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Heterotrophic microorganisms and viruses in the water of the Gorky reservoir during a period of anomalously high water temperature
Abstract
During the anomalously hot summer of 2010, the water temperature in the Gorky reservoir reached 27–33°C. Pronounced cyanobacterial blooms occurred in the limnetic part of the reservoir. The average values for bacterioplankton abundance (11.58 ± 1.25 × 106 cell/mL), biomass (886 ± 96 mg/m3), and production [169 ± 32 mg C/(m3 day)] were twice as high as in the year with temperatures comparable to long-term average values. These parameters were higher in the limnetic part than in the river one. The abundance (4.86 ± 0.75 × 103 cell/mL) and biomass (138 ± 9 mg/m3) of heterotrophic nanoflagellates were 2.3 and 1.7 times higher, respectively, than in years with regular temperature regimes. The average number of plank-tonic viral particles (N
v) in 2010 was 48.89 ± 9.54 × 106 particles/mL, while virus-induced bacterial mortality (VMB) accounted for 26.9 ± 4.6% of the bacterial production. The N
v and VMB values in the limnetic part of the reservoir were, respectively, 1.5 and 1.8 times higher than in the river one.
... Apparently, these processes have a significant effect on the development of heterotrophic bacteria in mesotrophic and eutrophic reservoirs of the Volga cascade. In summer 2010, a twofold increase in the abundance, biomass, and production of bacterioplankton was recorded in the Gorky Reservoir when compared to years with a normal thermal regime (Kopylov et al., 2013). ...
... In the sum- mer of 2010, phytoplankton bloom was observed in the Gorky Reservoir when the water temperature exceeded the normal temperature on average by 4.6-6.9 о С (Lazareva et al., 2012;Kopylov et al., 2013). The chlorophyll concentration in the surface (0-2 m) water layer in the lake part of the reservoir reached 119 mg/L during that period, which corresponded to hypertrophic waters. ...
... During the surveyed period, the frequency of infected bacterial cells (13.1 ± 1.2% N B ) and virusinduced mortality of bacterioplankton (17.2 ± 2.0% Р B ) were lower in the mesoeutrophic Rybinsk Reservoir than in eutrophic reservoirs of the Volga River: in the Gorky (17.8 ± 2.2% and 26.9 ± 4.6%) and Cheboksary (16.1 ± 1.2% and 22.4 ± 2.7%, respectively) reservoirs (Kopylov et al., 2013a(Kopylov et al., , 2013b. ...
The abundance, biomass, and production (Р
В) of bacrerioplankton; the taxonomic composition, abundance, biomass of heterotrophic nanoflagellates (HNF) and the rate of consumption of bacteria by HNFs; and the abundance of virioplankton, frequency of visibly infected bacterial cells, virus-induced mortality of bacterioplankton, and viral production were estimated in the mesoeutrophic Rybinsk Reservoir. The rate of bacterial mortality due to viral lysis (7.8–34.1%, on average 17.2 ± 2.0% of daily Р
В) was lower than the consumption of bacteria by the HNF community (15.4–61.3%, on average 32.0 ± 4.2% of daily Р
В). While consuming bacteria, HNFs simultaneously absorbed a significant number of viruses residing on the surface and inside the bacterial cells.
The distribution of virioplankton, abundance and production, frequency of visibly infected cells of heterotrophic bacteria and autotrophic picocyanobacteria and their virus-induced mortality have been studied in mesotrophic and eutrophic reservoirs of the Upper and Middle Volga (Ivankovo, Uglich, Rybinsk, Gorky, Cheboksary, and Sheksna reservoirs). The abundance of planktonic viruses (VA) is on average by 4.6 ± 1.2 times greater than the abundance of bacterioplankton (BA). The distribution of VA in the Volga reservoirs was largely determined by the distribution of BA and heterotrophic bacterioplankton production (PB). There was a positive correlation between VA and BA and between VA and PB. In addition, BA and VA were both positively correlated with primary production of phytoplankton. Viral particles of 60 to 100 µm in size dominated in the phytoplankton composition. A large number of bacteria and picocyanobacteria with viruses attached to the surface of their cells were found in the reservoirs. Viruses as the most numerous component of plankton make a significant contribution to the formation of the planktonic microbial community biomass. The number of phages inside infected cells of bacteria and picocyanobacteria reached 74‒109 phages/cell. Easily digestible organic matter, which entered the aquatic environment as a result of viral lysis of bacteria and picocyanobacteria, could be an additional source of carbon for living bacteria. The results of long-term studies indicate a significant role of viruses in functioning of planktonic microbial communities in the Volga reservoirs.
