Fragilaria Construens Research Articles

Ecological response to global changes in Lake Genco, a remote alpine lake on the Southeast Tibetan Plateau, over the past two centuries

The ways in which natural ecosystems respond to global change have become an urgent concern to society. Lakes play a pivotal role in ecosystem changes because of their central position within watersheds and their involvement in various endogenous and cross-system ecological and biogeochemical processes, leaving natural archives accumulated in sediments over time. However, how lake ecosystems have responded to atmospheric changes during the past few centuries is still not fully understood. To analyse the process in more detail, we conducted a case study at Lake Genco, a remote alpine on the southeastern Qinghai-Tibetan Plateau (QTP) and recovered a 170-year history of lake's ecosystem from a 210Pb-dated sediment core. The air temperature increased between 1900 and 1950 CE and 1980 and 2020 CE. Geochemical and physical proxies (magnetic susceptibility, Sr/Ba, K/Al, Na/Al, Ti, Pb, P flux, TN and δ15Norg) indicated greater degrees of weathering and erosion, and higher nutrient loadings as terrestrial systems responded to atmospheric changes after 1900 CE. Higher primary aquatic productivity, richer biodiversity and weaker structural stability were found in Lake Genco between 1852 and 2017 CE, although the ecological response was quiet in terms of the compositional change in the diatom community, which was generally dominated by small planktonic Cyclotella ocellata. During warmer periods, diatom PC1 changed directionally due to the overall increase in the abundance of tychoplanktonic Fragilaria construens and periphytic Achnanthes minutissima and the decreasing abundance (∼10%) of C. ocellata. This study provides empirical evidence that ecological changes in remote lakes rely on interactions between the atmosphere and the landscape and helps us to understand the complexity of the various impacts of global climate change. More local and regional studies are needed to generalise the mechanism of biological responses to atmospheric changes in remote lakes, especially in the QTP.

Изменения в развитии фитопланктона Среднего Каспия в 2021 году

The research of taxonomic diversity was completed in the water area of the Middle Caspian as a whole and by sections (Makhachkala - Cape Sagyndyk, Derbent - Cape Peschany, Divichi settlement - Kenderli Bay) for 2021. During the research period 108 samples were collected and processed. As a result of the work performed 105 taxonomic units were found, which is more than the average long-term value (87), but less than the indicators of the previous year of the research (130). The diatoms were the dominant group and accounted for 50% of the total composition. Dinophyte algae were the subdominants. The basis of the ecological complex of 2021 was formed by the representatives of seaweeds. A representative of green algae Ankistrodesmus pseudomirabilis v.spiralis influenced the formation of the abundance, reaching the greatest development in the section of the city of Derbent - Cape Peschany. In the same section of the sea the maximum biomass was also noted with a predominance of a group of dinophytes. In general, in the Middle Caspian the layer of 0–25 m was the most productive. The maximum concentration of plant cells was noted at a horizon of 25–50 m in the section of the city of Makhachkala - Cape Sagyndyk. In the section of the city of Derbent - Cape Peschany it increased from the surface horizon (34.22 mg/m3) up to a layer of 25–50 m. On the section of Divichi village - Kenderli Bay the highest concentrations were noted in the 10–25 m water layer. 
 In 2020–2021 b-mesosaprobes T. nitzschioides, E. cordata, Fragilaria construens were the dominant indicator species. These species are not so demanding to the environment. Organisms of the α-saprobic zone were less common, which suggests that the saprobiological state of the waters of the Middle Caspian is moderately polluted

Monitoring for the abundance and distribution of phytoplankton along the hypersaline Bardawil Lagoon, in Northern Sinai, Egypt (Multivariate Analysis Approach)

