Search Results (113)

Microcystis, a potentially toxigenic cyanobacterium known to form extensive blooms in eutrophic lakes globally, was investigated in the cold oligotrophic Lake Baikal. We report the isolation of two Microcystis strains, Microcystis aeruginosa and M. novacekii, and document the presence of the latter species in Lake Baikal for the first time. In M. aeruginosa strain BN23, we detected the microcystin synthetase gene mcyE. Liquid chromatography-mass spectrometry revealed the presence of two microcystin variants in BN23, with microcystin-LR, a highly potent toxin, being the dominant form. The concentration of MC-LR reached 540 µg/g dry weight. In contrast, M. novacekii strain BT23 lacked both microcystin synthesis genes and detectable toxins. The habitat waters were characterized as oligotrophic with minor elements of mesotrophy, exhibiting low phytoplankton biomass dominated by the chrysophyte Dinobryon cylindricum (76–77% of biomass), with cyanobacteria contributing 8–10%. The contribution of Microcystis spp. to the total phytoplankton biomass could not be quantified as they were exclusively found in net samples. The water temperature at both sampling stations was ~19 °C, which is considerably lower than optimal for Microcystis spp. and potentially conducive to enhanced microcystin production in toxigenic genotypes. Full article

Lake eutrophication, often driving harmful algal blooms (HABs) and ecosystem degradation, involves complex biogeochemical shifts within sediments. Changes in the sedimentary dissolved organic matter (DOM) composition during transitions from macrophyte to algal dominance are thought to critically regulate internal phosphorus (P) loading, yet the underlying mechanisms, especially in vulnerable plateau lakes like Qilu Lake, require further elucidation. This study investigated the coupled cycling of carbon (C) and P in response to historical ecosystem succession and anthropogenic activities using a 0–24 cm sediment core from Qilu Lake. We analyzed the total organic carbon (TOC), total phosphorus (TP), sequential P fractions, and DOM fluorescence characteristics (EEM-PARAFAC), integrated with chronological series data. The results revealed an asynchronous vertical distribution of TOC and TP, reflecting the shift from a submerged macrophyte-dominated, oligotrophic state (pre-1980s; high TOC, low TP, stable Ca-P dominance) to an algae-dominated, eutrophic state. The eutrophication period (~1980s–2010s) showed high TP accumulation (Ca-P and NaOH85 °C-P enrichment), despite a relatively low TOC (due to rapid mineralization), while recent surface sediments (post-2010s) exhibited a high TOC, but a lower TP following input controls. Concurrently, the DOM composition shifted from microbial humic-like dominance (C1) in deeper sediments to protein-like dominance (C3) near the surface. This study demonstrates that the ecosystem shift significantly regulates P speciation and mobility by altering sedimentary DOM abundance and chemical characteristics (e.g., protein-like DOM correlating negatively with Ca-P), reinforcing a positive feedback mechanism that sustains internal P loading and potentially exacerbates HABs. DOM molecular characteristics emerged as a key factor controlling the internal P cycle in Qilu Lake, providing critical insights for managing eutrophication in plateau lakes. Full article

Bacteriophages (phages) are one of the critical biotic drivers of prokaryotic community dynamics, functions, and evolution. Despite their importance in aquatic ecosystems, very few phages have been isolated from freshwater lakes, hampering our understanding of their ecological importance and usage in a variety of biotechnological applications. Limnohabitans, with a ubiquitous distribution, is a metabolically versatile, fast-growing, morphologically diverse freshwater lake bacterial genera. It is especially abundant in pH-neutral and alkaline aquatic habitats, where it represents an average of 12% of freshwater bacterioplankton and plays an important role in funneling carbon from primary producers to higher trophic levels. However, no phages infecting Limnohabitans have been reported to date. Here, we describe, for the first time, three phages infecting Limnohabitans, DC31, DC33, and YIMV22061, isolated from two freshwater lakes in China and characterized using genome content analysis and comparative genomics. DC31 and DC33, recovered from the eutrophic Dianchi Lake, with auxiliary metabolic genes (AMGs), associated with nucleotide metabolism, whereas YIMV22061, isolated from the oligotrophic Fuxian Lake, carried AMGs involved in antibiotic resistance. The AMGs they carried highlight their impacts on Limnohabitans in different environments. Comparative genomic analyses indicate that DC31, DC33, and YIMV22061 represent three novel species in the Caudoviricetes class. IMG/VR database alignment further reveal that these phages are widely distributed across diverse aquatic and terrestrial ecosystems globally, suggesting their ecological significance. This study provides a basis for better understanding Limnohabitans–phage interactions. Full article

