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Abstract

We analysed changes in the abundance, biomass and cell size of the microbial food web community (bacteria, heterotrophic nanoflagellates, ciliates) at contrasting nutrient concentrations and temperatures during a simulated heat wave. We used 24 mesocosms mimicking shallow lakes in which two nutrient levels (unenriched and enriched by adding nitrogen and phosphorus) and three different temperature scenarios (ambient, IPCC A2 scenario and A2 +%50) are simulated (4 replicates of each). Experiments using the mesocosms have been running un-interrupted since 2003. A 1-month heat wave was imitated by an extra 5 °C increase in the previously heated mesocosms (from 1st July to 1st August 2014). Changes in water temperature induced within a few days a strong effect on the microbial food web functioning, demonstrating a quick response of microbial communities to the changes in environment, due to their short generation times. Warming and nutrients showed synergistic effects. Microbial assemblages of heterotrophic nanoflagellates and ciliates responded positively to the heating, the increase being largest in the enriched mesocosms. The results indicate that warming and nutrients in combination can set off complex interactions in the microbial food web functioning.

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... Bacteria are thought to be a sensitive sentinel of climate change [11] and are closely related to the biogeochemical cycle [12,13]. Therefore, microorganisms can respond quickly to environmental changes in shallow-water ecosystems [14,15]. Microbial function and related processes are always determined by microbial communities [16]. ...
... The high concentration of substrate and nutrients in sediment constrains the enzyme's response to temperature [100]. Heat waves can stimulate an increase in bacterial abundance, and this change is more pronounced in sediment, a nutrient-rich substrate [14]. This can also explain why the stimulation of warming in sediment is stronger than that in water, which is possibly because sediment has a higher nutrient level. ...
... We found that, in the bacterial functional groups (chemoheterotrophy and aerobic chemoheterotrophy) mainly related to carbon decomposition in water column in spring and sediment in winter, decomposition significantly decreased under the stimulation of heat waves. The reason for this may be that the main microbial functional groups that maintain chemotrophy and aerobic chemoheterotrophy functions stimulated by fluctuating temperature rise have a limited tolerance to temperature [86,87], and microflora cannot adapt to short-term and large temperature fluctuations [14]. Correa-Araneda et al. (2020) also found that short-term extreme temperature changes will slow the decomposition of litter in rivers [110]. ...
Article
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Extreme climatic events, such as heat wave and large temperature fluctuations, are predicted to increase in frequency and intensity during the next hundred years, which may rapidly alter the composition and function of lake bacterial communities. Here, we conducted a year-long experiment to explore the effect of warming on bacterial metabolic function of lake water and sediment. Predictions of the metabolic capabilities of these communities were performed with FAPROTAX using 16S rRNA sequencing data. The results indicated that the increase in temperature changed the structure of bacterial metabolic functional groups in water and sediment. During periods of low temperature, the carbon degradation pathway decreased, and the synthesis pathway increased, under the stimulation of warming, especially under the conditions temperature fluctuation. We also observed that nitrogen fixation ability was especially important in the warming treatments during the summer season. However, an elevated temperature significantly led to reduced nitrogen fixation abilities in winter. Compared with the water column, the most predominant functional groups of nitrogen cycle in sediment were nitrite oxidation and nitrification. Variable warming significantly promoted nitrite oxidation and nitrification function in winter, and constant warming was significantly inhibited in spring, with control in sediments. Co-occurrence network results showed that warming, especially variable warming, made microbial co-occurrence networks larger, more connected and less modular, and eventually functional groups in the water column and sediment cooperated to resist warming. We concluded that warming changed bacterial functional potentials important to the biogeochemical cycling in the experimental mesocosms in winter and spring with low temperature. The effect of different bacteria metabolism functions in water column and sediment may change the carbon and nitrogen fluxes in aquatic ecosystems. In conclusion, the coupling response between different bacterial metabolic functions in water and sediment may improve the ability to mitigate climate change.
... The effects of global warming may include very hot periods in the summer or a complete lack of ice cover on water bodies during the winter (Cao et al., 2015;Audet et al., 2017;Nandini et al., 2019). The results of previous studies indicate that in natural lake ecosystems the share of smaller species increases in planktonic invertebrate communities, because the higher temperature causes an increase in mortality, mainly through pressure from top predators (Heckmann et al., 2012;Shurin et al., 2012;Rall et al., 2012;Zingel et al., 2018;Reczuga et al., 2018). According to Ohlberger (2013), warming-induced responses in average body size are not only determined by changes in individual growth and development rates, but also mediated through size-dependent feedbacks at the population level, as well as by competitive and predatory interactions within the community. ...
... Additionally, body-size structures can stabilize the strength of interactions across food webs and constitute an adaptive mechanism for effective use of food resources (Heckmann et al., 2012). On the other hand, the increase in temperature increases the competitive ability of small species compared to large ones through physiological adaptations to higher temperatures (Brown et al., 2004;Foster et al., 2013;Zingel et al., 2018). As dystrophic lakes are generally shallow, they react more rapidly to temperature changes. ...
... This may explain the exceptional species richness and abundance of ciliates in these experiments. Such relationships have also been observed in various types of peatlands and eutrophic lakes, in mesocosm systems in which the concentrations of biogenic compounds were manipulated (Mieczan et al., 2015;Zingel et al., 2018). Buosi et al. (2011) have also observed that the species richness of protozoa increased with habitat fertility. ...
Article
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One of the effects of warming is earlier retreat of the ice cover or a complete lack of ice cover on water bodies in the winter. However, there is still no information on how climate warming affects the 24-hour dynamics of the planktonic microbial loop in winter. The aim of this investigation was to assess the diurnal dynamics of the taxonomic composition and abundance of microbial communities in experimentally reproduced conditions (samples from under the ice, +2, +4 and +8°C) and to analyse the relationships between components of the microbial loop in relation to physical and chemical parameters. Samples were taken in winter from three dystrophic reservoir. The biological and physicochemical parameters in the water were analysed at the start (day 0), 15 and end of the experiment (day 30) over a 24-hour cycle. The increase in temperature caused an increase in the numbers of predators (particularly testate amoebae and ciliates) and a reduction in the body size of individual populations. During the period with ice cover, marked dominance of mixotrophic testate amoeba (Hyalosphenia papilio) and ciliates (Paramecium bursaria) was observed, while the increase in temperature caused an increase in the proportion of bacterivorous ciliates (Cinetochilum margaritaceum).
... The ongoing global climate warming is expected to deeply alter lacustrine zooplankton biomass and abundance (Gerten and Adrian 2002;Strecker et al. 2004;Brucet et al. 2010;Zingel et al. 2018). As demonstrated already more than three decades ago in Lake Windermere (UK), year-to-year zooplankton biomass fluctuations are mostly determined by water temperature (George and Harris 1985). ...
... Although there is rich published evidence on the temperature effects on ciliate density and biomass, it has been mostly studied in the context of seasonal fluctuations and successions (Gaedke and Wickham 2004;Pace 1982). Zingel et al. (2018) showed in a mesocosm study that ciliates responded quickly and positively to non-seasonal warming. We also reported a synergistic effect between temperature and nutrients with the largest increase in the more eutrophic enclosures (Zingel et al. 2018). ...
... Zingel et al. (2018) showed in a mesocosm study that ciliates responded quickly and positively to non-seasonal warming. We also reported a synergistic effect between temperature and nutrients with the largest increase in the more eutrophic enclosures (Zingel et al. 2018). However, in the present study conducted in the natural habitat for ciliates, nutrients (NO 3 in that case) ranked only as the third most important variable and explained a mere 4% of B cili variance. ...
