Plankton composition and water chemistry in the mixing zone of the Selenga River with Lake Baikal

Chemical and biological components of the Selenga River waters, the largest tributary of Lake Baikal, differ significantly from the lake waters. Active transformation processes of river waters into the lake ones occur in the vast barrier-like zone in the river-sea boundary areas. This study presents results on the spatial distribution and dynamics of water chemistry as well as the quantity and diversity of phyto- and bacterioplankton at a distance of 14 km off the Selenga River mouth. The most representative tracers of river and lake waters are total amount of ions and sulphates. Principal changes of chemical and biological parameters were fixed at 1–3 km off the Selenga River mouth that was determined as a mixing zone. Intense development of phytoplankton and eukaryotic picoplankton causing the decrease of nitrate and phosphate concentrations and organic matter rise were registered in this area. Gradual replacement of river phytoplankton by the lake one, abundance reduction of microorganisms and organotrophic bacteria and percentage increase of oligotrophic and psychrotolerant bacteria occurred in the mixing zone. Replacement of PC-rich picocyanobacteria by PE-rich ones was also recorded here. At a distance of 5–7 km off the shore, nutrient concentration and plankton composition were similar to those of Lake Baikal.     

Spatio-temporal niche partitioning of closely related picocyanobacteria clades and phycocyanin pigment types in Lake Constance (Germany)

We found that the clade-specific abundance dynamics of Synechococcus type picocyanobacteria in the pelagic and littoral zone macro-habitats of Lake Constance (Germany) challenge the hypothesis of a regular annual succession of picocyanobacteria genotypes in temperate zone lakes. Methods used in this study were quantitative Taq nuclease assays (TNA), denaturing gradient gel electrophoresis (DGGE), a 19-month time series analysis (with two isothermal and two stratified periods) and genotyping of a new littoral phycocyanin (PC)-rich Synechococcus strain collection. The recorded differences between the two macro-habitats and between seasons or years, and the observed effect of water column mixis in winter on the inversion of clade-specific dominance ratios in Lake Constance might explain the known inter-annual differences in abundance and dynamics of the autotrophic picoplankton (APP) in lakes. The APP in Lake Constance shows a high genetic diversity with a low overall abundance, similar to the APP in the Baltic Sea, but different from Lake Biwa in Japan or lakes in the UK. Our results indicate that APP bloom events in both macro-habitats of Lake Constance are driven by phycoerythrin-rich Synechococcus genotypes of the Subalpine Cluster I. DGGE revealed the presence of a diverse periphyton (biofilm) community of the PC-rich Synechococcus pigment type in the littoral zone in early spring, when no such community was detectable in the pelagic habitat. A more sensitive and quantitative approach with TNA, however, revealed an intermittent presence of one PC-rich genotype in the plankton. We discuss the seasonal development of the pelagic and littoral PC-rich community, and while we cannot rule out a strain isolation bias, we found that isolated PC-rich strains from the pelagic habitat have different genotypes when compared to new littoral strains. We also observed littoral substrates colonized by specific PC-rich Synechococcus genotypes.     

The impact of the River Ntahangwa, the most polluted Burundian affluent of Lake Tanganyika, on the water quality of the lake

Sources of pollution at the north end of Lake Tanganyika are concentrated around Bujumbura, Burundi. The impact of River Ntahangwa on the water quality of this part of Lake Tanganyika was compared with that of an unpolluted river, the Mugere. A shallow bay, not influenced by a river, was used as a reference station. Chemical analyses were carried out at four week intervals during nearly a year. Samples were taken at different distances from the shore and at different depths. River impact was detected up to 100 m from both river mouths. Even at 50 m from the mouth of the polluted River Ntahangwa, no important decrease of dissolved oxygen was detected. Chlorophyll-a maxima were found 100 m from the Ntahangwa mouth, but this was also the case 100 m from shore in the unpolluted bay. Lake water at 60 m depth was saturated with oxygen during the dry season, as it used to be in 1956. The rivers studied descent initially within the lake due to greater sediment load and lower water temperature. Nevertheless, it appears that these rivers mix completely in the lake within 100–300 m from the river mouths. The direct effects from organic pollution of the Ntahangwa on the lake seem to be rather negligible. Appropriate anti-erosion measures should reduce massive sediment discharge into the lake.     