Artificial reservoirs formed by hydroelectric dams are young ecosystems requiring water quality monitoring, as they often serve local populations. Traditionally, this is performed through hydrochemical and sanitary assessments, alongside phytoplankton composition analysis. This study aimed to assess the seasonal dynamics of microbial communities—both bacterioplankton and microeukaryotes including phytoplankton—in the Irkutsk Reservoir (IR), which is fed by the cold oligotrophic waters of Southern Baikal (SB). Using parallel metabarcoding of 16S and 18S rRNA gene fragments, we analyzed community composition during the open-water season and evaluated the ecological connectivity between these two freshwater systems. We demonstrated that seasonal changes in microeukaryotic communities were closely linked between SB and IR, with the greatest divergence observed in early summer and progressive convergence by autumn. Metabarcoding confirmed microscopy-based observations while providing higher taxonomic resolution and detecting otherwise overlooked groups. Bacterioplankton communities also exhibited seasonal variation and were shaped by environmental gradients and reservoir characteristics. Cyanobacteria peaked in SB in late summer but did not dominate communities, unlike in mesotrophic lowland reservoirs. These findings demonstrate the value of metabarcoding for freshwater monitoring and provide new insights into microbial community dynamics in river–reservoir systems influenced by oligotrophic lake inflow. Full article

Freshwater fish species play an important role in global aquaculture. Currently, sturgeon, carp, and tilapia are at the forefront of this industry. However, as human populations continue to grow, the demand for new sources of animal protein increases, making the use of other freshwater species in aquaculture essential. The pikeperch (Sander lucioperca) is one of the most promising fish species for European aquaculture, but its usage has been hindered by a lack of effective larval-rearing protocols. Most studies focus on using cultured or nutrient-rich zooplankton for larval cultivation, while natural zooplankton from the local environment are rarely used. In this study, we aim to investigate the nutritional requirements of pikeperch larvae by describing the taxonomic diversity and biochemical composition of zooplankton collected from a natural oligotrophic lake in Northwest Russia. The chemical composition of zooplankton is characterized by a high protein content (up to 70% of dry matter), a moderate lipid content (up to 25%), and a deficiency of certain fatty acids and amino acids. Specifically, there is a low concentration of docosahexaenoic acid and methionine. The dry matter content in the zooplankton averages 10%, with nitrogen-free extracts accounting for 4% and ash making up 4%. These biochemical parameters meet the nutritional requirements of freshwater pikeperch larvae, with the notable exception of the lower levels of DHA and methionine, which are typically characteristic of freshwater zooplankton. This information sheds light on the nutritional requirements of pikeperch larvae and the development of more efficient rearing methods. Full article

Floating photovoltaic systems (FPV) are one of the emerging technologies that are able to support the “green” energy transition. In Greece, the environmental impact assessment of such projects is still under early development. The scope of the present study was to provide insights into the potential impacts of a small-scale FPV system on the water quality of the oligotrophic Kremasta Lake, an artificial reservoir. For this reason, a hydrodynamic and water quality model was employed. The results showed that the water quality parameter variations were insignificant and limited only in the immediate area of the FPV construction and gradually disappeared toward the shoreline. Likewise, this variation was restricted to the first few meters of depth of the water column and was eliminated onwards. The water temperature slightly decreased only in the area of close proximity to the installation. Average annual dissolved oxygen, chlorophyll-a, and nutrient concentrations were predicted not to change considerably after the panels’ construction. FPV systems can provide an attractive alternative for energy production in artificial reservoirs, especially in regions of land use conflicts that are associated with land allocation for alternative energy development. Given the limited data on the long-term impact of such projects, robust monitoring programs are essential. These initiatives rely on public support, making collaboration between stakeholders and the local community crucial. Full article

