Lentic Research Articles

Adaptation of Wind Drag Coefficient Parameterization: Improvement of Hydrodynamic Modeling by a Wave‐Dependent Cd in Large Shallow Lakes

AbstractWind is a critical driving force in hydrodynamic and water quality modeling of large shallow lakes, and is characterized by the wind drag coefficient Cd, representing the momentum transfer at the air‐water interface. Contemporary empirical formulae for Cd estimation were derived over oceans and some of which are solely wind velocity U10 dependent. These formulae were previously found to be inadequate in inland lake models often resulting in the water velocity underestimation. To address this problem, a physical scale experiment was designed, in which Cd was measured using a wind profile and eddy covariance methodology. A new wind‐induced wave‐dependent Cd parameterization was also established and validated in two lake studies. The driving force was modified by the wave‐dependent Cd formula in a hydrodynamic model of the shallow Upper Klamath Lake (UKL), OR, USA. The experimental Cd was negatively correlated to the wind velocity up until the critical U10 = 1.6 m s−1 which was 1.0~3.1 times previous empirical extrapolations at light winds. The variation partitioning results showed that wave parameters contributed to more than 30% of Cd variation combined with wind parameters. The modified wind stress field was spatially heterogeneous and the modeled water velocity was closer to the observations at two sites. Significant main circulation and outer bank circulation were modeled accompanied by higher surface vorticity, compared to the original UKL model. Overall, the wave‐dependent Cd formula provided an improvement of the surface flow field in the UKL model and will improve the management of the lake ecosystems.

Diversity and distribution of chironomids in Central European ponds.

Ponds are common freshwater habitats in the European landscape that substantially contribute to local and regional biodiversity. Chironomids often dominate invertebrate communities in ponds but are usually disregarded in ecological studies due to relatively complicated taxonomy and identification issues. We present a comprehensive overview of the chironomid diversity in 246 ponds spanning a wide range of conditions extending from the Pannonian Plain to the Carpathians. Altogether, we recorded 225 taxa including 192 species from six subfamilies (Podonominae, Tanypodinae, Diamesinae, Prodiamesinae, Orthocladiinae and Chironominae). However, the chironomid taxa inventory is far from complete and about 16% of the total diversity of pond-dwelling chironomids remains undetected. Chironomid alpha diversity showed a significant unimodal pattern along the elevation gradient with the highest number of taxa per pond expected around 790 m a.s.l. Gamma diversity also peaked in mid-elevations (600-800 m), and the common chironomid taxa partitioned the 2100-m long altitudinal gradient relatively evenly. The heterogeneity of chironomid communities among ponds measured as beta diversity was significantly higher in elevations below 800 m. Temperature and the proportion of surrounding forests significantly influenced alpha diversity of chironomid communities, while urban land cover and pond size had no significant effect. Ponds with a mean annual air temperature of approximately 4.8°C and a low proportion of surrounding forests are expected to harbour the most diverse chironomid communities. Our study showed that chironomids represent a very diverse and often exceptionally rich group of pond-dwelling macroinvertebrates. Given the high diversity and broad range of occupied niches, chironomids should not be overlooked in pond ecology studies. On the contrary, they should be considered a potential model group.

Sources and fate of omega-3 polyunsaturated fatty acids in a highly eutrophic lake

Omega-3 polyunsaturated fatty acids (ω3-PUFA) are central to the growth and reproduction of aquatic consumers. Dissolved nutrients in aquatic ecosystems strongly affect algal taxonomic composition and thus the production and transfer of specific ω3-PUFA to consumers at higher trophic levels. However, most studies were conducted in nutrient-poor, oligotrophic lakes, leading to an insufficient understanding of how water nutrients affect algal ω3-PUFA and their trophic transfer in consumers in highly eutrophic lakes.We conducted a field investigation in a highly eutrophic lake and collected basal food sources (phytoplankton, periphyton and macrophytes) and aquatic consumers (invertebrates, zooplankton and fish), and measured their fatty acid (FA) composition.Our results showed that periphyton and phytoplankton were both important sources of ω3-PUFA supporting the highly eutrophic lake food web. High water nutrient levels led to low ω3-PUFA levels in phytoplankton and periphyton, resulting in decreased nutritional quality. Consequently, ω3-PUFA of invertebrates and zooplankton reflected variations in ω3-PUFA of phytoplankton and periphyton, respectively.The ω3-PUFA levels of fish decreased as phytoplankton and periphyton ω3-PUFA decreased. Among fish, the Redfin Culter (Cultrichthys erythropterus) and Bar Cheek Goby (Rhinogobius giurinus) exhibited significantly higher levels of EPA and DHA compared to the Pond Loach (Misgurnus anguillicaudatus), which may have been caused by their different feeding modes.Decreases in the ω3-PUFA levels of basal food sources may be one of the causes leading to the reduction of trophic links in aquatic food webs.Our study elucidated the sources and fate of ω3-PUFA in highly eutrophic lakes, complemented previous studies in oligo- and mesotrophic lakes, and emphasized the role of high-quality food sources. Our results offer new perspectives for the conservation and management of highly eutrophic lake ecosystems.

