A comparison of the fatty acid composition of Gammarus lacustris and its food sources from a freshwater reservoir, Bugach, and the saline Lake Shira in Siberia, Russia

We studied fatty acid (FA) composition in samples from bodies and intestinal contents of the littoral amphipod Gammarus lacustris Sars, from the Bugach freshwater reservoir. Simultaneously, samples of seston and bottom sediments were also collected from the reservoir during early August. There were no differences in FA composition of gut contents, seston and sediments of pebbly bottom. Seston was the main food source of Gammarus but some FAs Gammarus got from sediments. The FA composition of G. lacustris and seston from the Bugach freshwater reservoir were compared with those of the animals from the saltwater Lake Shira (Siberia). While FA composition of the two Gammarus populations differed significantly, those of seston were practically similar: the composition of long-chain unsaturated fatty acids, 20:53, 22:63 and 20:46, were significantly higher in animals from saline Shira Lake, whereas 16:1 and 16:0 were higher in the freshwater populations of amphipods from the Bugach freshwater reservoir. Taking into account the relevant literature data, we hypothesise that this difference in C16 acid might be a distinguishing characteristic of FA composition of freshwater and saltwater crustaceans.     

Dynamics of purple sulfur bacteria in a meromictic saline Lake Shunet (Khakassia,Siberia) in 2007–2013

According to the results of seasonal monitoring, in 2007–2013 purple sulfur bacteria morphologically similar to Thiocapsa sp. Shira_1 (AJ633676 in EMBL/GenBank) predominated in the anoxygenic phototrophic community of the water column of the meromictic Lake Shira (Khakassia, Siberia). No pronounced seasonal periodicity in the total cell number in the water column was revealed during the period of observation. In some years cell number during the period when the lake was covered with ice was reliably higher than in summer. The absence of seasonal periodicity was probably due to the low amplitude of seasonal variations in temperature and illumination in the redox zone, resulting from its relatively deep location (12–16 m). The year-to-year dynamics was characterized by a reliable decrease of the total cell number in 2009–2010 and maxima in 2007 and 2011–2012. Canonical correlation analysis revealed that water temperature in the redox zone was the best predictor of the PSB abundance in Lake Shira. Water temperature, in turn, depended on the depth of mixing of the water column. Intense mixing in 2009–2011 was probably responsible for decreased PSB abundance in the lake. On the other hand, the absence of deep winter mixing, resulting in stable conditions in the chemocline, favored the preservation of relatively high PSB biomass. Prediction of circulation depth, which depends mainly on the weather conditions and dynamics of the water level, is required for prediction of PSB abundance in Lake Shira. These results may be useful for paleolimnological reconstructions of the history of the lake based on the remnants of purple sulfur bacteria in bottom sediments.     

Microbial metabolism of the carbon and sulfur cycles in Shira Lake (Khakasia)

Microbiological and biogeochemical studies of the meromictic saline Lake Shira (Khakasia) were conducted. In the upper part of the hydrogen-sulfide zone, at a depth of 13.5-14 m, there was a pale pink layer of water due to the development of purple bacteria (6 x 10(5) cells/ml), which were assigned by their morphological and spectral characteristics to Lamprocystis purpureus (formerly Amoebobacter purpurea). In August, the production of organic matter (OM) in Lake Shira was estimated to be 943 mg C/(m2 day). The contribution of anoxygenic photosynthesis was insignificant (about 7% of the total OM production). The share of bacterial chemosynthesis was still less (no more than 2%). In the anaerobic zone, the community of sulfate-reducing bacteria played a decisive role in the terminal decomposition of OM. The maximal rates of sulfate reduction were observed in the near-bottom water (114 micrograms S/(1 day)) and in the surface layer of bottom sediments (901 micrograms S/(dm3 day)). The daily expenditure of Corg for sulfate reduction was 73% of Corg formed daily in the processes of oxygenic and anoxygenic photosynthesis and bacterial chemosynthesis. The profile of methane distribution in the water column and bottom sediments was typical of meromictic reservoirs. The methane content in the water column increased beginning with the thermocline (7-8 m), and reached maximum values in the near-bottom water (17 microliters/l). In bottom sediments, the greatest methane concentrations (57 microliters/l) were observed in the surface layer (0-3 cm). The integral rate of methane formation in the water column and bottom sediments was almost an order of magnitude higher than the rate of its oxidation by aerobic and anaerobic methanotrophic microorganisms.     

