A 1 Ma sedimentary ancient DNA (sedaDNA) record of catchment vegetation changes and the developmental history of tropical Lake Towuti (Sulawesi, Indonesia).

Studying past ecosystems from ancient environmental DNA preserved in lake sediments (sedaDNA) is a rapidly expanding field. This research has mainly involved Holocene sediments from lakes in cool climates, with little known about the suitability of sedaDNA to reconstruct substantially older ecosystems in the warm tropics. Here, we report the successful recovery of chloroplast trnL (UAA) sequences (trnL-P6 loop) from the sedimentary record of Lake Towuti (Sulawesi, Indonesia) to elucidate changes in regional tropical vegetation assemblages during the lake's Late Quaternary paleodepositional history. After the stringent removal of contaminants and sequence artifacts, taxonomic assignment of the remaining genuine trnL-P6 reads showed that native nitrogen-fixing legumes, C3 grasses, and shallow wetland vegetation (Alocasia) were most strongly associated with >1-million-year-old (>1 Ma) peats and silts (114-98.8 m composite depth; mcd), which were deposited in a landscape of active river channels, shallow lakes, and peat-swamps. A statistically significant shift toward partly submerged shoreline vegetation that was likely rooted in anoxic muddy soils (i.e., peatland forest trees and wetland C3 grasses (Oryzaceae) and nutrient-demanding aquatic herbs (presumably Oenanthe javanica)) occurred at 76 mcd (~0.8 Ma), ~0.2 Ma after the transition into a permanent lake. This wetland vegetation was most strongly associated with diatom ooze (46-37 mcd), thought to be deposited during maximum nutrient availability and primary productivity. Herbs (Brassicaceae), trees/shrubs (Fabaceae and Theaceae), and C3 grasses correlated with inorganic parameters, indicating increased drainage of ultramafic sediments and laterite soils from the lakes' catchment, particularly at times of inferred drying. Downcore variability in trnL-P6 from tropical forest trees (Toona), shady ground cover herbs (Zingiberaceae), and tree orchids (Luisia) most strongly correlated with sediments of a predominantly felsic signature considered to be originating from the catchment of the Loeha River draining into Lake Towuti during wetter climate conditions. However, the co-correlation with dry climate-adapted trees (i.e., Castanopsis or Lithocarpus) plus C4 grasses suggests that increased precipitation seasonality also contributed to the increased drainage of felsic Loeha River sediments. This multiproxy approach shows that despite elevated in situ temperatures, tropical lake sediments potentially comprise long-term archives of ancient environmental DNA for reconstructing ecosystems, which warrants further exploration.

How do seasonal temperature variations influence interplay between toxic and non-toxic cyanobacterial blooms? Evidence from modeling and experimental data.

Summer cyanobacterial blooms exhibit a dynamic interplay between toxic and non-toxic genotypes, significantly influencing the cyanotoxin levels within a lake. The challenge lies in accurately predicting these toxin concentrations due to the significant temporal fluctuations in the proportions of toxic and non-toxic genotypes. Typically, the toxic genotypes dominate during the early and late summer periods, while the non-toxic variants prevail in mid-summer. To dissect this phenomenon, we propose a model that accounts for the competitive interaction between toxic and non-toxic genotypes, as well as seasonal temperature variations. Our numerical simulations suggest that the optimal temperature of the toxic genotypes is lower than that of the optimal temperatures of the non-toxic counterparts. This difference of optimal temperature may potentially contribute to explain the dominance of toxic genotypes at the early and late summer periods, situation often observed in the field. Experimental data from the laboratory align qualitatively with our simulation results, enabling a better understanding of complex interplays between toxic and non-toxic cyanobacteria.

Clustering evaluation of water quality for various classes of in-flow rivers in connected brackish lakes.

