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A massive Planktothrix rubescens bloom was observed during 2022 in the Lake Avernus, a volcanic lake located in Campania Region (Southern Italy). The cyanobacterial mass migrated, through a channel, to the near Gulf of Pozzuoli, causing the contamination of two marine sites dedicated to mussel farming, thus posing a potential risk for consumers' health. Mussel and water samples, from both the sea and the lake were collected weekly and analyzed by liquid chromatography coupled to tandem mass spectrometry, for identification and quantification of 10 microcystins. Moreover, the samples were analyzed by high resolution mass spectrometry in untargeted mode to determine other cyanotoxins basing on the accurate mass of the precursor ions and their MS/MS spectra. The microcystins were not detected at all, whereas other bioactive peptides, such as anabaenopeptins and oscillamide Y, were detected according to the toxicological profiles described for Planktothrix rubescens in the scientific literature. The case reported represents a modern approach for rapid characterization of some environmental outbreaks, as well as an example regarding how the public Health Authority can manage the possible risk for food safety, due to unknown substances and to enforce legal follow up actions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Polycyclic aromatic hydrocarbons (PAHs) are a class of organic pollutants widely present in various environmental media. Some PAHs have carcinogenic, teratogenic, and mutagenic effects. Urban lakes are severely polluted by PAHs due to human activities. Longyang Lake (LL) and Moshui Lake (ML), which serve as entry lakes for Wuhan's "Six Lakes Connectivity" project, were chosen as the study areas to learn about the migration of PAHs. Water flows from LL to ML through the Mingzhu River. Multi-Media Mass Balance Model (MMBM) and fugacity fractions (ff) were used to characterize the migration of PAHs under the hydrological connectivity project. Compared to ff, the MMBM can describe the migration of PAHs in a more detailed and quantitative way. The concentration of PAHs in water of LL decreased from 36.5 ng L -1 to 26.59 ng L -1 over 43 days, while those in ML increased from 46.8 ng L -1 to 198.25 ng L -1 over 141 days. Sediment takes a longer time to decrease to stabilization. The concentration of PAHs in the sediment of LL decreased from 932 ng g -1 to 0.95 ng g -1 over 13.33 years, while those in ML decreased from 4812 ng g -1 to 1.04 ng g -1 over 16.96 years. The stabilized concentrations were consistently lower than the observed concentrations and fell below the modeled stabilized concentrations obtained in the unconnected case (2170 ng L -1 in water and 40.81 ng g -1 in sediment). The MMBM showed that PAHs in the lake are mainly exported through runoff. However, modeling results indicated that upstream LL did not increase total PAHs concentrations in the ML because the output from ML was significantly higher. Sediment parameters sensitively influenced the results of the model. Although the simulation results showed reductions of PAHs pollution in two lakes under the hydrological connectivity project, long-term monitoring results are needed to optimize the model., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Microplastics (MPs) are one of the most widespread environmental pollutants, but their risk assessment to freshwater ecosystems has not been clearly investigated. Risk assessment has been constrained by the absence of MP concentration in some environment, the diverse types and shapes of MPs, and limitations of polystyrene (PS)-biased toxicity studies. This study examined exposure to MPs in rivers and lakes worldwide, including China (the Three Gorges Dam & Yangtze River (TGD & YR) and the lakes of Wuhan city (WL)), Vietnam (seven lakes of Da Nang city (7UL)), Europe (the Rhine River (RR)), Finland (Kallavesi Lake (KL)), Argentina (nine lakes in the Patagonia region (9LP)), Brazil (Guaiba Lake (GL)), and South Korea (Nakdong River (NR), Han River (HR), and Anyang Stream (AS)), and assessed the risks to aquatic ecosystems based on the toxicity information and morphology of MPs. We also examine the limitations of the traditional risk quotient (RQ)-based risk assessment method for PS-biased toxicity studies. Potential ecological risks were assessed using pollution load index (PLI) and potential ecological risk index (PERI) considering the hazard scores of MP types. RQ was approximately 10 -6 to 10 -4 , indicating negligible risk to aquatic organisms. In contrast, the calculated PLI (>30: extreme danger) and PERI (>1200: extreme danger) values suggest that MPs represent serious ecological threats at all the study locations. Furthermore, principal component analysis (PCA) indicated that MP fibers and fragments have a significant impact on the risks for freshwater systems. These MP morphologies derive from surrounding fishing and agricultural activities, and household and clothing industries. The areas surrounding these rivers and lakes are expected to become more densely populated, potentially leading to increased MP emissions and higher risks, suggesting a need to expand wastewater treatment facilities, reduce consumption of single-use plastics, and raise societal awareness of waste plastics., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The prevalence of microplastics (MPs) in Tai Lake poses significant environmental concerns; however, research on MPs' ecological risk assessment is limited. To advance our understanding of MPs' toxicity in Tai Lake, species sensitivity distributions (SSDs) were used to evaluate how organisms respond to different MPs properties and endpoints in Tai Lake. A total of 102 data points were categorized and utilized in SSD estimation. It was found that the hazardous concentration for 5% of species (HC 5 ) for MPs is 237.98 (26.89-2.59 × 10 3 ) particles/L in Tai Lake. In terms of endpoints, the HC 5 follows the descending order: reproduction 1.03 × 10 3 (16.30-6.05 × 10 3 ) > growth 153.36 (11.37-2.53 × 10 3 ) > mortality 67.60 (4.55-4.29 × 10 3 ) particles/L. It was found that fibers and polyvinyl chloride (PVC) exhibit the most adverse effects among the MPs' shapes and types assessed. Among size fractions, 100-1000 μm exhibited higher toxicity to Tai Lake biota compared to 1-10 and 10-100 μm. The ecological risk assessment suggested that the likelihood of ecological risk from MPs in Tai Lake is higher for fibers and PVC. Notably, fish species were identified as the most sensitive species in Tai Lake compared to crustaceans and mollusks. This research leads to a better insight into the physical characteristics and toxicity endpoints of MPs in determining their toxicity for estimating SSDs in aquatic environments. Moreover, it highlights the importance of implementing effective management strategies to address the negative impacts of MPs in Tai Lake., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Use of phosphorus (P)-inactivating material to immobilize P released from sediment, typically under anoxic condition, is a method often considered to reduce lake internal P loading for eutrophication control. This study found that immobilizing the released P from sediment induced accumulation of algal-available P (NaHCO 3 and Fe oxide paper strip extractable P) in P-inactivating material which was even higher than those in raw sediment at initial stage (by 29.7% and 85.7%), although algal-available P substantially decreased in sediment after addition of the material and in the separated sediment from the mixtures. Given the possibility of exposing P-inactivating material to phytoplankton systems in overlying water typically during sediment resuspension, the accumulation suggested the potential of the resuspended material changing as P source for phytoplankton growth, increasing the uncertainties of sediment P immobilization method. Future work should focus more on the resuspension characteristics of P-inactivating material and on enhancing the capability of immobilizing algal-available P by the materials during internal P pollution control, especially in shallow lake., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

In the current study, a protected subtropical wetland in Bihar (India), Baraila Lake, was investigated for heavy metal (Pb and Hg) status. These metals tend to bioaccumulate in fish, posing a concern to human health. This study reported the concentration of lead and mercury in water, sediment, and fish muscles of Baraila Lake in the year 2022. The samples were collected from pre-monsoon and post-monsoon seasons at four sampling locations, i.e., Loma, Dhulwar, Chakaiya, and Kawai Baraila, and were analyzed in triplicates. Lead concentration in water samples of all four sites of Baraila Lake observed during pre-monsoon and post-monsoon season exceeded the permissible limit for drinking water, while the mercury concentration of all sites was under the permissible limit in both seasons as prescribed by WHO. The extent of elemental pollution was evaluated using the Geo-accumulation index (Igeo), contamination factor (CF), contamination degree (C d ), ecological risk factor (E r ), and the potential ecological risk index (R i ). Lead concentration in fish muscles of both seasons exceeded the permissible limit, while the concentration of mercury exceeded in Xenentodon cancila (0.55 ± 0.07 µg/g) during the pre-monsoon season. Also, estimated daily intake (EDI), target hazard quotient (THQ), and hazard index (HI) were calculated in different fish muscles to assess potential human health risks. A higher THQ value of 1.303 was observed in carnivore fish during the pre-monsoon season., Competing Interests: Declarations. Ethics Approval: Ethics clearance is not necessary. Competing Interests: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Lakes are sources of atmospheric carbon dioxide (CO 2 ), contributing to global climate change. Temporal variations in lake CO 2 emissions are pronounced, with algal growth and precipitation identified as important drivers. Eutrophic lakes often act as atmospheric CO 2 sinks during the growing season. However, these lakes can also emit CO 2 during the same period, a paradox that we hypothesize is driven by precipitation. This study tests this hypothesis and examines how rainstorms influence lake CO 2 emissions. To investigate, seven buoys were deployed in eutrophic Lake Taihu and a major inflow river to monitor water quality at 4-h intervals throughout 2021. CO 2 flux (FCO 2 ) was calculated using integrated methods, including gas diffusion models, the CO2calc program, and machine learning algorithms, based on water quality and meteorological data. Results revealed that only rainstorms (daily rainfall >50 mm) significantly increased FCO 2 . Although only three rainstorm events occurred, they accounted for 12.15% of the annual CO 2 emissions. During the growing season, the lake was a net CO 2 source, but without rainstorm-induced emissions, it would have functioned as a CO 2 sink, highlighting the crucial role of rainstorms in shifting lake dynamics. Piecewise structural equation modeling indicated that both abiotic factors (e.g., gas transfer velocity) and biotic factors (e.g., aquatic metabolism) influenced by rainstorms contributed to the elevated FCO 2 . These findings suggest that future reductions in lake FCO 2 due to eutrophication, combined with more frequent rainstorms under climate change, could amplify the impact of extreme precipitation on CO 2 emissions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The increase in dissolved organic carbon (DOC) concentrations in freshwater systems has received considerable attention due to its implications for drinking water treatment and numerous limnological processes. While past studies have documented the influence of recovery from acidification and climate change on long-term DOC trends, the emerging importance of these explanatory factors remains less understood. In addition, few studies have followed up on recent trends in sites that have undergone increases in DOC. Using a dataset from 1980 to 2020, we investigated interannual variations in DOC and dissolved organic nitrogen (DON) in 49 lakes across four eastern Canadian regions with a history of increases in DOC. We identified recent shifts in DOC patterns using LOESS smoothing and piecewise regression. We observed a stabilizing pattern or even a decrease (p < 0.001) in high acidification regions (Dorset and Nova Scotia), where increases in DOC were previously documented. At the low acid deposition region, IISD-Experimental Lakes Area, an increasing pattern in DOC stabilized in the early 2000s; however, DOC appears to be increasing again in recent years (p = 0.03). Our analysis identified precipitation and SO 4 deposition as the primary explanatory variables for DOC patterns (explaining 56-71% of variance). However, because acid deposition has declined substantially, climate and local watershed factors are becoming increasingly influential, leading to the emergence of new DOC patterns. Long-term changes in DOC and DON were not always synchronous, as these were often correlated with different factors (e.g., DON with ammonium deposition). This resulted in observable shifts in DOC:DON ratios, indicative of changes in dissolved organic matter (DOM) composition. We underscore the importance of ongoing monitoring in diverse regions because of the changing nature of environmental variables and new emerging trends., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Microplastic (MP) pollution has been observed in a variety of ecosystems, but there is a limited number of studies on reservoir ecosystems. The aim of this study was to determine the levels of MP contamination in sediment, water and commercially important fish species (Cyprinus carpio, Perca fluviatilis, Atherina boyeri and Sander lucioperca) collected from the Yamula Reservoir in Türkiye. Water samples were collectes at five stations. Four sediment samples were collected from the lake. As sediments from the lake represent a vital element of the lake ecosystem, they function as a historical archive that reflects alterations in land use and the characteristics of the lake over time. The average amounts of MPs observed in sediment and water samples were 0.12 MP/g and 0.58 MP/m 3 respectively. The digestive systems of 30 individuals of each fish species were examined. The highest amount of MP was observed for C. carpio (6 ± 5.9 MP/individual), while the lowest amount of MP was observed for A. boyeri (1.8 ± 1.7 MP/individual). MP abundance in S. lucioperca and P. fluviatilis was 2 ± 2.8 and 4.6 ± 6.3 MP per individual. The most commonly observed polymer types were polypropylene (67%), polyvinyl alcohol (13%), polyethylene resin (13%) and high-density polyethylene (7%). The pollution load indexes determined for each fish species from the highest to the lowest were as follows: 1.83 (C. carpio) 1.6 (S. lucioperca) 1.05 (P. fluviatilis) and, 1 (A. boyeri). The findings of the study indicate that all sampling stations, including both sediment and water, are contaminated with MPs. Furthermore, the results demonstrate that all examined fish species ingest MPs. Additionally, the results indicate that fish inhabiting a wide range of habitats and consuming diverse diets are more susceptible to MP contamination., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

A major consequence of the Industrial Revolution was the acidification of continental water bodies by sulfates (SO 4 2- ) and nitrates deposited over long-range distance from atmospheric emissions. Regulation policies were implemented in the 1980s leading to the general decrease of SO 4 2- concentrations in freshwaters and progressive recovery from acidification, a complex process that is still ongoing. The surface water SO 4 2- decrease has been linked to declining calcium (Ca 2+ ) and increasing dissolved organic carbon (DOC) concentration. Here, up to 40 years (1983-2023) of chemical data in 46 lakes of Eastern Canada are analyzed for long-term trends and spatial patterns along a large gradient of SO 4 2- deposition. The average lake SO 4 2- concentration decreased along the distance from sulfur dioxide sources. SO 4 2- concentration decreased significantly in every lake and faster close to the emission sources. In 70% of the lakes, the SO 4 2- decline drove concurrent but slower Ca 2+ and magnesium declines, leading to an overall increase in the Ca 2+ /SO 4 2- ratio, in pH and in alkalinity for 72% of the lakes. The Ca 2+ concentration is now below the crucial threshold for large zooplankton species in most lakes. Increasing trends in lake sodium concentration suggest an intensification of mineral weathering in catchment soils, potentially linked to rising temperatures, which could be involved in the observed recovery. DOC increased in 67% of lakes which drove a concurrent increase in aluminum in some lakes. The numerous environmental changes in progress across temperate and boreal lakes will deeply modify the structure and functioning of these systems, especially in the context of climatic changes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Microplastics (MPs) and polycyclic aromatic hydrocarbons (PAHs) have been found in all environment matrices and are of concern worldwide. In this study, PAHs were determined in Baiyangdian Lake, China, and the effects of MPs on the migration of PAHs at the lake interfaces were analyzed. The average abundances of detected MPs were 9595 items m -3 for water and 1023 items kg -1 for sediment. The detected MPs were polyamide 6, polypropylene, polyethylene, and polyethylene terephthalate. The average Σ 16 PAHs in the water, sediment, and air were 1338 ng L -1 , 751 ng g -1 dry weight, and 395 ng m -3 , respectively. At the air-water interface, naphthalene, and phenanthrene volatilized from water to air, whereas benzo(b)fluoranthene, benzo(k)fluoranthene, and dibenzo(a,h)anthracene deposited from air to water. The fugacity fraction between sediment and bottom water ranged from 0.88 to 0.99, which indicated net volatilization at the water-sediment interface. The adsorption capacities of the four MPs for the PAHs ranged from 39.4 to 99.8 μg g -1 with a desorption efficiency range of 0.01%-44.3% under oscillation. According