Late Holocene decoupling of lake and vegetation ecosystem in response to centennial-millennial climatic changes in arid Central Asia: A case study from Aibi Lake of western Junggar Basin

Central Asian lakes are crucial for sustaining fragile oasis ecosystems in arid regions. Understanding the response of ecosystems in these lake basins to climate change is essential for predicting future variations in these ecosystems. Aibi Lake is a notable terminal lake in arid Central Asia. In this study, a 95 cm lacustrine sediment core was drilled from Aibi Lake to investigate the response of lacustrine and terrestrial ecosystems in the lake basin to climate change over the past 3200 years. Accelerator mass spectrometry (AMS) 14C dating and multi-proxy analyses of diatoms, pollen, grain size, total organic content (TOC), total nitrogen (TN), and total hydrogen (TH) are applied to the sediment core. The grain size and geochemical results show that the lake experienced elevated levels and improved productivity and nutrition during the periods of 708–181 BCE, 0–740 CE, and 1428–1900 CE. The periods align with the Roman Warm Period, Dark Age Cold Period, and Little Ice Age, respectively. For the past 3200 years, benthic diatoms have consistently been the dominant species in the lake. During the climatic transition periods of the Dark Age Cold Period, Medieval Warm Period, and Little Ice Age, there were significant changes in the abundance and survival of certain species of diatoms. Specifically, the halophilic species (Nitzschia dissipata and Nitzschia hungarica), basophilic species (Synedra acus), and the nutrition level-relevant species (Navicula menisculus) experienced notable shifts. These changes ultimately resulted in a noticeable alteration in the structure and function of the diatom community. Over the past 3200 years, the lake ecosystem has undergone three noticeable regime shifts. In contrast, the vegetation in the lake catchment has remained relatively stable, primarily consisting of desert steppe. These results suggest that aquatic ecosystems in arid central Asia are more susceptible and exhibit more rapid responses to climate change compared to terrestrial vegetation.

Ecological response to global changes in Lake Genco, a remote alpine lake on the Southeast Tibetan Plateau, over the past two centuries

The ways in which natural ecosystems respond to global change have become an urgent concern to society. Lakes play a pivotal role in ecosystem changes because of their central position within watersheds and their involvement in various endogenous and cross-system ecological and biogeochemical processes, leaving natural archives accumulated in sediments over time. However, how lake ecosystems have responded to atmospheric changes during the past few centuries is still not fully understood. To analyse the process in more detail, we conducted a case study at Lake Genco, a remote alpine on the southeastern Qinghai-Tibetan Plateau (QTP) and recovered a 170-year history of lake's ecosystem from a 210Pb-dated sediment core. The air temperature increased between 1900 and 1950 CE and 1980 and 2020 CE. Geochemical and physical proxies (magnetic susceptibility, Sr/Ba, K/Al, Na/Al, Ti, Pb, P flux, TN and δ15Norg) indicated greater degrees of weathering and erosion, and higher nutrient loadings as terrestrial systems responded to atmospheric changes after 1900 CE. Higher primary aquatic productivity, richer biodiversity and weaker structural stability were found in Lake Genco between 1852 and 2017 CE, although the ecological response was quiet in terms of the compositional change in the diatom community, which was generally dominated by small planktonic Cyclotella ocellata. During warmer periods, diatom PC1 changed directionally due to the overall increase in the abundance of tychoplanktonic Fragilaria construens and periphytic Achnanthes minutissima and the decreasing abundance (∼10%) of C. ocellata. This study provides empirical evidence that ecological changes in remote lakes rely on interactions between the atmosphere and the landscape and helps us to understand the complexity of the various impacts of global climate change. More local and regional studies are needed to generalise the mechanism of biological responses to atmospheric changes in remote lakes, especially in the QTP.