Brackish waters and estuaries at the lower reaches of rivers accumulate organic matter and nutrients from various sources in the watershed. Sufficient light and shallow water depth stimulate phytoplankton growth, resulting in a more diversified ecosystem with higher trophic levels. For effective watershed management, it is crucial to characterize the water quality of all rivers, including small and medium-sized ones. Our field survey assessed water quality parameters in 26 inflow rivers surrounding Lakes Shinji and Nakaumi, two consolidated brackish lakes in Japan. The parameters included water temperature, salinity, chlorophyll-a, and nutrients. The study used hierarchical clustering. The Silhouette Index was used to assess clustering outcomes and identify any difficulties in dispersion across clusters. The 26 rivers surrounding Lakes Shinji and Nakaumi were classified into six groups based on their water quality characteristics. This classification distinguishes itself from earlier subjective methods that relied on geographical factors. The new approach identifies a need for improved management of river water quality. The results of the cluster analysis provide valuable insights for future management initiatives. It is important to consider these findings alongside established watershed criteria.

Sediment DNA Records the Critical Transition of Bacterial Communities in the Arid Lake.

It is necessary to predict the critical transition of lake ecosystems due to their abrupt, non-linear effects on social-economic systems. Given the promising application of paleolimnological archives to tracking the historical changes of lake ecosystems, it is speculated that they can also record the lake's critical transition. We studied Lake Dali-Nor in the arid region of Inner Mongolia because of the profound shrinking the lake experienced between the 1300 s and the 1600 s. We reconstructed the succession of bacterial communities from a 140-cm-long sediment core at 4-cm intervals and detected the critical transition. Our results showed that the historical trajectory of bacterial communities from the 1200 s to the 2010s was divided into two alternative states: state1 from 1200 to 1300 s and state2 from 1400 to 2010s. Furthermore, in the late 1300 s, the appearance of a tipping point and critical slowing down implied the existence of a critical transition. By using a multi-decadal time series from the sedimentary core, with general Lotka-Volterra model simulations, local stability analysis found that bacterial communities were the most unstable as they approached the critical transition, suggesting that the collapse of stability triggers the community shift from an equilibrium state to another state. Furthermore, the most unstable community harbored the strongest antagonistic and mutualistic interactions, which may imply the detrimental role of interaction strength on community stability. Collectively, our study showed that sediment DNA can be used to detect the critical transition of lake ecosystems.

Aerobic anoxygenic phototrophs play important roles in nutrient cycling within cyanobacterial Microcystis bloom microbiomes.

BACKGROUND: During the bloom season, the colonial cyanobacterium Microcystis forms complex aggregates which include a diverse microbiome within an exopolymer matrix. Early research postulated a simple mutualism existing with bacteria benefitting from the rich source of fixed carbon and Microcystis receiving recycled nutrients. Researchers have since hypothesized that Microcystis aggregates represent a community of synergistic and interacting species, an interactome, each with unique metabolic capabilities that are critical to the growth, maintenance, and demise of Microcystis blooms. Research has also shown that aggregate-associated bacteria are taxonomically different from free-living bacteria in the surrounding water. Moreover, research has identified little overlap in functional potential between Microcystis and members of its microbiome, further supporting the interactome concept. However, we still lack verification of general interaction and know little about the taxa and metabolic pathways supporting nutrient and metabolite cycling within Microcystis aggregates. RESULTS: During a 7-month study of bacterial communities comparing free-living and aggregate-associated bacteria in Lake Taihu, China, we found that aerobic anoxygenic phototrophic (AAP) bacteria were significantly more abundant within Microcystis aggregates than in free-living samples, suggesting a possible functional role for AAP bacteria in overall aggregate community function. We then analyzed gene composition in 102 high-quality metagenome-assembled genomes (MAGs) of bloom-microbiome bacteria from 10 lakes spanning four continents, compared with 12 complete Microcystis genomes which revealed that microbiome bacteria and Microcystis possessed complementary biochemical pathways that could serve in C, N, S, and P cycling. Mapping published transcripts from Microcystis blooms onto a comprehensive AAP and non-AAP bacteria MAG database (226 MAGs) indicated that observed high levels of expression of genes involved in nutrient cycling pathways were in AAP bacteria. CONCLUSIONS: Our results provide strong corroboration of the hypothesized Microcystis interactome and the first evidence that AAP bacteria may play an important role in nutrient cycling within Microcystis aggregate microbiomes. Video Abstract.