Microbiological and isotopic-geochemical investigations of meromictic lakes in Khakasia in winter

Microbiological and isotopic-geochemical investigations of the brackish meromictic lakes Shira and Shunet were performed in the steppe region of Khakasia in winter. Measurements made with a submersed sensor demonstrated that one-meter ice transmits light in a quantity sufficient for oxygenic and anoxygenic photosynthesis. As in the summer season, in the community of phototrophic bacteria found in Lake Shira, the purple sulfur bacteria Amoebobacter purpureus dominated, whereas, in Lake Shunet, the green sulfur bacteria Pelodictyon luteolum were predominant. Photosynthetic production, measured using the radioisotopic method, was several times lower than that in summer. The rates of sulfate reduction and production and oxidation of methane in the water column and bottom sediments were also lower than those recorded in summer. The process of anaerobic methane oxidation in the sediments was an exception, being more intense in winter than in summer. The data from radioisotopic measurements of the rates of microbial processes correlate well with the results of determination of the isotopic composition of organic and mineral carbon (delta13C) and hydrogen sulfide and sulfate (delta34S) and suggest considerable seasonal variations in the activity of the microbial community in the water bodies investigated.     

Meromixis and Seasonal Dynamics of Vertical Structure of Lake Uchum (South Siberia)

The seasonal dynamics of the vertical structure of small saline Lake Uchum, located in the steppe arid zone of the south of Siberia (Krasnoyarsk krai), has been studied in detail for the first time. This lake is a meromictic water body. We have revealed a heterogeneous vertical distribution of plankton organisms and a dense population of purple sulfuric bacteria in the redox zone. The taxonomic composition and seasonal dynamics of phyto- and zooplankton are described. Presumably, the meromixis of Lake Uchum is due to the inflow of fresh water to the surface of the saline water body during the rise of its level in the early 20th century, similarly to lakes Shira and Shunet located nearby. The processes of salt displacement into the solution during the formation of ice, as well as the precipitation of salts in the winter, also contribute to the maintenance of permanent stratification. The information on the current state of the lake can be useful for reconstructing the climate by bottom sediments, as well as for creating a model of water quality and investigating the therapeutic properties of lake mud.     

Effect of winter conditions on distributions of anoxic phototrophic bacteria in two meromictic lakes in Siberia,Russia

The year-to-year variations of vertical distribution and biomass of anoxic phototrophic bacteria were studied during ice periods 2003–2005 and 2007–2008 in meromictic lakes Shira and Shunet (Southern Siberia, Russian Federation). The bacterial layers in chemocline of both lakes were sampled with a thin-layer hydraulic multi-syringe sampler. In winter, biomass of purple sulphur bacteria varied considerably depending on the amount of light penetrating into the chemocline through the ice and snow cover. In relatively weakly stratified, brackish Shira Lake, the depth of chemocline varied between winters, so that light intensity for purple sulphur bacteria inhabiting this zone differed. In Shira Lake, increased transparency of mixolimnion in winter, high chemocline position and absence of snow resulted in light intensity and biomass of purple sulphur bacteria exceeding the summer values in the chemocline of the lake. We could monitor snow cover at the lake surface using remote sensing and therefore estimate dynamics and amount of light under ice and its availability for phototrophic organisms. In Shunet Lake, the light intensities in the chemocline and biomasses of purple sulphur bacteria were always lower in winter than in summer, but the biomasses of green sulphur bacteria were similar.     