to the distribution of PAHs on the MPs, the exchange fluxes of PAHs at the water-air and sediment-water interfaces were recalculated. The results showed that the MPs could increase deposition of the PAHs from air to the water (ΔF A-W : -221 × 10 -2 to -0.01 × 10 -2  ng m -2  d -1 ) and the volatilization of PAHs from sediment to water (ΔF W-S : -79.7 × 10 5 to 180 × 10 5  ng m -2  d -1 ), which suggests that MPs increase the risk of PAHs in water and to aquatic organisms., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Upgrading wastewater treatment plants (WWTPs) is a global practice for achieving increasingly stringent nutrient discharge objectives set by governments to accommodate population growth and reduce surface water pollution. However, associated downstream improvements in nutrient conditions are difficult to determine in nearshore regions of large aquatic ecosystems due to complex biophysical processes. We conducted a nine-year water quality study and analyzed the data using linear mixed models (LMMs) within a Before-After-Control-Impact (BACI) framework to assess effects of an upgrade to the Duffin Creek Water Pollution Control Plant (DCWPCP) on surface water nutrient conditions and proliferation of nuisance benthic algae (Cladophora glomerata) in nearshore Lake Ontario. The DCWPCP upgrade resulted in increased effluent concentrations and loads of nitrite+nitrate (NO 2+3 ) due to enhanced nitrification, while reducing total Kjeldahl nitrogen and ammonia+ammonium (NH 3+4 ). However, total phosphorus (TP) in effluent only changed slightly due to operational constraints during plant upgrade. For nearshore nutrient conditions, our LMM-BACI framework revealed that, after upgrade, NH 3+4 decreased at impact site relative to control sites. In contrast, following upgrade, an observed decline in NO 2+3 concentrations was less pronounced at impact site compared to control sites, suggesting increased NO 2+3 inputs into nearshore surface water from the DCWPCP. We could not detect obvious improvement in nearshore TP concentrations, stoichiometric ratios of total inorganic nitrogen to TP and NO 2+3 to TP, or phosphorus tissue content of Cladophora, likely due to the only slight reduction in TP from the DCWPCP. Overall, our findings showed that the DCWPCP upgrade increased NO 2+3 inputs, which could have important implications for nutrient management and trade-offs associated with WWTP upgrades that reduce one chemical species at the expense of another. Other researchers may find our LMM-BACI framework useful to detect localized impacts of nutrient inputs in nearshore and coastal areas where multiple physical and climate drivers influence water quality., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 The Authors. Published by Elsevier B.V. All rights reserved.)

A novel magnetic mesoporous fluorinated metal-organic framework material (Fe 3 O 4 @MIP-206-F) has been synthesized specifically for application as an adsorbent for perfluoroalkyl carboxylic acids (PFCAs) extraction by magnetic solid-phase extraction (MSPE). The carefully designed Fe 3 O 4 @MIP-206-F material features an appropriate porosity, open metal sites of Zr, and functional groups (fluorine and amino) conducive to the adsorption process. The distinctive architecture of the material endows it with exceptional extraction capabilities for PFCAs. Adsorption mechanisms encompass acid-base interactions, hydrophobic interactions, F-F interactions, electrostatic interactions, and size complementarity. Optimization of key parameters has significantly improved the extraction efficiency of MSPE. When coupled with gas chromatography-mass spectrometry (GC-MS), MSPE offers rapid and highly sensitive analysis of PFCAs. The method demonstrates wide linear range (0.050-50 ng mL -1 ), low detection limits (0.0010-0.0019 ng mL -1 ), good recoveries (86.7 % to 111 %), and exceptional intra- and inter-day precision. This approach accurately quantifies PFCAs in lake water and groundwater samples, enabling precise assessment of environmental contamination levels and supporting targeted remediation efforts., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

This study aims to determine the spatial distribution of heavy metal pollution in Ermenek Dam Lake, water quality assessment and pollution sources. For this purpose, samples were taken 6 times a year from 12 points determined in 2024. Physico-chemical parameters and heavy metals were analyzed in the study. Using the analysis results, indexes such as Water Quality Index and Heavy Metal Pollution Index were calculated. The results show that the lake water complies with TS 266 and WHO standards. The index results indicate that the lake water is at low pollution and risk level and is safe. The distribution and sources of heavy metals were examined using correlation analysis, Principal Component Analysis and Hierarchical Cluster Analysis. Correlation analyses showed that there were significant relationships between pH, temperature, conductivity, dissolved oxygen and TDS and heavy metals. PCA results revealed that Zn was positively correlated with temperature and pH, while Mn and Ni were inversely correlated. The alignment of Pb, Cu and Cd in the same direction showed that these parameters were affected by common sources. HCA results showed that Cr and Fe have similar transport and source properties, while Mn and Ni are affected by different sources. In general, it was determined that heavy metal pollution in lake water was at low levels and local concentrations were present. The study revealed the effects of anthropogenic activities on the lake ecosystem. The findings of the study provide a guiding basis for water quality management in similar hydrological systems., Competing Interests: Declarations. Conflict of interest: The authors declare no competing interests. Ethical approval: The author of this article has not conducted any studies involving human subjects or animals. The author has read, understood and complied with the "Ethical Responsibilities of Authors" statement in the Instructions for Authors., (© 2025. The Author(s).)