Abundance,growth and grazing loss rates of picophytoplankton in Barguzin Bay,Lake Baikal

The abundance, growth, and grazing loss rates of picophytoplankton were investigated in August 2002 in Barguzin Bay, Lake Baikal. Water samples for incubation were taken once at a near-shore station and twice at an offshore station. Contributions of picophytoplankton to total phytoplankton were high (56.9–83.9%) at the offshore station and low (5.8–6.8%) at the near-shore station. The picophytoplankton community in the offshore station comprised mainly phycoerythrin (PE)-rich cyanobacteria, with eukaryotic picophytoplankton being less abundant. In contrast, as well as PE-rich cyanobacteria and eukaryotic picophytoplankton, phycocyanin (PC)-rich cyanobacteria were found in the near-shore station. At the offshore station, growth and grazing loss rates on 25 August were 0.56 and 0.43 day⁻¹, respectively, and on 29 August, 0.69 and 0.83 day⁻¹, respectively. At the near-shore station, growth and grazing loss rates were 1.61 and 0.70 day⁻¹, respectively. These results show that there is a difference in the abundance, composition, and ecological role in the microbial food web of picophytoplankton between the near-shore and the offshore areas in Barguzin Bay.     

Oxygen concentration profiles in sediments of two ancient lakes: Lake Baikal (Siberia,Russia) and Lake Malawi (East Africa)

Oxygen concentration profiles have been measured, by means of with microelectrodes in sediments of Lake Baikal and Lake Malawi, along transects allowing to give a survey of two major ancient Rift lakes: Lake Baikal (Eastern Siberia) and Lake Malawi (East Africa), along depth transects in the constitutive basins of the lakes and/or of relevant depths with regard to oxygen (including including the deepest point, 1680 m, in Lake Baikal). Sediment oxygen penetration depths (SOPs) display very different patterns, depending on the lake in the two lakes. In Lake Baikal, SOPs are variable, show no significant relationship with bathymetric depth and are surprisingly deep on Akademichesky ridge (> 50.0 mm), emphasizing the distinctive feature of this region in the lake. While the Selenga river is an important source of eutrophication, the similarity of SOP-values in the Selenga shallow with those of most other sites suggests either a dilution of organic material by allochthonous matter, or a strong south-to-north transport of particles. In Lake Malawi, available oxygen is restricted to a maximum of three millimetres of the sediment, and there is a negative relationship with bathymetric depth, as a result of a steady decline of oxygen concentration with depth through the water column. Amongst the few parameters known to affect SOPs, the oxygen consumption by the sediment seems the most significant in both lakes. SOP-values furthermore confirm differences in the trophic status of Baikal and Malawi, respectively. The importance of oxygen as a factor likely to create ecological segregation for benthic organisms is discussed. Lake Malawi offers possibilities of bathymetric segregation but no vertical segregation in the sediment. In contrast, no bathymetric segregation related to oxygen is possible in Lake Baikal, but vertical segregation in the sediment is very likely. This revised version was published online in July 2006 with corrections to the Cover Date.     

