Meso-eutrophic Lake Research Articles

Dependence of evolution of Cyanobacteria superiority on temperature and nutrient use efficiency in a meso-eutrophic plateau lake

Algal blooms in lakes have been a challenging environmental issue globally under the dual influence of human activity and climate change. Considerable progress has been made in the study of phytoplankton dynamics in lakes; The long-term in situ evolution of dominant bloom-forming cyanobacteria in meso-eutrophic plateau lakes, however, lacks systematic research. Here, the monthly parameters from 12 sampling sites during the period of 1997–2022 were utilized to investigate the underlying mechanisms driving the superiority of bloom-forming cyanobacteria in Erhai, a representative meso-eutrophic plateau lake. The findings indicate that global warming will intensify the risk of cynaobacteria blooms, prolong Microcystis blooms in autumn to winter or even into the following year, and increase the superiority of filamentous Planktothrix and Cylindrospermum in summer and autumn. High RUETN (1.52 Biomass/TN, 0.95–3.04 times higher than other species) under N limitation (TN < 0.5 mg/L, TN/TP < 22.6) in the meso-eutrophic Lake Erhai facilitates the superiority of Dolichospermum. High RUETP (43.8 Biomass/TP, 2.1–10.2 times higher than others) in TP of 0.03–0.05 mg/L promotes the superiority of Planktothrix and Cylindrospermum. We provided a novel insight into the formation of Planktothrix and Cylindrospermum superiority in meso-eutrophic plateau lake with low TP (0.005–0.07 mg/L), which is mainly influenced by warming, high RUETP and their vertical migration characteristics. Therefore, we posit that although the obvious improvement of lake water quality is not directly proportional to the control efficacy of cyanobacterial blooms, the evolutionary shift in cyanobacteria population structure from Microcystis, which thrives under high nitrogen and phosphorus conditions, to filamentous cyanobacteria adapted to low nitrogen and phosphorus levels may serve as a significant indicator of water quality amelioration. Therefore, we suggest that the risk of filamentous cyanobacteria blooms in the meso-eutrophic plateau lake should be given attention, particularly in light of improving water quality and global warming, to ensure drinking water safety.

Spatiotemporal dynamics of phytoplankton biomass and community succession for driving factors in a meso-eutrophic lake

Effects of climate change and nutrient load caused by human activities on lake phytoplankton blooms have attracted much attention globally. However, their roles and synergistic effects on phytoplankton biomass and community historical succession are not well understood, especially for meso-eutrophic plateau lakes. In this study, a multi-year (1997–2022) monthly dataset including hydro-chemical and meteorological indicators of the meso-eutrophic plateau lake Erhai in China, was used to explore the contributions of climate change and nutrients on phytoplankton biomass variation and community succession. Phytoplankton biomass increased from 1997 to 2006, slowly decreased from 2006 to 2015, then increased again from 2015 to 2022, according to a generalised additive model (GAM). Alongside warming, nitrogen, phosphorus and organic matter are key drivers of long-term interannual variation in phytoplankton biomass and historical succession of the phytoplankton community. The extensive blooms in recent years were strongly associated with both organic matter accumulation and global warming. Phytoplankton biomass in northern and southern districts was greater than in central areas, with Cyanophyta and Pyrrophyta dominating in the north and Chlorophyta prevalent in the south. Since 2015, phytoplankton diversity has increased significantly, and biomass has declined in the southern district but increased markedly in the northern district. Spatial heterogeneity was caused by the spatial distribution of nutrients and the buoyancy regulation capacity of cyanobacteria. The results demonstrate that bloom mitigation responds strongly to nitrogen and phosphorus control in meso-eutrophic lakes, therefore preventing and controlling blooms through nitrogen and phosphorus reduction is still an effective measure. Given the accumulation of organic matter in recent years, synergistic control of organic matter and total nitrogen and phosphorus could effectively reduce the risk of cyanobacterial and dinoflagellate blooms.