Algal decomposition plays an important role in affecting phosphorus (P) release from sediments in eutrophic lakes under global warming. Yet how rising air temperature affect endogenous P release from sediments during the algal decomposition is poorly understood. In this study, effect of increasing air temperature on endogenous P release was investigated. A 22-day laboratory warming simulation experiment was conducted, with the overlying water and sediments collected from Lake Chaohu incubated in microcosms at three temperatures (21, 28 and 37°C). Dynamics of P fractions and related physiochemical properties in water and sediments were measured, and P release rate from sediments was calculated. Rising air temperature significantly reduced redox potential, but elevated pH, dissolved organic carbon (C) and alkaline phosphatase activity in water. For the average value during incubation, rising temperature significantly elevated P release rate and soluble reactive P by 3 times in overlying water, and greatly reduced total organic P (by 19.0%) in sediments, while did not affect total inorganic P in sediments. The NH4Cl-Po and NaHCO3-Po concentrations in sediments showed the greatest decrease (accounting for 97.6% of total decrease) during the experiment. Dynamics of P release rate, soluble reactive P, dissolved organic C in water and organic P, total organic C in sediments during incubation were also differed among different temperatures. The P release rate was significantly and negatively correlated with dissolved organic C and redox potential at all temperatures, negatively correlated with sediment inorganic P at 21°C, while negatively correlated with sediment organic P at 37°C. The results revealed that rising temperature strongly stimulated endogenous P release from sediments during the decay of algal residues, which was mainly due to the acceleration of organic P mineralization Warming-induced changes in the amount and dynamics of dissolved organic C played the dominant role in accelerating P release from sediments., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2025 Hu et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

In this study, the technique of fluorescence spectroscopy coupled with chemometric methods is used to analyse samples of Lake Chad Spirulina "Arthrospira platensis" (AP), either harvested and conditioned by using the traditional method at different seasons or industrially processed. The content of minor fluorescent nutrients is investigated. To this end, fluorescence excitation-emission matrices (EEMs) of 46 AP samples are recorded in aqueous solution. Synchronous fluorescence (SF) spectra are extracted from these EEMs and their important features are compared to those of PARAFAC methods. Synchronous fluorescence scanning allows different AP samples to be characterized in a single scan. The SF and PARAFAC methods yielded two groups of fluorescent compounds; the first group, consisting of vitamin-like molecules, shows excitation/emission (ex/em) peaks at 340/460, 390/462, 370/440 and 450/526 nm, attributed to caffeic acid, vitamin K, E and riboflavins respectively, while the second group, consisting of pigments, shows ex/em peaks at 610/654, 590/630 and 570/644 nm, attributed to phycocyanins, C-phycocyanin and allophycocyanin. Our fluorescence data showed that while both vitamins and pigments are present in AP during the rainy season, only fluorescent components of vitamin-like compounds are present during the dry season. PCA methods allowed classifying different AP samples according to their geographic origin and harvesting season. Fluorescence spectroscopy therefore appears to be a powerful technique for rapidly assessing the chemical composition of AP., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Floodplains function as global hotspots for the natural production of methane. Some of this methane can be oxidized by methanotrophic bacteria and assimilated into their biomass before reaching the atmosphere. Consequently, aquatic invertebrates that feed on methanotrophic bacteria may transfer methane-derived carbon to higher trophic levels in the aquatic food chain. Our objective was to investigate the proportion of methane-derived carbon in the biomass of apex fish across 34 lakes from four major Neotropical floodplains (Amazon, Pantanal, Araguaia, and Paraná) using stable isotopes of carbon (δ 13 C). We found that methane-derived carbon contributed between 5 % and 16 % to the biomass of 37 apex fish species, providing, for the first time, evidence of the fish's role in the methane cycle in the Neotropics. Consumers in the Amazon and Pantanal floodplains, the largest and most significant regions for methane production, exhibited higher levels of methane-derived carbon in their biomass (11.06 ± 2.87 % and 9.84 ± 3.08 %, respectively). These results underscore the role of aquatic consumers in mitigating methane emissions in floodplains, as methane oxidation and assimilation are linked to reduced emissions. Therefore, conserving fish assemblages in floodplains through strategies that maintain the natural dynamics of these ecosystems is essential for controlling natural methane emissions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Harmful Algal Blooms (HABs) can originate from a variety of reasons, including water pollution coming from agriculture, effluent from treatment plants, sewage system leaks, pH and light levels, and the consequences of climate change. In recent years, HAB events have become a serious environmental problem, paralleling population growth, agricultural development, increasing air temperatures, and declining precipitation. Hence, it is crucial to identify the mechanisms responsible for the formation of HABs, accurately assess their short- and long-term impacts, and quantify their variations based on climate projections for developing accurate action plans and effectively managing resources. From this point of view, this present study utilizes empirical dynamic modeling (EDM) to predict chlorophyll-a concentration of Lake Erie. This method is characterized by its nonlinearity and nonparametric nature. EDM has a key advantage in that it overcomes the limitations of traditional statistical modeling by utilizing data-driven attractor reconstruction. Chlorophyll-a is a critical parameter in the prediction of HAB events. Lake Erie is an inland water body that experiences frequent HAB phenomena due to its location. The EDM demonstrated exceptional performance, and these findings imply that the EDM model can effectively capture the underlying dynamics of chlorophyll-a changes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Human activities such as agriculture and urban development are linked to water quality degradation. Canada represents a large and heterogeneous landscape of freshwater lakes, where variations in climate, geography and geology interact with land cover alteration to influence water quality differently across regions. In this study, we investigated the influence of water quality and land use on bacterial communities across 12 ecozones. At the pan-Canadian scale, total phosphorus (TP) was the most significant water quality variable influencing community structure, and the most pronounced shift was observed at 110 μg/L of TP, corresponding to the transition from eutrophic to hypereutrophic conditions. At the regional scale, water quality significantly explained bacterial community structure in all ecozones. In terms of land use effect, at the pan-Canadian scale, agriculture and, to a lesser extent, urbanisation were significant land use variables influencing community structure. Regionally, in ecozones characterised by extensive agriculture, this land cover variable was consistently significant in explaining community structure. Likewise, in extensively urbanised ecozones, urbanisation was consistently significant in explaining community structure. Overall, these results demonstrate that bacterial richness and community structure are influenced by water quality and shaped by agriculture and urban development in different ways., (© 2025 John Wiley & Sons Ltd.)