The effects of intensive trapping on invasive round goby densities.

The round goby (Neogobius melanostomus) is an invasive benthic fish first introduced to the Laurentian Great Lakes in 1990 that has negatively impacted native fishes through increased competition for food and habitat, aggressive interactions, and egg predation. While complete eradication of the round goby is currently not possible, intensive trapping in designated areas during spawning seasons could potentially protect critical native fish spawning habitats. Baited minnow traps were spaced 10 meters apart in shallow water along a 100-meter stretch of shoreline within the Duluth-Superior Harbor during the round goby breeding period (June to October) with captured round gobies removed from interior traps (N = 10) every 48 hours. These traps were bracketed by two pairs of reference traps deployed weekly for 48 hours, from which round gobies were also tagged and released. The number of round gobies captured in the interior traps declined by 67% compared to reference traps over the course of the study, with extended periods of no captures. The tagged round gobies showed high site affinity, with 82.8% of tagged fish recaptured at the previous release site. The results indicate that even at open water sites, which allow natural migration of round gobies into the area, extensive trapping could reduce local population numbers.

Influence of land use change on habitat quality: a case study of coal mining subsidence areas.

Revealing the spatiotemporal evolution characteristics and key driving processes behind the habitat quality is of great significance for the scientific management of production, living, and ecological spaces in resource-based cities, as well as for the efficient allocation of resources. Focusing on the largest coal-mining subsidence area in Jiangsu Province of China, this study examines the spatiotemporal evolution of land use intensity, morphology, and functionality across different time periods. It evaluates the habitat quality characteristics of the Pan'an Lake area by utilizing the InVEST model, spatial autocorrelation, and hotspot analysis techniques. Subsequently, by employing the GTWR model, it quantifies the influence of key factors, unveiling the spatially varying characteristics of their impact on habitat quality. The findings reveal a notable surge in construction activity within the Pan'an Lake area, indicative of pronounced human intervention. Concurrently, habitat degradation intensifies, alongside an expanding spatial heterogeneity in degradation levels. The worst habitat quality occurs during the periods of coal mining and large-scale urban construction. The escalation in land use intensity emerges as the primary catalyst for habitat quality decline in the Pan'an Lake area, with other factors exhibiting spatial variability in their effects and intensities across different stages.

Metagenomics datasets of water and sediments from eutrophication-impacted artificial lakes in South Africa.

We present metagenomes of 16 samples of water and sediment from two lakes, collected from eutrophic and non-eutrophic areas, including pooled samples enriched with phosphate and nitrate. Additionally, we assembled 167 bacterial metagenome-assembled genomes (MAGs). These MAGs were de-replicated into 83 unique genomes representing different species found in the lakes. All the MAGs exhibited >70% completeness and <10% contamination, with 79 MAGs being classified as 'nearly complete' (completeness >90%), while 54 falling within 80-90% range and 34 between 75-80% complete. The most abundant MAGs identified across all samples were Proteobacteria (n = 80), Firmicutes_A (n = 35), Firmicutes (n = 13), and Bacteriodota (n = 22). Other groups included Desulfobacteria_I (n = 2), Verrucomicrobiota (n = 4), Campylobacterota (n = 4) and Actinobacteriota (n = 6). Importantly, phylogenomic analysis identified that approximately 50.3% of the MAGs could not be classified to known species, suggesting the presence of potentially new and unknown bacteria in these lakes, warranting further in-depth investigation. This study provides valuable new dataset on the diverse and often unique microbial communities living in polluted lakes, useful in developing effective strategies to manage pollution.