Changes in native fish communities in response to the presence of alien brown bullhead (Ameiurus nebulosus) in four lakes (Poland)

The aim of the study was to determine changes in the abundance of Ameiurus nebulosus and native fish in four lakes after 4–7 years. It was hypothesised that A. nebulosus would be the dominant species of fish in various types of lakes. The study was conducted in the summer of 2014 and 2018–2021, using Nordic multi-mesh gillnets. We indicated that relative numbers and biomass of A. nebulosus decreased in the oligo-mesotrophic lake, while increased in lakes of higher trophic conditions. Body weight and total length of A. nebulosus fluctuated from 3.2 to 283.3 g and 64 to 267 mm, respectively. The coefficient of condition of this species varied widely from 0.2 to 1.8 with the highest and lowest values in the meso-eutrophic lake. Ameiurus nebulosus accounted for 0.2–34.1% of the total numbers and 2.4–36.5% of the total biomass of the fish community. In the mesotrophic and meso-eutrophic lakes, A. nebulosus was a dominant component of the fish community after 7 years. The percentage contribution of A. nebulosus to the total numbers of fish decreased with the increasing trophic status of the studied lakes. Our study showed that A. nebulosus could be one of the factors responsible for a decrease in the number of native fish species and a change in the taxonomic structure of native fish in lakes of different trophic status (from oligo-mesotrophy to eutrophy).

Fish Species Richness in Polish Lakes

Global warming, eutrophication, fisheries overexploitation, species invasions, and habitat loss are the major threats to freshwater biodiversity. The aim of this study was to determine the species richness and diversity of fish in 535 Polish lakes of different morphometry (area of more than 50 ha and a maximum depth ranging from 0.4 to 108.5 m) and trophic status (from oligotrophy to hypereutrophy). A total of 39 fish species were found in the studied lakes, among which eight species were alien invasive. The Shannon diversity index varied between 0 and 2.04.The most common and frequent species were Rutilus rutilus (99.8% frequency) and Perca fluviatilis (99.6% frequency). Ten fish species, including five alien ones, were characterized by a very low frequency (&lt;1%). The number of fish species in single lakes ranged from 1 to 19. In most of the studied lakes, 11 and 12 species (104 and 108 lakes, respectively) were caught. The richest taxonomic composition (19 species) was recorded in the meso-eutrophic lake with an area of 80 ha and a maximum depth of 34.4 m, slightly poorer (18 species) in the hypereutrophic lake with an area of 168 ha and a maximum depth of 2.7 m. The poorest taxonomic composition (one species) was found in a lake with low conductivity and circumneutral pH. Statistical analysis showed that the number of fish species decreased with increasing eutrophication conditions of the studied lakes, while it increased with an increasing area and the maximum depth of these lakes.

Remote sensing of dissolved CO2 concentrations in meso-eutrophic lakes using Sentinel-3 imagery

Satellite observation can significantly reduce the uncertainties in CO2 emission estimations compared to insufficient field data. However, big challenges remain in developing remote sensing-based models for mapping concentrations of dissolved carbon dioxide (cCO2) in lakes at regional or global scales. We developed a cCO2 estimation model using Sentinel-3-derived lake environmental variables and near-synchronous field cCO2 data from 16 lakes in the middle and lower reaches of the Yangtze and Huai River (ML_YHR) basins in Eastern China (N = 248). Stepwise quadratic polynomial regressions of several combinations of chlorophyll-a (Chl-a), water temperature (Tw), Secchi disk depth (ZSD), and photosynthetic active radiation (PAR)-related variables were tested and validated to select the best approach. The final model showed high performance in calibration and validation (R2 > 0.72, RMSE < 6.35 μmol L−1, MAPE < 30.31%). The model sensitivity analysis, based on Monte Carlo simulations, showed the model's estimated bias as <25% based on uncertainties of all input variables. Spatial and temporal dynamics of dissolved CO2 concentrations in 113 lakes (≥ 10 km2) in the ML_YHR basins were mapped from 2016 to 2021 using the Sentinel-3 data. The result showed that CO2 concentrations were low in the summer and autumn but high in the winter and spring with dramatic variations (e.g., mean coefficient of variation: 52.59%). The annual mean CO2 concentrations of lakes revealed that about 28% of the lakes acted as weak atmospheric CO2 sinks (14.96 ± 1.13 μmol L−1) while the rest were sources (19.22 ± 2.02 μmol L−1), compared with a mean concentration of CO2 atmospheric equilibrium (16.29 μmol L−1). CO2 concentrations decreased with increasing eutrophication and decreasing lake size (p < 0.05). This study advances current knowledge about CO2 emissions from emerging meso-eutrophic lakes and shows how satellite remote sensing can expand the spatiotemporal coverage of lake CO2.