Mathematical models and computer programmes for the investigation of hydrophysical processes in Lake Shira

Physical processes determine to great extent the habitat of hydrobionts, as well as the transfer and sedimentation of substances, the intensity of pollution and rate of natural purification of water bodies. Mathematical models of different levels of complexity, developed to investigate hydrophysical processes in lakes, are discussed in this paper. The numerical algorithms and computer programmes described can be used to determine the influence of the morphometric characteristics and weather on the temperature regime of Lake Shira (Khakasia, Siberia) and the pattern of the wind currents. Examples of calculating the temperature regime in the context of a one- dimensional model and of calculating the parameters of wind currents in the water body of a simple geometrical form are given.The study suggests that the pattern of wind currents in Lake Shira is significantly affected by the density stratification, which depends not only on temperature but also on salinity. In order to construct a realistic pattern of currents a 3-D computer model of Lake Shira must be developed and used to estimate the validity of the two-dimensional and one-dimensional models. The present research can be further developed by extending the obtained algorithms to three-dimensional problems, taking into account the heat exchange, salinity and the geometry (bathymetric contours) of the water body. Calculations can be made for Lake Shira and the obtained data used in biophysical models.     

Asynchronous vertical migrations of zooplankton in stratified lakes

Asynchronous vertical migrations of calanoid copepods Arctodiaptomus salinus were studied in two stratified lakes in the south of Siberia using the method of two-section enclosures. It was found that the presence of a pronounced thermocline and a depth maximum of phytoplankton (Lake Shira) contributes to the appearance of intensive individual migrations of copepods between areas of the epi- and hypolimnion.     

Application of satellite data for investigation of dynamic processes in inland water bodies: Lake Shira (Khakasia, Siberia), a case study

This work describes avenues to use satellite information to analyse dynamic processes in aquatic ecosystems. Information for this analysis, was retrieved from AVHRR satellite sensor data. This information consisteds of time series of images of radiation temperature and turbidity. We expect this information will be of great value in analysing inland water bodies. Methods to process satellite information using original software and data processing techniques are proposed. For the investigation of the process and analyses of satellite information Shira Lake (Khakasia, Siberia) was used as a case study. To study the variability of the surface temperature and turbidity of the Lake in summer, the satellite and ground-truth data of the lake was applied. This study represents the first evaluation of the dynamic processes for Lake Shira based on satellite, ground-truth and modelling data. We developed algorithms and software to process satellite images to enable the reconstruction of time dependence of temperature and spectral reflectance of water bodies in the visible range, and to make computer-animated films visualising the spatial and temporal dynamics of the study parameters. The analyses of morphometric, meteorological and hydrological characteristics of Lake Shira have provided a realistic opportunity for processing the satellite information and to develop numerical models of variability of the hydrological regime of the lake. The results obtained demonstrate the feasibility of systematically retrieving the spatial information from the satellite data on the dynamics of the surface water temperature and of the suspended matter in the lake.     

Microbiological and Isotopic-Geochemical Investigations of Meromictic Lakes in Khakasia in Winter

Microbiological and isotopic-geochemical investigations of the brackish meromictic lakes Shira and Shunet were performed in the steppe region of Khakasia in winter. Measurements made with a submersed sensor demonstrated that one-meter ice transmits light in a quantity sufficient for oxygenic and anoxygenic photosynthesis. As in the summer season, in the community of phototrophic bacteria found in Lake Shira, the purple sulfur bacteria Amoebobacter purpureus dominated, whereas, in Lake Shunet, the green sulfur bacteria Pelodictyon luteolum were predominant. Photosynthetic production, measured using the radioisotopic method, was several times lower than that in summer. The rates of sulfate reduction and production and oxidation of methane in the water column and bottom sediments were also lower than those recorded in summer. The process of anaerobic methane oxidation in the sediments was an exception, being more intense in winter than in summer. The data from radioisotopic measurements of the rates of microbial processes correlate well with the results of determination of the isotopic composition of organic and mineral carbon (δ¹³C) and hydrogen sulfide and sulfate (δ³⁴S) and suggest considerable seasonal variations in the activity of the microbial community in the water bodies investigated.__________Translated from Mikrobiologiya, Vol. 74, No. 4, 2005, pp. 552–561.Original Russian Text Copyright © 2005 by Savvichev, Rusanov, Rogozin, Zakharova, Lunina, Bryantseva, Yusupov, Pimenov, Degermendzhi, Ivanov.     

