Vertical distribution of planktonic ciliates in strongly stratified temperate lakes

The vertical distribution of planktonic ciliates in eight strongly stratified temperate lakes was studied in summer 1998. Ciliate abundance and biomass were highest (mean 39.9 cells ml^–1 and 181.9 g C l^–1) in the epi-, and lowest (mean 8.2 cells ml^–1 and 97.6 g C l^–1) in the hypolimnion. The community of ciliates was dominated by five orders: Oligotrichida, Haptorida, Prostomatida, Scuticociliatida and Peritrichida. The community composition varied greatly with depth. In the epilimnion, the ciliate numbers were dominated by oligotrichs but small algivorous prostomatids, peritrichs and haptorids were also numerous. In the metalimnion, these groups were replaced by scuticociliates and mixotrophic prostomatids. In the hypolimnion species known as benthic migrants appeared. We found a positive significant correlation (p < 0.05) between ciliate numbers and Chl a and bacterial densities. Only in the hypolimnion, the correlation between ciliates numbers and Chl a was not significant.     

Microbial ecology of planktonic filamentous phototrophic bacteria in holomictic freshwater lakes

The microbial ecology of the filamentous phototrophic bacterium, Chloronema giganteum, has been studied in the water column of three central European lakes (Schlein, Buchen and Vechten). In these lakes an anoxic layer, termed the transition zone, was located between the oxycline and the redoxcline. The migration capacity of Chloronema through this zone appears to be responsible for the natural preponderance of either straight or spiral forms. When the transition zone is less than 1 m thick the straight form is dominant, but when this transition zone is wider than 2 m the spiral form is enriched. The intermediate situations favour both filamentous forms.     

Abundance, morphology and distribution of planktonic virus-like particles in two high-mountain lakes

Direct counts of virus-like particles (VLP) by transmissionelectron microscopy revealed abundances of up to 3 x 10⁷ ml^–1in the plankton of two remote high-mountain lakes in the Alpsand the Pyrenees. Most VLP were icosahedric without a tail,and with diameters between 40 and 90 nm, but very large oneswith diameters of up to 325 run were also observed. VLP outnumberedbacteria by a factor of 4.2–42.8 and bacterial cells wereinfected with large numbers (>50) of viral particles. Thisstudy constitutes the first report on aquatic viruses for alpinelakes and it suggests that they may be an important additionalsource of bacterial mortality in these systems.     

Compositional differences among planktonic ciliate communities in four subtropical eutrophic lakes in China

Ciliate community composition was investigated in four subtropical eutrophic lakes with cyanobacterial blooms in three seasons during 2009–2010 using the quantitative protargol staining approach. Among the four lakes, Lake Taihu and Chaohu are situated in the mid-lower Yangtze Plain near sea level, and Lake Dianchi and Xingyunhu are located on the Yunnan–Kweichow Plateau. A total of 102 ciliate species, representing 15 orders and 66 genera, were studied. Ciliate communities in Lake Taihu and Chaohu were characterized by abundant algivorous and mixotrophic oligotrichs and prostomatids, while Lake Dianchi and Xingyunhu ciliate communities were primarily characterized by voracious bacterivorous scuticociliates and peritrichids. Cluster analysis based on the transformed square root of ciliate abundance showed that samples from Lake Taihu and Chaohu composed one group whereas samples from Lake Dianchi and Xingyunhu composed another group in each season. Our results indicated that all dominant ciliate species are ubiquitous and that species dominance is regulated by different factors in different subtropical eutrophic lakes.     

The temperature of two welsh lakes and its effect on the distribution of two freshwater insects

Temperature data are presented from the littoral zones of two lakes in North Wales, Llyn Coron and Llyn Dinas. Recording, mainly on a continuous basis, was over a two year period. Despite their different situations, the lakes had similar temperature regimes. Regional weather factors were of greater importance than local variations. However, some differences were present, especially during the summer months. Laboratory experiments were conducted to determine the temperature relationships of Nemoura avicularis Morton (Plecoptera) and Leptophlebia vespertina (L.) (Ephemeroptera), common species in Llyn Dinas but absent from Llyn Coron. Aspects considered included nymphal temperature tolerance and the effect of temperature on egg development and emergence. From the background of the results, it was concluded that the differences in temperature regime between the two lakes were insufficient to explain the absence of the two species from Llyn Coron.     