A five-year study of autotrophic winter picoplankton in Lake Balaton,Hungary

Picoeukaryotes dominate the phytoplankton of Lake Balaton—the largest shallow lake in Central Europe—in the winter period. We examined the annual dynamics of picoplankton abundance and composition in the lake in order to establish if the picoeukaryotes merely survive the harsher winter conditions or they are able to grow in the ice-covered lake when the entire phytoplankton is limited by low light and temperature. Lake Balaton has an annual temperature range of 1–29°C, and it is usually frozen between December and February for 30–60 days. In the spring-autumn period phycocyanin and phycoerythrin rich Cyanobacteria are the dominant picoplankters, and picoeukaryotes are negligible. Our five-year study shows the presence of three types of picophytoplankton assemblages in Lake Balaton: (1) Phycoerythrin-rich Cyanobacteria—the dominant summer picoplankters in the mesotrophic lake area; (2) Phycocyanin-rich Cyanobacteria—the most abundant summer picoplankters in the eutrophic lake area and; (3) Picoeukaryotes—the dominant winter picoplankters in the whole lake. The observed winter abundance of picoeukaryotes was high (up to 3 × 10⁵ cells ml⁻¹), their highest biomass (520 μg l⁻¹) exceeded the maximum summer biomass of picocyanobacteria (500 μg l⁻¹). Our results indicate that the winter predominance of picoeukaryotes is a regular phenomenon in Lake Balaton, irrespective of the absence or presence of the ice cover. Picoeukaryotes are able to grow at as low as 1–2°C water temperature, while the total phytoplankton biomass show the lowest annual values in the winter period. In agreement with earlier findings, the contribution of picocyanobacteria to the total phytoplankton biomass in Lake Balaton is inversely related to the total phytoplankton biomass, whereas no such relationship was observable in the case of picoeukaryotes.     

Nutritional diagnosis of phytoplankton in Lake Baikal

To diagnose the nutritional status of phytoplankton in Lake Baikal, surveys for the determination of concentrations of particulate carbon (PC), nitrogen (PN) and phosphorus (PP) and their ratios were conducted at six stations in March, June, August and October 1999. The concentrations of PC and PN were lower than, and those of PP were similar to, those in another mesotrophic lake except at the station near the mouth of the largest input river, Selenga River, of Lake Baikal. The PC : PN : PP ratio was 102 : 13 : 1, considerably close to the Redfield ratio. The ratio was constant against spatiotemporal changes. These indicate that phytoplankton in Lake Baikal were exposed to no deficiency in nitrogen nor phosphorus. From a viewpoint of the nutritional status of phytoplankton, Lake Baikal might be viewed as an ocean rather than as a lake.     

Centric diatoms from Lake Frolikha (Transbaikal area) and peculiarities of distribution of some taxa in Asia

The species composition of centric diatoms from Lake Frolikha (Transbaikal area) has been studied. The lake is located on the eastern shore of Lake Baikal and connected with it by a river. Twenty-three species of Centrophyceae from 7 genera (Aulacoseira, Cyclostephanos, Cyclotella, Discostella, Handmania, Pliocaenicus, and Stephanodiscus) have been found. The most represented genus is Aulacoseira (11 species). Fifteen species and 4 genera are new for the lake record. All revealed species are known in other lakes of the Baikal region; however Baikal endemics are absent in Lake Frolikha. The flora of centric diatoms in Lake Frolikha can be divided into two groups. The first group includes taxa common in Lake Baikal, and the second group includes taxa not typical for Lake Baikal. The level of differences between flora in Lake Baikal and Lake Frolikha is high (43%) despite the close location and connection to the river. An analysis of distribution of interesting species in Asia is presented.     

Phytoplankton pigments and community composition in Lake Tanganyika

1. A 2‐year (2002–2003) survey of chlorophyll and carotenoid pigments is reported for two off‐shore stations of Lake Tanganyika, Kigoma (Tanzania) and Mpulungu (Zambia), and from three cruises between those sites. Chlorophyll a concentrations were low (0.3–3.4 mg m^?3) and average chlorophyll a integrated through the 100 m water column were similar for both stations and years (36.4–41.3 mg m^?2). Most pigments were located in the 0–60 m layer and decreased sharply downward. Chlorophyll a degradation products (phaeophytins and phaeophorbides) were detected at 100 m depth, whereas carotenoids became undetectable. Temporal and seasonal variation of the vertical distribution of pigments was high. 2. The biomass of phytoplankton groups was calculated from marker pigment concentrations over the 0–100 m water column using the CHEMTAX software. On average for the study period, chlorophytes dominated in the northern station, followed by cyanobacteria T1 (type 1, or Synechococcus pigment type), whereas cyanobacteria T1 dominated in the south. Cyanobacteria T2 (type 2, containing echinenone), presumably corresponding to filamentous taxa, were detected in the rainy season. Diatoms (and chrysophytes) developed better in the dry season conditions, with a deep mixed layer and increased nutrient availability. Very large variation in the vertical distribution of algal groups was observed. 3. Our observations on phytoplankton composition are broadly consistent with those from previous studies. Our pigment data provide evidence for the lake‐wide importance of picocyanobacteria and high interannual variation and spatial heterogeneity of phytoplankton in Lake Tanganyika, which may render difficult assessment of long‐term changes in phytoplankton driven by climate change.     