Article
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We aimed to investigate the influence of environmental factors and predict zooplankton biomass and abundance in shallow eutrophic lakes. We employed time series of zooplankton and environmental parameters that were measured monthly during 38 years in a large, shallow eutrophic lake in Estonia to build estimates of zooplankton community metrics (cladocerans, copepods, rotifers, ciliates). The analysis of historical time series revealed that air temperature was by far the most important variable for explaining zooplankton biomass and abundance, followed, in decreasing order of importance, by pH, phytoplankton biomass and nitrate concentration. Models constructed with the best predicting variables explained up to 71% of zooplankton biomass variance. Most of the predictive variables had opposing or antagonistic interactions, often mitigating the effect of temperature. In the second part of the study, three future climate scenarios were developed following different Intergovernmental Panel on Climate Change (IPCC) temperature projections and entered into an empirical model. Simulation results showed that only a scenario in which air temperature stabilizes would curb total metazooplankton biomass and abundance. In other scenarios, metazooplankton biomass and abundance would likely exceed historical ranges whereas ciliates would not expand. Within the metazooplankton community, copepods would increase in biomass and abundance, whereas cladocerans would lose in biomass but not in abundance. These changes in the zooplankton community will have important consequences for lake trophic structure and ecosystem functioning.
... To date, many studies have revealed that warming affects aquatic microbial abundance (Markensten et al., 2010), size (Zingel et al., 2018), growth rate (Özen et al., 2013), reproductive rate (Zingel et al., 2018), community turnover (Ren et al., 2013), metabolism , functional gene diversity , and network patterns (Guo et al., 2023). However, there is limited information about the impact of warming on the lake microeukaryotic community due to the lack of long-term field observation and experimental evidence at mesocosm scales. ...
... To date, many studies have revealed that warming affects aquatic microbial abundance (Markensten et al., 2010), size (Zingel et al., 2018), growth rate (Özen et al., 2013), reproductive rate (Zingel et al., 2018), community turnover (Ren et al., 2013), metabolism , functional gene diversity , and network patterns (Guo et al., 2023). However, there is limited information about the impact of warming on the lake microeukaryotic community due to the lack of long-term field observation and experimental evidence at mesocosm scales. ...
... Heatwaves were found to stimulate an increase in bacterial abundance, and this effect was more pronounced in sediment [97]. The richer substrate and higher relative temperature increase (from 7 • C to 11 • C) in the sediment would facilitate a stronger warming effect on microbial abundance during colder winters. ...
Article
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Bacteria in lake water bodies and sediments play crucial roles in various biogeochemical processes. In this study, we conducted a comprehensive analysis of bacterioplankton and sedimentary bacteria community composition and assembly processes across multiple seasons in 18 outdoor mesocosms exposed to three temperature scenarios. Our findings reveal that warming and seasonal changes play a vital role in shaping microbial diversity, species interactions, and community assembly disparities in water and sediment ecosystems. We observed that the bacterioplankton networks were more fragile, potentially making them susceptible to disturbances, whereas sedimentary bacteria exhibited increased stability. Constant warming and heatwaves had contrasting effects: heatwaves increased stability in both planktonic and sedimentary bacteria communities, but planktonic bacterial networks became more fragile under constant warming. Regarding bacterial assembly, stochastic processes primarily influenced the composition of planktonic and sedimentary bacteria. Constant warming intensified the stochasticity of bacterioplankton year-round, while heatwaves caused a slight shift from stochastic to deterministic in spring and autumn. In contrast, sedimentary bacteria assembly is mainly dominated by drift and remained unaffected by warming. Our study enhances our understanding of how bacterioplankton and sedimentary bacteria communities respond to global warming across multiple seasons, shedding light on the complex dynamics of microbial ecosystems in lakes.
... How water level changes affect the microbial community is relatively unexplored. There is only limited experimental evidence of direct and indirect effects of changes in water level, nutrient availability, macrophyte coverage and zooplankton grazing on the structure of the microbial community (Tzaras et al. 1999;Jezbera et al. 2003;Farjalla et al. 2006;Christoffersen et al. 2006;Özen et al. 2013Zingel et al. 2018;Šimek et al. 2019). Global warming may affect microbial communities indirectly through warming-induced eutrophication (Jeppesen et al. 2009 as these communities are highly sensitive to the changes in nutrient status and the top-down effect by consumers (Carrick et al. 1991;Nixdorf and Arndt 1993;Gaedke and Straile 1994;Mathes and Arndt 1994;Özen et al. 2018;Colby et al. 2020). ...
Article
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Eutrophication and lake depth are of key importance in structuring lake ecosystems. To elucidate the effect of contrasting nutrient concentrations and water levels on the microbial community in fully mixed shallow lakes, we manipulated water depth and nutrients in a lake mesocosm experiment in north temperate Estonia and followed the microbial community dynamics over a 6-month period. The experiment was carried out in Lake Võrtsjärv-a large, shallow eutrophic lake. We used two nutrient levels crossed with two water depths, each represented by four replicates. We found treatment effects on the microbial food web structure, with nutrients having a positive and water depth a negative effect on the bio-masses of bacterial and heterotrophic nanoflagellates (HNF) (RM-ANOVA, p < 0.05). Nutrients affected positively and depth negatively the mean size of individual HNF and ciliate cells (RM-ANOVA; p < 0.05). The interactions of depth and nutrients affected positively the biomass of bacterivorous and bacteri-herbivorous ciliates and negatively the biomass of predaceous ciliates (RM-ANOVA; p < 0.05). Bacterivorous ciliates had lowest biomass in shallow and nutrient-rich mesocosms, whilst predaceous ciliates had highest biomass here, influencing trophic interactions in the microbial loop. Overall, increased nutrient concentrations and decreased water level resulted in an enhanced bacterial biomass and a decrease in their main grazers. These differences appeared to reflect distinctive regulation mechanisms inside the protozoan community and in the trophic interactions in the microbial loop community.
... This is partly driven by the high sensitivity of freshwaters organisms to climate change, caused by their limited dispersal capacity, high dependence on external physicochemical conditions and water availability, and exposure to multiple, compounding anthropogenic stressors (Ormerod et al., 2010;Woodward et al., 2010). Ongoing climate warming is predicted to trigger complex but poorly understood interactive effects on aquatic biodiversity, particularly on microbial food webs (Zingel et al., 2018). The effects of warming on aquatic food webs can affect species composition and productivity, in addition to direct effects on biochemical and physiological rates that are linked to energetic processes, which influence fundamental processes for ecosystem functions and services (Gårdmark & Huss, 2020;Ohlberger et al., 2011). ...
Article
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Freshwaters are among the most vulnerable ecosystems to climate warming, with projected temperature increases over the coming decades leading to significant losses of aquatic biodiversity. Experimental studies that directly warm entire natural ecosystems in the tropics are needed, for understanding the disturbances on aquaticcommunities. Therefore, we conducted an experiment to test the impacts of pre -dicted future warming on density, alpha diversity, and beta diversity of freshwater aquatic communities, inhabiting natural microecosystems—Neotropical tank bromeli-ads. Aquatic communities within the tanks bromeliads were experimentally exposed to warming, with temperatures ranging from 23.58 to 31.72°C. Linear regression analysis was used to test the impacts of warming. Next, distance- based redundancy analysis was performed to assess how warming might alter total beta diversity and its components. This experiment was conducted across a gradient of habitat size (bro -meliad water volume) and availability of detrital basal resources. A combination of the highest detritus biomass and higher experimental temperatures resulted in the great-est density of flagellates. However, the density of flagellates declined in bromeliads with higher water volume and lower detritus biomass. Moreover, the combination of the highest water volume and high temperature reduced density of copepods. Finally, warming changed microfauna species composition, mostly through species substitu-tion (βrepl component of total beta- diversity). These findings indicate that warming strongly structures freshwater communities by reducing or increasing densities of dif -ferent aquatic communities groups. It also enhances beta- diversity, and many of these effects are modulated by habitat size or detrital resources.