Bardawil Lagoon is a source of wildlife and high-quality fish, so, it is imperative that it should be subject to continuous monitoring of both water quality and the phytoplankton composition. Samples were collected from ten sites representing different habitats of the lagoon, from summer 2017 to spring 2018. The water properties were determined; noticeable low concentrations of dissolved inorganic nutrients were recorded. A total of 106 species belonging to six groups were recorded, among them Bacillariophyta (69 species) and Dinophyta (26 species). The obtained results clarify that Bacillariophytes prevailed in the eastern sites of Bardawil; on the contrary, Dinophytes occupied the sovereignty in the western sites of the lagoon. The most abundant Bacillariophytes were Licmophora gracilis, Gyrosigma acuminatum, Fragilaria construens, and Nitzschia sigmoidea; which formed more than 50% of total abounded diatoms. While, Protoperidinium leonis, Prorocentrum gracile and Protoperidinium granii were the dominant Dinophytes, giving it maximum at El-Rewak. From reviewing previous studies on the lagoon, it becomes clear that the phytoplankton composition varied widely from previously recorded, including the dominant species and their rates of sovereignty, which reflected economically on its fish productivity. Besides, the water quality in Bardawil fluctuated from slightly-polluted to moderately-polluted according to the diversity index, as a result of the recent, noticeable increase in human activities, especially fishing, which will be in turn reflected in the environment. Therefore, continuous follow-up through ecological assessment and monitoring studies of Bardawil became an urgent necessity.

Distributions of phytoplankton in a coastal lagoon of Mahin, Ondo, Western Nigeria

Distributions of phytoplankton were investigated in Mahin Lagoon within Transgressive mud coast of Ondo, Western Nigeria. Collections and analyses of samples of phytoplankton and surface waters (for some physico-chemical parameters) were done at fifteen stations along the stretch of the lagoon in October 2013 and 2014 as well as March 2014 and 2015. Higher salinity levels were recorded at stations close the mouth of the Atlantic Ocean than those further upstream. Biochemical oxygen demand was high (7.7±2.3-10.6±1.8 mg/L) at stations with high levels of anthropogenic activities. Division Bacillariophyta (diatoms) dominated phytoplankton community in term of species diversity. Most species recorded during rainy season had relatively even spatial distributions. During March 2014 and 2015, high brackish water species such as Chaetoceros affinis , Asterionela japonica and Fragilaria construens were recorded only close to the Atlantic Ocean while stations further upstream had freshwater species such as Aulacoseira granulata , Synedra acus and Eudorina cylindrical . Stations close to high human population and anthropogenic activities had low phytoplankton abundance and diversity. Pollution indicator species, such as Microcystis aeruginosa and Oscillatoria borneti were recorded with relatively high abundance across fifteen stations. Implications of the anthropogenic activities on phytoplankton distributions and sustainable management of the lagoon are discussed. Keywords: Algae, species diversity, brackish waters, seasonality, anthropogenic activities

Analysis of diatom algae from the water column and bottom sediments of Shira Lake (Khakassia, Russia)

Lake Shira as a meromictic lake is object of interest for paleolimnological studies. In May 2011 core samples were collected from the bottom of Lake Shira and the species composition of diatom algae, which serve as bioindicators of the state of the lake, were studied. In addition, in 2012, seasonal water samples and material from sediment traps were collected and the species composition of diatoms in them was analyzed. The results of the analysis showed that the lake, like in previous years of research, was dominated by Cyclotella choctawhatcheeana Prasad. Diatoms were found twice in the studied core above the white carbonate layers and were absent in other layers. The species living in the lake at present were observed down to the first white carbonate layer, including the predominant Cyclotella choctawhatcheeana. This fact presumably proves the consistency of the species composition of diatoms and the overall stable condition of the lake since 1946 (Rogozin et al., 2005). Down to the second white carbonate layer, the dominant species were Aulcosira valida (Grunow) Krammer and Aulcosira italica (Grunow) Simonsen. Nitzchia sigmodea (Nitzsch) W. Smith and Fragilaria construens var. venter (Ehrenberg) Grunow were also observed at these depths, dating approximately to 1655–1690. These are freshwater species that belong to the diatoms of arctic, alpine, and temperate latitudes, which develop in shallow waters under moderate temperature conditions. This fact suggests that Lake Shira was less salty in the middle and end of the 17th century than today.

Epipelic algal distribution in Ismailia Canal and the possible use of diatoms as bioindicators and a biomonitoring tool