The abundance and production of planktonic viruses, frequency of infected bacterial cells and number of mature phages in infected bacterial cells, and virus-induced mortality of bacterioplankton were studied in two small rivers and the large Sheksna River flowing through a large city in April–October, 2011. High positive correlations have been determined between the abundance of planktonic viruses and bacteria and the number of viruses attached to bacterial cell walls and the frequency of infected bacteria. The number of planktonic viruses and the mortality of bacteria caused by virus-induced lysis in hypertrophic and eutrophic small rivers are higher than in the mesotrophic Sheksna River.
The bioenergetics of growth of 6 species of heterotrophic (bacterivorous) microflagellates was studied in batch cultures. Maximum growth rates varied between 0.15 and 0.25 h-' among the species, but growth as slow as 0.028 h-' could be maintained. Yield (gross growth efficiency) was found to be ca. 30 % (volume) or, in 2 cases, 34 and 43 % (C basis) respectively; net growth efficiency (C) was 60 %. Respiratory and growth rates were directly proportional to consumption rate within the range of growth rates studied. Clearance (volume of water cleared for bacteria per unit time and measured in fractions of cell volume) ranged from about 5 X 104 to about 106 h-'; this large variation can in part be explained as a consequence of specialization to different food particle slzes. In general, the parameter values suggest that the type of flagellates studied may grow on and possibly control the concentration of bacteria found in marine plankton.
A new nucleic acid stain, SYBR Green I, can be used for the rapid and accurate determi-nation of viral and bacterial abundances in diverse marine samples. We tested this stain with formalin-preserved samples of coastal water and also from depth profiles (to 800 m) from sites 19 and 190 km off-shore, by filtering a few m1 onto 0.02 pm pore-size filters and staining for 15 min. Comparison of bacterial counts to those made with acridine orange (AO) and virus counts with those made by trans-mission electron microscopy (TEM) showed very strong correlations. Bacterial counts with A 0 and SYBR Green 1 were indistinguishable and almost perfectly correlated (r2 = 0.99). Virus counts ranged widely, from 0.03 to 15 X 10' virus ml-l. Virus counts by SYBR Green 1 were on the average higher than those made by TEM, and a SYBR Green 1 versus TEM plot yielded a regression slope of 1.28. The cor-relation between the two was very high with an value of 0.98. The precision of the SYBR Green I method was the same as that for TEM, with coefficients of variation of 2.9%. SYBR Green I stained viruses and bacteria are intensely stained and easy to distinguish from other particles with both older and newer generation epifluorescence microscopes. Detritus is generally not stained, unlike when the alternative dye YoPro I is used, so this approach may be suitable for sediments. SYBR Green I stained samples need no desalting or heating, can be fixed with formalin prior to filtration, the optimal staining time is 15 min (resulting in a total preparation time of less than 25 min), and counts can be easily per-formed at sea immediately after sampling. This method may facilitate incorporation of viral research into most aquatic microbiology laboratories.
We examined grazing of marine viruses and bacteria by natural assemblages and cultures of phagotrophic nanoflagellates. Ingestion rates were determined using fluorescently labelled viruses (FLVs) and bacteria (FLB), and 50 or 500 nm diameter fluorescent microspheres (FMs). Calculated clearance rates of viruses by natural nanoflagellate assemblages were about 4 % of those for bacteria when the bacteria and viruses were present at natural concentrations. Different viruses were ingested at different rates with the smallest virus being ingested at the slowest rate. Further, we found differences in digestion times for the same flagellates grazing on different viruses and for different flagellate assemblages grazing on the same viruses. FMs of 50 nm diameter were used as a control for egestion of undigested particles. As rates of digestion were greater than those for ingestion both processes would occur simultaneously; hence, our estimates of grazing rate are likely conservative. Ingestion rates were positively correlated with the concentration of 50 nm FMs. Discrimination against 50 nm FMs in favor of FLVs was also observed. Our calculations suggest that viruses may be of nutritional significance for phagotrophic flagellates. When there are 10(6) bacteria ml-1 and 10(7) to 10(8) Viruses ml-1, viruses may represent 0.2 to 9 % of the carbon, 0.3 to 14 % of the nitrogen and 0.6 to 28 % of the phosphorus that the flagellates obtain from ingestion of bacteria. This study demonstrates that both natural assemblages and cultures of phagotrophic nanoflagellates consume and digest a variety of marine viruses, thereby deriving nutritional benefit and serving as a natural sink for marine viral particles. In addition, these results imply that some nanoflagellates are likely capable of consuming a wide spectrum of organic particles in the colloidal size range.