... Biogeochemical cycles of carbon (C), nitrogen (N), and phosphorus (P) in sediments and riparian soils of aquatic environment can influence eutrophication of water body (Gaget et al., 2017), environmental behavior of persistent organic pollutants (Stubbins et al., 2014), morphology and toxicity of heavy metals (Li et al., 2018), and structure and functional response of microbial communities (Zingel et al., 2018). Some factors/conditions, like temperature, redox conditions, pH, and the concentrations of other inorganic species such as sulfide and iron in the sediment and the water column can also influence the carbon, nitrogen, and phosphorus and environmental behavior (Hayakawa et al., 2015;Ribeiro et al., 2008). ...
Article
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The contamination of nutrients has caused considerable worry about the environment, resource value, and ecological worth of drinking water reservoirs. Therefore, we comprehensively studied the abundance, sources, distribution, and environmental behavior of carbon, nitrogen, and phosphorus in Fengshuba Reservoir (FSBR) (a large drinking reservoir, China). A graded leaching technique (introduced in 2003), the European Standard, Measurement and Testing (SMT) protocol, and spectrometry combined with parallel factor analysis (EEMs-PARAFAC) were used to assess nitrogen, phosphorus forms, and spectra data in the sediment and soil phases, respectively. The study demonstrates that seasonal hydrological variation had no significant effect on the nutrient abundance and nutrient structure composition of the FSBR, while different environmental media (e.g., sediment and soil phase) exhibited considerable differences in nutrient abundance, composition, and environmental behavior. The abundance of colored dissolved organic matter (CDOM), as well as molecular weight, aromatization degree, and humification degree of dissolved organic matter (DOM) were all lower in sediments than in soils, whereas the authigenic component was greater than in soils. Microbial-derived humus (C1), terrestrial-derived humus (C2), and protein-like tryptophan (C3) were identified as the three primary fluorescence components. Principal component analysis indicated that three components were closely associated with phosphorus in the sediment phase, whereas nitrogen and phosphorus in the soil phase were mainly related to C1 and C2. In summary, soil media (drawdown area) must be carefully considered in the management and control of water environment nutrients in reservoirs.
... Microbial communities form an integral component of lake ecosystems due to their diverse roles in nutrient cycling and position near the base of food webs (Newton et al., 2011). However, lake microbial communities are highly sensitive to environmental perturbations (Zingel et al., 2018), and many lakes worldwide are experiencing a complex mix of interacting pressures from the effects of human activities, such as nutrient enrichment and climate change (Birk et al., 2020). Eutrophication from increased nutrient pollution can change ecosystem dynamics, lead to a change and loss of biodiversity, and increase the frequency and severity of cyanobacterial blooms which can produce toxic compounds that are harmful to wildlife and humans . ...
Article
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Microbial communities play important roles in lake ecosystems and are sensitive to environmental change. However, our understanding of their responses to long‐term change such as eutrophication is limited, as long‐term lake monitoring is rare, and traditional paleolimnological techniques (pigments and microfossils) are restricted to a low taxonomic resolution, or organisms with well‐preserved structures. Sedimentary DNA (sedDNA) is a promising technique to reconstruct past microbial communities in sediments, but taphonomic processes and the ability of sedDNA to record bacterial pelagic history accurately are largely unknown. Here, we sequenced the 16S rRNA gene in triplicate sediment cores from Esthwaite Water (English Lake District) which has concurrent long‐term monitoring and observational data. The sediment record spanned 113 years and included an episode of increased nutrient availability from the 1970s, followed by a more recent decline. Trends in bacterial community composition were broadly similar among the three sediment cores. Cyanobacterial richness in the sediment cores correlated significantly with that of cyanobacteria in a 65‐year microscopy‐based monitoring record, and some known pelagic bacterial taxa were detected in the sediment. sedDNA revealed distinct shifts in community composition in response to changing lake physicochemical conditions. The relative abundance of cyanobacteria closely reflected nutrient enrichment, and Proteobacteria, Bacteroidetes, and Verrucomicrobia were relatively more abundant in recent sediments, while Chloroflexi, Firmicutes, Acidobacteria, Nitrospirae, Spirochaetes, and Planctomycetes declined in more recent sediments. Following lake restoration efforts to reduce nutrient enrichment, the relative abundance of cyanobacteria returned to pre‐1970 levels, but the bacterial community did not fully recover from the period of intense eutrophication within the time scale of our study. These results suggest that sedDNA is a valuable approach to reconstruct lake microbial community composition over the 100‐year time scale studied, but an improved understanding of DNA deposition and degradation is required to further the application of sedDNA in paleolimnology. Lake sedimentary DNA (sedDNA) is a promising technique to reconstruct past microbial communities, but the ability of sedDNA to record bacterial pelagic history accurately is largely unknown. Here, we combine a 113‐year sedDNA record, validated by a microscopy record of cyanobacteria, with long‐term monitoring of lake physicochemical conditions to identify drivers of past bacterial and cyanobacterial community change. Our results demonstrate the significant potential of sedDNA to reconstruct past changes in lake microbial community composition.
... Biogeochemical cycles of carbon (C), nitrogen (N) and phosphorus (P) in sediments and riparian soils of aquatic environment can in uence eutrophication of water body (Gaget et al. 2017), environmental behavior of persistent organic pollutants (Stubbins et al. 2014), morphology and toxicity of heavy metals (Li et al. 2018), and structure and functional response of microbial communities (Zingel et al. 2018). Some factors/conditions, like temperature, redox conditions, pH, and the concentrations of other inorganic species such as sul de and iron in the sediment and the water column can also in uence the carbon, nitrogen, and phosphorus and environmental behavior (Hayakawa et al. 2015, Ribeiro et al. 2008). ...
Preprint
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The contamination of nutrients has caused considerable worry about the environment, resource value, and ecological worth of drinking water reservoirs. Therefore, we comprehensively studied the abundance, sources, distribution, and environmental behavior of carbon, nitrogen, and phosphorus in Fengshuba Reservoir (FSBR) (a large drinking reservoir, China). Seasonal hydrological circumstances had little influence on the nutrient abundance and structural component of the FSBR, while carbon, nitrogen, and phosphorus abundance, composition, and environmental behavior varied significantly between various environmental media (sediment and soil phases). Microbial-derived humus (C1), terrestrial-derived humus (C2), and protein-like tryptophan (C3) were identified as the three primary fluorescence components using parallel factor analysis. The abundance of colored dissolved organic matter (CDOM), molecular weight, aromatization degree, and humification degree of dissolved organic matter (DOM) in the sediment were lower than in the soil, whereas the authigenic component was greater than in the soil, according to spectral index analysis. The main sources of humus in FSBR were biogenic contributions. Principal component analysis indicated that three components were closely associated to phosphorus in the sediment phase, whereas nitrogen and phosphorus in the soil phase were mainly related to C1 and C2. In summary, in the management and control of water environment nutrients in reservoirs, soil media in the riparian zone must be carefully considered.
... Riemann [13] showed that an experimental increase in fish abundance was conducive to an increase in the abundance of heterotrophic flagellates, most likely due to reduced predation pressure from cladocerans, which are consumed by fish. An additional factor that may influence the size structure of aquatic organisms is temperature [14][15][16]. However, there is no literature data on the trophic relationships between brown bullhead and the major microbial elements of the food web in peat pools, taking into account the global increase in water temperature. ...
Article
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Disturbances in the functioning of peatlands, due to growing human impact, climate change and the appearance of alien invasive species, are becoming increasingly common. Analysis of trophic relationships in the predator (invasive alien species)–prey system is extremely important for understanding the functioning of peat pools—small water bodies formed in peatlands by peat extraction. These issues are, as yet, very little understood. The aim of this study was to examine the impact of Ameiurus nebulosus, an alien and invasive fish species dominant in these pools, on the microbial communities and small metazoa (phycoflora, bacteria, heterotrophic flagellates, ciliates, and crustaceans) in peat pools. The laboratory experiment included two groups of treatments simulating natural conditions: treatments without fish and treatments with brown bullhead. The water temperature was manipulated as well. The presence of brown bullhead in combination with climate changes was shown to cause a change in the structure of microbial communities. This is reflected in a decrease in the abundance of planktonic crustaceans and an increase in ciliates. The overlapping effects of alien species and gradual climate warming may intensify the eutrophication of peatland ecosystems and the increase in the proportion of cyanobacteria, thereby affecting the carbon cycle in these ecosystems.