Ecology of Ismailia Canal and its branches were studied under a comprehensive program of the Freshwater and lakes Division, National Institute of Oceanography and Fisheries. Sixteen stations were selected quarterly in Ismailia Canal and its branches during 2011. Physical and chemical characters of water with surface sediment were sampled. Diatoms dominated the epipelon community, whereas chlorophyceae and cyanobacteria were rarely present. One hundred sixty-seven epipelic species were recorded. Diatoms were dominated by the centric diatoms Cyclotella spp. and Aulacoseira spp. Most frequent diatom species underwent multivariate analysis of TWINSAPN to clarify the classification of diatom species and CCA to correlate them to the most effective environmental parameters. Most species were positively affected by eutrophication, PO4 and NH4, and seasonal related factor, temperature, whereas some other species were negatively affected by pH and SiO2. Three diatom indices were applied to assess the ecological status of the studied area. Diatom species were tested as ecological bioindicators and four diatom taxa. Cocconeis placentula, Achnanthidium minutissimum, Fragilaria construens var. venter, Navicula atomus and Nitzschia gracilis satisfied the indicator selection criteria for some ecological parameters. Trophic Diatom Index (TDI), Eutrophication Pollution Index (EPI-D) and the Pampean Diatom Index (IDP) were applied. The results of the TDI revealed that the majority of the canal stations were in the acceptable ring but showed non-significant relation with the eutrophication parameters. Both IDP and EPI-D classified the stations of the canal and its branches in the high and good category of ecological status, respectively, which were not the real state in the canal and its branches as revealed by their correlation with the eutrophication parameters. The application of diatomic indices developed in foreign country cannot be applied in Egyptian environment and the development of indices based on the Egyptian ecoregions is very necessary.

Okrzemki środkowego plejstocenu w osadach jeziornych z Krępca (Wyżyna Lubelska)

Osady jeziorne z profilu Krepiec 13 kolo Łecznej zostaly uznane na podstawie analizy pylkowej (Z. Janczyk-Kopikowa, 1980) za rownowiekowe z osadami z Ciechanek Krzesimowskich, ktore wedlug A. Środonia (1969) reprezentują interglacjal lubelski. W nawiązaniu do podzialu palinologicznego opisywanego profilu dokonano korelacji wydzielonych okresow rozwoju roślinności wyzszej z fazami rozwoju okrzemek – diatomofazami (KI, K2, K3). W obrebie diatomofaz wyrozniono ponadto ich cześci oraz subdiatomofazy reprezentujące poszczegolne etapy rozwoju jeziora interglacjalnego. MIDDLE PLEISTOCENE DIATOMS FROM LACUSTRINE DEPOSITS FROM KRĘPIEC (LUBUN UPLAND) A thick packet of lacustrine deposits, about 20 m thick, was found at depth from 21.15 m to 41.50 m in the Krepiec 13 borehole column. They are represented by silts varying in lithology and with intercalations of gyttja, peat and peaty silts. They are underlain by sands with boulders, resting on till, and overlain by sands, peats, clay silts, chalk gravels and sandy silts. The pollen analysis, carried out by Z. Janczyk-Kopikowa (in print), has shown that the Krepiec borehole column comprises Interglacial deposits coeval with those from Ciechanki Krzesimowskie. According to A. Środon (1969), the latter do not correspond to the Masovien I Interglacial but to the Lublin Interglacial. On the basis of palynological subdivision of the studied borehole column, the differentiated periods of development of higher plants were correlated with phases of development of diatoms – diatom phases (K1, K2, K3). The diatom phases were further subdivided into parts and diatom subphases representing individual stages in evolution of the interglacial lake (Fig. 2). The bulk of the studied lacustrie deposits from Krepiec, comprising diatom phases Kl, K2A and K3A, are characterized by predominance of nannoplankton diatoms Stephanodiscus and Cyclotella in the dominant group (Tables I – IV). Fragilaria crotonensis , Asterionella formosa and Synedra ulna and S. acus are fairly common in the subdominant group. Middle part of the studied column (diatom phase K2B) displays a transitional stage in the development of the lake, characterized by decrease of plankton, accompanied by increase in number of littoral, mainly epiphytic, and rheophilous species typical of flowing water. Upper part of the section (diatom phase K3B) is characterized by predominance of Melosira italica and Epithemia zebra and, subsequently, Synedra ulna and Fragilaria construens . The development of these species indicates a marked shallowing, eutrophication of waters in the lake, and its overgrowing by macrophytes. The changes are related to further amelioration of climate, recorded as an Interglacial optimum in the pollen spectrum (III) by Z. Janczyk-Kopikowa (in print). The Krepiec section seems most close to that of the Lichwm Interglacial from Gwoznica in south-western Byelorussia (G.G. Gruzman et al., 1975).