Biotic and abiotic factors driving water hyacinth, Pontederia crassipes, phenology in Nyanza Gulf, Lake Victoria, Kenya

While isolated patches of water hyacinth have persisted in most parts of Lake Victoria since the rapid decline in biomass beginning in 1999/2000, Nyanza Gulf has maintained extensive but cyclical coverage over the years. High water hyacinth productivities were found to coincide with the western region associated with upwelling and regenerated nutrients, and also with periods of complete lake turnover. River discharge sites, which are numerous in the eastern region, expressed relatively low water hyacinth productivities. High productivity meant better nutritional quality, a state preferred by the Neochetina weevils. Although the difference in productivities between the eastern and western regions were statistically insignificant, the feeding scars were notably different. This implies that any slight change in water hyacinth’s nutritional quality as a result of change in resource water quality, significantly affects the weevil’s productivities. During complete lake turnover, water hyacinth productivity is highly enhanced, likely due to upwelling of hypolimnetic nutrient enriched waters with subsequent spontaneous weevil invasion. During times of such high nutrient quality, the rates of leaf turnover outstrips the herbivory by the weevils. The nutrient dynamics from primary sources coupled with secondary regenerated loads through lake turnovers influences the water hyacinth’s varying nutritional quality and weevil population, which ultimately determines the water hyacinth phenology within the semi-enclosed Nyanza Gulf. The objectives of this study were to study the spatial influence of resource water quality to the consumer water hyacinth productivity and how temporal hydrologic dynamics drives its cyclicity.

Responses of Protozoan Communities to Multiple Environmental Stresses (Warming, Eutrophication, and Pesticide Pollution).

To explore the impacts of multiple environmental stressors on animal communities in aquatic ecosystems, we selected protozoa-a highly sensitive group of organisms-to assess the effect of environmental change. To conduct this simulation we conducted a three-factor, outdoor, mesocosm experiment from March to November 2021. Changes in the community structure and functional group composition of protozoan communities under the separate and combined effects of these three environmental stressors were investigated by warming and the addition of nitrogen, phosphorus, and pesticides. The results were as follows: (1) Both eutrophication and pesticides had a considerable promotional effect on the abundance and biomass of protozoa; the effect of warming was not considerable. When warming was combined with eutrophication and pesticides, there was a synergistic effect and antagonistic effect, respectively. (2) Eutrophication promoted α diversity of protozoa and affected their species richness and dominant species composition; the combination of warming and pesticides remarkably reduced the α diversity of protozoa. (3) Warming, eutrophication, and pesticides were important factors affecting the functional groups of protozoa. Interaction among different environmental factors could complicate changes in the aquatic ecological environment and its protozoan communities. Indeed, in the context of climate change, it might be more difficult to predict future trends in the protozoan community. Therefore, our results provide a scientific basis for the protection and restoration of shallow lake ecosystems; they also offer valuable insights in predicting changes in shallow lakes.

Evaluation of water quality and trophic status in relation to seasonal water mixing in a highland Lake Ardibo, Ethiopia.

The aim of the present study was to evaluate the spatio-temporal variability of various physical and chemical parameters of water quality and to determine the trophic state of Lake Ardibo. Water samples were collected from October 2020 to September 2021 at three sampling stations in four different seasons. A total of 14 physico-chemical parameters, such as water temperature, pH, dissolved oxygen (DO), electrical conductivity, turbidity, alkalinity, Secchi-depth, nitrate, ammonia, silicon dioxide, soluble reactive phosphorus, total phosphorus, chloride, and fluoride were measured using standard methods. The results demonstrated that temporal variation existed throughout the study period. Except for turbidity, the water quality of the lake varied significantly within the four seasons (ANOVA, p < 0.05). DO levels decreased significantly during the dry season following water mixing events. Chlorophyll-a measurements showed significant seasonal differences ranging from 0.58 μg L-1 in the main-rainy season to 8.44 μg L-1 in the post-rainy period, indicating moderate algal biomass production. The overall category of Lake Ardibo was found to be under a mesotrophic state with medium biological productivity. A holistic lake basin approach management is suggested to maintain water quality and ecological processes and to improve the lake ecosystem services.