Ecosystem-scale primary production may be proximately limited by nitrogen (N) but ultimately limited by phosphorus (P) because N 2 fixation contributes new N that accumulates relative to P at ecosystem scales. However, the duration needed to transition between proximate N limitation and ultimate P limitation remains unknown for most ecosystems, including lakes. Here we present the results of a fully replicated, multi-annual lake mesocosm experiment that permitted full air-water-sediment interactions that mimicked lake ecosystem ecology. We manipulated N supply relative to P to achieve a gradient of N:P stoichiometry. Despite N 2 fixation contributing as much as 80% of reactive N in the low N treatments, phytoplankton biomass in these treatments was not different from the unfertilized controls. This suggests that primary production remained N limited in the lowest N treatments, even when N 2 fixation was substantial. Although fixed N inputs reduced the N imbalance relative to P in the low N treatments seasonally, fixed N did not accumulate over multiple years. Additionally, reactive N did not readily accumulate in the high N treatments. Instead, water column stoichiometry was proportional to the experimental N and P additions, suggesting a strong influence from external nutrient loading. Thus, we found no evidence that N accumulation from N 2 fixation was sufficient to trigger a transition to ultimate P limitation seasonally or across our 3-year experiment. Rather, our results indicate that proximate N limitation perpetuates in eutrophic lakes, likely due to N export being proportional to its inputs. These findings offer new insight regarding the biogeochemical controls on ecosystem stoichiometry and their influence on the timeframe for proximate N limitation and ultimate P limitation in freshwater, marine, and terrestrial ecosystems., (© 2025 The Author(s). Ecology published by Wiley Periodicals LLC on behalf of The Ecological Society of America.)

Lake Baiyangdian is one of China's largest macrophyte - derived lakes, facing severe challenges related to water quality maintenance and eutrophication prevention. Dissolved organic matter (DOM) was a huge carbon pool and its abundance, property, and transformation played important roles in the biogeochemical cycle and energy flow in lake ecosystems. In this study, Lake Baiyangdian was divided into four distinct areas: Unartificial Area (UA), Village Area (VA), Tourism Area (TA), and Breeding Area (BA). We examined the diversity of DOM properties and sources across these functional areas. Our findings reveal that DOM in this lake is predominantly composed of protein - like substances, as determined by excitation - emission matrix and parallel factor analysis (EEM - PARAFAC). Notably, the exogenous tyrosine-like component C1 showed a stronger presence in VA and BA compared to UA and TA. Ultrahigh - resolution mass spectrometry (FT - ICR MS) unveiled a similar DOM molecular composition pattern across different functional areas due to the high relative abundances of lignan compounds, suggesting that macrophytes significantly influence the material structure of DOM. DOM properties exhibited specific associations with water quality indicators in various functional areas, as indicated by the Mantel test. The connections between DOM properties and NO 3 N and NH 3 N were more pronounced in VA and BA than in UA and TA. Our results underscore the viability of using DOM as an indicator for more precise and scientific water quality management., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to affect the work reported in this article., (Copyright © 2023. Published by Elsevier B.V.)