... This study was conducted using mesocosm experiments. Many studies use these controlled environments to examine ecosystem responses to factors such as nutrient addition (Escaravage et al., 1995;Tonetta et al., 2018;Zingel et al., 2018); light limitation (Escaravage et al., 1995;Gillette et al., 2014;Winder et al., 2012); and climate change (Landkildehus et al., 2014;Sommer et al., 2007;Stewart et al., 2013). The use of in situ mesocosms to study the effects of floating photovoltaic cover as a way to evaluate and assess the ecological processes under closed system. ...
Conference Paper
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The applications of floating photovoltaic (FPV) on water bodies are currently on a global demand. Despite the increasing popularity of floating photovoltaic industry, studies on ecological effects of lake coverage using floating photovoltaic-especially in tropical countries-haven't been widely conducted. This study evaluates the effect of floating photovoltaic on dissolved oxygen and trophic state changes in water bodies using mesocosm experiment. Trophic state is an indicator of the degree of transformation and ecological disruption in water bodies. The parameters used to assess trophic index (Trophic State Index, TSI) are total phosphorus, chlorophyll-a, and water transparency. TSI uses mathematical equations to calculate data of the experiments, so that the expression of trophic level can be determined. The mesocosm experiment was conducted from March 25 th to April 15 th 2021 in Mahoni Lake, in which a total amount of 7 water samples were collected from each mesocosms. Our results show that mesocosms with 100% FPV cover have a lower dissolved oxygen (p-value < 0,05) and a lower TSI value (p-value < 0,05) compared to mesocosms without FPV cover (control). According to the TSI value, despite the decrease in TSI value, the trophic state was still classified as eutrophic. The results obtained are an important tool for further studies focusing on water quality and ecology impact regarding FPV on water bodies.
... The inconsistent effect of constant warming and heatwave on litter bacterial may be due to a consensus conclusions drawn in a varies of studies examining disturbance: the microbial communities are not resistant to many factors but highly resilient to disturbance [22,47], Finlay indicated that the composition of the microbial community usually changes when environmental factors change at high amplitude or high frequency. For example, in similar mesocosm experiments, the researchers found that heating induced a positive effect on the bacteria within a few days [48] and long-term warming had not significant effects on bacterial alpha diversity but significantly shifted bacterial community composition [49]. In addition, some studies reported the increase in bacterial diversity during the late stage of organic matter decomposition [50,51]. ...
Article
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Global climate change scenarios predict that lake water temperatures will increase up to 4 °C and extreme weather events, such as heat waves and large temperature fluctuations, will occur more frequently. Such changes may result in the increase of aquatic litter decomposition and on shifts in diversity and structure of bacteria communities in this period. We designed a two-month mesocosm experiment to explore how constant (+4 °C than ambient temperature) and variable (randomly +0~8 °C than ambient temperature) warming treatment will affect the submerged macrophyte litter decomposition process. Our data suggests that warming treatments may accelerate the decomposition of submerged macrophyte litter in shallow lake ecosystems, and increase the diversity of decomposition-related bacteria with community composition changed the relative abundance of Proteobacteria, especially members of Alphaproteobacteria increased while that of Firmicutes (mainly Bacillus) decreased.
... All of these metabolic process variables also responded to a cool and cloudy-low irradiance event in the middle of the heatwave, resulting in a severe drop in O 2 , not least in the heated mesocosms. In the same experiment, substantial effects associated with the heatwave were also found on the biomass of bacterioplankton, heterotrophic flagellates, and ciliates, respectively [25], and to some degree also on the greenhouse gas (GHG) dynamics [26]. The results from this experiment collectively indicated that microbial communities and ecosystem processes are more sensitive to a short-term heatwave than larger-bodied and more slow-growing organisms such as zooplankton [24]. ...
Article
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The Earth is facing a major change in climate due to ongoing global warming, and as a result of this warming, the occurrence of more extreme weather is also expected to in-crease. Accordingly, the impacts of extreme climatic events on lakes have been receiving more and more attention in recent years. Furthermore, advances in real-time high-resolution monitoring, together with an increase in the use of in-situ monitoring platforms on many lakes across the globe, now make it possible to track even the short-term effects of such events in lakes with differing characteristics and local climates. Such high-resolution data can also be used to better validate dynamic models of lake pro-cesses, models which are essential if the projected effects of global warming on lake eco-systems are to be quantified. Extreme climatic events include heatwaves, storms, extreme calm periods, sudden and intense rainfall, and droughts. These changes in local weather have the potential to result in physical, chemical, and biological changes within lakes. In deep lakes, for example, heatwaves and calm periods lead to stronger stratification and, if the lakes are nutrient enriched, often to higher levels of cyanobacterial biomass. Similar conditions can lead to temporary stratification of shallow lakes and this, in turn, can result in higher internal loading of phosphorus and thus eutrophication]. Storms often deepen the mixed layer depth and, combined with rain, it may enhance the input of dissolved and particu-late matter and ultimately increase eutrophication. Extreme drought may result in reduced water level, higher salinity, and higher nutrient concentration , and extreme rain may result in increases in the flux of dissolved organic carbon from catchments. Such effects may be of short-term duration, but if severe, they may have long-lasting con-sequences, particularly in lakes with longer retention times. There is no universally accepted approach to define extreme events for lake studies. Extremes in climatic and hydrological datasets are generally defined by the use of thresholds based on, for example, a top or bottom percentile of the observed data from the site. This type of threshold approach does allow for a systematic identification and assessment of events but has the drawback that the absolute threshold values will differ de-pending on location and the local climate. Nevertheless, thresholds based on local meteorological data have been used to identify potential extreme events within lakes. Definitions based on within-lake physical changes can, however, be more complex due to inconsistency in the metrics used to define such extremes. Other commonly used and equally valid approaches focus on the effects of, for example, named storms or studies on extreme or episodic responses within the lakes, even though the meteorological conditions that trigger the response may not in itself be over any extreme threshold. This Special Issue includes all of these approaches and addresses effects of extreme events based on field studies, controlled experiments, and modelling.
... These results demonstrate the higher risk of dramatic shifts in shallow lake ecosystems in HW periods in a future warmer world and that the risk increases with eutrophication. Rapid responses to changes in temperature, including the cooling period in the middle of the HW, were also found for the biomasses of bacterioplankton, heterotrophic flagellates, ciliates [56] and for the methane emission [47]. By contrast, a modest effect of the HW was found for phytoplankton [55] and zooplankton [35], suggesting that the microbial community and process rates are particularly sensitive to heat waves in already warm lakes, at least in the short-term. ...
Article
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Global changes (e.g., warming and population growth) affect nutrient loadings and temperatures , but global warming also results in more frequent extreme events, such as heat waves. Using data from the world's longest-running shallow lake experimental mesocosm facility, we studied the effects of different levels of nutrient loadings combined with varying temperatures, which also included a simulated 1-month summer heat wave (HW), on nutrient and oxygen concentrations , gross ecosystem primary production (GPP), ecosystem respiration (ER), net ecosystem production (NEP) and bacterioplankton production (BACPR). The mesocosms had two nutrient levels (high (HN) and low (LN)) combined with three different temperatures according to the IPCC 2007 warming scenarios (unheated, A2 and A2 + 50%) that were applied for 11 years prior to the present experiment. The simulated HW consisted of 5 °C extra temperature increases only in the A2 and A2 + 50% treatments applied from 1 July to 1 August 2014. Linear mixed effect modeling revealed a strong effect of nutrient treatment on the concentration of chlorophyll a (Chl-a), on various forms of phosphorus and nitrogen as well as on oxygen concentration and oxygen percentage (24 h means). Applying the full dataset, we also found a significant positive effect of nutrient loading on GPP, ER, NEP and BACPR, and of temperature on ER and BACPR. The HW had a significant positive effect on GPP and ER. When dividing the data into LN and HN, temperature also had a significant positive effect on Chl-a in LN and on orthophosphate in HN. Linear mixed models revealed differential effects of nutrients, Chl-a and macrophyte abundance (PVI) on the metabolism variables , with PVI being particularly important in the LN mesocosms. All metabolism variables also responded strongly to a cooling-low irradiance event in the middle of the HW, resulting in a severe drop in oxygen concentrations, not least in the HN heated mesocosms. Our results demonstrate strong effects of nutrients as well as an overall rapid response in oxygen metabolism and BACPR to changes in temperature, including HWs, making them sensitive ecosystem indicators of climate warming.