Numerical modeling of vertical stratification of Lake Shira in summer

A one-dimensional numerical model and a two-dimensional numerical model of the hydrodynamic and thermal structure of Lake Shira during summer have been developed, with several original physical and numerical features. These models are well suited to simulate the formation and dynamics of vertical stratification and provide a basis for an ecological water-quality model of the lake. They allow for the quantification of the vertical mixing processes that govern not only the thermal structure but also the nutrient exchange, and more generally, the exchange of dissolved and particulate matter between different parts of the lake. The outcome of the calculations has been compared with the field data on vertical temperature and salinity distributions in Lake Shira. Lake Shira is meromictic and exhibits very stable annual stratification. The stratification is so stable because of the high salinity of the water. If the water in Lake Shira were fresh and other parameters (depth, volume, and meteorology) were the same, as now, the lake would be mixed in autumn. Using the newly developed models and using common meteorological parameters, we conclude that Lake Shira will remain stratified in autumn as long as the average salinity is higher than 3‰.     

Microbial Processes of the Carbon and Sulfur Cycles in Lake Shira (Khakasia)

Microbiological and biogeochemical studies of the meromictic saline Lake Shira (Khakasia) were conducted. In the upper part of the hydrogen-sulfide zone, at a depth of 13.5–14 m, there was a pale pink layer of water due to the development of purple bacteria (6 × 10⁵ cells/ml), which were assigned by their morphological and spectral characteristics toLamprocystis purpurea (formerly Amoebobacter purpureus). In August, the production of organic matter (OM) in Lake Shira was estimated to be 943 mg C/(m²day). The contribution of anoxygenic photosynthesis was insignificant (about 7% of the total OM production). The share of bacterial chemosynthesis was still less (no more than 2%). In the anaerobic zone, the community of sulfate-reducing bacteria played a decisive role in the terminal decomposition of OM. The maximal rates of sulfate reduction were observed in the near-bottom water (114 g S/(l day)) and in the surface layer of bottom sediments (901 g S/(dm³ day)). The daily expenditure of C_org for sulfate reduction was 73% of C_org formed daily in the processes of oxygenic and anoxygenic photosynthesis and bacterial chemosynthesis. The profile of methane distribution in the water column and bottom sediments was typical of meromictic reservoirs. The methane content in the water column increased beginning with the thermocline (7–8 m) and reached maximum values in the near-bottom water (17 l/l). In bottom sediments, the greatest methane concentrations (57 l/l) were observed in the surface layer (0–3 cm). The integral rate of methane formation in the water column and bottom sediments was almost an order of magnitude higher than the rate of its oxidation by aerobic and anaerobic methanotrophic microorganisms.     