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.     

Environmental conditions and phytoplankton in the Mwenda River,a small intermittent river flowing into Lake Kariba

Small intermittent rivers play an important role in the limnology of African lakes. The Mwenda River occurs on the southern shore of Lake Kariba. Its flow is governed by the incidence of tropical thunderstorms. During the dry period the river is reduced to a series of turbid pools. Physicochemically the river behaves similarly to a sheltered region of the lake. One river station deviates from the normal pattern because of the insulating effect of a Salvinia mat, and because of its permanent connection with the lake. River flooding flushes both nutrients and major ions into the lake. River phytoplankton populations peak prior to the flushing out of the river. Diatom populations are composed of cosmopolitan tropical taxa.     

Genetic diversity among Synechococcus spp. (cyanobacteria) isolated from the pelagial of Lake Constance

Abstract: Seven phycoerythrin (PE)-rich and six phycocyanin (PC)-rich unicellular cyanobacteria of the Synechococcus type were isolated from the pelagial of Lake Constance. The genetic diversity among the isolates was evaluated using restriction fragment length polymorphism (RFLP) within the psbA gene family. Nine out of 13 isolates exhibit different DNA structures in the probed areas and, furthermore, they differ from morphologically similar strains collected from other lakes. The data set does not support a principal distinction between PC-rich and PE-rich strains but it reveals less heterogeneity in the coding region of the psbA genes among PE-rich isolates than among PC-rich isolates. The isolation of distinct strains in different seasons suggests species diversity and seasonal occurrence of Synechococcus spp. in Lake Constance.     

Ecophysiological analysis reveals distinct environmental preferences in closely related Baltic Sea picocyanobacteria

Cluster 5 picocyanobacteria significantly contribute to primary productivity in aquatic ecosystems. Estuarine populations are highly diverse and consist of many co-occurring strains, but their physiology remains largely understudied. In this study, we characterized 17 novel estuarine picocyanobacterial strains. Phylogenetic analysis of the 16S rRNA and pigment genes (cpcB and cpeBA) uncovered multiple estuarine and freshwater-related clusters and pigment types. Assays with five representative strains (three phycocyanin rich and two phycoerythrin rich) under temperature (10–30°C), light (10–190 μmol photons m⁻² s⁻¹), and salinity (2–14 PSU) gradients revealed distinct growth optima and tolerance, indicating that genetic variability was accompanied by physiological diversity. Adaptability to environmental conditions was associated with differential pigment content and photosynthetic performance. Amplicon sequence variants at a coastal and an offshore station linked population dynamics with phylogenetic clusters, supporting that strains isolated in this study represent key ecotypes within the Baltic Sea picocyanobacterial community. The functional diversity found within strains with the same pigment type suggests that understanding estuarine picocyanobacterial ecology requires analysis beyond the phycocyanin and phycoerythrin divide. This new knowledge of the environmental preferences in estuarine picocyanobacteria is important for understanding and evaluating productivity in current and future ecosystems.     