A regional model to predict the occurrence of natural events: Application to phytoplankton blooms in continental waterbodies

There are significant social, economic and environmental costs related to phytoplankton blooms, particularly when they are dominated by cyanobacteria. However, the climatic, physiographic and morphological drivers involved in bloom phenology create complex spatiotemporal patterns in biomass and taxonomic composition, making monitoring and forecasting challenging. This complexity also limits the ability of process-based algorithms to model bloom phenology. Stochastic approaches and predictive modelling are valuable risk management tools for natural events. This paper presents a novel model to estimate the conditional density of phytoplankton blooms based on environmental covariates, namely the physiography and climate descriptors of lake watersheds. The goal was to provide a tool to project future scenarios of bloom phenology in response to climate change and anthropogenic developments, and to test the efficiency of mitigating approaches. Specifically, we developed a non-stationary regional model to estimate the probability of bloom occurrence in 580 lakes in Quebec, Canada, and to study the impact of physiographic or climate changes over our reference period and future horizons. Results show that the regional model is more precise and accurate than local models, which are usually used in frequency analyses of extreme values. Simulations conducted for different climatic and physiographic scenarios on the watershed of Lake Brome indicate a 65% increase in bloom frequency on the horizon of years 2080–2100. The model also evaluates the effects of different environmental disturbances on bloom phenology, such as agriculture or settlement increase in the watershed. Disturbance case studies were carried out on lakes with different trophic levels, physiographic and climatic characteristics. Simulations indicate that bloom frequency in a highly urbanized meso-eutrophic lake (Lake Brome) and a eutrophic lake with a watershed dominated by agriculture (Missisquoi Bay) would be more responsive to changes in climate rather than land cover, although physiographic disturbances would still generate considerable effects. A meso-eutrophic lake with a watershed dominated by forest (Lake Aylmer) would neither respond to increases in agriculture nor settlement but would be most affected by increases in degree days. Another scenario focused on a highly forested oligo-mesotrophic lake (Lake St. Jean). Bloom phenology in this lake was most affected by disturbances in agriculture or settlement land use. Overall, these results suggest that lakes with a high level of eutrophication are the least responsive to the pressures resulting from land cover changes.

Performance and ecological impacts of benthic barriers for the control of an invasive plant in a small urban lake

Yellow Floating Heart (YFH), Nymphoides peltata, is a rooted aquatic plant that is not native to North America, and can quickly establish nuisance populations in shallow lakes, rivers, and wetlands. There are few documented methods for effectively eradiating or controlling YFH. Little Albro Lake is a small (3 ha), shallow (<5 m deep) meso-eutrophic lake in Dartmouth, Nova Scotia, Canada that experiences an annual YFH infestation covering >50% of the lake during the growing season. A pilot study was conducted during the 2021 growing season to: (i) assess the feasibility of using benthic barriers to control YFH growth, and (ii) investigate the potential impacts of benthic barriers on ecosystem components. Two commercially available benthic barriers (Aquascreen, a permeable barrier, and Lake Bottom Blanket, an impermeable barrier) were tested in shallow (1 m water depth) and deep (3 m water depth) areas of the lake. A total of 18 test plots (6 permeable, 6 impermeable, 6 control), each measuring 3 m × 3 m, were established in early May 2021, and monitored throughout the growing season (May–September). Both types of barriers were effective in reducing YFH growth, with barriered plots possessing significantly less YFH coverage than control plots. Inspection of the permeable barriers after their removal from the lake, however, revealed that YFH had been able to grow through this type of barrier material. Several maintenance issues were also noted with both barriers including: (i) gas build-up under the barriers, which caused billowing, and (ii) an accumulation of sediment on top of the barriers and growth of YFH through these sediment layers. Both issues would need to be managed during a full-scale benthic barrier application program. An environmental effects monitoring program was also undertaken to understand the lake ecosystem and impacts of the barriers on the chemical and biological properties of the lakebed. The barriers had measurable impacts on the lakebed and generated lower oxidation reduction potential (ORP) in sediments, as compared to control plots with no barriers. Reduced ORP in lake sediments could facilitate the mobilization of redox-sensitive metals, such as arsenic and iron. There were only minor differences in benthic macroinvertebrate populations when comparing barriered and control plots. The bacterial alpha-diversity of the lakebed sediment was shown to differ by depth, with the shallow zone having higher observed ASVs and diversity levels. However, within the two depth zones, the barriers did not appear to have a large impact on bacterial community composition and potential functionality. In conclusion, benthic barriers can be used to prevent YFH growth, however barrier installations require maintenance and may reduce sediment ORP, potentially leading to release of redox-sensitive metals and nutrients.