Breeding waterbird species as ecological indicators of shifts from turbid to clear water conditions in northwest European shallow eutrophic lakes

AbstractWe used biological and physical responses at 71 shallow waterbodies with contrasting nutrient levels undergoing recovery from eutrophication to predict potential changes in waterbird species abundance, an important component of lake ecosystems. These general predictions were tested using 28 years of breeding waterbird data from three Danish shallow eutrophic lakes, comparing species-specific responses to improved nutrient and water transparency in two lakes with a third where conditions remained constantly suitable for breeding waterbirds. We predicted positive responses to improved water quality from pursuit diving predators (three grebe species), a specialist zooplankton feeder (northern shoveler Anas clypeata) and waterbirds feeding on (common pochard Aythya ferina) or within (tufted duck A. fuligula) submerged macrophyte underwater canopies. These species were characterised by positive waterbird community composition changes (using Principal Components Analysis) associated with decreasing nutrient loading and increasing water transparency at two lakes, with no change in breeding waterbird community at the third. Secchi depth explained 73–95% of variance in both PC axes at both restored lakes, but not at the third, suggesting water transparency was the major factor driving waterbird community composition. These examples show predicting waterbird species-specific responses to management can usefully direct the use of breeding waterbirds as indicator species.

Ecosystem changes in eight Danish lakes after zebra mussel invasion

AbstractInvasion of zebra mussels (Dreissena polymorpha) can have profound effects on lake ecosystems. We investigated the overall ecological effects after invasion and fast expansion of zebra mussels in eight lakes in Denmark belonging to the same watercourse systems but with different morphological and eutrophication characteristics. A few years after the invasion, most of the lakes had experienced profound changes in lake water quality, e.g. chlorophyll a had been reduced by 18–62% and Secchi depth had increased by 38–171%. Nutrient concentrations also decreased, total phosphorus to 37–64% and total nitrogen to 49–77% of pre-invasion concentrations. Seasonally, differences between both summer and winter phosphorus and nitrogen concentrations diminished, suggesting a change in internal nutrient cycling after the invasion. In most lakes, the abundance of submerged macrophytes rose substantially, and often coverage increased by a factor 10 or more, and the maximum colonisation depth increased by up to 5.4 m. Plant species numbers increased markedly in four of the six lakes with macrophyte data. The fish community changed towards higher dominance of potential piscivorous perch and an increase in their body size. The profound effects of zebra mussel invasion may affect lake management and how ecological quality should be interpreted.

Leveraging Bayesian network to reveal the importance of water level in a shallow lake ecosystem: A study based on Paleo-diatom and fish community

Lake ecological processes and nutrient patterns are increasingly affected by water level variation around the world. Still, the long-term effects of water level change on lake ecosystems and their implications for suitable lake level management have rarely been studied. Here, we studied the ecosystem dynamics of a mesotrophic lake located in the cold and arid region of northern China based on long-term paleo-diatom and fishery records. Utilizing a novel Copula-Bayesian Network model, possible hydrological-driven ecosystem evolution was discussed. Results show that increased nutrient concentration caused by the first water level drop in the early 1980s incurred a transition of sedimental diatoms towards pollution-resistant species, and the following water level rise in the mid-1980s brought about considerable external loading, which attributed to eutrophication and caused the miniaturization of fishery structure. In the 21st century, a continuous water level plummet further reduced the sediment diatom biomass and the fish biomass by altering nutrient concentration. However, with the implementation of the water diversion project in 2011, oligotrophic species increased, and the ecosystem developed for the better. From the perspective of water quality protection requirements and the ecological well-being of Lake Hulun, the appropriate water level should be around 542.42–544.15 m. In summary, our study highlights the coupling effect of water level and water quality on Lake Hulun ecosystem and gives shed to lake water level operation and management under future climate change and human activities.