Environmental and depositional characteristics of diatomite deposit, Alayunt Neogene Basin (Kutahya), West Anatolia, Turkey

This paper describes the geological-depositional and environmental characteristics of diatomite. The diatomite deposit is situated in the southern part of the Alayunt (Kutahya) Basin. Samples of 18 diatomites and 12 host rocks were collected from four sedimentary profiles in the spring season. Basement rocks are Paleozoic-aged metamorphic rocks (schist, phyllite, quartzite, etc.) and Mesozoic-aged ophiolitic and complex rocks. Host rocks are rhyodacitic–rhyolitic tuffite, volcanic glass. Diatomite is composed of Upper Miocene–Upper Pliocene-aged diatom species. Diatomite shows layer morphology and lies on volcanic glass layer. XRD characteristic peaks of diatomite show that it comprises dominantly of Opal-A silica, whereas volcanic glass has Opal-CT constituent. SEM and NPM photomicrographs indicate that diatomites are dominantly composed of benthic freshwater diatom species, such as Pinnularia microstauron, Pinnularia lundii, Pinnulariasubrostrata, Pinnularia brevicostata, Pinnularia tenuis, Pinnularia sp., Navicula eligensis, Fragilaria construens, Mastogloia braunii Grunow, Melosira varians Agardh, Surirellacapronii Brebisson, Cymbella lanceoloata, Amphora venata, Gomphonema germainii, Gomphonema angustatum and Rhapalodia gibba. These species are general indicators of shallow paleolake environment and cool climate conditions. Due to the fluvial currents and climatic conditions; lake water levels, temperature and nutrient content fluctuated through the time. Chemical data obtained from 18 diatomite samples show that while silica is the bodybuilding material for diatomite (over 89 % SiO2), Al, Mg and Fe contents of diatomite samples might be derived from clastic materials. The concentration of Al, Mg and Fe decreases toward the lake center. Diatom genera, sedimentary profile sections and mineralogic data suggest that diatomite deposited in lacustrine-type freshwater shallow lake is associated with Upper Miocene-aged extension tectonics. Physical and filtration tests along with environmental characteristics of diatomite suggest that calcined diatomite can be used for waste treatment processes in the filter aid industry.

Late Quaternary environmental changes in Helambu Himal, Central Nepal, recorded in the diatom flora assemblage composition and geochemistry of Lake Panch Pokhari

This study presents changes in diatom flora assemblage composition, TOC, TOC/N and biogenic opal in a 450 cm core of Lake Panch Pokhari, Central Nepal (4,050 m asl), indicating Late Quaternary environmental fluctuations. Four Diatom Zones (DZ) were detected, with two major changes. The first one was found in ~430 cm depth (~14.8 cal. kyr BP), where the original flora characterized by Navicula digitulus Hustedt, Pinnularia rhombarea Krammer, P. aff. viridiformis var. minor Krammer, Encyonema silesiacum (Bleisch) D. G. Mann, Cymbopleura naviculiformis (Auerswald) Krammer and Nitzschia sp. was fully replaced by an assemblage consisting of Aulacoseira alpigena (Grunow) Krammer, Diatoma hyemalis (Roth) Heib., Tabellaria flocculosa (Ehrenberg) Kutzing, Brachysira brebissonii Ross and Pinnularia subgibba Krammer, creating a stable diatom assemblage for ~8 kyr (DZ3). The second change was found at ~70 cm (~2.1 cal. kyr BP) when increased nutrient inputs lead to emergence of new taxa such as Fragilaria construens var. subsalina Hustedt, F. tenera (W. Smith) Lange-Bertalot, Eunotia cf. pseudopapilio Lange-Bertalot and M. Norpel-Schempp and Gomphonema subclavatum Grunow. In order to evaluate the past environmental conditions in the Lake Panch Pokhari, the detected diatom taxa were subjected to analyses of their autecological preferences and dominance within the specific assemblage. We also assumed that TOC/N ratios >10 indicate accelerated erosion due to the strengthening of the Summer Monsoon starting at ~14.8 and between 13.7 and 12.8 cal. kyr BP. Monsoon intensity was most pronounced during the Early Holocene and at the beginning of the Late Holocene. The fluctuations of TOC and TOC/N in the Late Glacial sediments seem to correlate temporally and climatically with oscillations in the Northern Atlantic region.