The transport of aquatic viruses to particles can be described in terms of diffusive transport from solution. Such transport is influenced by motion of the water relative to the particle. Because transport rate is determined purely by physical factors it is independent of whether the particle is a host or non-host organism. The low viral diffusivity relative to that for dissolved nutrients makes transport enhancement from organism swimming more important for viruses. The virus contact rate with bacteria is relatively unaffected by such motions because of small bacterial sizes. Transport rates for phytoplankton and protozoa can increase over an order of magnitude when swimming motions are considered. Although larger organisms have much higher transport rates per individual, their far lower concentrations in sea water should make small organisms the preferred targets for viruses. Rates of host-virus interactions in culture are closely related to predictions from transport theory. There is a fairly close relationship between bacterial populations and virus disappearance rates in the marine environment, suggesting that non-host organisms are a major cause of viral mortality at the higher ionic strengths typical of sea water. Other factors, such as UV radiation, must also be included when estimating viral mortality in seawater.
Abstract. Knowledge on the expected effects of climate change on aquatic ecosystems is defined by three
ways. On the one hand, long-term observation in the field serves as a basis for the possible changes; on
the other hand, the experimental approach may bring valuable pieces of information to the research field.
The expected effects of climate change cannot be studied by empirical approach; rather mathematical
models are useful tools for this purpose. Within this study, the main findings of field observations and
their implications for future were summarized; moreover, the modelling approaches were discussed in a
more detailed way. Some models try to describe the variation of physical parameters in a given aquatic
habitat, thus our knowledge on their biota is confined to the findings based on our present observations.
Others are destined for answering special issues related to the given water body. Complex ecosystem
models are the keys of our better understanding of the possible effects of climate change. Basically, these
models were not created for testing the influence of global warming, rather focused on the description of
a complex system (e. g. a lake) involving environmental variables, nutrients. However, such models are
capable of studying climatic changes as well by taking into consideration a large set of environmental
variables. Mostly, the outputs are consistent with the assumptions based on the findings in the field. Since
synthetized models are rather difficult to handle and require quite large series of data, the authors
proposed a more simple modelling approach, which is capable of examining the effects of global
warming. This approach includes weather dependent simulation modelling of the seasonal dynamics of
aquatic organisms within a simplified framework.
Keywords: ecological modelling, model system, community ecology, global warming, seasonal dynamics
Climate change will alter freshwater ecosystems but specific effects will vary among regions and the type of water body. Here,
we give an integrative review of the observed and predicted impacts of climate change on shallow lakes in the Netherlands
and put these impacts in an international perspective. Most of these lakes are man-made and have preset water levels and poorly
developed littoral zones. Relevant climatic factors for these ecosystems are temperature, ice-cover and wind. Secondary factors
affected by climate include nutrient loading, residence time and water levels. We reviewed the relevant literature in order
to assess the impact of climate change on these lakes. We focussed on six management objectives as bioindicators for the functioning
of these ecosystems: target species, nuisance species, invading species, transparency, carrying capacity and biodiversity.
We conclude that climate change will likely (i) reduce the numbers of several target species of birds; (ii) favour and stabilize
cyanobacterial dominance in phytoplankton communities; (iii) cause more serious incidents of botulism among waterfowl and
enhance the spreading of mosquito borne diseases; (iv) benefit invaders originating from the Ponto-Caspian region; (v) stabilize
turbid, phytoplankton-dominated systems, thus counteracting restoration measures; (vi) destabilize macrophyte-dominated clear-water
lakes; (vii) increase the carrying capacity of primary producers, especially phytoplankton, thus mimicking eutrophication;
(viii) affect higher trophic levels as a result of enhanced primary production; (ix) have a negative impact on biodiversity
which is linked to the clear water state; (x) affect biodiversity by changing the disturbance regime. Water managers can counteract
these developments by reduction of nutrient loading, development of the littoral zone, compartmentalization of lakes and fisheries
management.
