a decline in large bloom-forming diatoms

Understanding the influence of biotic and abiotic factors on riverine phytoplankton dynamics is challenging, particularly as anthropogenic stressors such as eutrophication, invasive species, and climate change alter these relationships. We examined a 14 yr (January 2005 to December 2018) dataset of phytoplankton and water quality variables, along with zooplankton and nutrient concentrations, from the Columbia River (the largest river in the US Pacific Northwest) to identify seasonal and interannual patterns of phytoplankton assemblage structure and their environmental associations. Non-metric multidimensional scaling, cluster, and indicator species analyses revealed: (1) a diatom/flagellate cluster in spring/summer, associated with chlorophylla, discharge, ciliates, and Sarcodina; (2) a cyanobacteria/chlorophyte cluster in late summer/early fall, associated with higher water temperatures, increased clarity, the invasive copepodPseudodiaptomus forbesi, and veligers of the invasive Asian clamCorbicula fluminea; and (3) a mixed-taxa winter cluster of minimal abundance and biomass. Nutrients were not strongly associated with the observed structural patterns. Phytoplankton bloom duration varied interannually, between years with short springtime blooms vs. years when blooms extended across multiple months. Springtime blooms of the diatomAsterionella formosadecreased in recent years, giving way to blooms of a mixed diatom assemblage. Further, high temperature, low discharge, and more invasive zooplankton were associated with cyanobacterial blooms, suggesting that increased temperature and reduced river flows predicted due to climate change in the Pacific Northwest may lead to further impacts on the late summer/early fall Columbia River plankton community.

Divergent responses of diverse microalgae commonly found in drinking water source water to UV-C treatment

Microalgae pose major problems for drinking water treatment processes either through membrane fouling or through blooming events in source water during the summer months. Disinfection treatments such as chlorination and UV-C treatment of drinking water are designed to remove microorganisms including microalgae and bacteria. In order to treat water efficiently it is critical to understand the effect of UV-C treatment on the viability and vitality of phytoplankton. Moreover, this information can be used to assess the utility of UV-C treatment as a potential pre-treatment option for water clean-up. In this study we tested the population growth of 6 phytoplankton species representing three major taxonomic groups (green algae, diatoms and cyanobacteria), commonly found in freshwater lakes in North America and relevant for water treatment facilities. We exposed these species to UV-C treatment and monitored their post-exposure population growth over a 52–55-day period using a plate-based MPN (most probable number) method. We found the green alga Scenedesmus quadricauda and the cyanobacterium Anabaena flos-aquae to be most tolerant to the treatment, while the cyanobacterium Microcystis aeruginosa and the diatom Asterionella formosa were found to be most sensitive with viability being reduced at comparatively lower doses. No significant delays in growth post treatment (i.e. time lags) were reported within species. Asterionella formosa and Aulacoseira granulata showed the longest time lags of all species, which might be in part correlated with DNA repair mechanisms and other physiological adaptations. This work provides the basis for the assessment of UV-C treatment efficacy on freshwater phytoplankton.

A 450-year record of environmental change from Castle Lake, California (USA), inferred from diatoms and organic geochemistry