Heavy metal levels and human health risk implications associated with fish consumption from the lower Omo river (Lotic) and Omo delta lake (Lentic), Ethiopia.

This study is the first to determine the levels of heavy metals in commercially important fish species, namely Lates niloticus and Oreochromis niloticus and the potential human health risks associated with their consumption. A total of 120 fish samples were collected from the lower Omo river and Omo delta, with 60 samples from each water source. The fish tissue samples (liver and muscle) were analyzed using a flame atomic absorption spectrometer for nine heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn). The human health risk assessment tools used were the target hazard quotient (THQ), the hazard index (HI), and the target cancer risk (TCR). The mean levels of heavy metals detected in the liver and muscle of L. niloticus from the lower Omo river generally occurred in the order Fe > Zn > Pb> Cu > Mn> Cr > Co > Ni and Pb > Cu > Mn > Co > Ni, respectively. The mean levels of metals in the muscle and liver tissues of O. niloticus were in the order Fe > Pb > Zn > Mn > Cu > Cr > Co > Ni and Pb > Zn > Mn > Fe > Cu > Co > Ni, respectively. Similarly, the mean levels of heavy metals detected in the liver and muscle of L. niloticus from Omo delta occurred in the order Fe > Zn > Pb > Cu > Mn > Cr > Co > Ni and Fe > Pb > Zn > Mn > Cu > Co > Cr > Ni, respectively. The mean levels in the muscle and liver tissues of O. niloticus from the Omo delta were in the order Fe > Pb > Zn > Mn > Cu > Cr > Co > Ni and Pb > Fe > Zn > Mn > Co > Cu > Ni, respectively. The study revealed that the THQ values were below 1, indicating that consumption of L. niloticus and O. niloticus from the studied sites does not pose a potential non-carcinogenic health risk. Although the TCR values for Pb in this study were within the tolerable range, it's mean concentration in the muscle and liver tissues of both fish species from the two water bodies exceeded the permissible limit established by FAO/WHO. This is a warning sign for early intervention, and it emphasizes the need for regular monitoring of freshwater fish. Therefore, it is imperative to investigate the pollution levels and human health risks of heavy metals in fish tissues from lower Omo river and Omo delta for environmental and public health concerns.

A novel GH3-ß-glucosidase from soda lake metagenomic libraries with desirable properties for biomass degradation.

Beta-glucosidases catalyze the hydrolysis of the glycosidic bonds of cellobiose, producing glucose, which is a rate-limiting step in cellulose biomass degradation. In industrial processes, ß-glucosidases that are tolerant to glucose and stable under harsh industrial reaction conditions are required for efficient cellulose hydrolysis. In this study, we report the molecular cloning, Escherichia coli expression, and functional characterization of a ß-glucosidase from the gene, CelGH3_f17, identified from metagenomics libraries of an Ethiopian soda lake. The CelGH3_f17 gene sequence contains a glycoside hydrolase family 3 catalytic domain (GH3). The heterologous expressed and purified enzyme exhibited optimal activity at 50 °C and pH 8.5. In addition, supplementation of 1 M salt and 300 mM glucose enhanced the ß-glucosidase activity. Most of the metal ions and organic solvents tested did not affect the ß-glucosidase activity. However, Cu2+ and Mn2+ ions, Mercaptoethanol and Triton X-100 reduce the activity of the enzyme. The studied ß-glucosidase enzyme has multiple industrially desirable properties including thermostability, and alkaline, salt, and glucose tolerance.

Differences in archaeal diversity and potential ecological functions between saline and hypersaline lakes on Qinghai-Tibet Plateau were driven by multiple environmental and non-environmental factors beyond the salinity.