The quantitative distribution of viruses and their impact on heterotrophic bacterioplankton were studied in mesotrophic and
eutrophic reservoirs of the Volga and Volga-Baltic waterway. The abundance of planktonic virus particles ranged from 9.4 ×
106 to 120 × 106 ml−1 and was from 2.5 to 9 times greater than the bacterial numbers. Production of virioplankton varied from 2.1 × 106 to 132 × 106 particles (ml day)−1 and the population turnover time values were between 0.3 and 11.6 days. The maximum values of numbers and production of virio-
and bacterioplankton were observed in the eutrophic Ivan’kovo reservoir. Distribution of the viruses in the Volga reservoirs
depended to a significant degree on the number and activity of heterotrophic bacterioplankton. The infected bacteria accounted
for 5.5–33.5% of the total bacterial abundance. Phages were an important factor of bacterial mortality. During July to September
virus-induced bacterial mortality varied between 6.1 and 40.6% (20.2% on average) of daily bacterioplankton production.
Keywordsquantitative distribution of viruses and bacterioplankton–viral lysis–bacterial mortality–lowland reservoirs
On the basis of the data obtained during field observations in the summer low water period of 2001, the patterns of chlorophyll
distribution and its relation to hydrological and hydrochemical factors in two eutrophic reservoirs of the Middle Volga are
studied. The hydrological structure of the Gorky Reservoir, where the Volga water mass dominates, is homogeneous, while in
the Cheboksary Reservoir along with the eutrophic Volga waters, the mesotrophic Oka water masses can be distinguished keeping
their abiotic and biotic features over a long distance. Phytoplankton in the two contiguous reservoirs with different flow
regimens and anthropogenic loads responds differently to the external influence. An autotrophic community in the Gorky Reservoir
is more stable and depends little on abiotic factors which account for ∼63% of the explained chlorophyll variation. In the
Cheboksary Reservoir under maximal for the Volga cascade flow velocity and anthropogenic load, the development and distribution
of phytoplankton are almost completely (R
2 = 0.93) controlled by these factors. The trophic state of the reservoirs has not changed as compared to the beginning of
the 1990s.
This paper describes a dilution technique for estimating the micro-zooplankton grazing impact on natural communities of marine phytoplankton. Experiments performed in coastal waters off Washington, USA (October, 1980), yield estimates of micro-zooplankton impact equivalent to 6 to 24% of phytoplankton standing biomass and 17 to 52% of production per day. Indirect evidence suggests that most of this impact is due to the feeding of copepod nauplii and tintinnids; in contrast, non-loricate ciliates, comprising 80 to 90% of numerical abundance, appeared to contribute little to phytoplankton mortality.
Bacterioplankton from a meso-eutrophic dam reservoir was size fractionated to reduce (<0.8-microm treatment) or enhance (<5-microm treatment) protistan grazing and then incubated in situ for 96 h in dialysis bags. Time course samples were taken from the bags and the reservoir to estimate bacterial abundance, mean cell volume, production, protistan grazing, viral abundance, and frequency of visibly infected cells. Shifts in bacterial community composition (BCC) were examined by denaturing gradient gel electrophoresis (DGGE), cloning and sequencing of 16S rDNA genes from the different treatments, and fluorescence in situ hybridization (FISH) with previously employed and newly designed oligonucleotide probes. Changes in bacterioplankton characteristics were clearly linked to changes in mortality rates. In the reservoir, where bacterial production about equaled protist grazing and viral mortality, community characteristics were nearly invariant. In the "grazer-free" (0.8-microm-filtered) treatment, subject only to a relatively low mortality rate (approximately 17% day(-1)) from viral lysis, bacteria increased markedly in concentration. While the mean bacterial cell volume was invariant, DGGE indicated a shift in BCC and FISH revealed an increase in the proportion of one lineage within the beta proteobacteria. In the grazing-enhanced treatment (5-microm filtrate), grazing mortality was approximately 200% and viral lysis resulted in mortality of 30% of daily production. Cell concentrations declined, and grazing-resistant flocs and filaments eventually dominated the biomass, together accounting for >80% of the total bacteria by the end of the experiment. Once again, BCC changed strongly and a significant fraction of the large filaments was detected using a FISH probe targeted to members of the Flectobacillus lineage. Shifts of BCC were also reflected in DGGE patterns and in the increases in the relative importance of both beta proteobacteria and members of the Cytophaga-Flavobacterium cluster, which consistently formed different parts of the bacterial flocs. Viral concentrations and frequencies of infected cells were highly significantly correlated with grazing rates, suggesting that protistan grazing may stimulate viral activity.