Forms and distribution of inorganic phosphorus in sediments of two shallow eutrophic lakes in Florida

Physicochemical attributes were measured and aquatic macroinvertebrates were collected from six wetlands near Perth, Western Australia at three weekly intervals over a 13 month period from August 1988 to September 1989. The six wetlands encompassed a range of depths, pH, concuctivities, nutrient concentrations and colours. Temporal changes in the macroinvertebrate communities appeared to be related to seasonal changes in the physical and chemical characteristics of the wetlands. Community composition differed more between the less enriched wetlands then the higly enriched wetlands where communities were generally similar. High species richness was associated with seasonal drying. High macro invertebrate abundance appeared to be associated with the presence of either green algal or cyanobacterial blooms in the enriched wetlands. The highest macroinvertebrate biomass was recorded in wetlands with both cyanobacterial blooms and abundant macrophytes present.     

Short-term productivity responses of algae and bacteria to zooplankton grazing in two freshwater lakes

SUMMARY. 1. The specific productivities of algae and bacteria were measured in short-term (4 day) experiments consisting of enclosures with natural or reduced zooplankton biomass. Experiments were repeated five times over a season in each of two lakes that differed in the background concentration of dissolved organic carbon (DOC).
2. Algal biomass as estimated by chlorophyll a was suppressed in enclosures with ambient grazer levels in six of ten experiments and enhanced in one experiment. Distribution of chlorophyll among net and nanoplankton was not significantly affected by grazing.
3. Relative to enclosures with reduced zooplankton, normal grazer biomass (97–466μg 1⁻¹ dry weight) enhanced specific algal productivity in only one of five experiments in the low DOC take and had no effect in all five experiments in the high DOC lake. The main effects of grazers on algae was through removal of biomass rather than through indirect changes in turnover rate.
4. Between experiments, bacterial density was either unaffected, or mildly enhanced (4–87%) in enclosures with ambient macrozooplankton compared to those with reduced levels. Bacterial productivity and turnover estimated by incorporation of [³H]thymidine into DNA showed different responses across experiments; increasing, declining or remaining the same with grazer minipulation. This variability was not related to differences in dissolved primary production or to background DOC between lakes or experiments. Comparison of bacterial productivities based on thymidine incorporation rates with changes in cell densities indicated that control of bacterial loss processes by macrozooplankton is more important than control of growth rates.     

Submerged vegetation development in two shallow, eutrophic lakes

Submerged macrophyte vegetation in two shallow lakes in the Netherlands, Lake Veluwemeer and Lake Wolderwijd, has been affected by eutrophication in the late 1960's and 1970's. Recent changes in the vegetation occurred in the period following lake restoration measures. Between 1987 and 1993, the dominance of Potamogeton pectinatus decreased, while Charophyte meadows expanded over the same time interval. The pattern of change of the dominant macrophyte species might result from changes in the underwater light climate. Seasonally persistent clear water patches associated with the Chara meadows have been observed in the last few years. The interaction between submerged macrophyte vegetation succession and water transparency in the lakes is discussed.     

乌梁素海富营养化湖区浮游细菌多样性及系统发育分析

水生生态系统富营养化与细菌群落之间的关系尚不明确。本文通过构建和分析16S rRNA基因片段克隆文库, 以期揭示乌梁素海富营养化水体细菌的多样性及其系统发育关系, 并探讨富营养化与细菌多样性之间的关系。利用Hae III对文库中的87个克隆子进行单酶切, 产生了23种带型, 文库覆盖度达到了73.6%, 反映出文库有较好的代表性。选择每种OTU的一个代表克隆进行测序分析, 基因序列系统发育分析结果表明, 乌梁素海中多数细菌与淡水生态系统中常见的细菌门类相同, 即α-, β-, γ-Proteobacteria, Bacteroidetes, Actinobacteria, 它们分别占总菌数的10.3%、41.4%、4.6%和6.9%, 其中β-Proteobacteria和Bacteroidetes是优势细菌类群。与典型淡水生态系统细菌群落组成不同的是, 乌梁素海中存在约10.3%的轻度嗜盐碱细菌。水体中83.9%的细菌与已培养的细菌的同源性低于97%, 其中58.9%的细菌未能鉴定到属; 其余总菌数16.1%的克隆与具有降解污染物生物活性的已知菌相近。Bacteroidetes、Firmicutes和β-Proteobacteria中的某些类群成为优势菌群可能是对乌梁素海水体富营养化的响应。     