Water samples were collected during each of the 2012-2019 Cooperative Science and Monitoring Initiative (CSMI) cruises aboard the U.S. EPA R/V Lake Guardian as part of the Great Lakes Fish Monitoring and Surveillance Program (GLFMSP) lower food web contaminant assessment. The CSMI rotates around each of the Great Lakes in a 5-year cycle providing top-to-bottom biological, chemical, and physical environmental assessments, including dissolved-phase surface water studies at two sample locations. Average polychlorinated biphenyl (∑PCB) concentrations across the Great Lakes was 268 pg/L with a station range of 72 pg/L (Keweenaw Point-Lake Superior) to 834 pg/L (Middle Bass Island-Lake Erie). The highest average Great Lakes concentration (pg/L-sample year) were measured in Lake Erie (645 pg/L-2014) and decreased in the order of Lake Huron (378 pg/L-2012) > Lake Erie (364 pg/L-2019) > Lake Ontario (300 pg/L-2013) > Lake Michigan (125 pg/L-2015) > Lake Huron (123 pg/L-2017) > Lake Superior (74 pg/L-2016). Lake Erie registered a 44 % reduction over the 2014-2019 period, attributed to sediment remediation in the late-1990's on the Detroit River, whereas Lake Huron exhibited a 67 % decrease over the 2012-2017 sample period. Our results indicate that dissolved-phase PCB water concentrations in Lake Ontario have significantly increased, rebounding from a low-point in the late-1990's likely due to the bioenergetic diversion of dissolved- and particulate-phase PCBs into the benthic food web by invasive zebra and quagga mussel colonization. Trend analyses uncovered breakpoints in the early 1990's documenting significantly slowing rates of PCB declines for both Lakes Superior and Michigan., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

In the Lake Koocanusa-Kootenai River system (Montana, USA and British Columbia, Canada), selenium (Se) contamination has become an international concern and is suspected to contribute to the observed burbot (Lota lota) population collapse. Due to our limited ability to sample burbot in Lake Koocanusa for monitoring studies, we used a reference population to develop tools to model tissue Se disposition for a focal species in systems with elevated Se. Total Se concentrations in otoliths, biofluids (blood and endolymph), and tissues (muscle, liver, and ovary) from burbot in reference lakes in northwestern Ontario, Canada, were measured to document tissue-to-tissue Se relationships and evaluate the potential for otoliths to retrace Se exposure in fish. Among burbot tissue, Se concentrations were the highest in the ovary (mean ± SD = 4.55 ± 2.23 μg g-1 dry mass [dm]), followed by the liver (2.69 ± 1.96 μg g-1 dm) and muscle (1.87 ± 1.14 μg g-1 dm), and decreased with body size (p < 0.05). In otoliths, Se was detected at low levels (<1 μg g-1). Selenium concentrations in burbot samples were positively correlated among muscle, ovary, liver, and endolymph tissues, but not for the most recent annually averaged or lifetime-averaged Se concentrations in otoliths. We hypothesize that Se concentrations were too low in this study to establish links between otoliths and other fish tissues and to detect significant lifetime variation in individuals, and that further validation using archived otoliths from burbot exposed to elevated Se levels in Lake Koocanusa-Kootenai River is needed to reconstruct exposure histories. However, intercompartmental models proved valuable for estimating Se concentrations in burbot tissues only available by means of lethal sampling (i.e., ovary), although additional work should confirm whether the established models are reliable to predict concentrations in Se-impaired systems as tissue distributions are likely to differ with increasing Se levels., (© 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).)

Understanding oxidative stress in high-mountain lake fish offers crucial insights into their health, resilience, and adaptation to extreme environmental changes. This study investigates the oxidative stress response of Cottus gobio in a high-mountain lake (Dimon Lake) located in the northeast Italy during the ice-free season, focusing on the relationship between oxidative stress biomarkers and physicochemical water parameters, as well as persistent and emerging contaminants. Significant seasonal variations were observed in water parameters, with lower oxygen, pH, conductivity, and phosphate levels in summer compared to autumn, while temperature, ammonium, and nitrate were higher in summer. Metal concentrations in C. gobio muscle were higher in autumn, with Zn showing the most significant increase. PAHs, NDL-PCBs, and pesticides were all below the limit of quantification in the fish muscle samples. No microplastics items were found in the gastrointestinal tracts of fish. Oxidative stress biomarkers revealed organ-specific and seasonal variations. The liver exhibited the highest activities of catalase (CAT), glutathione peroxidase (GPx), glutathione S-tranferase (GST), and glutathione reductase (GR), highlighting its central role in detoxification and metabolic processes. Superoxide dismutase (SOD) activity was notably higher in muscle tissue during summer, suggesting increased metabolic activity. A strong correlation was found between pH and the activities of SOD, CAT, GPx, GR, and metallothioneins (MTs), emphasizing the importance of water chemistry in influencing oxidative stress responses. This approach not only aids in understanding the local adaptations of these fish but also highlights the impacts of environmental stressors on high-mountain ecosystems. Continuous monitoring of water chemistry, particularly pH, is crucial for understanding and managing oxidative stress in aquatic organisms, especially in the context of global environmental changes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Lakes are vital sources of drinking water and essential habitats for humans and various other living organisms. However, many lakes face organic pollution due to anthropogenic disturbance and climatic influence, and the spatiotemporal changes of organic pollution in lakes over a large area are still unclear. Based on three monitoring datasets of chemical oxygen demand (COD) in 390 lakes, this study demonstrated the apparent spatiotemporal differences of organic pollution in lakes during the 1980s-2010s and the effects of water eutrophication and salinization. Throughout China, lake organic pollution showed a general spatial