BACKGROUND: Saline lakes are home to various archaea that play special and crucial roles in the global biogeochemical cycle. The Qinghai-Tibet Plateau hosts a large number of lakes with diverse salinity ranging from 0.1 to over 400 g/L, harboring complex and diverse archaea. To the best of our knowledge, the formation mechanisms and potential ecological roles of archaea in Qinghai-Tibetan Plateau saline lakes remain largely unknown. RESULTS: Using High-throughput Illumina sequencing, we uncovered the vastly distinct archaea communities between two typical saline lakes with significant salinity differences on the Qinghai Tibet Plateau (Qinghai saline lake and Chaka hypersaline lake) and suggested archaea played different important roles in methanogenesis-related and nitrate reduction-related functions of these two lakes, respectively. Rather than the individual effect of salinity, the composite effect of salinity with diverse environmental parameters (e.g., temperature, chlorophyll a, total nitrogen, and total phosphorus) dominated the explanation of the variations in archaeal community structure in different habitats. Based on the network analysis, we further found the correlations between dominant archaeal OTUs were tight but significantly different between the two habitats, implying that archaeal interactions may also largely determine the shape of archaeal communities. CONCLUSION: The present study improved our understanding of the structure and function of archaea in different saline lakes on the Qinghai-Tibet Plateau and provided a new perspective on the mechanisms underlying shaping their communities.

Microbacterium salsuginis sp. nov., a halotolerant actinobacterium with antimicrobial activity.

A novel Gram-staining-positive actinobacterium with antimicrobial activity, designated CFH 90308T, was isolated from the sediment of a salt lake in Yuncheng, Shanxi, south-western China. The isolate exhibited the highest 16S rRNA gene sequence similarities to Microbacterium yannicii G72T, Microbacterium hominis NBRC 15708T and Microbacterium xylanilyticum S3-ET (98.5, 98.4 and 98.2 %, respectively), and formed a separate clade with M. xylanilyticum S3-ET in phylogenetic trees. The strain grew at 15-40 ºC, pH 6.0-8.0 and could tolerate NaCl up to a concentration of 15 % (w/v). The whole genome of strain CFH 90308T consisted of 4.33 Mbp and the DNA G+C content was 69.6 mol%. The acyl type of the peptidoglycan was glycolyl and the whole-cell sugars were galactose and mannose. The cell-wall peptidoglycan mainly contained alanine, glycine and lysine. The menaquinones of strain CFH 90308T were MK-12, MK-13 and MK-11. Strain CFH 90308T contained anteiso-C15:0, anteiso-C17:0, iso-C16:0 and iso-C15:0 as the predominant fatty acids. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between CFH 90308T and the other species of the genus Microbacterium were found to be low (ANIb <81.3 %, dDDH <25.6 %). The secondary metabolite produced by strain CFH 90308T showed antibacterial activities against Bacillus subtilis, Pseudomonas syringae, Aeromonas hydrophila and methicillin-resistant Staphylococcus aureus. Based on genotypic, phenotypic and chemotaxonomic results, the isolate is considered to represent a novel species of the genus Microbacterium, for which the name Microbacterium salsuginis sp. nov. is proposed. The type strain is CFH 90308T (=DSM 105964T=KCTC 49052T).

Size Distributions of Microplastics in the St Louis Estuary and Western Lake Superior.

Identifying the sources and fate of microplastics in natural systems has garnered a great deal of attention because of their implications for ecosystem health. This work characterizes the size fraction, morphology, color, and polymer composition of microplastics in western Lake Superior and its adjacent harbor sampled in August and September 2021. The results reveal that the overall microplastic counts are similar, with the harbor stations ranging from 0.62 to 3.32 microplastics per liter and the lake stations ranged from 0.83 to 1.4 microplastics per liter. However, meaningful differences between the sample locations can be seen in the size fraction trends and polymer composition. Namely, the harbor samples had relatively larger amounts of the largest size fraction and more diversity of polymer types, which can be attributed to the urbanized activity and shorter water residence time. Power law size distribution modeling reveals deviations that help in the understanding of potential sources and removal mechanisms, although it significantly underpredicts microplastic counts for smaller-sized particles (5-45 µm), as determined by comparison with concurrently collected microplastic samples enumerated by Nile Red staining and flow cytometry.