Coaggregation between freshwater bacteria within biofilm and planktonic communities

The coaggregation ability of bacteria isolated from a freshwater biofilm was compared to those derived from the coexisting planktonic population. Twenty-nine morphologically distinct bacterial strains were isolated from a 6-month-old biofilm, established in a glass tank under high-shear conditions, and 15 distinct strains were isolated from the associated re-circulating water. All 44 strains were identified to genus or species level by 16S rDNA sequencing. The 29 biofilm strains belonged to 14 genera and 23.4% of all the possible pair-wise combinations coaggregated. The 15 planktonic strains belonged to seven genera and only 5.8% of all the possible pair-wise combinations coaggregated. Therefore, compared to the planktonic population, a greater proportion of the biofilm strains coaggregated. It is proposed that coaggregation influences biofilm formation and species diversity in freshwater under high shear.     

Epiphytic diatoms in two freshwater maritime Antarctic lakes

SUMMARY.

• 1 An ecological study of two small maritime Antarctic lakes on Signy Island, South Orkney Islands, was undertaken from January 1986 to March 1987. Analysis of diatom counts from the lakes provided examples of oligotrophic and mesotrophic ecosystems.
• 2 A diverse community of 104 epiphytic taxa was identified. Twenty-eight taxa had a percentage abundance greater than 1% in both lakes. Distinctive dominant taxa were identified from each lake.
• 3 A variety of ordination techniques was performed on the abundance data and a principal components analysis demonstrated differences in the diatom assemblages between the two lakes. Clear separations of sites and species were evident between the lakes, and accounted for the greatest percentage variance.
• 4 Species composition varied with depth within each lake and was also important in influencing changes in assemblage composition between sites.
• 5 A redundancy analysis indicated that species composition was correlated to concentrations of nitrogen and phosphorus but the total variance accounted for by the four physical and chemical factors measured was low (24%).

     

Long-term pattern of alternative stable states in two shallow eutrophic lakes

• 1 Lake Tåkern and Lake Krankesjön, two moderately eutrophic, shallow lakes in southern Sweden, have during the past few decades shifted several times between a clear-water state with abundant submerged vegetation and a turbid state with high phytoplankton densities.
• 2 Between 1985 and 1991, Lake Takern was in a clear state, whereas Lake Krankesjon shifted from a turbid to a clear state. During this shift, the area covered by submerged macrophytes expanded, followed by an increase in water transparency, plant-associated macroinvertebrates, and piscivorous fish. Nutrient concentrations, phytoplankton biomass and abundance of planktonic cladocerans decreased.
• 3 In both lakes, water level fluctuations were the most common factor causing shifts, affecting submerged macrophytes either through changes in light availability or through catastrophic events such as dry-out or mechanical damage by ice movement.
• 4 Our data give further support for the existence of two alternative stable states in shallow lakes maintained by self-stabilizing feedback mechanisms.

     

Ammonium excretion by some freshwater zoobenthos from a eutrophic lake

Relationships between the ammonium excretion rate of zoobenthos and temperature were examined for two chironomids, Chironomus, plumosus and Tokunagayusurika akamusi, one chaoborid, Chaoborus flavicans, and two tubificids, Limnodrilus spp. and Branchiura sowerbyi, which often dominate in eutrophic lakes. The representative Q₁₀ value and excretion rate at 15° C for each species were as follows: C. plumosus, 1.67, 1.40, (µg N mg dry w.^–1 d^–1 ); T. akamusi, 1.02 (< 15° C), 0.33; C. flavicans, 1.49, 2.87; Limnodrilus spp., 2.98, 0.59; and B. sowerbyi, 3.15, 0.79.     