This unique textbook takes a broad look at the rapidly expanding field of freshwater microbiology. Concentrating on the interactions between viruses, bacteria, algae, fungi and micro-invertebrates, the book gives a wide biological appeal. Alongside conventional aspects such as phytoplankton characterisation, seasonal changes and nutrient cycles, the title focuses on the dynamic and applied aspects that are not covered within the current textbooks in the field. Complete coverage of all fresh water biota from viruses to invertebrates. Unique focus on microbial interactions including coverage of biofilms, important communities on all exposed rivers and lakes. New information on molecular and microscopical techniques including a study of gene exchange between bacteria in the freshwater environment. Unique emphasis on the applied aspects of freshwater microbiology with particular emphasis on biodegradation and the causes and remediation of eutrophication and algal blooms.
Estimates of viral production and decay rates provided the valuable confirmation that viruses are active members of the marine community. Viral production involves the lysis of host cells and the release of cellular material as dissolved and colloidal organic carbon. Therefore, measurements of viral replication rates are also useful for assessing the contribution of viruses to bacterial mortality and organic matter cycling in the ocean. By assuming a burst size, viral productivity can be used to estimate rates of bacterial lysis. This approach provides an additional means to assess bacterial mortality along with the visualization of intracellular viral particles by transmission electron microscopy. A wide variety of different approaches for measuring viral productivity include: (1) quantifying net increases in viral abundance over time; (2) measuring rates of viral decay; (3) estimating viral DNA synthesis rates by radiolabeling; (4) calculating expected viral release rates from estimated rates of bacterial lysis and an assumed burst size; and (5) measuring tracer dilution rates using fluorescently labeled viruses (FLV) as tracers.
A new nucleic acid stain, SYBR Green I, can be used for the rapid and accurate determination of viral and bacterial abundances in diverse marine samples. We tested this stain with formalin-preserved samples of coastal water and also from depth profiles (to 800 m) from sites 19 and 190 km offshore, by filtering a few mi onto 0.02 mu m pore-size filters and staining for 15 min. Comparison of bacterial counts to those made with acridine orange (AO) and virus counts with those made by transmission electron microscopy (TEM) showed very strong correlations. Bacterial counts with AO and SYBR Green I were indistinguishable and almost perfectly correlated (r(2) = 0.99). Virus counts ranged widely, from 0.03 to 15 x 10(7) virus ml(-1). Virus counts by SYBR Green I were on the average higher than those made by TEM, and a SYBR Green I versus TEM plot yielded a regression slope of 1.28. The correlation between the two was very high with an r(2) value of 0.98. The precision of the SYBR Green I method was the same as that for TEM, with coefficients of variation of 2.9%. SYBR Green I stained viruses and bacteria are intensely stained and easy to distinguish from other particles with both older and newer generation epifluorescence microscopes. Detritus is generally not stained, unlike when the alternative dye YoPro I is used, so this approach may be suitable for sediments. SYBR Green I stained samples need no desalting or heating, can be fixed with formalin prior to filtration, the optimal staining time is 15 min (resulting in a total preparation time of less than 25 min), and counts can be easily performed at sea immediately after sampling. This method may facilitate incorporation of viral research into most aquatic microbiology laboratories.
The timing of lytic phage development and the relationship between host generation times and latent periods were investigated by electron microscopy of one-step growth experiments in two strains of marine Vibrio species. Results were used in a correction factor developed to interpret field studies of phage-infected marine bacteria. Both the number of mature phage per average cell section and the percentage of cells with mature phage increased exponentially by 73-86% into the latent periods. Assuming that bacterial infection and lysis take place continually in the ocean, conversion factors for relating the percentage of visibly infected bacteria to the total percentage of the bacterial community that are phage-infected were calculated as 3.70-7.14. When this range of factors was applied to previously-collected field data [Proctor LM, Fuhrman JA (1990) Nature (Lond) 343:60-62; Proctor LM, Fuhrman JA (1991) Mar Ecol Prog Ser 69:133-142] from 3 to 31% of the free-living bacteria and 3 to 26% of particulate-associated bacteria appeared to be phage-infected at any given time. Based upon a steady-state model in which half the daughter cells survive to divide again, the percent of total mortality would be twice the total percentage of phage-infected cells. From 6 to 62% and from 6 to 52% of mortality for the free-living and particulate-associated bacterial community, respectively, may be due to viruses.
