Diatoms from surface sediments of the northern part of Lake Tanganyika

227 Diatom taxa were observed in the surface sediments of the northern part of Lake Tanganyika, including 1 new to science: Amphora tanganyikae. The diatom community of these sediments is mainly composed of benthic organisms while planktonic diatoms are rather rare. Many brackish-water and a few marine organisms were observed. Cosmopolitan organisms (77.1%) dominate the diatom flora but tropical, tropical African and African taxa are also well represented (22.9%)Deceased.Deceased.     

DIATOM PALEOLIMNOLOGY OF TWO FLUVIAL LAKES IN THE ST. LAWRENCE RIVER: A RECONSTRUCTION OF ENVIRONMENTAL CHANGES DURING THE LAST CENTURY

Water quality degradation is a serious concern for the St. Lawrence River. While some environmental data are available for the St. Lawrence ecosystem, long-term monitoring data are generally lacking. To infer past environmental changes, we undertook a paleolimnological assessment of diatom assemblages preserved in four ²¹⁰Pb- and ¹³⁷Cs-dated sediment cores from two fluvial lakes in the river, and used diatom transfer functions to infer past shoreline habitat characteristics. At sites in Lake Saint-François, a fluvial lake downstream from Cornwall, water quality decreased this century in response to human impacts (e.g. macrophyte density and nutrient levels increased). These trends were apparent from an increase in epiphytic diatom taxa, followed by an increase in eutrophic planktonic taxa. Water quality, however, appears to have improved somewhat in response to rehabilitation measures during the last two decades. From a sediment core near Montréal (Lake Saint-Louis), we also noted a large proportion of eutrophic and epiphytic taxa, but less evidence was recorded of a recent improvement in water quality. The diatom-based inference model for habitat characteristics appeared to reconstruct environmental conditions in the St. Lawrence River during the last century. The most notable shift has been an increase in diatom taxa commonly associated with macrophyte substrates. Trends in some of the planktonic diatoms were similar to those recorded in paleolimnological investigations from Lake Ontario, but cores from the river also may be reflecting local environments. This study shows that diatom-based paleolimnological studies are possible in large river systems, if coring sites (e.g. fluvial lakes) are carefully selected.     

Water level fluctuations in Lake Baringo,Kenya, during the 19th and 20th centuries: Evidence from lake sediments

This article presents a fossil diatom-based, semi-quantitative reconstruction of water level fluctuations for Lake Baringo over the past 200 years as a consequence of climatic variations. A 285 cm long sediment core sample was collected using a Rod-Operated Single-drive Stationary Piston corer. Lake level was inferred using indices based on the proportion of planktonic to benthic diatom taxa (P/B ratio). The sediment archive presented distinct zones dominated by planktonic and benthic diatom flora. An initial transgression in the early 19th century was characterised as a shallow water environment dominated by planktonic Aulacoseira spp. This was a response to extreme drought during the late 18th to early 19th century. Mid-19th century was defined by a high lake stand. The late 19th to early 20th centuries experienced low water level following the widely documented aridity at the time. The mid-20th century was marked by a spectacular rise in water level that coincided with remarkably wet years during the early 1960s and late 1970s. The first decade of the 21st century witnessed widespread changes in water level. The proxy records show that lake ramping and drawdown over the years follow approximately 50-year climatic cycles.     

Relationship Between Periodic Resuspension Events and Planktonic Diatom Community Structure in Lake Michigan: A Field and Laboratory Investigation