Distribution patterns of benthic diatoms during summer in the Niyang River, Tibet, China

The aim of this study was to investigate the distribution, density, community structure and biodiversity characteristics of benthic diatoms, and to analyze whether differences in species composition and abundance exist in different regions of the Niyang River, Tibet. Among the 157 taxa observed in 15 sampling sites in the main river and tributary, most were casual species (>100), the relative abundance of the genera Achnanthes and Fragilaria was 67% of the total relative abundance. Achnanthes minutissima was the most important species and dominated the whole river reaches (average relative abundance was 30%); the average diatom densities were 7.4 x 10(5) cell/cm(2) at all sites, and increased slowly from the upper section to downriver. The significant indicator taxa with higher relative abundance were Achnanthes biasolettiana (18.0%) and Fragilaria arcus (18.2%), Fragilaria capucina var. vaucheriae (31.2%), Fragilaria construens var. venter (11.3%) and Cymbella affinis (11.0%) in the upper, tributary and mid-river sections, respectively. Achnanthes minutissima was the most abundant species (56%) in the downriver section. Biodiversity indices showed a gradual decrease from the up-to down-river section, and dominant species were more abundant in the upper and mid-river sections than in the downriver section. A two-way indictor species analysis (TWINSPAN) of diatom composition clearly showed four different groups, namely the upper, mid, lower and tributary sections. Detrended correspondence analysis (DCA) supported the results of TWINSPAN, and the characteristics of site distribution and species composition in the Niyang River supported the spatial structure of diatom assemblages. This study indicates that bio-assessment programs utilizing benthic diatoms could clearly benefit lotic water with regional stratification.

Littoral diatoms as indicators of recent water and sediment contamination by metals in lakes

We studied the response of benthic diatoms to recent metal contamination in littoral cores collected at 25 sites in 11 lakes situated at different distances from a smelter in the Rouyn-Noranda mining region (Quebec). Diatom response was described in terms of density, diversity, and taxonomic composition of the entire assemblages and as abundance of individual indicator taxa. Metal concentrations were measured in sediment and in the overlying water (as total dissolved and as free-ions). Sediment metal contamination was significantly higher in lakes located <10 km from the smelters than in lakes farther away. Such difference was not significant when metal concentrations in the overlying water were considered. Metal contamination did not affect diatom density, which indeed was highest in the most contaminated lake. Diversity (either measured as number of taxa or as Shannon and evenness indices) was instead significantly higher in lakes close to the smelter than elsewhere. Redundancy analysis indicated that diatom composition changed along a gradient in alkalinity (CO₃) and one in sediment metal contamination (Cd, Hg, Cu). We identified three diatom taxa (Fragilaria construens var. venter, F. construens var. pumila, and Brachysira vitrea) that increased in relative and absolute abundance with metal contamination. Benthic diatom responses at the community (density, diversity, assemblage composition) and population levels (abundance of selected benthic taxa) were stronger to the sediment metal contamination than to the contamination of overlying water. Comparisons with available literature indicated that, for monitoring recent sediment contamination, diatoms in littoral sediments are preferable to invertebrates that mostly respond to overlying water. Diatoms in littoral cores are therefore unique as tools for monitoring recent contamination of lake sediments.

Analysis of the type of Fragilaria construens var. subsalina (Bacillariophyceae) and description of two morphologically related taxa from Europe and the United States

Cejudo-Figueiras C., Morales E.A., Wetzel C.E., Blanco S., Hoffmann L. and Ector L. 2011. Analysis of the type of Fragilaria construens var. subsalina (Bacillariophyceae) and description of two morphologically related taxa from Europe and the United States. Phycologia 50: 67–77. DOI: 10.2216/09-40.1Fragilaria construens var. subsalina is a common diatom found in a wide variety of aquatic systems worldwide. It was described by Hustedt (1925) from brackish waters in Oldesloe, Germany; a lectotype specimen was established by Simonsen (1987). We analysed the ultrastructure of specimens from the lectotype material by means of light (LM) and scanning electron microscopy (SEM) and show that this taxon should be placed at the species level within the genus Pseudostaurosira (as Pseudostaurosira subsalina). A similar but distinct taxon from the United States, found in waters with low electrolyte content, is proposed as a new species of Pseudostaurosira, namely Pseudostaurosira americana sp. nov. We also describe a second new species from Spain (Pseudostaurosira alvareziae sp. nov.), found in waters with moderate conductivity, which was misidentified as P. subsalina in the past. A morphometric analysis of the valve shape supports the morphological separation between the three species. The present study clarifies the taxonomy, ecology and systematic position of these three taxa and provides a comparison with other, similar taxa.