Using oxygen isotopes in phosphate to assess biological phosphorus cycling in a small and shallow freshwater lake system

AbstractReducing excess phosphorus (P) loads that cause eutrophication in aquatic systems is essential for meeting water quality standards. The oxygen isotopic composition of phosphate (δ18Op) is a powerful tool for tracking P sources and cycling in diverse natural ecosystems. Here, we use δ18Op distribution in a small freshwater body (a lagoon–lake system) with high biological activity. We report δ18Op values seasonally along the water flow path in lagoon–lake system adjacent to Lake Biwa, Japan. The δ18Op values of inflowing water originating as agricultural runoff were constant throughout the study period at +16.3‰ ± 0.2‰. The δ18Op values in the system were generally offset from temperature‐dependent isotopic equilibrium with the surrounding water, ranging from +11.1‰ to +17.8‰. The δ18Op values of the lake water approached equilibrium values in July and October, when dissolved inorganic P (DIP) retention rates were high, consistent with extensive biologically mediated phosphate cycling. A δ18Op two end‐member mixing model, involving inflowing P and biologically recycled P, suggests that P turnover rates in the lagoon–lake system were high during the productive seasons. In contrast, the longer lake water residence time in the non‐irrigation season (winter) allowed δ18Op values to deviate toward lower values relative to both equilibrium and agricultural source δ18Op values, suggesting that P metabolism was dominated by extracellular/ecto‐enzymatic hydrolysis of dissolved organic P under low DIP concentrations. This work highlighted the utility of δ18Op for understanding P dynamics in shallow lake ecosystems.

Nitrogen and sulfur cycling and their coupling mechanisms in eutrophic lake sediment microbiomes

Microorganisms play important roles in the biogeochemical cycles of lake sediment. However, the integrated metabolic mechanisms governing nitrogen (N) and sulfur (S) cycling in eutrophic lakes remain poorly understood. Here, metagenomic analysis of field and bioreactor enriched sediment samples from a typical eutrophic lake were applied to elucidate the metabolic coupling of N and S cycling. Our results showed significant diverse genes involved in the pathways of dissimilatory sulfur metabolism, denitrification and dissimilatory nitrate reduction to ammonium (DNRA). The N and S associated functional genes and microbial groups generally showed significant correlation with the concentrations of NH4+, NO2− and SO42, while with relatively low effects from other environmental factors. The gene-based co-occurrence network indicated clear cooperative interactions between N and S cycling in the sediment. Additionally, our analysis identified key metabolic processes, including the coupled dissimilatory sulfur oxidation (DSO) and DNRA as well as the association of thiosulfate oxidation complex (SOX systems) with denitrification pathway. However, the enriched N removal microorganisms in the bioreactor ecosystem demonstrated an additional electron donor, incorporating both the SOX systems and DSO processes. Metagenome-assembled genomes-based ecological model indicated that carbohydrate metabolism is the key linking factor for the coupling of N and S cycling. Our findings uncover the coupling mechanisms of microbial N and S metabolism, involving both inorganic and organic respiration pathways in lake sediment. This study will enhance our understanding of coupled biogeochemical cycles in lake ecosystems.

Fish Development in Lake Ecosystems, Effect of Heavy Metals

Heavy metals enter the water bodies and combine with the water buffer system, then turn into poorly soluble hydroxides, carbonates, sulfides and phosphates, and also form metal-organic complexes, accumulate in the bottom sediments and in general in the bodies of the fish fauna of the reservoirs of the area, seriously affecting their development. It was determined that the amount of Ca2+ ions varied from 17 mg/l to 112 mg/l, and the amount of Mg2+ ions from 5.5 mg/l to 83.5 mg/l, in other words, towards autumn. water hardness has increased. The amount of alkali metal (Na+ + K+) ions is much lower in spring than in summer and autumn. According to the cations, the amount of chloride and sulfate ions increases in autumn. Thus, the impact of anthropogenic factors on fish is diverse and manifests itself primarily in morphological anomalies and changes in the basic biological parameters of fish populations. The main of them is the reduction of productivity and the complete loss of their natural forms, the increase of individuals and the increase of mortality.