Biogeochemistry of selenium compounds in the water column of warm monomictic Lake Kinneret

The biogeochemistry of dissolved selenium (Se) was investigated over 3 years (2015–2017) in the subtropical, warm monomictic and meso-eutrophic Lake Kinneret (Sea of Galilee, Israel). We monitored seasonal variation and vertical distribution of dissolved total Se (T.Se), inorganic oxyanions (Se(IV) & Se(VI)), reduced Se fraction (Red.Se), organic (Org.Se) and volatile Se compounds. T.Se varied between ~ 100 and 160 ng L−1 with Red.Se comprising 40–80% of the Se inventory, and Se(VI) dominating over Se(IV) most of the time. The variation in T.Se and species correlated with winter holomixis vs. summer fall stratification periods. The annual cycle includes: (a) increase of T.Se from fall/winter to spring, representing increased allochthonous Se input flux, along with Se recycling via holomixis; (b) decrease of T.Se from spring to the end of the year, representing the diminishing Se inputs and the evolving output fluxes to the lake’s bottom and to the atmosphere. Org.Se variations are directly associated with Chlorophyll-a and primary production attesting for the significant role of phytoplankton activity in the Se cycle. An important Se output flux comprises spring to summer Se uptake by phytoplankton and further volatile compounds production and volatilization accounting for ~ 10% of estimated Se input. The similarity of total dissolved Se concentrations in this work and from mid 1990s attests for long-term stability of the Se inventory. The TVSe concentrations in lacustrine systems being similar to that of estuary systems, the biological role of phytoplankton and eventually the degradation of organic material may produce similar fluxes of volatile Se to the atmosphere.

Short Communication: Assessing phytoplankton species structure in trophically different water bodies of South Ural, Russia

Abstract. Kostryukova A, Mashkova I, Belov S, Shchelkanova E, Trofimenko V. 2021. Short Communication: Assessing phytoplankton species structure in trophically different water bodies of South Ural, Russia. Biodiversitas 22: 3530-3538. The study aims to analyze the species structure of the phytoplankton communities of four water bodies in South Ural (Lakes-Turgoyak, Uvildy, Ilmenskoe and Shershnevskoe reservoir). These water bodies are characterized by different trophic states and levels of anthropogenic impact. Lake Turgoyak is oligotrophic; Lake Uvildy is oligomesotrophic. Both water bodies are protected areas and natural monuments. But tourism and recreation are not prohibited on their territories. The mesoeutrophic Lake Ilmenskoe is partially located within the Ilmen State Reserve, and it experiences less anthropogenic impact. The eutrophic Shershnevskoe reservoir is located within the boundaries of the city of Chelyabinsk. It is used as a source of drinking water. Cyanobacteria was the dominant division in the eutrophic Shershnevskoe reservoir. Bacillariophyta dominated in the plankton communities in oligotrophic Lake Turgoyak and oligomesotrophic Lake Uvildy. Green and blue-green algae biodiversity increased in the oligomesotrophic Lake Uvildy. For the mesoeutrophic Lake Ilmenskoe, diatom algae are dominant, but a higher proportion of Chlorophyta (especially Cyanobacteria) was revealed. Species similarity among phytoplankton communities in the given lakes was studied through cluster analysis based on the Sorensen-Czekanowski coefficient. The higher level of similarity between plankton species compositions could be explained by their locality rather than their trophic status.

Temperature, phytoplankton density and bacteria diversity drive the biotransformation of micropollutants in a lake ecosystem

For most micropollutants (MPs) present in surface waters, such as pesticides and pharmaceuticals, the contribution of biotransformation to their overall removal from lake ecosystems is largely unknown. This study aims at empirically determining the biotransformation rate constants for 35 MPs at different periods of the year and depths of a meso-eutrophic lake. We then tested statistically the association of environmental parameters and microbial community composition with the biotransformation rate constants obtained. Biotransformation was observed for 14 out of 35 studied MPs for at least one sampling time. Large variations in biotransformation rate constants were observed over the seasons and between compounds. Overall, the transformation of MPs was mostly influenced by the lake's temperature, phytoplankton density and bacterial diversity. However, some individual MPs were not following the general trend or association with microorganism biomass. The antidepressant mianserin, for instance, was transformed in all experiments and depths, but did not show any relationship with measured environmental parameters, suggesting the importance of specific microorganisms in its transformation. The results presented here contribute to our understanding of the fate of MPs in surface waters and thus support improved risk assessment of contaminants in the environment.