... However, fish kill in HN-A2 and not least in HN-A2+ enhanced the effect of the HW. Modest effects of the HW were also found for phytoplankton in the same experiment [51], whereas temperature changes had a substantial effect on the biomass of bacterioplankton, heterotrophic flagellates, ciliates [95], and macrophytes [13], oxygen metabolism (gross ecosystem production and ecosystem respiration), and bacterioplankton production [96], as well as on greenhouse gases dynamics [70]. These results suggest that microbial communities and ecosystem processes are more sensitive to short-term HWs than the larger-bodied and more slow-growing organisms, such as zooplankton, which are likely to exhibit a delayed or weak response, unless a major fish kill occurs. ...
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Shallow lakes are globally the most numerous water bodies and are sensitive to external perturbations, including eutrophication and climate change, which threaten their functioning. Extreme events, such as heat waves (HWs), are expected to become more frequent with global warming. To elucidate the effects of nutrients, warming, and HWs on zooplankton community structure, we conducted an experiment in 24 flow-through mesocosms (1.9 m in diameter, 1.0 m deep) imitating shallow lakes. The mesocosms have two nutrient levels (high (HN) and low (LN)) crossed with three temperature scenarios based on the Intergovernmental Panel on Climate Change (IPCC) projections of likely warming scenarios (unheated, A2, and A2 + 50%). The mesocosms had been running continuously with these treatments for 11 years prior to the HW simulation, which consisted of an additional 5 • C increase in temperature applied from 1 July to 1 August 2014. The results showed that nutrient effects on the zooplankton community composition and abundance were greater than temperature effects for the period before, during, and after the HW. Before the HW, taxon richness was higher, and functional group diversity and evenness were lower in HN than in LN. We also found a lower biomass of large Cladocera and a lower zooplankton: phytoplankton ratio, indicating higher fish predation in HN than in LN. Concerning the temperature treatment, we found some indication of higher fish predation with warming in LN, but no clear effects in HN. There was a positive nutrient and warming interaction for the biomass of total zooplankton, large and small Copepoda, and the zooplankton: phytoplankton ratio during the HW, which was attributed to recorded HW-induced fish kill. The pattern after the HW largely followed the HW response. Our results suggest a strong nutrient effect on zooplankton, while the effect of temperature treatment and the 5 • C HW was comparatively modest, and the changes likely largely reflected changes in predation.
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Elevated temperatures and extreme climatic events, such as heat waves, can negatively affect submerged macrophytes. Here, we investigated how submerged macrophytes adapted to three different temperatures: 1) ambient, 2) ca. +3 oC and 3) ca. +4.5 oC responded to a heat wave. After ten years of adaptation, the shoots of two species of submerged macrophytes, Elodea canadensis and Potamogeton crispus, were collected from each of the three temperature treatments and transferred to the two heated treatments for one month. Thereafter, the two heated treatments were exposed to a one-month heat wave with an additional 5 oC temperature increase. For P. crispus, total biomass did not differ among the plants adapted to the different temperatures or between the two heated treatments for the whole duration of the experiment. Plants adapted to the highest temperatures, however, produced a larger number of smaller turions before the heat wave and allocated less biomass to elongation before and after the heat wave. As to E. canadensis, the plants adapted to higher temperatures had higher total biomass before and during the heat wave and allocated more biomass to roots and leaves during the heat wave. Most indicators (e.g. length and biomass) of the macrophyte performance measured during the experiment did not differ between the two heated treatments. In summary, after the ten-year adaptation to higher temperatures, the submerged macrophytes showed adaptive changes in growth and asexual reproduction and responded in a complex way to the heat wave depending on species, growth status and adaptation temperature.
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Determining how climate change will affect global ecology and ecosystem services is one of the next important frontiers in environmental science. Many species already exhibit smaller sizes as a result of climate change and many others are likely to shrink in response to continued climate change, following fundamental ecological and metabolic rules. This could negatively impact both crop plants and protein sources such as fish that are important for human nutrition. Furthermore, heterogeneity in response is likely to upset ecosystem balances. We discuss future research directions to better understand the trend and help ameliorate the trophic cascades and loss of biodiversity that will probably result from continued decreases in organism size.
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During 1989 and 1990 the carbon dynamics in the shallow eutrophic Lake Müggelsee (Berlin) were investigated by analysing the seasonal succession of phytoplankton, metazooplankton, protozooplankton and bacteria. Size fractionated algal primary production and exudation were measured as well as bacterial production in order to calculate the amount of carbon covering the bacterial carbon demand by primary production. The impact of bacterivorous protozoans and metazoans was estimated by comparison of the calculated feeding rate and the bacterial production. Our results show a shift within the metabolic interactions of the microbial food web from winter/spring to summer, indicating a high significance of the protozooplankton as a regulator on bacteria during the colder season, whereas from early summer the influence of metazooplankton dominated by cladocerans was evident in this eutrophic lake.
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Components of the pelagic food web in four eutrophic shallow lakes in two wetland reserves in Belgium (Blankaart and De Maten) were monitored during the course of 1998–1999. In each wetland reserve, a clearwater and a turbid lake were sampled. The two lakes in each wetland reserve had similar nutrient loadings and occurred in close proximity of each other. In accordance with the alternative stable states theory, food web structure differed strongly between the clearwater and turbid lakes. Phytoplankton biomass was higher in the turbid than the clearwater lakes. Whereas chlorophytes dominated the phytoplankton in the turbid lakes, cryptophytes were the most important phytoplankton group in the clearwater lakes. The biomass of microheterotrophs (bacteria, heterotrophic nanoflagellates and ciliates) was higher in the turbid than the clearwater lakes. Biomass and community composition of micro- and macrozooplankton was not clearly related to water clarity. The ratio of macrozooplankton to phytoplankton biomass – an indicator of zooplankton grazing pressure on phytoplankton – was higher in the clearwater when compared to the turbid lakes. The factors potentially regulating water clarity, phytoplankton, microheterotrophs and macrozooplankton are discussed. Implications for the management of these lakes are discussed.
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Shallow lakes are a key component of the global carbon cycle. It is, therefore, important to know how shallow lake ecosystems will respond to the current climate change. Global warming affects not only average temperatures, but also the frequency of heat waves (HW). The impact of extreme events on ecosystems processes, particularly greenhouse gas ( GHG ) emissions, is uncertain. Using the world's longest‐running shallow lake experiment, we studied the effects of a simulated summer HW on the fluxes of carbon dioxide ( CO 2 ), methane ( CH 4 ) and nitrous oxide (N 2 O). The experimental mesocosms had been exposed to different temperature treatments and nutrient loading for 11 years prior to the artificial HW. In general, there was an increase in total GHG emissions during the 1‐month artificial HW, with a significant increase in CO 2 , CH 4 and N 2 O being observed in the shallow lake mesocosms. No significant effect of the HW on CO 2 emissions could be traced, though, in the mesocosms with high nutrient levels. Furthermore, the data suggested that in addition to the direct effect of increased temperature on metabolic processes during the HW, biotic interactions exerted a significant control of GHG emissions. For example, at low nutrient levels, increased CO 2 emissions were associated with low macrophyte abundance, whereas at high nutrient levels, decreased phytoplankton abundance was linked to increased emissions of CO 2 and CH 4 . In contrast to the observable heat‐wave effect, no clear general effect of the long‐term temperature treatments could be discerned over the summer, likely because the potential effects of the moderate temperature increase, applied as a press disturbance, were overridden by biotic interactions. This study demonstrates that the role of biotic interactions needs to be considered within the context of global warming on ecosystem processes.