A one-dimensional model of vertical stratification of Lake Shira focussed on winter conditions and ice cover

In meromictic lakes such as Lake Shira, horizontal inhomogeneity is small in comparison with vertical gradients. To determine the vertical distribution of temperature, salinity, and density of water in a deep zone of a Lake Shira, or other saline lakes, a one-dimensional (in vertical direction) mathematical model is presented. A special feature of this model is that it takes into account the process of ice formation. The model of ice formation is based on the one-phase Stefan problem with the linear temperature distribution in the solid phase. A convective mixed layer is formed under an ice cover due to salt extraction in the ice formation process. To obtain analytical solutions for the vertical distribution of temperature, salinity, and density of water, we use a scheme of vertical structure in the form of several layers. In spring, the ice melts as top and bottom. These processes are taken into account in the model. The calculated profiles of salinity and temperature of Shira Lake are in good agreement with field measurement data for each season. Additionally, we focussed on the redox zone, which is the zone in which the aerobic layers of a water column meet the anaerobic ones. Hyperactivity of plankton communities is observed in this zone in lakes with hydrogen sulphide monimolimnion, and Lake Shira is among them. The location of the redox zone in the lake, which is estimated from field measurements, coincides with a sharp increase in density (the pycnocline) during autumn and winter. During spring and summer, the redox zone is deeper than the pycnocline. The location of pycnocline calculated with the hydro physical model is in good agreement with field measurement data.     

Microbial sulfate reduction in a brackish meromictic steppe lake

Patterns of sulfate reduction were studied in water and sediments of Lake Shira, South Siberia, Russia. The lake was characterized by a high level of sulfate (91-116 mM). The concentration of hydrogen sulfide in the anoxic waters of the lake reached 0.6 mM. In summer the sulfate reduction rate in the water column, measured by radiometric technique, varied from 0.25 to 9.81 mol sulfate l^-1 d^-1. There were two peaks of sulfate reduction activity: just below the chemocline and near the sediment surface. Sulfate reduction rate in the profundal silts ranged from 4.1 to 90.6 mol l^-1 d^-1. The zone of the most active sulfate reduction was restricted to the surface sediment layers. The acceleration of sulfate reduction rate (up to 236 mol l^-1 d^-1) and the increase of density of viable sulfate reducers (up to 2 x 10⁵ cells ml^-1) were recorded in the littoral sediments adjacent to the mouth of the Son River and sewage discharge. It was apparently caused by the input of allochthonous organic substrates and also by a high environmental temperature. On an areal basis, sulfate reduction rate in the water was approximately 8 times higher than that in the profundal sediments. Sulfate reduction was the most important process of anaerobic oxidation of organic carbon in Lake Shira. In summer in the profundal zone of the lake, sulfate reducers were able to mineralize about 67% of the daily integrated primary production of phototrophic and chemotrophic organisms.     

Vertical stratification of physical,chemical and biological components in two saline lakes Shira and Shunet (South Siberia,Russia)

A feature of meromictic lakes is that several physicochemical and biological gradients affect the vertical distribution of different organisms. The vertical stratification of physical, chemical and biological components in saline, fishless meromictic lakes Shira and Shunet (Siberia, Russia) is quite different mainly because both mean depth and maximum depth of lakes differ as well as their salinity levels differ. The chemocline of the Lake Shira, as in many meromictic lakes, is inhabited by bacterial community consisting of purple sulphur and heterotrophic bacteria. As the depth of the chemocline is variable, the bacterial community does not attain high densities. The mixolimnion in Lake Shira, which is thermally stratified in summer, also creates different habitat for various species. The distribution of phytoplankton is non-uniform with its biomass peak in the metalimnion. The distribution of zooplankton is also heterogeneous with rotifers and juvenile copepods inhabiting the warmer epilimnion and older copepods found in the cold but oxic hypolimnion. The amphipod Gammarus lacustris which can be assigned to the higher trophic link in the fishless lake’s ecosystem, such as Lake Shira, is also distributed non-uniformly, with its peak density generally observed in the thermocline region. The chemocline in Lake Shunet is located at the depth of 5 m, and unlike in Lake Shira, due to a sharp salinity gradient between the mixolimnion and monimolimnion, this depth is very stable. The mixolimnion in Lake Shunet is relatively shallow and the chemocline is inhabited by (1) an extremely dense bacterial community; (2) a population of Cryptomonas sp.; and (3) ciliate community comprising several species. As the mixolimnion of Lake Shunet is not thermally stratified for long period, the phytoplankton and zooplankton populations are not vertically stratified. The gammarids, however, tend to concentrate in a narrow layer located 1–2 m above the chemocline. We believe that in addition to vertical inhomogeneities of both physicochemical parameters, biological and physical factors also play a role in maintaining these inhomogeneities. We conclude that the stratified distributions of the major food web components will have several implications for ecosystem structure and dynamics. Trophic interactions as well as mass and energy flows can be significantly impacted by such heterogeneous distributions. Species spatially separated even by relatively short distances, say a few centimetres will not directly compete. Importantly, we demonstrate that not only bacteria, phytoflagellates and ciliate tend to concentrate in thin layers but also larger-sized species such Gammarus (amphipods) can also under certain environmental conditions have stratified distribution with maxima in relatively thin layer. As the vertical structure of the lake ecosystem is rather complex in such stratified lakes as ours, the strategy of research, including sampling techniques, should consider potentially variable and non-homogeneous distributions.     