Genome analysis and classification of Xanthomonas bacteriophage AhaSv, a new member of the genus Salvovirus.

Xanthomonas phage AhaSv was isolated from lake water. Genome sequencing showed that its genome is a linear dsDNA molecule with a length of 55,576 bp and a G+C content of 63.23%. Seventy-one open reading frames (ORFs) were predicted, and no tRNAs were found in the genome. Phylogenetic analysis showed that AhaSv is closely related to members of the genus Salvovirus of the family Casjensviridae. Intergenomic similarity values between phage AhaSv and homologous phages were up to 90.6%, suggesting that phage AhaSv should be considered a member of a new species in the genus Salvovirus.

Migration and transformation behaviors of antibiotics in water-sediment system under simulated light and wind waves.

Antibiotics can generally be detected in the water-sediment systems of lakes. However, research on the migration and transformation of antibiotics in water-sediment systems based on the influences of light and wind waves is minimal. To address this research gap, we investigated the specific impacts of light and wind waves on the migration and transformation of three antibiotics, norfloxacin (NOR), trimethoprim (TMP), and sulfamethoxazole (SMX), under simulated light and wind waves disturbance conditions in a water-sediment system from Taihu Lake, China. In the overlying water, NOR was removed the fastest, followed by TMP and SMX. Compared to the no wind waves groups, the disturbance of big wind waves reduced the proportion of antibiotics in the overlying water. The contributions of light and wind waves to TMP and SMX degradation were greater than those of microbial degradation. However, the non-biological and biological contributions of NOR to degradation were almost equal. Wind waves had a significant impact on the microbial community changes in the sediment, especially in Methylophylaceae. These results verified the influence of light and wind waves on the migration and transformation of antibiotics, and provide assistance for the risk of antibiotic occurrence in water and sediments.

Seasonal variation and concentration of PAHs in Lake Balaton sediment: A study on molecular weight distribution and sources of pollution.

The temporal and spatial variations of 16 Polycyclic Aromatic Hydrocarbons (PAHs) were examined at multiple sites around Lake Balaton from February 2023 to January 2024. The results indicated that the concentrations of PAHs in sediment were high during the winter months, 448.35 to 619.77 ng/g dry weight, and low during the summer months, 257.21 to 465.49 ng/g dry weight. The concentration of high molecular weight PAHs (HMWPAHs), consisting of 5-6 rings, was greater than that of low molecular weight PAHs (LMWPAHs), which had 2-3 rings. The total incremental lifetime cancer risk (ILCR) for both dermal and ingestion pathways was high for both adults and children during the four seasons, with the highest records as the following: winter > spring > summer > autumn. The ecological effects of the 16 PAHs were negligible except for acenaphthylene (Acy) and fluorene (Fl), which displayed slightly higher concentrations during the autumn and spring, respectively.

Impact of typhoons on anthropogenic nitrogen sources in Lake Sihwa, South Korea.

This study investigated the nitrate dual isotopic compositions (δ15NNO3 and δ18ONO3) of water samples to trace nitrate sources in Lake Sihwa, which encompasses various land-use types (e.g., urban, industry, wetland, and agriculture). The biogeochemical interactions of anthropogenic nitrogen sources (e.g., soil, road dust, and septic water) were also evaluated through multiple pathways from terrestrial boundaries to the water column. Based on increased concentrations of dissolved total nitrogen (DTN; 3.1 ± 1.6 mg/L) after typhoon, the variation of element stoichiometry (N:P:Si) in this system shifted to the relatively N-rich conditions (DIN/DIP; 14.1 ± 8.1, DIN/DSi; 1.4 ± 1.8), potentially triggering the occurrence of harmful algal blooms. Furthermore, discriminative isotopic compositions (δ15NNO3; 4.0 ± 2.1 ‰, δ18ONO3; 6.1 ± 4.3 ‰) after the typhoon suggested the increased DTN input of anthropogenic origins within Lake Sihwa would be mainly transported from urban sources (76 ± 9 %). Consequently, the isotopic-based approach may be useful for effective water quality management under increased anthropogenic activities near aquatic systems.