Summary1. A series of growth experiments were conducted with natural plankton communities from a lake and river in northern Quebec, to evaluate the response of microbial foodweb structure to changes in ambient temperature and solar ultraviolet radiation (UVR).2. Bioassays were incubated for 6 days at two temperatures (10 and 20 °C) and three near-surface irradiance conditions [photosynthetically active radiation (PAR) + UVA + UVB, PAR + UVA, and PAR only).3. The concentration of total bacteria showed no net response to temperature, but the percentage of actively respiring bacteria, as measured with the cellular redox probe5-cyano-2,3-ditolyl tetrazolium chloride (CTC), was up to 57% higher at 20 °C relative to 10 °C. Chlorophyll a concentrations in the < 2 μm size fraction also reacted strongly to temperature, with a net increase of up to 61% over the temperature range of 10–20 °C.4. The UVR effects were small or undetectable for most of the measured variables; however, the percentage of actively respiring bacteria was significantly inhibited in the presence of UVR at 20 °C, decreasing by 29–48% on day 6 in the lake experiments and by 59% on day 2 in one river experiment.5. The results show differential sensitivity to temperature among organisms of microbial communities in subarctic freshwaters, and a resilience by the majority of micro-organisms to their present UVR conditions. Microbial foodwebs in northern freshwaters appear to be relatively unresponsive to short-term (days) changes in UVR. However, the observed responses to temperature suggest that climate change could influence community structure, with warmer temperatures favouring picoplanktonic phototrophs and heterotrophs, and a shift in nanoplankton species composition and size structure.
The relative contribution of viral lysis to overall mortality in aquatic bacterial populations is often estimated as twice the frequency of infected cells (FIC). The 'factor-of-two rule' upon which this estimate is based assumes (l) steady-state conditions, (2) that latent period is equivalent to generation time, a n d (3) that infected cells are not grazed. FIC values for this calculation are themselves derived from measurements of the frequency of vlsibly infected cells (FVIC) by the use of a slmple conversion factor. A steady-state model was developed to more ngorously define the relationships between FIC, FVIC, and the fraction of mortality from viral lysis (FMVL). This model shows that even under the restrictive assumptions listed above, the factor-of-two rule systematically overestimates FMVL for typ-ically reported values of FVIC. The model also shows that although grazing on infected cells further reduces FMVL for a given estimate of FIC, at the same time such grazing increases FIC for a given mea-surement of FVIC. In combination, these 2 effects mnimize the influence of grazing on the calculation of FMVL from FVIC. Overall, the relationship between FMVL and FVIC is well approxin~ated as fol-lows: FMVL S FVIC/[y ln(2) (1 -E -FVIC)], where y = the ratio between the latent period and genera-tion time, and E = the fraction of the latent period during which viral particles are not yet visible. Using typically observed values of FVIC, and assuming that y = 1 (per assumption 2, above) and E = 0 186 (per literature estimates), the model suggests that, on average, viral lysis accounts for approximately 22% (range: 4.5 to 45' ::) of total bacterial mortality in a range of aquatic environments, corresponding to a mean overestimate of 24 % (range: 4 to 44'%) by the factor-of-two rule. Perhaps most importantly, the model shows that calculations of FMVL from FIC or FVIC are very sensitive to changes in the relative length of the latent period (y) and in the assumed proportion of the latent period during which viral par-ticles are not recognizable (E). Constraining these 2 factors would greatly improve the reliability of FMVL calculations.
Global warming scenarios foresee increases in air temperatures of 3–5°C in Northern European regions within the next 70years.