Retrospective analysis of phytoplankton community structure in water bodies of South Ural (Russia)

The current paper considers changes of phytoplankton community structure in three South Ural (Russia) water bodies different in trophicity: Lake Uvildy, Lake Ilmenskoe, and Shershnevskoe Reservoir. There is no clear relation between the changes of species structure of phytoplankton communities and water-bodies trophicity. The least significant changes in the phytoplankton community structure are registered for the mesoeutrophic Lake Ilmenskoe, which is located on the territory of the State Reserve. Diatomic, green and blue-green algae groups are the most diverse in composition in the studied periods of 1936-1937, 1964-1984 and 1998-2016. But for the last 20 years, Cyanophyta has increased its contribution into the phytoplankton number and biomass of Lake Ilmenskoe. The representatives of the Bacillariophyta group dominate in oligotrophic Lake Uvildy. In 1965-1985, the Chlorophyta group was the most abundant in Shershnevskoe reservoir (34 % of the total number of species), Bacillariophyta -32 % and Cyanophyta – 18 %. In 2003-2005 and 2017 the number of green algae increased (Chlorophyta – 40 %) and that of diatoms decreased (Bacillariophyta -21%) with the number of blue-green algae being unchanged (Cyanophyta -19 %). The ecological status of the Shershenevskoe Reservoir has transformed from a long-term sustainable mesotrophic to eutrophic. So, for oligotrophic lake Uvildy and mesoeutrophic lake Ilmenskoe, Bacillariophyta group is characterized by the greatest taxonomic diversity. While for eutrophic Shershnevskoe Reservoir the absolute abundance of Chlorophyta algae group is marked, which is growing in time. The growing importance of blue-green algae is one more feature of the change of a trophic status.

Zebra or quagga mussel dominance depends on trade-offs between growth and defense-Field support from Onondaga Lake, NY.

Two invasive mussels (zebra mussel, Dreissena polymorpha and quagga mussel D. rostriformis bugensis) have restructured the benthic habitat of many water bodies in both Europe and North America. Quagga mussels dominate in most lakes where they co-occur even though zebra mussels typically invade lakes first. A reversal to zebra mussel over time has rarely been observed. Laboratory experiments have shown that quagga mussels grow faster than zebra mussels when predator kairomones are present and this faster growth is associated with lower investment in anti-predator response in quagga mussels than zebra mussels. This led to the hypothesis that the dominance of quagga mussels is due to faster growth that is not offset by higher vulnerability to predators when predation rates are low, as may be expected in newly colonized lakes. It follows that in lakes with high predation pressure, the anti-predatory investments of zebra mussels should be more advantageous and zebra mussels should be the more abundant of the two species. In Onondaga Lake, NY, a meso-eutrophic lake with annual mussel surveys from 2005 to 2018, quagga mussels increased from less than 6% of the combined mussel biomass in 2007 to 82% in 2009 (from 3 to 69% by number), rates typical of this displacement process elsewhere, but then declined again to 11–20% of the mussel biomass in 2016–2018. Average total mussel biomass also declined from 344–524 g shell-on dry weight (SODW)/m2 in 2009–2011 to 34–73 g SODW/m2 in 2016–2018, mainly due to fewer quagga mussels. This decline in total mussel biomass and a return to zebra mussel as the most abundant species occurred as the round goby (Neogobius melanostomus) increased in abundance. Both the increase to dominance of quagga mussels and the subsequent decline following the increase in this molluscivorous fish are consistent with the differences in the trade-off between investment in growth and investment in defenses of the two species. We predict that similar changes in dreissenid mussel populations will occur in other lakes following round goby invasions, at least on the habitats colonized by both species.