Paleolimnology of a small oligotrophic lake on Wolin Island,Baltic Sea,Poland

Paleolimnological studies which included analyses of diatoms, fossil pigments and physico-chemical characteristics of bottom sediments have been used to describe the limnological history of Racze Lake. The influx of terrigenous material into the lake have been determined on the basis of stratigraphy of elements associated with mineral content. The successively eroded soils as well as process of chemical erosion caused increase leaching of metals Mg, Fe, Al into the lake basin. However the concentration of these metals finally deposited in bottom sediments was also effected by the oxygen regime at the sediment-water interface. Both ratios, chlorophyll derivatives to total carotenoids (CD:TC) and Fe:Mn indicated hypolimnetic oxygen depletion in the middle part of the profile. The development of blue-green algal population, estimated by the ratio epiphasic to hypophasic carotenoids (EC:HC) was correlated with periods of redox conditions in the lake. The pH changes ranged from 6.5 to 7.7. The most important factors effecting pH changes were inflow of mineral matter from the watershed and structural changes in the littoral biocenosis.     

Bioluminescence characteristics of Lake Shira water

Bioluminescence bioassays based on luminous bacteria (Photobacterium phosphopreum) and coupled enzyme system NADH-FMN-oxidoreductase-luciferase were adapted for monitoring the saline-water conditions of Lake Shira (Khakasia, Siberia). The differences in bioluminescence responses have been found to be related to the salt composition and the oxidation-reduction properties of water. Bioluminescent kinetics parameters, which are mostly sensitive to pollution under conditions of saline water, have been observed. The enzymatic system in the presence of 1,4-benzoquinone are shown to be more sensitive to redox characteristics of the salt water than this in the absence of 1,4-benzoquinone. 1,4-benzoquinone should be applied for the preparation of a model solution for the monitoring of redox properties of the salt water. Using this technique, the results of bioluminescence analysis are used to construct a heterogeneity map that characterizes the spatial and temporal water quality of lake Shira. A partial map was based on the bioluminescence characteristics of water samples taken along the shoreline, sampling stations in the different places and in different depths of the lake. It has been demonstrated that the bioluminescence assay measurements must be done within two hours after the sampling time.     