Variability of myxospores in the myxosporidian genus Henneguya depending on host and geography in the transect "Khubsugul Lake (Mongolia)--Baikal Lake--Laptev Sea (Russia)"

Analysis of variability and estimation of significance of the differences in morphometric parameters of spores have been carried out for three species of the genus Henneguya (Myxosporidia). Representatives of these species collected both in the same water body (but from different host species) and in geographically distant localities were compared. Thus, we compared samples of Henneguya zschokkei from different host species in Chivyrkui Bay of Baical Lake and in Laptev Sea, and also we compared samples of this species from Baikal Lake with those from Laptev Sea. Materials on Henneguya cerebralis from Baikal Lake were compared with those from Khubsugul Lake; samples of H. cutanea from one host species (Siberian dace) but from water bodies of different type (lake or river) were compared.     

Lake Superior Supports Novel Clusters of Cyanobacterial Picoplankton

Very little is known about the biodiversity of freshwater autotrophic picoplankton (APP) in the Laurentian Great Lakes, a system comprising 20% of the world's lacustrine freshwater. In this study, the genetic diversity of Lake Superior APP was examined by analyzing 16S rRNA gene and cpcBA PCR amplicons from water samples. By neighbor joining, the majority of 16S rRNA gene sequences clustered within the “picocyanobacterial clade” consisting of freshwater and marine Synechococcus and Prochlorococcus. Two new groups of Synechococcus spp., the pelagic Lake Superior clusters I and II, do not group with any of the known freshwater picocyanobacterial clusters and were the most abundant species (50 to 90% of the sequences) in samples collected from offshore Lake Superior stations. Conversely, at station Portage Deep (PD), located in a nearshore urbanized area, only 4% of the sequences belonged to these clusters and the remaining clones reflected the freshwater Synechococcus diversity described previously at sites throughout the world. Supporting the 16S rRNA gene data, the cpcBA library from nearshore station PD revealed a cosmopolitan diversity, whereas the majority of the cpcBA sequences (97.6%) from pelagic station CD1 fell within a unique Lake Superior cluster. Thus far, these picocyanobacteria have not been cultured, although their phylogenetic assignment suggests that they are phycoerythrin (PE) rich, consistent with the observation that PE-rich APP dominate Lake Superior picoplankton. Lastly, flow cytometry revealed that the summertime APP can exceed 10⁵ cells ml⁻¹ and suggests that the APP shifts from a community of PE and phycocyanin-rich picocyanobacteria and picoeukaryotes in winter to a PE-rich community in summer.     

The classification and the monitoring of the state of mouth riverine and lacustrine ecosystems in lake Baikal based on the composition of local microbiocenoses and their activity

The paper presents the results of the long-term investigation of microbial communities in the technogenically vulnerable mouth riverine and lacustrine ecosystems of Lake Baikal. The structural and functional parameters of the microbial communities were analyzed from the standpoint of developing destructive processes. The analysis showed that the total number of microorganisms (TNM), the number of saprophytic bacteria (NSB), and bacterial production (BP) were greater in the river-mouth water than in the near-mouth lake water. In the offshore direction, TNM and NSB decreased by a factor of 1.5 to 2, and BP decreased by a factor of 4 to 7. Based on TNM, NSB, and BP data, we classified the Lake Baikal rivers with respect to the degree of the impact of human activities on them. The degrading capability of the riverine microbial communities was found to be such that they degrade daily from tenths of a percent to 3.5% of the total amount of organic compounds polluted the river waters.     

The Classification and the Monitoring of the State of Mouth Riverine and Lacustrine Ecosystems in Lake Baikal Based on the Composition of Local Microbiocenoses and Their Activity

The paper presents the results of the long-term investigation of microbial communities in the technogenically vulnerable mouth riverine and lacustrine ecosystems of Lake Baikal. The structural and functional parameters of the microbial communities were analyzed from the standpoint of developing destructive processes. The analysis showed that the total number of microorganisms (TNM), the number of saprophytic bacteria (NSB), and bacterial production (BP) were greater in the river-mouth water than in the near-mouth lake water. In the offshore direction, TNM and NSB decreased by a factor of 1.5 to 2, and BP decreased by a factor of 4 to 7. Based on TNM, NSB, and BP data, we classified the Lake Baikal rivers with respect to the degree of the impact of human activities on them. The degrading capability of the riverine microbial communities was found to be such that they degrade daily from tenths of a percent to 3.5% of the total amount of organic compounds polluting the river waters.     