Occurrence and Risk Assessment of Antibiotics in Urban River–Wetland–Lake Systems in Southwest China

Antibiotics in the aquatic environment are of great concern as novel contaminants. In this study, we investigated the occurrence, distribution, potential sources, and risk assessment of antibiotics in an interconnected river–wetland–lake system. Thirty-three target antibiotics, including sulfonamides (SAs), macrolides (MLs), fluoroquinolones (FQs), tetracyclines (TCs), and chloramphenicol (CLs) belong to five common groups of antibiotics, were tested from water samples collected in the Panlong River, Xinghai Wetland, and Lake Dian (or Dianchi). Mass spectrophotometry was used to detect the target antibiotics, and the water quality parameters were measured in situ. We found four antibiotics, lincomycin (LIN), trimethoprim (TMP), sulfamethoxazole (SMX), and ofloxacin (OFL), with relatively low concentrations at the ng/L level, and detection rates among sample sites ranged from 42.3% to 76.9%, with maximum concentrations of 0.71 ng/L~5.53 ng/L. TMP was not detected in the Panlong River but appeared in the wetlands and Lake Dian. Midstream urban areas of the Panlong River showed the highest pollution among sites. Antibiotic concentrations were positively correlated with total nitrogen (TN) (p &lt; 0.05) and showed some negative correlation with pH, salinity, and DO. According to the risk assessment, antibiotics in water do not pose a threat to human health and aquatic ecosystems, but a potentially harmful combined effect cannot be excluded. Our research offers a geographical summary of the distribution of antibiotics in urban river, wetland, and lake ecosystems in the plateau (PWL), which is important for predicting the distribution characteristics of antibiotics in the plateau water environment and establishing a standardized antibiotic monitoring and management system for the government.

Assessment of Physicochemical Parameters in Selected Water Bodies in Laguna, Philippines

This study was aimed to examine the frequent variations in four selected physico-chemical parameters of surface water of two lakes in Laguna: Laguna de Bay in Calamba City and Sampaloc Lake in San Pablo City. Parameters such as conductivity, dissolved oxygen (DO), pH, and temperature were determined using in-situ water quality tester. The two lakes are both freshwater body, different data are collected and observed throughout the sampling. Due to various anthropogenic activities, the lakes are biotically affected. The water quality of the two important lakes in Laguna have been compared in different parameters like pH, DO, conductivity, water temperature and color. The result indicates that both lakes are within the standard (25-31°C) of DENR Administrative Order (DAO 2016-08 for Class C), but except for water temperature which exceeds the standard value (36.37°C mean values). The results support insights about the future effects of increased water temperature on fish management and the lake ecosystem for numerous aquatic purposes. This is also for the management and call on action for the residents and local government unit in said municipalities of Laguna especially after pandemic season.

Bacterial and fungal community structures in Hulun Lake are regulated by both stochastic processes and environmental factors.

Microorganisms are a crucial component of lake ecosystems and significant contributors to biogeochemical cycles. However, the understanding of how primary microorganism groups (e.g., bacteria and fungi) are distributed and constructed within different lake habitats is lacking. We investigated the bacterial and fungal communities of Hulun Lake using high-throughput sequencing techniques targeting 16S rRNA and Internal Transcribed Spacer 2 genes, including a range of ecological and statistical methodologies. Our findings reveal that environmental factors have high spatial and temporal variability. The composition and community structures vary significantly depending on differences in habitats. Variance partitioning analysis showed that environmental and geographical factors accounted for <20% of the community variation. Canonical correlation analysis showed that among the environmental factors, temperature, pH, and dissolved oxygen had strong control over microbial communities. However, the microbial communities (bacterial and fungal) were primarily controlled by the dispersal limitations of stochastic processes. This study offers fresh perspectives regarding the maintenance mechanism of bacterial and fungal biodiversity in lake ecosystems, especially regarding the responses of microbial communities under identical environmental stress.IMPORTANCELake ecosystems are an important part of the freshwater ecosystem. Lake microorganisms play an important role in material circulation and energy flow owing to their unique enzymatic and metabolic capacity. In this study, we observed that bacterial and fungal communities varied widely in the water and sediments of Hulun Lake. The primary factor affecting their formation was identified as dispersal limitation during stochastic processes. Environmental and geographical factors accounted for <20% of the variation in bacterial and fungal communities, with pH, temperature, and dissolved oxygen being important environmental factors. Our findings provide new insights into the responses of bacteria and fungi to the environment, shed light on the ecological processes of community building, and deepen our understanding of lake ecosystems. The results of this study provide a reference for lake management and conservation, particularly with respect to monitoring and understanding microbial communities in response to environmental changes.