Lake Michigan provides an ideal location for comparing episodic physical forcing events (storms) on phytoplankton processes and the more persistent seasonal variability of phytoplankton communities. This is due to the duration and extent of the highly turbid, recurrent coastal plume (RCP) in the lake during the winter/early spring. Although the RCP can coincide with the initiation of the basin wide spring diatom bloom, linkages between the duration and intensity of the plume and the prominent role of light availability in regulating Lake Michigan phytoplankton growth during the spring isothermal period have been postulated, but not verified. The concurrent physical and biological events provide a novel opportunity to examine phenomena associated with the RCP affecting the distribution and abundance of species in Lake Michigan's planktonic diatom flora. In this study, planktonic diatom assemblages from pre, post and active spring plume events were examined from stations along Lake Michigan's southern shoreline. Species abundance changed rapidly during storm events. Sediment resuspension via storm activity created a suboptimal growth environment. Post‐storm event diatom phytoplankton communities were floristically distinct from prestorm event communities, with resting cell‐forming taxa playing a significant role in these community‐restructuring periods. Laboratory simulations of resuspension events using Lake Michigan sediments were conducted under a variety of environmental conditions. Parameters varied included day length, temperature, and silica. The resulting assemblages were quantitatively counted. A statistically significant relationship was identified between day length and the vegetative growth of many resting cell‐forming diatom species. When day length was calculated for poststorm event field data, it revealed a high correlation between poststorm event communities and those predicted by the laboratory simulations. Timing of storm events and latitudinal position of the aquatic system are then important elements for consideration when predicting diatom phytoplankton community structure due to the relationship these factors have with day length.     

The diatom flora and limnology of lakes in the Amery Oasis,East Antarctica

The diatom flora of three lakes in the ice-free Amery Oasis, East Antarctica, was studied. Two of the lakes are meltwater reservoirs, Terrasovoje Lake (31 m depth) and Radok Lake (362 m depth), while Beaver Lake (>435 m depth) is an epishelf lake. The lakes can be characterized as cold, ultra-oligotrophic and alkaline, displaying moderate (Radok and Terrasovoje lakes) to high (Beaver Lake) conductivities. There was no diatom phytoplankton present in any of the three lakes. While 34 benthic diatom taxa were identified from modern and Holocene sediments of Terrasovoje and Radok lakes, a 30-cm long sediment core recovered in Beaver Lake was barren. Five species (Luticola muticopsis, Muelleria peraustralis, Pinnularia cymatopleura, Psammothidium metakryophilum, P. stauroneioides) are endemic to the Antarctic region. All identified taxa are photographically documented and brief notes on their taxonomy, biogeography and ecology are provided. The most abundant diatom taxa are Amphora veneta, Craticula cf. molesta, Diadesmis spp, M. peraustralis and Stauroneis anceps. This is the first report on the diatom flora in lakes of the Amery Oasis.This revised version was published online in May 2004 with corrections to Figure 1.     

The diatom flora of Lake Eyre South: a large episodically filled salt lake in South Australia

Thirty-three diatom taxa were collected from the large terminal salt lake, Lake Eyre South, located in south-central Australia. The diatom assemblage included taxa that were widely distributed in marine and saline athalassic habitats in both northern and southern hemispheres, with the diatom flora of Lake Eyre South most similar to that of southern Africa. This study represents the first report on the diatom flora of Lake Eyre South and supports the findings that episodically filled lakes do not appear to be good evolutionary loci.     

Developing biomonitoring protocols for shallow Arctic lakes using diatoms and artificial substrate samplers

Growing concerns over effects of climate warming and other stressors on shallow Arctic lakes and ponds stimulate the need to develop and implement effective protocols to track changes in ecological integrity. This study assesses seasonal and spatial variability of periphytic diatom communities in a shallow Arctic lake in northern Yukon Territory to establish biomonitoring protocols. Artificial substrate samplers, which mimic macrophytes, allow direct measurement of biotic responses to shifting environmental conditions and control for possible confounding factors (e.g., accrual time and microhabitat type). Artificial substrate samplers were deployed at three locations and retrieved at three times (early, mid, and late) during the ice-free season. Analyses identified that diatom abundance increased exponentially and community composition changed significantly over the ice-free season, despite little variability in water chemistry, but did not differ among the three sampling locations within the lake. Patterns of seasonal succession in diatom community composition were characterized by first arrival of well-dispersed taxa, which included several planktonic taxa, followed by a transitional phase composed of planktonic and periphytic taxa, and culminated with dominance by periphytic species, mainly Achnanthes minutissima (Kützing). Results highlight the role of seasonal succession on artificial substrate colonization and the need to deploy artificial substrate samplers for the duration of the ice-free season to capture peak periphytic algal abundance. Low spatial variability of shallow Arctic lakes allows for samplers to be deployed at one single location to characterize diatom community composition.     