Bacterial Communities of Three Saline Meromictic Lakes in Central Asia

Meromictic lakes located in landlocked steppes of central Asia (~2500 km inland) have unique geophysiochemical characteristics compared to other meromictic lakes. To characterize their bacteria and elucidate relationships between those bacteria and surrounding environments, water samples were collected from three saline meromictic lakes (Lakes Shira, Shunet and Oigon) in the border between Siberia and the West Mongolia, near the center of Asia. Based on in-depth tag pyrosequencing, bacterial communities were highly variable and dissimilar among lakes and between oxic and anoxic layers within individual lakes. Proteobacteria, Bacteroidetes, Cyanobacteria, Actinobacteria and Firmicutes were the most abundant phyla, whereas three genera of purple sulfur bacteria (a novel genus, Thiocapsa and Halochromatium) were predominant bacterial components in the anoxic layer of Lake Shira (~20.6% of relative abundance), Lake Shunet (~27.1%) and Lake Oigon (~9.25%), respectively. However, few known green sulfur bacteria were detected. Notably, 3.94% of all sequencing reads were classified into 19 candidate divisions, which was especially high (23.12%) in the anoxic layer of Lake Shunet. Furthermore, several hydro-parameters (temperature, pH, dissolved oxygen, H₂S and salinity) were associated (P< 0.05) with variations in dominant bacterial groups. In conclusion, based on highly variable bacterial composition in water layers or lakes, we inferred that the meromictic ecosystem was characterized by high diversity and heterogenous niches.     

Lipid and hydrocarbon compositions of a collection strain and a wild sample of the green microalga Botryococcus

Lipid composition and hydrocarbon structure of two colonial green algae of the genus Botryococcus, i.e., a museum strain and a field sample collected for the first time from Lake Shira (Khakasia, Siberia), have been compared. Polar lipids, diacylglycerols, alcohols, triacylglycerols, sterols, sterol esters, free fatty acids and hydrocarbons have been identified among lipids in the laboratory culture. The dominant fraction in the museum strain was formed by polar lipids (up to 50% of the lipids) made up of fatty acids from C₁₂ to C₂₄. Palmitic, oleic, C₁₆ - C₁₈ dienoic and trienoic acids were the main fatty acids of the museum strain. Aliphatic hydrocarbons were found in the lipid of the museum strain. However, these amounted maximally to about 1% of the dry biomass at the end of exponential growth phase. The qualitative and quantitative compositions of FAs and hydrocarbons of the museum strain of Botryococcus, (registered at the Cambridge collection as Botryococcus braunii Kutz No LB 807/1 Droop 1950 H-252) differed from those of the Botryococcus strain described in the literature as Botryococcus braunii. The Botryococcus sp. found in Lake Shira is characterized by a higher lipid content (<40% of the dry weight). Polar lipids, sterols, triacylglycerols, free fatty acids and hydrocarbons have been identified among lipids in the field sample. The main lipids in this sample were dienes and trienes (hydrocarbons <60% of total lipid). Monounsaturated and very long chain monounsaturated fatty acids, including C_28:1 and C_32:1 acids, were identified in the Botryococcus found in Lake Shira. The chemo-taxonomic criteria allow us to unequivocally characterize the organism collected from Lake Shira as Botryococcus braunii, race A.     

Paleopigment evidence of competition between phytoplankton and a cyanobacterial algal mat in a meromictic lake near Toronto,Ontario Canada

Crawford Lake, a meromictic lake located near Toronto, Canada, was cored to determine if algal pigments preserved in its sediments would make it possible to infer past changes in lake productivity over the last five hundred years. From 1500 to 1910 A.D. the sediments display extremely high levels of oscillaxanthin and myxoxanthophyll while chlorophyll derivatives and total carotenoids were relatively low. As the lake became increasingly more eutrophic in the latter part of the twentieth century, this relationship reversed itself. Competition for light between the deep dwelling cyanobacteria in the algal mat on the lake's bottom (8–14 m) and phytoplankton in the overlying surface layers of the water column (5–7 m) was attributed to the observed reduction in oscillaxanthin and myxoxanthophyll as Crawford Lake eutrophied. Because the major cyanobacteria in Crawford Lake are benthic mat forming Lyngbya and Oscillatoria, and not phytoplankton, competition for light with the overlying phytoplankton is critical in determining the total quantity of oscillaxanthin and myxoxanthophyll preserved in the lake's profundal sediments. These findings have major implications for the use of cyanobacterial pigments as indicators of lake trophic status in lakes where benthic algal mats are present.