Diatom-inferred Holocene climatic and environmental changes in an unusually subsaline high Arctic nunatak pond on Ellesmere Island (Nunavut, Canada)

Stygge Nunatak Pond is a small, shallow, closed-basin pond situated on a nunatak in Stygge Glacier at the head of Jokel Fiord, east-central Ellesmere Island, Nunavut, Canada. Its ionic concentration is unusually high by inland Arctic standards, with specific conductivity measured at up to 1,090 μS/cm, making this site a rare example of a subsaline athalassic Arctic pond. Small, closed-basin lakes and ponds are particularly sensitive to changes in the balance between precipitation and evaporation (P–E), which affect the site’s chemical, physical and biological characteristics. Such lakes and ponds therefore have the potential to serve as sensitive archives of past environmental change, which can be reconstructed using paleolimnological techniques. Diatom assemblages from two sediment cores (a short gravity core [21.5 cm] and a long core of frozen material [387 cm]) were examined so as to reconstruct regional environmental changes. Basal radiocarbon dating of the long core suggests that the pond has existed since before 10,500 cal. year BP. The diatom assemblages from both cores record similar ecological changes since approximately 2,200 cal. year BP, with a stable, coldwater assemblage dominated by Fragilaria construens var. venter. This assemblage was replaced in the early- to mid-20th century by dramatic, unprecedented expansion in periphytic taxa with more complex life forms, especially Cymbella descripta, Navicula halophila and Achnanthes minutissima. These assemblage shifts are indicative of recent warming, with a longer open-water period, expanded littoral substrates, and increased ionic concentration, as would be expected with enhanced evaporation relative to precipitation. Between ~10,500 and ~6,200 cal. year BP, the diatom assemblages underwent a shift from a near monoculture of F. construens var. venter to a more complex, epiphytic assemblage, which then reverted back to the former virtual monoculture. These shifts may provide further evidence for an early Holocene thermal maximum in this region of the Arctic, followed by Neoglacial cooling. However, interpretation of assemblages before ~6,200 cal. year BP is complicated by the fact that the sediment beneath 47 cm depth is unconsolidated and embedded within a core of solid ice, a feature that has not been reported in any other Arctic paleolimnological study to date. Superficial examination of the contact surfaces of the ice, and the fact that radiocarbon ages obtained from entrained sediment are chronologically consistent with those from the sediment above, suggest that the ice might be intrasedimental segregation ice.

Contemporary distributions of saltmarsh diatoms in the Seymour–Belize Inlet Complex, British Columbia, Canada: Implications for studies of sea-level change

Surface diatom samples were collected from two saltmarshes in the Seymour–Belize Inlet Complex on the mainland coast of British Columbia to examine the controls on diatom distribution and provide training sets for regional studies of sea-level change. Cluster analysis and detrended correspondence analysis (DCA) were used to examine diatom distributions within and between the two marshes whilst canonical correspondence analysis (CCA) and partial canonical correspondence analysis (pCCA) were used to analyse species–environment relationships. The diatom assemblages were shown to be quite different between the two marshes, Waump and Wawwat'l. Q-mode cluster analysis separated the diatom assemblages from Waump into three zones corresponding to recognized vegetation zones; diatom zone C corresponds to the high marsh and is dominated by Pinnularia obscura, Caloneis bacillum and Diploneis ovalis, zone B spans the high- and mid marsh and is characterised by Fragilaria exigua, Nitzchia palea and D. ovalis, whilst zone A from the low marsh/tidal flat includes high frequencies of Diploneis smithii, Ctenophora pulchella and F. exigua. Three different diatom zones were recognised at Wawwat'l; two upper zones, E and F, corresponding to the mid-marsh which are dominated by mixed abundances of N. palea and Fragilaria construens var. venter, Navicula peregrina and Navicula clementis and zone D from the low marsh/tidal flat with increased frequencies of F. exigua and Achnanthes delicatula. At Waump, the major controls on diatom distribution were found to be elevation and to a lesser extent pH, whilst at Wawwat'l, the primary controls were grain size/organic content, conductivity and elevation. The results confirm that saltmarsh diatoms may have potential for future sea-level studies in this region. However, caution must be exercised as the significant difference in the diatom assemblages between the two marshes suggests that the diatoms are responding to a number of environmental variables on a local scale. Some of this variation may reflect highly seasonal changes in sedimentation and salinity resulting from the proximity of the marshes to adjacent streams which are subject to spring freshet. Local differences in elevation between the collected samples may also account for some of the assemblage variability. The results emphasize the great diversity and high sensitivity of intertidal diatom species to environmental controls.