Diatom succession in the post-glacial sediments of the Komořany Lake,North-West Bohemia,Czechoslovakia

The Late-glacial and Postglacial sediments of the former Komo?any Lake in North-West Bohemia were studied by means of diatom analysis to trace the pattern of past environmental change in the lake. Several phases of lake development could be distinguished. Originally the Komo?any Lake was a eutrophic shallow water basin. The diatom succession in the early Postglacial sediment indicates alternating alkaliphilic, epiphytic and planktonic diatom communities associated with changes in water level in the basin. At the beginning of the Subatlantic period the water level began to rise and the development of planktonic diatoms, typical of small eutrophic lakes, occurred. Later, the basin became shallow again and the number of indifferent and acidophilous diatoms increased. This is typical for the final phase of the infilling process of a lake before its transformation to peatland     

Ecological Regime Shifts in Lake K?lksj?n, Sweden, in Response to Abrupt Climate Change Around the 8.2?ka Cooling Event

A detailed diatom record from Lake K?lksj?n, west-central Sweden, reveals two periods of abrupt ecological change correlative with the 8.2?ka cooling event. Using a combination of abrupt step changes and piece-wise linear regressions, the diatom data were analyzed for change points over time, and two sudden and large events that are described as regime shifts were detected. During the first event at c. 8040?cal. y BP, a doubling in diatom biomass took place over 5?C10?years. This increase in primary productivity can be connected to an erosion event in the catchment that resulted in an abrupt increase in nutrient supply to the lake. The second event was characterized by a substantial shift within the planktonic diatom community from taxa indicative of colder conditions to those indicating warm over 5?C10?years at c. 7850?cal. y BP. This event was superimposed on a successive change from periphytic to planktonic diatom dominance over a 250-year period and a gradual diversification of the periphytic community that spanned c. 150?years. Rapid climate warming following the 8.2?ka event likely caused these changes and both regime shifts are examples of externally driven abrupt ecological change. This study demonstrates that it is possible to detect, quantify and test for regime shifts in paleoecological data, and it highlights the need for high sampling resolution and precise chronological control. High-resolution paleoecological reconstructions of ecological regime shifts in response to climate change can provide useful analogues of future changes in ecosystem structure and functioning.     

PERIPHYTIC DIATOM ASSEMBLAGES FROM BATHURST ISLAND, NUNAVUT, CANADIAN HIGH ARCTIC: AN EXAMINATION OF COMMUNITY RELATIONSHIPS AND HABITAT PREFERENCES

Diatoms are potentially the most important biomonitors of environmental change in high arctic lakes and ponds, but to date few autecological data are available. Because of the shallow nature of many of these water bodies, a large proportion of taxa are periphytic and planktonic diatoms are absent for the most part. By determining the microhabitat and substrate preferences of these benthic diatom taxa, the potential exists to infer past changes in available habitats from fossil diatom assemblages collected from sediment cores and ultimately to reconstruct past environmental and climatic changes responsible for these shifts in habitat availability. To refine our understanding of high arctic diatom habitat preference, the common diatom taxa found on submerged moss (bryophyte), sediment, and rock substrates from lakes and ponds on Bathurst Island, Nunavut, Canadian High Arctic were examined. The relationships among key limnological variables and the common taxa from each habitat were examined. Many diatom taxa exhibited varying degrees of microhabitat preference, with moss representing the more unique habitat. In addition, the following limnological variables significantly ( P ≤ 0.05) explained the species variance for each of the three substrates: Na ⁺ and total nitrogen for moss; total phosphorus (filtered) and pH for rock; and Fe^{3 +} , total phosphorus (unfiltered), total nitrogen, temperature, and pH for sediment. These data can be used to help interpret monitoring and paleolimnological studies in this environmentally sensitive region.     