A 39-cm sediment core from Castle Lake, California (USA) spans the last ~ 450 years and was analyzed for diatoms and organic geochemistry (δ15N, δ13C, and C:N), with the goal of determining sensitivity to natural climate variation and twentieth century anthropogenic effects. Castle Lake is a subalpine, nitrogen-limited lake with ~ 5 months of annual ice cover. Human impacts include light recreational use, past fish stocking, and experimental use by the Castle Lake Research Station. The base of the core (below 32 cm; pre mid-1700s) represents the period of maximum ice cover. In contrast, the end of the Little Ice Age (mid 1700s–early 1800s) is dominated by cyclotelloids (mostly Discostella stelligera), indicating significant open-water periods, a condition that persisted into the early 1900s. Cyclotelloids began to decline in the 1960s and were replaced by the Fragilaria tenera grp. (peak in 1970s), succeeded by Asterionella formosa (peak ~ 2010), and accompanied by a reduction in δ15N values and a decrease in C:N that may represent increased atmospheric nitrogen deposition. Another anthropogenic signal was discerned in the core and was interpreted to be the result of an ammonium nitrate fertilization experiment of the epilimnion that was conducted in 1980 and 1981. This signal was manifested in the core largely by a negative excursion in δ15N, possibly caused by fractionation during denitrification in surface sediment. A phytoplankton monitoring dataset collected by the Castle Lake Research Station from 1967 to 1984 corroborates the timing of increased araphid euplanktonic species in the 1970s, and increases in two benthic diatoms (Staurosirella pinnata and Tabellaria fenestrata), entrained in the phytoplankton tows during the experimentation years. Both ice cover and nitrogen addition appear to be strong drivers that affected the lake diatoms, although additional drivers, such as fish stocking and associated cascade effects need further exploration. These data will be helpful for interpreting longer core records from Castle Lake, should the opportunity arise, as well as cores from similar systems in the region.

Pollen and diatom evidence of sea water intrusion, east flood canal (Banjir Kanal Timur), Semarang, Indonesia

Semarang City, Indonesia is plagued by a combination of widespread flooding during the wet season and a lack of fresh (potable) water during the dry season, the latter related to saltwater intrusion. The East Flood Canal (Banjir Kanal Timur = BKT) was built to address these problems by improving runoff (drainage) and increasing groundwater recharge. This research was conducted to reconstruct the history of environmental change, including seawater intrusion, along the coast of Semarang using pollen and diatom assemblages from a 190-cm-long, 210Pb-dated sediment core extracted from the estuary at the mouth of the BKT. The age of the sediments within the core ranged over 160 years (the surface dated to 2014). The sediments could be subdivided into three zones on the basis of pollen assemblages and 2 zones on the basis of diatom assemblages. Lower zone assemblages, dominated by Sonneratia alba (mangrove), Acrostichum aureum (Pteridophyte), and Cocconeis pediculus (an epiphytic diatom), indicate that historically, the estuarine ecosystem was relatively open to the Java Sea and characterized by periods of marine and freshwater conditions. Thereafter, an upward increase in saline mangrove species of pollen and diatoms, combined with the loss of freshwater species (e.g., Avicennia and Rhizophora), indicates an increasing prevalence of marine conditions at the mouth of the BKT. Increasing salinity was associated with a landward shift in the mangrove ecosystem, a trend indicated by the progressive increase in mangrove plant diversity as statically manifested by the three pollen zones. This landward shift was associated with a “closing off” of marine flow in response to a significant (order of magnitude) increase in the estuarine sedimentation rates at about 1981. Increased sedimentation was presumably related to land-use changes that enhanced sediment delivery to the coast via the BKT. Inherent in these sediments were allochthonous fragments of Asterionella formosa, a freshwater species found in the upper sediment layers. The results of this study are consistent with the increased saltwater intrusion along the coast and a decline in groundwater quality.

Diatoms constrain forensic burial timelines: case study with DB Cooper money

Diatoms are found universally in waters around the world. Some diatom species such as Asterionella formosa have a broad variation in seasonal abundance leading to the possibility that diatoms could constrain the time of year when an object was immersed in water. Here we apply this technique to the cold case of DB Cooper’s money. Nine years after the crime, six thousand dollars in three bundles were found on the shore of the Columbia River near Portland, Oregon. This burial site was ~30 km from his reported jump location which gave no apparent reason for the money to end up there. This study found diatoms on a recovered bill which indicates that the money was immersed before burial. The species mix found on the bills was compared to a test bill submerged in the Columbia River in November which was the timeframe for the crime. The Cooper bill contained diatoms from summer bloom species suggesting that the money was not directly buried dry and the immersion happened months after the late November hijacking. This finding rules out of a majority of current theories related to the crime and proposes diatoms as a feasible methodology to constrain seasonal timelines in forensics.