Benthic-pelagic coupling in lake energetic food webs

Understanding how energy and matter flow among habitats is a central issue in ecology. In lake ecosystems, benthic-pelagic coupling (B-P coupling) was mainly studied based on the diets of top consumers at a population level or through food chains. However, how B-P coupling operates at the ecosystem level is largely unknown.In the present study, we revealed B-P coupling within an energetic food web framework, combining stable isotope analyses and mass balanced model. We constructed the energetic food webs of two large shallow lakes of different trophic status based on field survey data. We also defined benthic and pelagic components based on the proportion of consumer energy uptake from phytoplankton (benthic: <50%; pelagic:>50%; benthivore: <20%; planktivore:>80%; coupler: 20–80%) and quantified the energy flux through B-P coupling in the two lake food webs.The total consumption was estimated to be 699 t/km2/y in Lake Erhai (mesoeutrophic lake) and 2094 t/km2/y in Lake Dianchi (hypereutrophic lake), and the B-P coupling energy was 405 t/km2/y and 213 t/km2/y, respectively. In these lakes, B-P coupling occurred on multiple trophic levels; lower trophic level consumers contributed the largest proportion (90% and 98%), while top consumers were of limited importance; most coupling links were weak, and energy exchange was highly asymmetric with the total amount of energy exported from benthic part to pelagic part being over 4 folds of the counter flux.The quantity and pattern of B-P coupling vary between the mesoeutrophic and hypereutrophic lakes. In terms of energy flux per unit area, the total system throughput in the mesoeutrophic lake (Lake Erhai) was 3.73 times of that in the hypereutrophic lake (Lake Dianchi), while the proportion of coupling energy was much lower in the former (19%) than the latter (31%). A greater energy flux through pelagic-to-benthic pathways was found in the hypereutrophic lake, and most of the coupling energy was contributed by consumers at higher trophic levels. Besides, the coupling strength was stronger in the hypereutrophic than the mesoeutrophic lake.We showed for the first time how B-P coupling operates in lake energetic food webs. Our results provided new insights into understanding the energy flux through B-P coupling of lake ecosystems, and how such coupling could be changed by environmental disturbances. We also provided a new approach to reveal habitat coupling within an energetic food web framework.

Wide-spread inconsistency in estimation of lake mixed depth impacts interpretation of limnological processes

The mixed layer, or epilimnion, is a physical concept referring to an isothermal layer at the surface of a water body. This concept is ubiquitous within limnology, is fundamental to our understanding of chemical and ecological processes, and is an important metric for water body monitoring, assessment and management. Despite its importance as a metric, many different approaches to approximating mixed depth currently exist. Using data from field campaigns in a small meso-eutrophic lake in the UK in 2016 and 2017 we tested whether different definitions of mixed depth resulted in comparable estimates and whether variables other than temperature could be assumed to be mixed within the layer. Different methods resulted in very different estimates for the mixed depth and ecologically important variables were not necessarily homogenously spread through the epilimnion. Furthermore, calculation of simple ecologically relevant metrics based on mixed depth showed that these metrics were highly dependent on the definition of mixed depth used. The results demonstrate that an idealised concept of a well-defined fully mixed layer is not necessarily appropriate. The widespread use of multiple definitions for mixed depth impairs the comparability of different studies while associated uncertainty over the most appropriate definition limits the confirmability of studies utilising the mixed depths.

Structural and functional microbial diversity along a eutrophication gradient of interconnected lakes undergoing anthropopressure

We present the results of an analysis of the 16S rRNA-based taxonomical structure of bacteria together with an analysis of carbon source utilization ability using EcoPlate (Biolog, USA) metabolic fingerprinting assessment against the backdrop of physicochemical parameters in fifteen interconnected lakes. The lakes exhibit a wide spectrum of trophic gradients and undergo different intensities of anthropopressure. Sequences of V3–V4 16S rRNA genes binned by taxonomic assignment to family indicated that bacterial communities in the highly eutrophicated lakes were distinctly different from the bacterial communities in the meso-eutrophic lakes (ANOSIM r = 0.99, p = 0.0002) and were characterized by higher richness and more diverse taxonomical structure. Representatives of the Actinobacteria, Proteobacteria, Cyanobacteria, Planctomycetes, Verrucomicrobia, Bacteroides phyla predominated. In most cases their relative abundance was significantly correlated with lake trophic state. We found no similar clear relationship of community-level physiological profiling with lake trophic state. However, we found some significant links between the taxonomic and metabolic structure of the microbes in the studied lakes (Mantel’s correlation r = 0.22, p = 0.006). The carbon source utilization ability of the studied microorganisms was affected not only by the taxonomic groups present in the lakes but also by various characteristics like a high PO43− concentration inhibiting the utilization of phosphorylated carbon.