COASTAL DIATOM–ENVIRONMENT RELATIONSHIPS FROM THE GULF OF FINLAND,BALTIC SEA1

Eutrophication of the Baltic Sea has become a serious concern in recent decades. To provide a potential means for quality assessments of coastal waters in this area, we collected a data set of 49 embayments in the Gulf of Finland, and explored the relationship between surface sediment diatom assemblages and 15 environmental variables, with special emphasis on nutrients. Total dissolved nitrogen, total phosphorus, depth, and salinity all accounted for significant and independent fractions of variation in the diatom data and explained 34% of the total variation. There were clear changes in diatom assemblage structures along the nutrient gradients. Although these changes were gradual, we could identify a number of taxa that were more abundant in a particular nutrient environment. These taxa could be used as potential indicators of the quality of coastal waters in the Baltic Sea. Diatom assemblages that were least affected by nutrient enrichment included a variety of benthic species and a relatively high species richness. Small planktonic taxa such as Cyclotella atomus Hustedt, Cyclotella meneghiniana Kützing and Thalassiosira pseudonana Hasle and Heimdal were good indicators of highly elevated nutrient concentrations (>600 lg·L^?1 total dissolved nitrogen and 60 lg·L^?1 total phosphorus) together with low species richness. The first appearance of these small planktonic taxa in regular monitoring could be used as an early warning sign for deteriorating water quality. Diatoms could be applied to water quality classification and monitoring purposes in the coastal waters of the Baltic Sea area using techniques such as weighted‐averaging regression and calibration.     

Stratified distribution of nutrients and extremophile biota within freshwater ice covering the surface of Lake Baikal

Biological entities and gradients of selected chemicals within the seemingly barren ice layers covering Lake Baikal were investigated. Ice cores 40-68 cm long were obtained from in shore and offshore sites of Southern Lake Baikal during the cold period of a year (March-April) in 2007 and 2008. In microscopic observations of the melted ice, both algae and bacteria were found in considerable numbers (>10(3) cells/L and >10(4) cells/ml, respectively). Among all organisms found, diatom was generally the most predominant taxon in the ice. Interestingly, both planktonic and benthic algae were present in considerable numbers (2-4×10(4) cells/L). Dominant phototrophic picoplankton were comprised of small green algae of various taxa and cyanobacteria of Synechococcus and Cyanobium. The bacterial community consisted mostly of short rod and cocci cells, either free-living or aggregated. Large numbers of yeast-like cells and actinomycete mycelium were also observed. Concentrations of silica, phosphorus, and nitrate were low by an order of magnitude where biota was abundant. The profile of the ice could be interpreted as vertical stratification of nutrients and biomass due to biological activities. Therefore, the organisms in the ice were regarded to maintain high activity while thriving under freezing conditions. Based on the results, it was concluded that the freshwater ice covering the surface of Lake Baikal is considerably populated by extremophilic microorganisms that actively metabolize and form a detritus food chain in the unique large freshwater ecosystem of Lake Baikal.     

The insight into diatom diversity,ecology, and biogeography of an extreme cold ultraoligotrophic Lake Labynkyr at the Pole of Cold in the northern hemisphere

The freshwater ultraoligotrophic Lake Labynkyr is located near the Pole of Cold in the northern hemisphere (Yakutia, Russia). The lake is covered by ice during 240 days a year. We undertook several expeditions to the lake during the ice and open water periods for sampling ice fouling, plankton and periphyton that were then analyzed by means of scanning electron microscopy. As a result, we identified a high biodiversity of diatoms—123 species and intraspecific taxa from 53 genera, among them 3 species were new for Russia and 26 taxa were new for the algal flora of Yakutia. The oligo- and xenosaprobionts and their variations dominate—71 taxa. 18 Species were evaluated as tolerant to cold oligotrophic waters, 12 occurred on the ice bottom, and 62 in the water column under ice (0–25 m). 104 taxa were found during the open water period, 70 taxa were identified in the periphyton. We showed the diatom flora of Lake Labynkyr to be unique compared with other lakes of Yakutia and to share taxa with the diatom flora of Lake Baikal. The diatoms being indicators of the global climate changes and ecological status of lakes, our data can be used as an evidence of such changes as well as to be useful studies of biogeography and history of formation of flora in Arctic and Subarctic waters.