Cold-water lakes in high-latitude regions are experiencing rapid changes in community structure and functioning associated with local and global stressors (e.g., climate change, hydropower and invasive species). However, the long-term ecological responses of cold-adapted top predators are relatively poorly monitored despite their high importance for structuring ecological communities and for the provisioning of ecosystem services. We studied long-term changes (2010–2021) in the population structure and trophic niche of two cold-adapted coregonid fishes in oligotrophic Lake Osensjøen, southeastern Norway. Our gillnet surveys indicated that the whitefish (Coregonus lavaretus) population declines simultaneously with the increasing population density of roach (Rutilus rutilus), whereas vendace (Coregonus albula) showed more stable densities. Both whitefish and vendace became increasingly dominated by small-sized individuals following the increase in coexisting roach and perch (Perca fluviatilis) populations. Our stomach content and stable isotope data indicated a marked overlap in the trophic niches of whitefish and roach, with both species showing high among-individual variation in δ¹³C and δ¹⁵N values as compared to the more specialized zooplanktivorous vendace. Our study provides further evidence that the ongoing environmental changes in high-latitude lakes may induce rapid changes in community structures and lead to the population declines of cold-adapted fishes, likely associated with strong resource competition with warm-adapted cyprinid and percid fishes. Such shifts in fish community structure may, in turn, affect the benthic and pelagic food-web compartments and reduce valuable ecosystem services such as local fisheries targeting salmonids. Full article

Human activities have led to an increased influx of carbon into lakes due to changes in land use that result in higher erosion rates, eutrophication, and the introduction of organic matter. This, in turn, causes greater carbon exports and carbon accumulation in sediments. In our study, we estimated the fluxes of total particulate carbon (F_TPC), particulate organic carbon (F_POC), and particulate inorganic carbon (F_PIC) in three lakes with different trophic statuses. Two lakes, one eutrophic (Bosque Azul) and one mesotrophic (San José), are in the anthropically impacted zone of the plateau. In contrast, an oligotrophic lake (Tziscao) is in the mountainous, pristine area of “Lagunas de Montebello” National Park, a tropical karst lake district in Chiapas, Mexico. Our findings revealed that the highest F_POC values were observed in the eutrophic lake (0.47 ± 0.2 g m⁻² d⁻¹), while the highest F_PIC were observed in the mesotrophic lake (1.11 ± 0.8 g m⁻² d⁻¹). In contrast, the oligotrophic lake exhibited the lowest fluxes. Eutrophication increased the levels of F_POC, while deforestation and erosion contributed to the rise in F_PIC. Eutrophication and erosion in the lakes of LMNP led to five-, two-, and sixteen-fold increases in the F_TPC, F_POC, and F_PIC, respectively. Full article

The phytoplankton communities in lakes change seasonally within competitive areas, referred to as seasonal succession, which results in high compositional diversity if conditions remain stable. However, glacial lakes are generally far from human and terrestrial influences due to their location so very few species can be identified and large changes in phytoplankton composition cannot be anticipated. Nonetheless, molecular techniques, as well as classical methods, help us to determine the existence of different species. Additionally, these techniques allow us to evaluate the ecology of glacial lakes from different perspectives with developing technology. Horseshoe Island is located in the area known as Marguerite Bay on the Peninsula region in western Antarctica. This study was carried out to determine phytoplankton genome biodiversity by using the metagenomic analysis method used in 18S rRNA, 16S rRNA, and 23S rRNA gene analyses. 16S rRNA and 23S rRNA gene analyses revealed that bacteria belong to broadly distributed Cyanobacteria taxa, whereas 18S rRNA gene analysis revealed other eukaryotic phytoplankton groups. This method was used for the first time for Horseshoe Island lakes (Col 1, Col 2, Skua, and Zano), and species belonging to Cyanobacteria, Chlorophyta, Ochrophyta, and Bacillariophyta were identified. As a result, the phytoplankton genomic diversity of shallow and oligotrophic glacial lakes was determined, and benthic algal species were also identified in the water samples. These results indicate that benthic algae associated with the sediment can also contribute to aquatic phytoplankton communities in addition to oligotrophic lake phytoplankton biodiversity. Cyanobacterial biodiversity can also be recognized as a sentinel by which to monitor adaptation responses to climate change in this rapidly warming region. Full article