Influence of heavy Canadian crude oil on pristine freshwater boreal lake ecosystems in an experimental oil spill.

The overall impact of a crude oil spill into a pristine freshwater environment in Canada is largely unknown. To evaluate the impact on the native microbial community, a large-scale in situ model experimental spill was conducted to assess the potential role of the natural community to attenuate hydrocarbons. A small volume of conventional heavy crude oil (CHV) was introduced within contained mesocosm enclosures deployed on the shoreline of a freshwater lake. The oil was left to interact with the shoreline for 72h and then free-floating oil was recovered using common oil spill response methods (i.e. freshwater flushing and capture on oleophilic absorptive media). Residual polycyclic aromatic hydrocarbon (PAH) concentrations returned to near preoiling concentrations within 2 months, while the microbial community composition across the water, soil, and sediment matrices of the enclosed oligotrophic freshwater ecosystems did not shift significantly over this period. Metagenomic analysis revealed key polycyclic aromatic and alkane degradation mechanisms also did not change in their relative abundance over the monitoring period. These trends suggest that for small spills (<2l of oil per 15 m2 of surface freshwater), physical oil recovery reduces polycyclic aromatic hydrocarbon concentrations to levels tolerated by the native microbial community. Additionally, the native microbial community present in the monitored pristine freshwater ecosystem possesses the appropriate hydrocarbon degradation mechanisms without prior challenge by hydrocarbon substrates. This study corroborated trends found previously (Kharey et al. 2024) toward freshwater hydrocarbon degradation in an environmentally relevant scale and conditions on the tolerance of residual hydrocarbons in situ.

Stable isotope analysis provides novel insights for measuring lake ecosystem recovery following acidification

Unstable and simplified freshwater food webs impair the resilience of Canadian fisheries facing environmental stressors. This study utilizes stable isotope analyses to assess trophic recovery to explore food web resiliency in lakes historically impacted by metal mining in Sudbury, Ontario. Carbon (δ13C) and nitrogen (δ15N) stable isotope ratios were quantified in yellow perch ( Perca flavescens), smallmouth bass ( Micropterus dolomieu), and baseline organisms to develop quantitative population metrics and describe dietary niche partitioning. The most severely damaged lake with a barren watershed had the lowest trophic positioning, smallest body size and niche area, and greatest niche overlap among fish species. Semi-barren and forested watershed lakes were more similar to reference lakes in isotopic metrics; however, elevated niche overlap and reduced trophic positioning suggests recovery in these lakes is ongoing. We found that including stable isotope analyses in lake recovery studies provided critical insights not captured by traditional biomonitoring approaches.

Chemical, biochemical, and bioactivity studies on some soda lakes, Wadi El-Natrun, Egypt

Wadi El-Natrun is one of the most observable geomorphological features in the North-Western Desert of Egypt; it contains several old saline and saline soda lakes. This study investigates physicochemical and biochemical characteristics and estimates the total phenolic content (TPC), total flavonoid content (TVC), and bioactivities of sediment, cyanobacteria, and brine shrimp (Artemia salina) in soda lakes, i.e., El-Hamra Lake 1 (H1) and El-Hamra Lake 2 (H2). These soda lakes are unique extreme ecosystems characterized by high pH (> 9.3), high alkalinity, and salinity. Some extremophilic microorganisms are hosted in this ecosystem. The results revealed that the chemical water type of studied lakes is soda-saline lakes according to the calculated percentage sequence of major cations and anions. Sodium ranked first among major cations with an abundance ratio of e% 58, while chloride came first among anions with an abundance ratio of e% 71, and bicarbonate and carbonate occupied the last rank with an abundance of 6%. The biochemical investigations showed that TPC and TVC are present in concern contents of sediment, cyanobacteria, and brine shrimp (A. salina) which contribute 89% of antioxidant capacity and antimicrobial activities. Thus, this study helps better understand the chemical and biochemical adaptations in soda lake ecosystems and explores natural sources with potential applications in antioxidant-rich products and environmental conservation efforts.