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ABSTRACT: Elevated temperatures and extreme climatic events, such as heat waves, can negatively affect submerged macrophytes. Here, we investigated how submerged macrophytes adapted to 3 different temperatures (ambient, ca. +3°C and ca. +4.5°C) responded to a heat wave. After 10 yr of adaptation, the shoots of 2 species of submerged macrophytes, Elodea canadensis and Potamogeton crispus, were collected from each of the 3 temperature treatments and transferred to 2 heated treatments for 1 mo. The 2 heated treatments were then exposed to a 1 mo heat wave with an additional 5°C temperature increase. For P. crispus, total biomass did not differ among the plants adapted to the different temperatures or between the 2 heated treatments for the duration of the experiment. Plants adapted to the highest temperatures, however, produced a larger number of smaller turions before the heat wave and allocated less biomass to elongation before and after the heat wave. For E. canadensis, the plants adapted to higher temperatures had higher total biomass before and during the heat wave and allocated more biomass to roots and leaves during the heat wave. Most indicators (e.g. length and biomass) of macrophyte performance measured during the experiment did not differ between the 2 heated treatments. In summary, after the 10 yr adaptation to higher temperatures, the submerged macrophytes showed adaptive changes in growth and asexual reproduction and responded in a complex way to the heat wave depending on species, growth status and adaptation temperature.
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Socio-economic stress from the unequivocal warming of the global climate system could be mostly felt by societies through weather and climate extremes. The vulnerability of European citizens was made evident during the summer heatwave of 2003 (refs,) when the heat-related death toll ran into tens of thousands. Human influence at least doubled the chances of the event according to the first formal event attribution study, which also made the ominous forecast that severe heatwaves could become commonplace by the 2040s. Here we investigate how the likelihood of having another extremely hot summer in one of the worst affected parts of Europe has changed ten years after the original study was published, given an observed summer temperature increase of 0.81 K since then. Our analysis benefits from the availability of new observations and data from several new models. Using a previously employed temperature threshold to define extremely hot summers, we find that events that would occur twice a century in the early 2000s are now expected to occur twice a decade. For the more extreme threshold observed in 2003, the return time reduces from thousands of years in the late twentieth century to about a hundred years in little over a decade.
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According to the Intergovernmental Panel on Climate Change report released in September 2014, unprecedented changes in temperature and precipitation patterns have been recorded globally in recent decades and further change is predicted to occur in the near future, mainly as the result of human activity. In particular, projections show that the Mediterranean climate zone will be markedly affected with significant implications for lake water levels and salinity. This may be exacer-bated by increased demands for irrigation water. Based on long-term data from seven lakes and reservoirs covering a geographical gradient of 52° of latitudes and a literature review, we discuss how changes in water level and salinity related to climate change and water abstrac-tion affect the ecosystem structure, function, biodiversity and ecological state of lakes and reservoirs. We discuss mitigation measures to counteract the negative effects on ecological status that are likely to result from changes in climate and water abstraction practices. Finally, we highlight research required to improve knowledge of the impacts of anthropogenically induced changes on lake water level and consequent changes in salinity.
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Introduction.- Data management and software.- Advice for teachers.- Exploration.- Linear regression.- Generalised linear modelling.- Additive and generalised additive modelling.- Introduction to mixed modelling.- Univariate tree models.- Measures of association.- Ordination--first encounter.- Principal component analysis and redundancy analysis.- Correspondence analysis and canonical correspondence analysis.- Introduction to discriminant analysis.- Principal coordinate analysis and non-metric multidimensional scaling.- Time series analysis--Introduction.- Common trends and sudden changes.- Analysis and modelling lattice data.- Spatially continuous data analysis and modelling.- Univariate methods to analyse abundance of decapod larvae.- Analysing presence and absence data for flatfish distribution in the Tagus estuary, Portugual.- Crop pollination by honeybees in an Argentinean pampas system using additive mixed modelling.- Investigating the effects of rice farming on aquatic birds with mixed modelling.- Classification trees and radar detection of birds for North Sea wind farms.- Fish stock identification through neural network analysis of parasite fauna.- Monitoring for change: using generalised least squares, nonmetric multidimensional scaling, and the Mantel test on western Montana grasslands.- Univariate and multivariate analysis applied on a Dutch sandy beach community.- Multivariate analyses of South-American zoobenthic species--spoilt for choice.- Principal component analysis applied to harbour porpoise fatty acid data.- Multivariate analysis of morphometric turtle data--size and shape.- Redundancy analysis and additive modelling applied on savanna tree data.- Canonical correspondence analysis of lowland pasture vegetation in the humid tropics of Mexico.- Estimating common trends in Portuguese fisheries landings.- Common trends in demersal communities on the Newfoundland-Labrador Shelf.- Sea level change and salt marshes in the Wadden Sea: a time series analysis.- Time series analysis of Hawaiian waterbirds.- Spatial modelling of forest community features in the Volzhsko-Kamsky reserve.
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• 1 A user‐friendly guide to 300 ciliate species (Protozoa, Ciliophora) used as bioindicators by river, lake and waste water ecologists is provided. The guide is an English translation of the flow charts written in German and published by Foissner et al. (1991, 1992, 1994, 1995) in the Ciliate Atlas, a monograph on the ciliates used as bioindicators in the saprobic system. This guide is designed for users not specifically trained in identification of ciliates. Main groups and species are keyed dichotomously on forty‐seven flow charts using simple characters usually recognizable in live specimens. Species with conspicuous characters, e.g. large size or distinct colour, are shown on thirty‐two separate charts designated ‘special keys’. Although the flow charts give a high probability of correct species identifications, these should nevertheless be checked against the detailed figures and descriptions contained in the Ciliate Atlas. • 2 A table with the species keyed and their main ecological characteristics (biomass, food preference, salinity tolerance, preferred occurrence, saprobiological classification) is also provided. • 3 Typical ciliate communities found in natural and polluted habitats are briefly described and figured on thirteen plates. • 4 A detailed systematic index is provided for all taxa mentioned in the flow charts.
Article
1. As grazers on picoplankton and nanoplankton, planktonic ciliates form an important link in pelagic food webs. Ciliate communities may be controlled by predation by metazooplankton. In eutrophic systems, however, where the number of large crustaceans is often low, the mechanisms that regulate ciliate dynamics have rarely been described. 2. We conducted an enclosure experiment with natural and screened (145 μm) summer plankton communities to investigate the effect of the small-sized crustacean zooplankton on ciliate community structure and the microbial loop in a shallow eutrophic lake. 3. The removal of the larger fraction of crustaceans initiated a decrease in total ciliate abundance. At the community level, we observed a substantial increase in large-sized predacious ciliates (>100 μm) and a simultaneous decrease in the abundance of smaller ciliates (<20–40 μm) that were mostly bacterivores and bacterio-herbivores. The compositional shift in the ciliate community, however, did not cascade down to the level of bacteria and edible phytoplankton.