Ecotoxicological risk assessments and components of persistent organic pollutants and metals in the historical settlement area (Iznik (Nicea) lake) large water resource sediments.

The main objectives of this study are to measure permanent organic and inorganic pollutants in detail in an area that hosts historical structures underneath and feeds the huge ecosystem with water, to reveal risk values. Total PAH concentrations in the samples ranged from 43.41 to 202.7 ng/g. Total OCP concentration ranged from 5.15 to 17.98 ng/g, while total PCB concentration ranged from 0.179 to 0.921 ng/g. PCB 28/31, 138, and 153 are the highest detected PCBs. It was found that the lake sediment reached toxic equivalent quotient (TEQ) values of 29.21 for total PAHs and 28.90 for carcinogenic PAHs. Negligible concentration risk quotient had a low to moderate ecological and toxicological risk between 12.91 and 64.42. Highest pollution index value was found 3.81 and the risk index value reached 417.4. It has been revealed that toxicologically risky components accumulate over many years even in the best-protected water resources.

Regime shift in microalgal dynamics: Impact of water level changes on planktonic and benthic algal biomass.

Whole-lake microalgal biomass surveys were carried out in Lake Balaton to investigate the seasonal, spatial, and temporal changes of benthic algae, as well as to identify the drivers of the phytobenthos. Phytobenthos was controlled mainly by light: the highest benthic algal biomass was in the shallow littoral region characterized by large grain size (sand) with good light availability but lower nutrient content in the sediment. During the investigated period, phytoplankton biomass showed a significant decrease in almost the entire lake. At the same time, the biomass of benthic algae increased significantly in the eastern areas, increasing the contribution of total lake microalgae biomass (from 20 % to 27 %). Benthic algal biomass increase can be explained by the better light supply, owing to the artificially maintained high water level which greatly mitigates water mixing. The decrease in planktonic algal biomass could be attributed to increased zooplankton grazing, which is otherwise negatively affected by mixing. As a result of the high water level, the trophic structure of the lake has been rearranged in recent decades with a shift from the planktonic life form to the benthic one while the nutrient supply has largely remained unchanged.

Effects of metformin on wild fathead minnows (Pimephales promelas) using in-lake mesocosms in a boreal lake ecosystem.

Due to its widespread use for the treatment of Type-2 diabetes, metformin is routinely detected in surface waters globally. Laboratory studies have shown that environmentally relevant concentrations of metformin can adversely affect the health of adult fish, with effects observed more frequently in males. However, the potential risk to wild fish populations has yet to be fully elucidated and remains a topic of debate. To explore whether environmentally relevant metformin exposure poses a risk to wild fish populations, the present study exposed wild fathead minnows (Pimephales promelas) to 5 or 50 µg/L metformin via 2 m diameter in-lake mesocosms deployed in a natural boreal lake in Northern Ontario at the International Institute for Sustainable Development - Experimental Lakes Area (IISD-ELA). Environmental monitoring was performed at regular intervals for 8-weeks, with fish length, weight (body, liver and gonad), condition factor, gonadosomatic index, liver-somatic index, body composition (water and biomolecules) and hematocrit levels evaluated at test termination. Metabolic endpoints were also evaluated using liver, brain and muscle tissue, and gonads were evaluated histologically. Results indicate that current environmental exposure scenarios may be sufficient to adversely impact the health of wild fish populations. Adult male fish exposed to metformin had significantly reduced whole body weight and condition factor and several male fish from the high-dose metformin had oocytes in their testes. Metformin-exposed fish had altered moisture and lipid (decrease) content in their tissues. Further, brain (increase) and liver (decrease) glycogen were altered in fish exposed to high-dose metformin. To our knowledge, this study constitutes the first effort to understand metformin's effects on a wild small-bodied fish population under environmentally relevant field exposure conditions.