     

Assessing the vulnerability of endemic diatom species in Lake Baikal to predicted future climate change: a multivariate approach

Diatoms in Lake Baikal exhibit significant spatial variation, related to prevailing climate, lake morphology and fluvial input into the lake. Here we have assessed the threats to endemic planktonic diatom species (through the development of empirical models), which form a major component of primary production within the lake. Multivariate techniques employed include redundancy analysis (RDA) and Huisman–Olff–Fresco (HOF) models. Our analyses suggest that eight environmental variables were significant in explaining diatom distribution across the lake, and in order of importance these are snow thickness on the ice, water depth, duration of days with white ice, suspended matter in the lake, days of total ice duration, temperature of the water surface in July, concentration of zooplankton and suspended organic matter. Impacts on dominant phytoplankton diatom species are highlighted using t‐value biplots. Predictions of future climate change on Lake Baikal are likely to result in shorter periods of ice cover, decreased snow cover across the lake in spring, increased fluvial input into the lake, and an increase in the intensification of surface water stratification during summer months. All these factors are likely to impact negatively on the slow‐growing, cold‐water endemics such as Aulacoseira baicalensis and Cyclotella minuta, which currently dominate diatom assemblages. Instead, taxa that are only intermittently abundant, at present, in offshore areas (e.g. Stephanodiscus meyerii) are likely to become more frequent. However, given the climatic gradient across the lake, the timing and extent of changes in community structure are likely to vary. Moreover, palaeolimnological records show that Lake Baikal diatom assemblages have been dynamic throughout the Holocene, with both endemic and cosmopolitan species exhibiting periods of dominance. Effects of climate change on the entire lake ecosystem may yet be profound as the structure of the pelagic food web may change from one based on endemic diatom taxa to one dominated by nondiatom picoplankton, and as limnological functioning (e.g. stratification and mixing) affects deepwater oxygen availability, nutrient cycling and trophic linkages.     

Seasonal changes on planktonic diatom communities along an inshore-offshore gradient in the Gulf of Gabes (Tunisia)

We investigated the composition, biomass and cell size dynamics of the marine planktonic diatom species along a coastal-open sea gradient in relation to the hydrological characteristics, during four oceanographic cruises in July 2005, May–June 2006, September 2006 and March 2007 in the Gulf of Gabes. The study of the marine planktonic diatoms throughout the sampling period showed the presence of 40 different species belonging to 22 pennate and 18 centric diatom species. Centric diatoms were more abundant than the pennate ones; 56% and 44% of total diatom abundance, respectively. Diatoms were very abundant, representing about 60% of the total phytoplankton abundance, with an exception in July 2005 (19%) during which Dictyochophyceae were the most dominant group (41% of the total phytoplankton abundance). Diatoms, which were dominant in the coastal samples, mainly proliferate in the semi-mixing conditions (May–June 2006), whereas they declined in the offshore area, most likely due to silicate shortage. In this period, in spite of the high abundance of diatom planktonic cells, only diatom biomass was correlated with silica amount, proving that biomass was a better ecological bio-indicator than abundance. The results suggest that the marine planktonic diatoms taxa were generally adapted to specific hydrological structure. In fact, the dominance index of diatoms showed that the biodiversity of diatoms increased gradually along the coastal-open sea gradient except in May–June 2006 during which a slight decrease along the inshore towards offshore areas was observed. This index increase depended on a coastal-open sea distance during thermal stratification (July 2005 and September 2006) and mixing periods (March 2007).     