Environmental factors responsible for the gyrogonite formation by an endangered macroalga, Lychnothamnus barbatus, a fertility indicator of past and present lacustrine ecosystems

Gyrogonites (calcified oospores) of charophytes are commonly used in palaeoecology. Although, the study of morphometry and gyrogonite production by extant charophytes is limited. This concerns the genus Lychnothamnus, frequent in the past but contemporarily represented only by L. barbatus, the rare and endangered species applied in assessment of water quality as a bioindicator of oligo-mesotrophic lakes. In this study two hypotheses were verified: (1) the length and width of L. barbatus gyrogonites increase with increasing depth; (2) at the deeper sites, L. barbatus produces more numerous gyrogonites compared to shallower lake areas.Gyrogonites were picked from L. barbatus thalli (n = 170) collected at three depths (2-3 m, 3-4 m and 4-5 m) and three permanent transects in a meso-eutrophic lake hosting one of few largest populations of the species (Lake Kuźnickie). Subfossil gyrogonites (n = 730) were also analyzed from three sediment cores taken at the same depths. The study was conducted in autumn 2016, spring, summer and autumn 2017. In addition to depth, photosynthetically active radiation (PAR), nutrients and other indices of water chemistry, and interspecific competition were studied.Studied L. barbatus gyrogonites were more circular and wider compared to existing literature data. Gyrogonites production was positively correlated with depth. The smallest, but most numerous gyrogonites occurred at the deepest sites (ANOVA). Subfossil gyrogonites were slightly wider and more circular compared to extant gyrogonites. Reversely to depth, PAR was positively correlated with sizes of gyrogonites and negatively correlated with amount of gyrogonites. Gyrogonites formation was negatively correlated with ammonium ion concentration and Myriophyllum spicatum biomass, but positively with phosphate concentrations.Our results supplement the gaps in the knowledge regarding the ecology of L. barbatus because the species produced numerous gyrogonites in meso-eutrophic waters. We postulate that L. barbatus gyrogonites can be applied in ecology and palaeoecology to interpret water depth and trophic status.

Internal Loading of Phosphorus from Bottom Sediments of Two Meso-eutrophic Lakes

The aim of the study was to determine the seasonal and spatial variability of phosphorus release from bottom sediments of two lakes in Poland (Wielkopolska Region): Lusowskie Lake and Prawe Lake. The comparison of results from these two lakes could have been reliably made, because they were characterized by a similar trophic state (meso-eutrophic), were located in the same climatic zone, and were examined at the same time but differed in terms of morphometry (area, depth, and shape) as well as land use of catchment area. These dimictic lakes were characterized by hypolimnetic oxygen deficits in summer. The internal loading of phosphorus was analysed on the basis of ex situ experiments with intact cores of bottom sediments sampled at two stations, situated in the profundal (the deepest place in the lake) and in the littoral (2.0 m depth). The results indicated that a higher phosphorus load was released from bottom sediments in the profundal zone than in the littoral zone of both lakes. Phosphorus release from the profundal zone was twofold higher in Prawe Lake than in Lusowskie Lake. It reached 2.6 mg P m−2 d−1 in spring and winter in the larger and deeper Lusowskie Lake, compared to 6.04 mg P m−2 d−1 in autumn in the smaller and shallower Prawe Lake. In the littoral zone, phosphorus release reached 1.67 mg P m−2 d−1 and 0.16 mg P m−2 d−1 in both lakes, respectively. Differences in phosphorus internal loading between the lakes were due to differences in the stability of thermal stratification, time of water mixing and oxygen concentration in the depth profile of the lake.

The Broad Habitat Spectrum of the CL500-11 Lineage (Phylum Chloroflexi), a Dominant Bacterioplankton in Oxygenated Hypolimnia of Deep Freshwater Lakes.