The lakes known as El Sol and La Luna are high mountain water deposits located in Mexico within an inactive volcanic system. These lakes are of ecological importance because they are unique in Mexico. However, currently, the lakes have experienced changes in their shape and an increase in algae blooms, coupled with the degradation of the basin, which has alerted government entities to the need to address the lakes’ problems. To address the environmental status of El Sol and La Luna, a trophic study was conducted during the period of 2021–2023, including an analysis of the influence of climatic variables, lake water quality, and eutrophication conditions. The trophic state was established based on the eutrophication index. The Pearson correlations defined the eutrophication interrelation between the distinct factors influencing the lakes’ status. El Sol registered higher eutrophication conditions than La Luna. El Sol was identified as seasonal eutrophic and La Luna as transitioning from oligotrophic to mesotrophic, showing high levels of chlorophyll, total phosphorus, and total nitrogen and low water transparency. The principal factors altering the eutrophic conditions were water pollution and climatic variables (precipitation and ambient temperature). Eutrophication was the prime factor impacting perimeter loss at El Sol, whereas at La Luna, it was due to a decline in precipitation. Full article

Kellicottia bostoniensis is a rotifer species originating from North America, with numerous reports documenting its spread to Europe and South America. Meanwhile, in Asia, the occurrence of this non-native species has been scarcely documented, but its presence was recently reported in Korea in 2020. In Korea, the close geographic proximity of artificial reservoirs within a small area is expected to make the region vulnerable to the spread of K. bostoniensis. Therefore, it is deemed necessary to study the spatio-temporal distribution of K. bostoniensis, which appears to have extensively proliferated across the region, and its relationship with environmental factors. We analyzed the response of K. bostoniensis occurrence to environmental factors and aimed to compare its response patterns with those of potential competitor and predator groups, which were classified based on a functional group approach. This study, conducted on 12 small lakes located under similar climatic conditions, revealed that the response of K. bostoniensis to variables representing the trophic state of the lakes differed from those of the potential competitor and predator groups. The study sites, encompassing a wide range of trophic states from oligotrophic to hypereutrophic, across various lakes and survey periods, were well-suited for examining these relationships. Furthermore, when TSI was calculated to compare the abundance of K. bostoniensis and potential competitors across trophic conditions, the abundance of potential competitors was proportional to TSI. In contrast, K. bostoniensis exhibited higher abundances in mesotrophic and lower eutrophic environments, which distinguished it from its competitors. Our results indicate that the impact of introduced K. bostoniensis on native communities is minimal, while the resistance of native communities through the biological filter based on biological interactions is ineffective against this non-native rotifer species. This provides key evidence for explaining the widespread distribution of K. bostoniensis across continents. Full article

Lake Bacalar, a fragile oligotrophic ecosystem located in the southeast of Yucatan Peninsula, Mexico, suffered from a sudden brownification after the tropical storm Cristobal in June 2020 in the Gulf of Mexico. The color change was the most visible effect of the storm, but all other water variables changed towards eutrophication. We used light traps and DNA barcoding of the zooplankton specimens based on previous baseline constructed for comparison with the species found after the change. A dramatic shift in the zooplankton community occurred: biomass was reduced to a minimum and 20 species of water mites, five copepods, three cladocerans, three chironomids and six species of fish larvae disappeared for a period of at least one year. They were replaced by three species of water mites, four cladocerans, one copepod, 23 chironomids and one ephemeropteran previously not registered, most of the species being characteristic of more eutrophic environments. The southernmost part of the lake, Laguna Xul-Ha, which conserved its oligotrophic characteristics, apparently became a refuge for the original fauna from the whole system. The ecosystem did not fully recover to its original condition until about two years later. While the system has returned to its original state after the storm described here, future changes in land use, including unsustainable tourism expansion, may compromise its resilience and induce hysteresis. Full article