Abundance and composition of the summer phytoplankton community along a transect from the Barguzin River to the central basin of Lake Baikal

The abundance and composition of phytoplankton were investigated at six stations along a transect from the Barguzin River inflow to the central basin of Lake Baikal in August 2002 to clarify the effect of the river inflow on the phytoplankton community in the lake. The water temperature in the epilimnion was high near the shore at Station 1 (17.3°C), probably due to the higher temperature of the river water, and gradually decreased offshore at Station 6 (14.5°C). Thermal stratification developed at Stations 2–6, and a thermocline was observed at a 17–22-m depth at Stations 2–4 and an 8–12-m depth at Stations 5 and 6. The concentrations of nitrogen and phosphorus nutrients in the epilimnion at all stations were <1.0 μmol N l⁻¹ and <0.16 μmol P l⁻¹, respectively. Relatively high concentrations of nutrients (0.56–7.38 μmol N l⁻¹ and 0.03–0.28 μmol P l⁻¹) were detected in the deeper parts of the euphotic zone. Silicate was not exhausted at all stations (>20 μmol Si l⁻¹). The chlorophyll a (chl. a) concentration was high (>10 μg l⁻¹) near the shore at Station 1 and low (<3 μg l⁻¹) at five other stations. The <2 μm fraction of chl. a in Stations 2–6 ranged between 0.80 and 1.85 μg l⁻¹, and its contribution to total chl. a was high (>60%). In this fraction, picocyanobacteria were abundant at all stations and ranged between 5 × 10⁴ and 5 × 10⁵ cells ml⁻¹. In contrast, chl. a in the >2 μm fraction varied significantly (0.14–11.17 μg l⁻¹), and the highest value was observed at Station 1. In this fraction, the dominant phytoplankton was Aulacoseira and centric diatoms at Station 1 and Cryptomonas, Ankistrodesmus, Asterionella, and Nitzschia at Stations 2–6. The present study demonstrated the dominance of picophytoplankton in the pelagic zone, while higher abundance of phytoplankton dominated by diatoms was observed in the shallower littoral zone. These larger phytoplankters in the littoral zone probably depend on nutrients from the Barguzin River.     

Riverine transport and nutrient inputs affect phytoplankton communities in a coastal embayment

1. Rivers often transport phytoplankton to coastal embayments and introduce nutrients that can enrich coastal plankton communities. We investigated the effects of the Nottawasaga River on the nearshore (i.e. within 500 μm of shore) phytoplankton composition along a 10-km transect of Nottawasaga Bay, Lake Huron in 2015 and 2016. Imaging flow cytometry was used to identify and enumerate algal taxa, which were resolved at sizes larger than small nanoplankton (i.e. >5 μm). Multivariate analysis (perMANOVA and redundancy analysis) and a dilution model were used to examine how nutrients and the transport of algal taxa affected community composition in the bay.
2. Sampling stations with different percentages of river water had significantly different phytoplankton communities. Phytoplankton community composition was also strongly associated with nutrients, including total phosphorus, which also varied with the percentage of river water. The majority of the 51 phytoplankton taxa identified in 2016 had numerical abundances in the bay that could be explained simply by the dilution of incoming river water.
3. Phytoplankton transported from the river had a higher proportion of edible-sized cells (<30 μm), particularly in summer when colonial cyanobacteria were numerically dominant in the bay. Six taxa were more abundant than expected from the dilution of river water and included some cyanobacteria with late summer maxima. Five of the taxa that were transported from the river were less abundant than expected in the bay.
4. Whereas impacts of fertilisation due to the characteristically higher nutrient concentration in the river are to be expected, the strong and highly correlated effects of transport within the narrow coastal band of this study largely concealed any distinct fertilisation effects.
5. Riverine inputs may strongly influence the nearshore assemblage of phytoplankton in oligotrophic embayments in large lakes, creating hotspots for productivity, species turnover, and trophic dynamics.