Studies on metabolic activity of planktonic bacteria isolated from three lakes.

Studies were carried out on metabolic activity of 480 bacterial isolates on 9 substrates. All bacterial isolates studied except one utilized the casamino acids. Also with casamino acids the highest oxygen uptake values were obtained. Among the carbohydrates, glucose was most frequently utilized by the planktonic bacteria. Bacteria isolated from water of the various lakes differed in their metabolic activity as well as in the capability of utilizing the individual substrates. The capability of attacking by the bacteria the substrates applied depended largely upon the time of their isolation.     

Cladoceran and rotifer grazing on bacteria and phytoplankton in two shallow eutrophic lakes: in situ measurement with fluorescent microspheres

Metazooplankton grazing on bacteria and on the phytoplanktonof various sizes was estimated in shallow eutrophic lakes Kaiavereand Võrtsjärv (Estonia) by in situ feeding experimentswith fluorescent microspheres (diameters 0.5 µm for bacteriaand 3, 6 and 24 µm for phytoplankton). Zooplankton communitycomposition, abundance and food density were important factorsdetermining grazing rates in these lakes. Cladocerans and rotifersfiltering rates (FR) and ingestion rates (IR) on bacteria andphytoplankton were several times higher in Lake Kaiavere wherebacterivorous rotifers and Daphnia contributed more to zooplanktonassemblage. While cladocerans were generally the main phytoplanktonconsumers, both lakes differed with respect to the groups ofbacterivores. Based on consumption of fluorescent microspheres,the metazooplankton grazing rates were relatively low and hadlow impact on production and standing stock of bacteria andingestible phytoplankton (<30 µm). On average, 0.5and 0.1% of standing stock of bacteria and 2.6 and 1.0% of standingstock of ingestible phytoplankton was grazed daily by metazooplanktonin lakes Kaiavere and Võrtsjärv, respectively. Thatcorresponded to daily grazing of 4.1% of the bacterial productionand 0.43% of the total primary production (PP) by metazooplanktonin Lake Kaiavere compared with 4.3 and 0.06% in Lake Võrtsjärv,respectively. The results suggest that the majority of consumptionof the bacterial and phytoplankton PP is most likely channelledthrough the microbial loop.     

Diel variation in concentration,assimilation and respiration of dissolved free amino acids in relation to planktonic primary and secondary production in two eutrophic lakes

Concentration of dissolved free amino acids (DFAA) and assimilation of the 5 most abundant DFAA (glutamic acid, serine, glycine, alanine and ornithine) were measured at 3-h intervals over 27 h in two Danish, eutrophic lakes. The carbon flux of the amino acid assimilation was compared with the major routes of carbon flux, including primary production, bacterial production and zooplankton grazing. In Frederiksborg Slotssø, the mean DFAA concentration was 275 nM with distinct peaks (up to 783 nM) 3 h after sunrise. Assimilation rates of the 5 amino acids amounted on the average to 2.03 µg Cl^–1 h^–1, but high values up to 7.41 µg Cl^–1 h^–1 occurred 3 h after sunrise and at midnight. The mean turnover time of the amino acid pools was 3.2 h. In Lake Mossø, the mean DFAA concentration was 592 nM with peak of 1 161 nM at dusk. The assimilation rate averaged 0.44 µg Cl^–1 h^–1, and the mean turnover time of the amino acid pools was 39 h. In Lake Mossø, similar turnover times of glutamic acid and serine were determined from the ¹⁴C-amino acid tracer technique and Michaelis-Menten uptake kinetics, indicating that the tracer technique gave reliable values of the actual assimilation. The average respiration percentages of the assimilated amino acids were 45% in Frederiksborg Slotssø and 51% in Lake Mossø. Extracellular organic carbon (EOC) released from the phytoplankton contributed DFAA to the water. In Lake Mossø, 81% of the ambient EOC pool was <700 daltons and 9.3% of the EOC was DFAA. This corresponded to about 2.4% of the DFAA pool. Bacterial productivity, determined by means of frequency of dividing cells and ³⁵S-SO₄ dark uptake techniques gave similar results and constituted 4.5 and 3.7 µg Cl^–1 h^–1 in Frederiksborg Slotssø and Lake Mossø, respectively. The bacterial productivity suggested that DFAA were essential substrates to the bacteria, especially in Frederiksborg Slotssø. The zooplankton biomass in Frederiksborg Slotssø was six times larger than that in Lake Mossø, but cladocerans were dominant in both lakes. The zooplankton grazing probably was an important regulatory factor for the bacterial productivity.     