Recent environmental changes on Banks Island (N.W.T., Canadian Arctic) quantified using fossil diatom assemblages

Banks Island (N.W.T.) has become a focal point for climate change studies in the Canadian Arctic. However, long-term climatic and environmental data are very sparse from this large island, as they are for the entire southwestern region of the Canadian Arctic Archipelago. In this paleolimnological study, diatom species assemblage shifts documented in cores collected from a pond and a lake on Banks Island were interpreted to represent a response to climate warming commencing in the nineteenth century. We found that, although the timing and overall nature of the species changes in the two cores were consistent, the signal was muted in the deeper site likely as a result of differences in ice cover extent and duration between lakes and ponds. A high-resolution study was also conducted from a second pond, at sub-decadal resolution, that only spanned the last ∼60 years. In the deeper lake site, Fragilaria construens and F. pinnata dominated the assemblages, similar to those noted in other high Arctic regions where lakes are characterized by extended ice cover. In contrast, Denticula kuetzingii dominated the shallower ponds and, in the case of the pond core representing the longer time period, this taxon increased in the post-1850 sediments, likely coincident with climate warming. In all cores, diatom assemblages became more diverse and Achnanthes species (particularly A. minutissima) increased from ∼1850 to the present, similar to changes documented in other Arctic regions. Beta diversity values calculated for the diatom species changes indicated that assemblage shifts in the Banks Island cores were of similar magnitude to those recorded in other Arctic regions with high species turnover, such as Ellesmere Island. A diatom-based Total Nitrogen (TN) transfer function previously developed for Banks Island was applied to the three 210Pb dated cores as an exploratory tool for inferring past changes in nitrogen concentrations. In both the lake and pond cores, diatom-inferred TN concentrations tended to increase in the more recent sediments, as may be expected with warming; however these trends were not very distinct.

Diatom- and Chironomid-Inferred Eutrophication of Bouchie Lake, British Columbia

Abstract Diatom and chironomid analysis of sediments encompassing the past 400 years from Bouchie Lake, British Columbia, suggests two distinct periods of limnological conditions. Prior to 1950 AD, Fragilaria construens and F. pinnata are the most common diatom species, and Chironomus, Procladius and Tanytarsini dominate the chironomid record. Moderately low nutrient concentrations consistent with oligo-mesotrophic lakes are inferred. From 1950, the diatom assemblage is dominated by Stephanodiscus parvus, a eutrophic indicator, whereas the chironomid communities show a relative increase in littoral taxa coincident with lower head capsule abundance. Higher nutrient levels, specifically total phosphorus, which increased from 8 µg L-1 prior to 1950 to 20 µg L-1 currently, are coincident with midge communities indicative of lower oxygen concentrations. Observed biotic changes and nutrient levels inferred from the sediment core correspond to historical land-use changes.

강원도 동강의 수질과 식물플랑크톤군집

The present study is to examine the water quality and to analyze the plank tonic and benthic phytoplankton communities at 6 stations in the Dong River and its tributary streams of Kangwon Province from November, 2001 to March, 2002. During the studies, water temperature ranged from 3.5 to 12.8℃; pH, 6.5-7.9; DO, 9.29-11.36 mg·l^(-1); BOD_5, 0.20-2.38 mg·l^(-1); TN, 1.2842-3.1871 mg·l^(-1); TP, 0.0052-0.0576 mg·l^(-1); and SS, 0.85-9.62 mg·l^(-1). The standard of water quality according to the Korean Environmental Preservation Law showed the first class except St. 6 through the survey. Six taxa of plank tonic phytoplankton identified were poor flora in November, 2001. The representative species frequently observed were the diatoms Achnanthes lanceolata, Achnanthes minutissima, Cymbella minuta, Cymbella parva, Diatoma vulgare, Fragilaria construens, Gomphonema pervulum, Navicula cryptocephala, Nitzschia palea., Scenedesmus sp. of green algae and Stephanodiscus hantzschii. Monthly dominant species of phytoplankton were Achnanthes lanceolata and A. minutissima in both February and March, 2002, but the blue-green algae, Oscillatoria sp. and the diatom, Stephan discus hantzschii were predominant at some stations in March. Phytoplankton standing crops ranged from 9.84 10 to 3.56 10 cell·l in November and 1.68-2.99 10 cell·l in February, while it changed 4.52-8.01 10 cell·l at St. 1, 2, 3 and 1.03-1.71 10 cell·l at St. 4, 5, 6 in March. Benthic phytoplankton communities was composed of 38 taxa in November, 31 taxa in February and 23 taxa in March. It showed a contrary tendency to planktonic phytoplankton diversity. Benthic diatoms which were more than 25% of the total populations were Cymbella turgida, Diatoma vulgare, Cocconeis placentula, Navicula cryptocephala var. intermedia in November; Achnanthe lanceolata, Cocconeis placentula, Achnanthes minutissima in February; and Achnanthes lanceolata and Cyclotella meneghiniana in March.