Article
We assessed feeding of planktivorous fish larvae on ciliate protozooplankton in shallow eutrophic Lake Võrtsjärv, Estonia to determine whether ciliates are an important part of larval fish diet. We collected larvae of the most common fish species and examined their gut contents by gut segmentation and epifluorescence microscopy. Ciliates were present in the gut of all fish larvae. Gut segmentation analysis showed clear differences in food composition between gut quarters. The hard-bodied food items were quite evenly distributed in the gut, but the soft-bodied ciliates and rotifers were present only in the first gut quarters. Neglecting differences in prey digestion rate leads to underestimation of diet amount and composition and, especially, to underestimation of the role of protists in food. In Võrtsjärv, ciliates account for ∼ 60% of the total carbon biomass consumed by fish larvae. The food requirement of fish larvae during first feeding stages (May-Jun) would not be met without consumption of ciliates.
Article
Shallow lakes are likely to be strongly impacted by climate changes and, in particular, by increased tempera- tures. To enable realistic experimental studies of the effects of higher temperatures on in-lake processes and dynamics, technologically advanced systems are required. This paper presents design details, operating charac- teristics, and background information on a currently operating experimental flow-through mesocosm system that allows investigation of the interactions between simulated climate warming and eutrophication and their impacts on biological structure and ecosystem processes in shallow lakes. We use 24 mesocosms to combine three temperature scenarios (one unheated and two heated relative to the Intergovernmental Panel on Climate Change climate scenario A2 and A2 + 50%, respectively) and two nutrient levels (enriched and nonenriched). Planktivorous fish (male sticklebacks, Gasterosteus aculeatus) are stocked in accordance with the nutrient level. The water residence time is regulated by the semicontinuous addition of water and is approximately 2.5 mo in each mesocosm. For heating, we use electrically powered heating elements. The heating system has performed well over 16 mo of continuous heating, and seasonal and diurnal temperature variations of the unheated refer- ence mesocosms were paralleled well by the heated mesocosms. The performance of the flow-through system and the heating technique are discussed with special emphasis on strengths, limitations, and potential improvements of the system. To illustrate the performance of the system and its potential, we present data for selected periods on total phosphorus retention in the mesocosms and system primary production and respiration.
Article
The biomass of marine "oligotrichous' ciliates has often been estimated by measuring the cell volume of preserved samples and converting to units of carbon based on theoretical carbon:volume (C:vol) ratios of 0.07-0.11 pg μm-3. Using laboratory cultures of strains of Laboea strobila, Strombidium spp., and Strobilidium spiralis, a C:vol conversion factor of 0.19 pg μm-3 was experimentally derived for cells preserved with 2% vol:vol Lugol's iodine. A C:vol ratio of 0.14 pg μm-3 applies to Formalin-preserved cells. -from Authors
Article
Amounts of C, N, and P in relation to dry weight were measured in natural populations of crustacean zooplankton from a humic lake. The elemental composition within a given species showed little seasonal variation, and experimental starvation or feeding did not cause any significant changes in the P content. C constituted 48 ± 1% of dry weight with only minor variation among species. Mean C:N:P atomic ratios reflected large interspecific differences in P and N content and ranged from 212:39:1 in Acanthodiaptomus denticornis to 85:14:1 in Daphnia longispina. This pattern is quite general and probably constitutional. -from Authors
Article
Quick changes in community composition and population dynamics of planktonic ciliates were studied in the ponds of two fish farms obtaining water from different sources (from a fast flowing river or a stillwater reservoir). Samples were taken at two-day intervals during a short period after springtime filling of the ponds. At the beginning of the investigation period the community in the lotic ponds was dominated by species that favour periphyton or benthos as their habitat. They were gradually replaced by euplanktonic species. In the lentic ponds euplanktonic species dominated throughout our study. The similarity index ISJ between lotic ponds and their inflow was 0.67 at the start of our study but decreased to 0.2 during 14 days. If the inflow was from a stillwater reservoir, the similarity index decreased only moderately. In the lotic ponds ciliate community shifted from bacterivory to algivory while in the case of lentic ponds the situation was the opposite – algivorous species were gradually replaced by bacterivores. Abiotic and biotic factors that determine ciliate community structure were separated. The abiotic features are ruling when the system goes through major changes (in our study the lotic pond system where water flow ceased dramatically). The biotic factors are crucial in more stable systems (in our study the lentic pond system) and can change the community structure in same degree as the abiotic ones.
Article
An analysis of plankton seasonal succession in large shallow eutrophic lake Võrtsjärv (270 km2, mean depth 2.8 m, max. depth 6 m) is presented. Weekly samples for 1995 have been analysed using the PEG model approach. In winter, light was the main factor controlling phytoplankton growth. In early spring phytoplankton was mainly resource-controlled, competition for phosphorus being the main driving force. Ciliates (Paradileptus sp., Strobilidium sp. and Vorticella sp.) were the first herbivores which started to increase in April causing a twofold decline of phytoplankton biomass. The annual maximum of primary production (PP) in early May was probably caused by soluble reactive phosphorus (SRP), regenerated by herbivores, and stirred up from bottom sediments as a result of strong wind stress. This primary production peak provided substrate for further increase of bacterial biomass. The more abundant food supply supported the development of the second spring peak of herbivores (ciliates, rotifers, juvenile copepods) which was followed by the second modest “clear water phase” in late May. Silicon was depleted by the end of May causing a strong decrease in primary production of the diatom-dominated community, whereas the biomass of the cyanophytes increased under the improved nutrient conditions. Some weeks later, inorganic N was depleted and the period of N limitation with the appearance of N-fixing cyanophytes began. The ciliate collapse at the beginning of June coincided with the start of the cladoceran development and with the increase of other metazooplankton groups. This explains the further decrease of the biomass of phytoplankton and bacteria in spite of their high production. Beginning from late June, silicon appeared again and SRP started to occur periodically, while inorganic N remained close to zero until November. During this period, phytoplankton development relied to a great extent on the N-fixation and N-regeneration potential. The collapse of the ciliate community in September removed the top-down control from bacteria and their biomass increased, while the development of cladocerans still suppressed phytoplankton biomass in spite of a quite high PP. In October phytoplankton biomass and chlorophyll a (Chla) increased, SRP was completely depleted by the middle of October reflecting a slow regeneration due to the declined activity of zooplankton in cold water. In November nitrates appeared again, and silicon reached the same level as in spring. The biomass of N-fixing Aphanizomenon skujae decreased while Limnothrix redekei and L. planctonica were quite abundant together with diatoms.
Article
1. 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 probe 5‐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.