To evaluate the potential effects of global warming on shallow eutrophic lakes, a flow-through experiment combining three
temperature scenarios and two nutrient levels was conducted in 24 outdoor mesocosms. Eight mesocosms were unheated and acted
as controls, while sixteen were heated – eight according to the Intergovernmental Panel on Climate Change’s (IPCC) climate
scenario A2 down-scaled to regional level (2.5–4.4°C, depending on season) and eight according to scenario A2+ with an additional
50% temperature increase. Half of the mesocosms were enriched with nitrogen and phosphorus to simulate increased runoff from
terrestrial sources due to the increased precipitation predicted by the A2 scenario. The other half were un-enriched and received
only natural nutrient input from the groundwater that fed all the mesocosms. The abundance and development pattern of the
microbial communities within the mesocosms were tracked during a 16-month period. Generally, the results showed that the abundances
of picoalgae, bacteria and heterotrophic nanoflagellates changed in a similar manner over time; abundances being lower in
winter than in summer. Warming in itself had no effect on abundance, albeit it significantly modified the positive effect
of the nutrients. Only at ambient temperatures did the whole microbial assemblage respond positively to nutrients. In the
A2 scenario, only picoalgae responded to nutrients, while in the A2+ scenario all but the heterotrophic nanoflagellates showed
a response. Elevated winter temperatures seemed not to be more important for the microbial assemblage than elevated summer
temperatures. Our results demonstrate that the direct effects of warming were far less important than the nutrient effect.
The results furthermore reveal that warming and nutrients in combination set off complex interactions. In consequence, global
warming may possibly have pronounced effects on aquatic ecosystems if accompanied by increased nutrient loading.
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A new method is described that uses the fluorochrome primulin and epifluorescence microscopy for the enumeration of heterotrophic and phototrophic nanoplankton (2 to 20 μm). Phototrophic microorganisms are distinguished from heterotrophs by the red autofluorescence of chlorophyll a . Separate filter sets are used which allow visualization of the primulin-stained nanoplankton without masking chlorophyll a fluorescence, thus allowing easy recognition of phototrophic cells. Comparison with existing epifluorescence techniques for counting heterotrophic and phototrophic nanoplankton shows that primulin provides more accurate counts of these populations than the fluorescein isothiocyanate or proflavine techniques. Accuracy is comparable to that with the acridine orange technique, but this method requires only one filter preparation for the enumeration of both phototrophic and heterotrophic populations.
Images
Bakterioplankton vodokhranilishch Verkhnei i Srednei Volgi (Bacterioplankton of Reservoirs of the Upper and Middle Volga)
- A I Kopylov
- D B Kosolapov
- AI Kopylov
Formation, Movement, and Transformation of Water Masses in the Gorky Reservoir
- Edel
- K K Shtein
Zakonomernosti pervichnoi produktsii v limnicheskikh eosistemakh (Patterns of Primary Producc tion in Limnetic Ecosystems
- V V Bul 'on
Bul'on, V.V., Zakonomernosti pervichnoi produktsii v limnicheskikh eosistemakh (Patterns of Primary Producc tion in Limnetic Ecosystems), St. Petersburg: Nauka, 1994.
Hydrological Characteristics of Reservoirs, in Sovremennaya ekologicheskaya situatsiya v Rybinskom i Gor’kovskom vodokhranilishchakh (Current Ecological Situation in the Rybinsk and Gorky Reservoirs)
- A S Litvinov
- A V Zakonnova
- AS Litvinov
Pigments of Phytoplankton of the Rybinsk Reservoir, in Ekologicheskie problemy Verkhnei Volgi (Environmental Problems of the Upper Volga), Yaroslavl: Izd
- I L Pyrina
Characteristics of Thermal Conditions
- A S Litvinov
- V F Roshchupko
- AS Litvinov
Complex ecological classification of the quality of surface inland waters
- O P Oksiyuk
- V N Zhukinskii
- L P Braginskii
- OP Oksiyuk
Mikrobiologicheskie protsessy produktsii i destruktsii organicheskogo veshchestva vo vnutrennikh vodoemakh
- V I Romanenko
Ekologiya mikroorganizmov presnykh vodoemov. Laboratornoe rukovodstvo (Ecology of Microorganisms of Freshwater Bodies: A Laboratory Manual)
- V I Romanenko
- S I Kuznetsov
- VI Romanenko
The Relationship between Biomass and Volume of Bacteria, Handbook of Methods in Aquatic Microbial Ecology
- S Norland
Pigments of Phytoplankton of the Rybinsk Reservoir
- I L Pyrina
- IL Pyrina
Mikrobiologicheskie protsessy produktsii i destruktsii organicheskogo veshchestva vo vnutrennikh vodoemakh (Microbiological Processes of Production and Destruction of Organic Matter in Inland Water Bodies)
- V I Romanenko
- VI Romanenko