HIPPODONTA SUBCOSTULATA (HUSTEDT) LANGE-BERTALOT, METZELTIN ET WITKOWSKI AND SOME FRAGILARIOID DIATOM TAXA FROM THE HOLOCENE LACUSTRINE SEDIMENTS OF THE FAEROE ISLANDS

The present paper deals with several freshwater diatom taxa from the Faeroe Islands that were either recently described using only light microscope observations or that were known for a longer period but without SEM documentation. They belong to two genera, StaurosiraEhrenberg and Hippodonta Lange-Bertalot, Metzeltin et Witkowski. The material studied was derived from early Holocene lacustrine deposits documented in sediment cores from the Skalafjord, Faeroe Islands. The diatom flora of these sediments represents a rather unique assemblage inhabiting oligotrophic to dystrophic, acidic to circumneutral habitats that have nearly disappeared from most of the continental part of Europe. They only persist in northern Scandinavia, Iceland and in some intact peat bogs (e.g. in Pomerania). The taxa studied include Hippodonta subcostulata (Hustedt) Lange-Bertalot, Metzeltin et Witkowski, Fragilaria opacolineata Lange-Bertalot and Fragilaria construens var. binodis f. borealis Foged. SEM studies revealed that the two fragilarioid taxa possess features typical of the genus Staurosira sensu lato. Therefore a formal transfer is made to Staurosira borealis (Foged) nom. nov. et comb. nov. and S. opacolineata (Lange-Bertalot) comb. nov. H. subcostulata and S. borealis seem to be very rare species, so far known only from the type locality and a few sites elsewhere in Europe. The distribution of S. opacolineata is less known.

Stability of diatom composition in a variable lake environment: Lake Chascom�s, Argentina

Water and surficial sediment samples of Lake Chascomus and its tributaries were analyzed in order to relate changes in diatom community structure to chemical variables. Over the course of 13 months of sampling, the lake exhibited major changes in water level (1.15–1.98 m average depth), total dissolved solids (821–1972 mg l−1), silica (0.098–8.22 mg l−1), and total algal biomass (21.4–145.9 μg Chl a l−1). However, despite these large fluctuations, the diatom species composition was relatively stable. The dominant species in the water column was always Synedra berolinensis (68.9%–90.1% total frustules), with Fragilaria construens and F. brevistriata as subdominants. In the sediments the latter two species dominated the frustule counts. These results indicate an unusual floristic stability of this eutrophic ecosystem, with persistent dominance by broadly tolerant, generalist species.

Miocene Brackish Water and Lacustrine Deposition in the Suez Rift, Sinai, Egypt

Abstract From its inception during the early Miocene, the Suez Rift has been dominated by marine sedimentation. New high-resolution biostratigraphic and sedimentologic analyses of synrift deposits have resulted in the recognition of late Burdigalian-early Langhian brackish water and lacustrine deposits in the Wadi Abu Gaada-Gebel Gushia area, Sinai Peninsula. The Abu Gaada section is unique because: (1) it is an anomalously thick section of non-calcareous shale and mudstone in the Lagia Member of the Ayun Musa Formation; and (2) the mudstones contain an abundant microflora consisting of marine and nonmarine diatoms and freshwater algae that indicate they were deposited in a freshwater to brackish water environment. The abundant freshwater and shallow marine algae include the nonmarine diatoms Aulacoseira Thwaites, Fragilaria construens (Ehrenberg) Grunow, Synedra ulna (Nitzsch) Ehrenberg, and SurrirellaTurpin, as well as the freshwater algae Botryococcus Kutzing and Pediastrum Meyen. Shallow marine diatom...