Geochemistry of suspended and settling solids in two freshwater lakes

This study describes the 1987–1992 time variationof the bulk chemical composition, levels of heavymetals, arsenic, nitrogen and phosporous insuspended and settling solids in Lake Volkerak andLake Zoom (The Netherlands). Suspended and setlingsolids were collected with continuous flowcentrifuges and sediment traps, respectively. Therelations between solids characteristics and metalconcentrations in the particles were investigatedusing correlation and factor-analysis. Heavy metals,except manganese, were associated with clay contentof the particles and with organic carbon which wasmainly determined by phytoplankton growth. Manganesewas correlated with Org-C only. Clay and organicmatter with associated heavy metals showed negativetrends on all locations, and a seasonality due toalgal biomass dilution. It is concluded that thetrophic state significantly affects trace metalcycling. Sediment traps collect different types ofparticles than continuous flow centrifuges. Thetraps collect particles with higher clay content,lower Org-C concentrations and higher Org-C/Nelemental ratios than the centrifuges. This revised version was published online in July 2006 with corrections to the Cover Date.     

Regulation of bacterial secondary production in two eutrophic lakes and in experimental enclosures

Bacterial cell number and secondary production of bacterioplanktonwere measured during two periods of 14 and 19 days, respectively,in experimental enclosures of lake water (each containing about5–7 m³ and in two Danish, eutrophic lakes. Additions ofphosphate and planktivorous fish to some of the enclosures inducedrapid changes in the phytoplankton biomass, primary productionand release of extracellular organic carbon (EOC). In some ofthe enclosures containing fish, release of EOC from phytoplanktoncon stituted from 36 to 55% of the bacterial secondary productiondetermined by means of [³H]thymidine incorporation into DNA.In others, such a relationship was not found, suggesting thatphytoplankton species-specific release rates of compositionof EOC might play a role in the microbial response. In enclosureswithout fish, released dissolved organic carbon from zooplanktongrazing activities could Sustain     

Flavobacteria blooms in four eutrophic lakes: linking population dynamics of freshwater bacterioplankton to resource availability

Heterotrophic bacteria are major contributors to biogeochemical cycles and influence water quality. Still, the lack of representative isolates and the few quantitative surveys leave the ecological role and significance of single bacterial populations to be revealed. Here we analyzed the diversity and dynamics of freshwater Flavobacteria populations in four eutrophic temperate lakes. From each lake, clone libraries were constructed using primers specific for either the class Flavobacteria or Bacteria. Sequencing of 194 Flavobacteria clones from 8 libraries revealed a diverse freshwater Flavobacteria community and distinct differences among lakes. Abundance and seasonal dynamics of Flavobacteria were assessed by quantitative PCR with class-specific primers. In parallel, the dynamics of individual populations within the Flavobacteria community were assessed with terminal restriction fragment length polymorphism analysis using identical primers. The contribution of Flavobacteria to the total bacterioplankton community ranged from 0.4 to almost 100% (average, 24%). Blooms where Flavobacteria represented more than 30% of the bacterioplankton were observed at different times in the four lakes. In general, high proportions of Flavobacteria appeared during episodes of high bacterial production. Phylogenetic analyses combined with Flavobacteria community fingerprints suggested dominance of two Flavobacteria lineages. Both drastic alterations in total Flavobacteria and in community composition of this class significantly correlated with bacterial production, emphasizing that resource availability is an important driver of heterotrophic bacterial succession in eutrophic lakes.