Ecosystem shift of a mountain lake under climate and human pressure: A move out from the safe operating space

A multiproxy approach including chironomid, diatom, pollen and geochemical analyses was applied on short gravitational cores retrieved from an alpine lake (Lacul Bâlea) in the Southern Carpathians (Romania) to unveil how this lake responded to natural and anthropogenic forcing over the past 500 years. On the basis of chironomid and diatom assemblage changes, and supported by sediment chemical data and historical information, we distinguished two main phases in lake evolution. Before 1926 the lake was dominated by chironomids belonging to Micropsectra insignilobus-type and benthic diatoms suggesting well-oxygenated oligotrophic environment with only small-scale disturbance. We considered this state as the lake's safe operational space. After 1926 significant changes occurred: Tanytarsus lugens-type and T. mendax-type chironomids took over dominance and collector filterers increased until 1970 pointing to an increase in available nutrients. The diatom community showed the most pronounced change between 1950 and 1992 when planktonic diatoms increased. The highest trophic level was reconstructed between 1970 and 1992, while the indicator species of increasing nutrient availability, Asterionella formosa spread from 1982 and decreased rapidly at 1992. Statistical analyses evidenced that the main driver of the diatom community change was atmospheric reactive nitrogen (Nr) fertilization that drastically moved the community towards planktonic diatom dominance from 1950. The transformation of the chironomid community was primarily driven by summer mean temperature increase that also changed the dominant feeding guild from collector gatherers to collector filterers. Our results overall suggest that the speed of ecosystem reorganisation showed an unprecedented increase over the last 100 years; biological systems in many cases underwent threshold type changes, while several system components displayed non-hysteretic change between alternating community composition. We conclude that Lake Bâlea is outside of its safe operating space today. The main trigger of changes since 1926 was climate change and human impact acting synergically.

Heterogeneous response of diatom assemblages since ca. 1945 in lakes from boreal regions of northern Alberta and Saskatchewan, Canada

The degree to which climate variability and anthropogenic stressors have impacted the rich array of boreal lakes in northern Saskatchewan and Alberta was explored in a dataset of 42 lakes from previous paleolimnological investigations of this region. This dataset was used to evaluate the extent of change in diatom assemblages over the past ~ 60 to 70 years in relation to lake and watershed characteristics. Similarity analysis was used to define the degree of change in diatom composition in lake sediment cores from each lake with a focus on post ca. 1945 changes to establish a common time frame to compare across all lakes. This time frame incorporates pre- and post-development of the Athabasca Oil Sands Region and additionally integrates pre- and post-periods of distinct changes in temperature and precipitation. Beta regression analysis was used to identify potential links between diatom assemblage change and lake physical–chemical and landscape characteristics (limno and landscape models, respectively). Similarity analysis indicated nearly 80% of the lakes showed only a very low degree of change (0–25%) since ca. 1945. Lakes with larger percent change in similarity (> 25%) showed increases in planktonic diatoms, although the specific taxa that changed varied from oligotrophic Discostella spp. to meso-eutrophic taxa, such as Asterionella formosa and Stephanodiscus minutulus. Lake volume and percent peat in the catchment were the most important limno and landscape explanatory variables, respectively, albeit the models had low predictive power. The lakes with large diatom compositional change were dispersed across the region, located in various geological and ecological zones and varying degrees of human disturbance. The interplay of climate and morphometric features of lakes is likely an influential driver of these changes, with larger heat-storage capacity in higher-volume lakes that potentially increases the sensitivity to warming. The small surface areas and shallow morphometry of most lakes, a heterogeneous hydrological and geological landscape, and frequent dominance of diatom assemblages by benthic generalists may explain the minimal responses of diatom assemblages over the past ~ 70 years to anthropogenic influences and climate.