CL500-11 (phylum Chloroflexi) is one of the most ubiquitous and abundant bacterioplankton lineages in deep freshwater lakes inhabiting the oxygenated hypolimnion. While metagenomics predicted possible eco-physiological characteristics of this uncultured lineage, no consensus on their ecology has so far been reached, partly because their niche is not clearly understood due to a limited number of quantitative field observations. This study investigated the abundance and distribution of CL500-11 in seven deep perialpine lakes using catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). Samples were taken vertically (5–12 depths in each lake) and temporally (in two lakes) at the deepest point of the lakes located in Switzerland, Italy, and Austria with varying depth, trophic state, mixing regime, and water retention time. The results showed a dominance of CL500-11 in all the lakes; their proportion to total prokaryotes ranged from 4.3% (Mondsee) to 24.3% (Lake Garda) and their abundance ranged from 0.65 × 105 (Mondsee) to 1.77 × 105 (Lake Garda) cells mL-1. By summarizing available information on CL500-11 occurrence to date, we demonstrated their broad habitat spectrum, ranging from ultra-oligotrophic to meso-eutrophic lakes, while low abundances or complete absence was observed in lakes with shallow depth, low pH, and/or short water retention time (<1 year). Together with available metagenomic and geochemical evidences from literatures, here we reviewed potential substrates supporting growth of CL500-11. Overall, the present study further endorsed ubiquity and quantitative significance of CL500-11 in deep freshwater systems and narrowed the focus on their physiological characteristics and ecological importance.

Impact of enhanced summer temperatures on the distribution and structure of zooplankton communities in the heated stratified lakes: Implications for climate change

Long-term studies demonstrated that temperature increases of 3–6 °C above natural levels caused reduction in zooplankton biomass. We hypothesized that large-bodied species would respond more strongly to temperature increases than small-bodied species because they are less adapted to high temperatures. Studies were conducted in three similar stratified meso-eutrophic lakes with different thermal regimes. Enhanced temperature, migrations, food abundance and dissolved oxygen concentrations were analyzed as potential factors that could affect zooplankton biomass. The warmest lake differed from the other lakes by lower total biomass of zooplankton less abundance of large-bodied zooplankton species, smaller population body sizes of abundant cladoceran species and higher food concentrations. Day and night abundances of zooplankton did not differ between the vertical strata and between the pelagic and littoral zones in the three study lakes suggesting that zooplankton did not vertical or horizontal migrations. We suggest that decreases of dissolved oxygen below the epilimnion prevented zooplankton from vertically migrating. As a result, zooplankton accumulated in the epilimnion where temperatures were higher than in the lower strata. Regression analysis showed that temperature had a significant negative impact on the total biomass of zooplankton in the epilimnion of the warmest study lake. Therefore, our results are in accordance with the ecological Bergmann’s and James’ rules dealing with the temperature-size relationships.

Dinâmica do fitoplâncton e evolução trófica de reservatório no Semiárido brasileiro

O presente estudo objetivou analisar a dinâmica de grupos funcionais do fitoplâncton e a variação do grau de trofia em reservatório do semiárido brasileiro durante estiagem prolongada. O estudo foi realizado no reservatório de Cordeiro, no município do Congo, Paraíba, com amostragens no período de junho a dezembro de 2015, com frequência trimestral, no ponto próximo ao barramento do reservatório. As espécies do fitoplâncton foram identificadas e quantificadas para obtenção da densidade, posteriormente as espécies foram classificadas de acordo com suas estratégias e grupos funcionais. O estado trófico foi determinado à partir do Índice do estado trófico para ambientes tropicais. O período de estudo foi caracterizado pela redução dos níveis de água acumulados no reservatório. A transparência do Secchi foi baixa, cujos valores foram inferiores a 1m. As concentrações de fósforo total durante o período de estudo foram elevadas (acima de 200 μg/L). As concentrações de clorofila a, tiveram valores mínimos de 8,17μg/L em julho de 2015, e máximos de 93,67 μg/L em outubro de 2015, com oscilações durante todo o período de estudo. O ambiente foi classificado como mesotrófico no mês de junho e eutrófico nos meses de outubro e dezembro. Foram identificadas dez espécies descritoras, agrupadas em quatro estratégias de vida (CS, C, R, e S) e 08 grupos funcionais (D, F, H1, N, P, X1 e Z). Os grupos funcionais refletiram as mudanças ambientais, sendo notória a presença de grupos típicos de lagos rasos meso-eutróficos. As espécies potencialmente tóxicas encontradas no estudo podem representar riscos à saúde das pessoas que utilizam essa água para consumo.