Article
Climate change might have profound effects on the nitrogen (N) dynamics in the cultivated landscape as well as on N transport in streams and the eutrophication of lakes. N loading from land to streams is expected to increase in North European temperate lakes due to higher winter rainfall and changes in cropping patterns. Scenario (IPCC, A2) analyses using a number of models of various complexity for Danish streams and lakes suggest an increase in runoff and N transport on an annual basis (higher during winter and typically lower during summer) in streams, a slight increase in N concentrations in streams despite higher losses in riparian wetlands, higher absolute retention of N in lakes (but not as percentage of loading), but only minor changes in lake water concentrations. However, when taking into account also a predicted higher temperature there is a risk of higher frequency and abundance of potentially toxic cyanobacteria in lakes and they may stay longer during the season. Somewhat higher risk of loss of submerged macrophytes at increased N and phosphorus (P) loading and a shift to dominance of small-sized fish preying upon the key grazers on phytoplankton may also enhance the risk of lake shifts from clear to turbid in a warmer North European temperate climate. However, it must be emphasised that the prediction of N transport and thus effects is uncertain as the prediction of regional precipitation and changes in land-use is uncertain. By contrast, N loading is expected to decline in warm temperate and arid climates. However, in warm arid lakes much higher N concentrations are currently observed despite reduced external loading. This is due to increased evapotranspiration leading to higher nutrient concentrations in the remaining water, but may also reflect a low-oxygen induced reduction of nitrification. Therefore, the critical N as well as P loading for good ecological state in lakes likely has to be lower in a future warmer climate in both north temperate and Mediterranean lakes. To obtain this objective, adaptation measures are required. In both climate zones the obvious methods are to change agricultural practices for reducing the loss of nutrients to surface waters, to improve sewage treatment and to reduce the storm-water nutrient runoff. In north temperate zones adaptations may also include re-establishment of artificial and natural wetlands, introduction of riparian buffer zones and re-meandering of channelised streams, which may all have a large impact on, not least, the N loading of lakes. In the arid zone, also restrictions on human use of water are urgently needed, not least on the quantity of water used for irrigation purposes. KeywordsClimate change–Nitrogen loading–Lakes–Ecological state–Modelling–Streams–Subtropics–Temperate–Warm arid
Article
Based on data from 233 Danish lakes, enclosure experiments, full-scaleexperiments and published empirical models we present evidence that top-downcontrol is more important in shallow lakes than in deep lakes, excepting lakeswith a high abundance of submerged macrophytes. The evidence in support is: (1)That at a given epilimnion total phosphorus concentration (TP) the biomass offish per m2 is independent of depth, which means that biomassper m3is markedly higher in shallow lakes. (2) That the biomass of benthic invertebratesis higher in shallow lakes, which means that the benthi-planktivorous fish areless dependent on zooplankton prey than in deep lakes. By their ability to shiftto zooplankton predation their density can remain high even in periods whenzooplankton is scarce and they can thereby maintain a potentially high predationpressure on zooplankton. (3) That the possibilities of cladocerans to escapepredation by vertical migration are less. (4) That the zooplankton:phytoplanktonmass ratio per m2 is lower and presumably then also thegrazing pressure onphytoplankton. (5) That nutrient constraints appear to be weaker, as evidenced bythe fact that at a given annual mean TP, summer TP is considerably higher inshallow lakes, especially in eutrophic lakes lacking submerged macrophytes. (6)That negative feedback on cladocerans by cyanobacteria is lower as cyanobacterialdominance is less frequent in shallow lakes and more easily broken (at least inNorthern temperate lakes), and (7) That top-down control by benthi-planktivorousfish is markedly reduced in lakes rich in submerged macrophytes because theplants serve as a refuge for pelagic cladocerans and encouragepredatory fish at the expense of prey fish. We conclude that manipulation of fishand submerged macrophytes may have substantial impact on lake ecosystems, inparticular in shallow eutrophic lakes. On the contrary, if the conditions formore permanent changes in plant abundance or fish community structure are lackingthe feed-back mechanisms that endeavour a return to the original turbid state willbe particularly strong in shallow lakes.
Article
The abundance and biomass of ciliates, rotifers, cladocerans and copepods were studied in Lake Peipsi and Lake Võrtsjärv, both of which are shallow, turbid and large. Our hypothesis was that in a large shallow eutrophic lake, the ciliates could be the most important zooplankton group. The mean metazooplankton biomass was higher in Peipsi than in Võrtsjärv (mean values and SD, 1.8±0.7 and 1.3±0.6mgWMl−1). In Peipsi, the metazooplankton biomass was dominated by filtrators that feed on large-sized phytoplankton and are characteristic of oligo-mesotrophic waters. In Võrtsjärv, the metazooplankton was dominated by species characteristic of eutrophic waters. The planktonic ciliates in both lakes were dominated by oligotrichs. The biomass of ciliates was much greater in Võrtsjärv (mean 2.3±1.4mgWMl−1) than in Peipsi (0.1±0.08mgWMl−1). Ciliates formed about 60% of the total zooplankton biomass in Võrtsjärv but only 6% in Peipsi. Thus, the food chains in the two lakes differ: a grazing food chain in Peipsi and a detrital food-chain in Võrtsjärv. Consequently, top-down control of phytoplankton can be assumed to be much more important in Peipsi than in Võrtsjärv. When the detrital food chain prevails, the planktonic ciliates become the most important zooplankton group in shallow, eutrophic and large lake. Neglecting protozooplankton can result in serious underestimates of total zooplankton biomass since two-thirds of the zooplankton biomass in Võrtsjärv comprises ciliates.
Article
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.
Article
The Intergovernmental Panel on Climate Change (IPCC) predicts increases in global average surface temperature from 1.1 to 6.4 °C for the year 2100. Here, we focus on the impact of climate warming on eutrophic shallow lakes in the Netherlands, using three representative lakes that cover the full range of lake sizes and depths. In these lakes, temperature has been shown to be the main determinant of hatching and growth of young-of-the-year fish. Because records of water temperature of our study lakes are incomplete, we applied an existing model to predict water temperatures from air temperatures for shallow, wind exposed and holomictic water bodies. To evaluate the implications of our results for marine systems, we also analyzed water temperature data of Marsdiep, a tidal inlet to the Waddensea. The lake water temperature model fitted equally well to all four water bodies. Applying the water temperature model to the period 1961–2006 showed an annual increase of 0.042 °C irrespective of lake size and depth. We extrapolated the consequences of lake warming for the onset of growth of larval bream and the size of young-of-the-year bream at the end of the year using an existing fish hatching and growth model. Both models were tested against data from Lake Tjeukemeer, which is intermediate in size compared to Lake Zwemlust and Lake IJsselmeer. The main conclusions of this study are that 1) there is a very tight coupling between air and water temperatures in Dutch shallow lakes, irrespective of their size, resulting in highly similar patterns of lake temperature and a direct translation of climate warming into lake warming; 2) on average water temperature has increased by 2 °C in the period 1961–2006; 3) temperature patterns in the tidal inlet showed a surprising resemblance with the lake temperature patterns, the coastal marine system essentially behaving like an extremely large lake; 4) there are, however, strong seasonal patterns in the extent of warming in a given period of the year; 5) lake warming leads to ca. 3 weeks earlier onset of growth and 20 mm larger sizes in bream during 1971–2006 under the assumption of temperature limited growth in these eutrophic ecosystems.
Article
For at least 200 years, since the time of Malthus, population growth has been recognized as providing a critical link between the performance of individual organisms and the ecology and evolution of species. We present a theory that shows how the intrinsic rate of exponential population growth, and the carrying capacity, r(max) K, depend on individual metabolic rate and resource supply rate. To do this, we construct equations for the metabolic rates of entire populations by summing over individuals, and then we combine these population- level equations with Malthusian growth. Thus, the theory makes explicit the relationship between rates of resource supply in the environment and rates of production of new biomass and individuals. These individual-level and population- level processes are inextricably linked because metabolism sets both the demand for environmental resources and the resource allocation to survival, growth, and reproduction. We use the theory to make explicit how and why r(max) exhibits
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Article
Lakes have, rather grandly, been described as sentinels, integrators and regulators of climate change (Williamson et al., Limnol. Oceanogr. 2009; 54: 2273-82). Lakes are also part of the continuum of the water cycle, cogs in a machine that processes water and elements dissolved and suspended in myriad forms. Assessing the changes in the functioning of the cogs and the machine with respect to these substances as climate changes is clearly important, but difficult. Many other human-induced influences, not least eutrophication, that impact on catchment areas and consequently on lakes, have generally complicated the recording of recent change in sediment records and modern sets of data. The least confounded evidence comes from remote lakes in mountain and polar regions and suggests effects of warming that include mobilisation of ions and increased amounts of phosphorus. A cottage industry has arisen in deduction and prediction of the future effects of climate change on lakes, but the results are very general and precision is marred not only by confounding influences but by the complexity of the lake system and the infinite variety of possible future scenarios. A common conclusion, however, is that warming will increase the intensity of symptoms of eutrophication. Direct experimentation, though expensive and still unusual and confined to shallow lake and wetland systems is perhaps the most reliable approach. Results suggest increased symptoms of eutrophication, and changes in ecosystem structure, but in some respects are different from those deduced from comparisons along latitudinal gradients or by inference from knowledge of lake behaviour. Experiments have shown marked increases in community respiration compared with gross photosynthesis in mesocosm systems and it may be that the most significant churnings of these cogs in the earth-air-water machine will be in their influence on the carbon cycle, with possibly large positive feedback effects on warming.