Over recent decades, Northern Patagonia in Chile has seen significant growth in agriculture, livestock, forestry, and aquaculture, disrupting lake ecosystems and threatening native species. These environmental changes offer a chance to explore how anthropization impacts zooplankton communities from a molecular–ecological perspective. This study assessed the anthropogenic impact on Daphnia pulex by comparing its proteomes from two lakes: Llanquihue (anthropized) and Icalma (oligotrophic). Results showed substantial differences in protein expression, with 17 proteins upregulated and 181 downregulated in Llanquihue, linked to elevated levels of copper, manganese, dissolved solids, phosphate, and nitrogen. These stressors caused metabolic damage and environmental stress in D. pulex. Our findings highlight the importance of monitoring pollution’s effects on Northern Patagonian ecosystems, especially on keystone species like D. pulex, essential for ecosystem stability. This research provides fresh molecular–ecological insights into pollution’s impacts, a perspective rarely addressed in this region. Understanding these effects is critical for conserving natural resources and offers pathways to study adaptive mechanisms in keystone species facing pollution. This approach also informs strategies for ecosystem management and restoration, addressing both immediate and long-term challenges in Northern Patagonian aquatic environments. Full article

An important top-down predator, the northern pike (Esox lucius), faces harsh environmental conditions in the northern boreal ecoregion. They are often managed for recreational fishing and, more recently, to create environmental offsets; strategies aimed at balancing ecological impacts by enhancing or restoring habitats. Our study examines northern pike populations in two remote boreal lakes in northern Alberta: Steepbank and Wappau. The lakes differ in size, vegetation cover, and trophic status, providing a natural experiment for investigating northern pike growth, condition, diet, and population density. Over three years (2018–2020), northern pike were sampled using gill nets. Population metrics, including growth, condition, and stomach contents, were compared between the lakes. Steepbank, a smaller, oligotrophic lake with low vegetation cover, showed lower prey fish densities compared to the larger, eutrophic Wappau, but it did not differ in northern pike catch per unit effort. Growth rates and body condition varied significantly between the lakes, with the northern pike in Wappau exhibiting faster growth and a better condition in the older age groups, while the younger northern pike in Steepbank had higher relative weights. A diet analysis revealed significant differences in prey consumption: Steepbank northern pike displayed higher rates of conspecific predation and invertebrate consumption, particularly in the younger age classes. These findings highlight how lake characteristics and prey availability shape northern pike population dynamics, offering valuable insights for lake management approaches in northern Alberta. Full article

The application of the Multispectral Instrument (MSI) aboard Sentinel-2A/B constellation for assessing water quality in Chilean lakes represents an emerging area of research, particularly for the environmental monitoring of optically complex water bodies. Similarly, atmospheric correction processors applied to aquatic environments, such as the Case 2 Networks (C2RCC-Nets), are notably underrepresented. This study evaluates the capability of C2RCC-Nets using different neural networks—Case-2 Regional/Coast Color (C2RCC), C2X-Extreme (C2X), and C2X-Complex (C2XC)—to estimate Secchi depth in Lake Lanalhue (eutrophic), Lake Villarrica (oligo-mesotrophic), and Lake Panguipulli (oligotrophic). The evaluation used different statistical methods such as Spearman’s correlation and normalized error metrics (nRMSE, nMAE, and nbias) to assess the agreement between satellite-derived data and in situ measurements. C2XC demonstrated the best fit for Lake Lanalhue, with an nRMSE = 33.13%, nMAE = 23.51%, and nbias = 8.57%, in relation to the median ground truth values. In Lake Villarrica, the C2XC neural network displayed a moderate correlation (r_s = 0.618) and error metrics, with an nRMSE of 24.67% and nMAE of 20.67%, with an nbias of 4.21%. In the oligotrophic Lake Panguipulli, no relationship was observed between estimated and measured values, which could be related to the fact that the selected neural networks were developed for very case 2 waters. These findings highlight the need for methodological advancements in processing satellite-derived water quality products for Chile’s optical water types, particularly for very clear waters. Nonetheless, this study underscores the need for model-specific calibration of C2RCC-Nets, as lakes with different optical water types and trophic states may require tailored training ranges for inherent optical properties. Full article