Diatom assemblages in sediments of Lake Juusa, Southern Estonia with an assessment of their habitat

Diatom analysis of surface sediments and two sediment cores from different sedimentation areas of a small closed lake was undertaken with the aim of acquiring knowledge on the dependence of the distribution of diatom assemblages on lake bathymetry. Lake Juusa was selected for the study because we have for this lake a large data set about the lithological composition of sediments and macrofossil and cladoceran records for the Holocene. A high carbonate content (20–60%) in the sediment sequence indicates high carbonacity and relatively stable pH values during the Holocene. On the basis of comprehensive analysis, abrupt water-level fluctuations and changes in the trophic status were established. Results of this study showed that the fluctuations of the water-level were the leading factor determining the habitats of diatom assemblages in the lake. In the surface sediment samples planktonic species such as Cyclotella spp., Stephanodiscus spp. and Aulacoseira spp. had a depth optimum at 3–4 m and the most abundant periphytic taxa were distributed mostly at depths shallower than 3.5 m. The same regularity was established in sediment cores where a good correlation between planktonic species and lake water depth was found in sediments accumulated at water depths >4 m. Lake Juusa appears to be a proper site for detailed environmental reconstructions over the Holocene, and the results will give us a good opportunity to analyse the history of water-level fluctuations in other small Estonian lakes. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: K. Martens     

Water level changes in a large shallow lake as reflected by the plankton:periphyton-ratio of sedimentary diatoms

Biostratigraphic diatom analyses were carried out on a short sediment core from the large shallow-water Lake Võrtsjärv, Estonia, in order to relate the diatom composition to the instrumental water level record. We dated the sediment core by radiometric methods (²¹⁰Pb, ¹³⁷Cs, ²⁴¹Am) and spheroidal fly-ash particle abundance chronology and evaluated the statistical significance of the relationships between the percentage of planktonic diatoms and the water level continuously monitored since 1871. Before the 1960s, the percentage of planktonic diatoms in the sediment showed quite strong positive relationship to water level. The impact of eutrophication after the 1960s presumably masked the influence of water level changes on the diatom community. In addition, statistical analysis of the upper part of the sediment core (1970—present day) together with measured limnological parameters of the lake showed that water transparency had the strongest influence on diatoms, while temperature, pH and alkalinity had lesser impacts. Our study shows that the planktonic:periphytic diatom ratio in the sediment can be used to track overall trends of the lake-level changes in Lake Võrtsjärv before the onset of cultural eutrophication; however, the results have to be interpreted carefully, taking into consideration other possible limnological factors such as water transparency, nutrients and wind.     

Effects of increased salinity on the diatom assemblage in Fonda Lake,Michigan

A salt storage facility has been located adjacent to Fonda Lake since 1953. In February 1981 a core was taken from the profundal sediments of the lake and analyzed to determine the effects of salt perturbation on the diatom community over a 32-year period. Diatom assemblages from different levels were compared using multivariate techniques including cluster analysis and principal component analysis. Shifts in diatom composition related to salinification were revealed most clearly by subdominant taxa. Five distinct groups of diatom taxa were found to correspond with 5 depth intervals. The diatom component of the lake up to 1960 included two groups of taxa which were alkaliphilous and chloride indifferent. A reduction in species diversity beginning in 1960 may indicate a salt effect. By 1968, when diversity reached a minimum, a variety of halophilic taxa (including Diatoma tenue, Navicula gregaria and Synedra fasciculata) attained their highest relative abundances. At the top of the core, diversity increased slightly and some halophilic taxa decreased in relative abundance, which suggests a possible decrease in salt loading to the lake.     

Phytoplankton community composition in Lake Xolotlán (Managua)

Results of two years of research on phytoplankton species composition in Lake Xolotlán (Managua) are presented. A summary of the planktonic algae from other Nicaraguan lakes is also included. One hundred and twenty phytoplankton taxa were identified. A list of species and comments about relevant properties of the most frequent taxa are given. The qualitative composition of Lake Xolotlán phytoplankton is compared with that of other tropical waterbodies.     

湖南省大通湖百余年环境演化历史及营养物基准的建立

科学有效地治理退化湖泊需要知晓湖泊的演化历史,并设立合理的参照目标(即环境基准)来及时评判治理效果.湖南省大通湖位于经济发达的长江中下游地区,发挥着重要的湖泊水生态系统服务功能.在强烈的人类活动干扰下,该湖近年来生态系统退化严重,但其水环境演变的历史缺少详细的记录.研究对大通湖沉积钻孔的年代、烧失量、化学元素、沉积物总...