trend of being more severe in the north compared to the south. This pattern is reflected in the positive linear correlations between in-situ COD concentrations and lake latitude, observed in both the 1980s (p < 0.05) and the 2010s (p < 0.01). In terms of spatial differences, the influence of total nitrogen concentrations increased from 0.27% in the 1980s to 35.24% in the 2010s. Moreover, with increasing human activity, 78.31% of the studied lakes (N = 83) showed increasing COD concentrations during the 1980s-2010s. In addition, the logarithmic dissolved organic carbon concentrations were linearly correlated with log water conductivities (Pearson's r = 0.49, p < 0.01), suggesting that lake expansion would attenuate organic pollution in saline lakes through dilution effects. These results are valuable for understanding the spatiotemporal dynamics of organic pollution and are crucial for effective management of organic pollution in different lakes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Seasonal fluctuations present significant challenges to drinking water treatment by altering the properties of Dissolved Organic Matter (DOM) within watersheds, thereby influencing the potential for disinfection by-product (DBP) formation. DOM is a complex mixture of organic matter that serves as a critical DBP precursor and is closely linked to adverse health outcomes. The prediction of DBP formation is complicated by the variability in DOM concentrations and compositions in lake source water, a situation exacerbated by seasonal changes in water systems. We examined the seasonality of lake DBP formation potential (DBPFP) and the dynamics of precursors across four distinct seasons based on water temperature. Utilizing the Excitation-Emission Matrix (EEM) coupled with parallel factorial (PARAFAC) analysis, three-dimensional fluorescence difference spectroscopy (3D-FDS), and molecular weight distribution (MWD), we elucidated the compositions and fates of lake DBP precursors. The findings revealed that DBPFP (THMFP and HAAFP) were markedly influenced by seasonal variations, with peak fluorescence intensity occurring during the summer. Contributions to the water system were dominated by microbial metabolites (region IV) and protein-like substances (region I and region II). 3D-FDS analysis further substantiated the low homogeneity of DBP precursors between summer and autumn, with fulvic acid (FA) substances comprising up to 36.89 % of the variance. Distinct fluorescence intensities were detected at Peak B (266.29 A.U.) and Peak T (376.19 A.U.). Throughout the year, a total of four fluorescent components were characterized, encompassing humic-like substances (C3) and protein-like substances (C1, C2, C4), indicative of biogenic pollution. The source of DBP precursors was identified as small molecular weight organic matter (0.2-5 KDa), resulting from microbial metabolic processes and the degradation of aquatic plants. In addition, external factors such as chlorination, pH levels, and contact time significantly influence THMFP and HAAFP. Overall, these findings advance our comprehension of the transport and fate of DBP precursors within drinking water sources and lake ecosystems. This knowledge is pivotal for optimizing water treatment protocols in relevant water treatment facilities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Lanthanum carbonate (LC) represents a novel material for the immobilization of internal phosphorus (P) in sediments. Activated carbon (AC) is a traditional adsorbent that has been employed in the remediation of sediments on a wide scale. The objective of this study is to examine the mechanisms and effects of the combined use of LC and AC capping materials on the immobilization of P and dissolved organic matter (DOM) in sediments, through a 90-day incubation experiment. The results of isotherm experiments showed that the adsorption mechanism of P on LC and AC was mainly chemisorption. The XPS analyses showed the adsorption mechanism of P on LC was mainly ligand exchange and inner-sphere complexation; while the adsorption mechanism of P on AC was mainly ligand exchange and electrostatic adsorption. The results demonstrated that the concentrations of soluble reactive phosphorus (SRP) and DOM in the 0 to -100 mm sediment layer were reduced by 69.79% and 33.93%, respectively, in comparison to the control group with the LC + AC group. Moreover, the HCl-P and Res-P (stable P) in the 0-5 cm sediment layer were increased by 50.07% and 21.04%, respectively, in the LC + AC group. This indicates that the combined application of LC and AC has the potential to reduce the risk of P release. Furthermore, the formation of Fe(III)/Mn(IV) oxyhydroxides by LC + AC treatment resulted in an increased adsorption of SRP and DOM. Moreover, the effect of LC + AC capping on microbial community was smaller than that of LC/AC capping alone. The findings of this study indicated that the combined use of LC and AC represents a novel approach to the effective treatment of internal P and DOM in eutrophic lake sediments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Selenium (Se) contamination of aquatic ecosystems has led to the local extirpation of some Se-sensitive fish species. Although Se exposure occurs primarily via diet, considerable uncertainty lies in modeling Se transfer and bioaccumulation from sediment, detritus, and/or periphyton through benthic macroinvertebrates (BMI) to fish. Here we estimated Se concentrations in four coldwater fish species (northern pike, white sucker, lake whitefish, and ninespine stickleback) inhabiting boreal lakes downstream from a uranium mill in northern Canada. In addition, we evaluated the potential effects of BMI and periphyton sampling methods (artificial substrates vs. grab samples), seasons (summer vs. winter), and models (USEPA vs. Assessment of the Dispersion and Effects of Parameter Transport) on the estimated Se concentrations in fish tissue. Results were compared with site-specific benchmarks and observed Se concentrations in resident fish. In summer 2019, periphyton and BMI were sampled at 10 sampling stations (two in Vulture Lake and eight in McClean Lake) using artificial substrates (n = 4) and sediment grab samples (n = 3). In winter 2021, samples were collected in McClean Lake (n = 3) through ice holes using a sediment grab sampler. Estimated Se concentrations in fish tissue depended on the surface sediment or periphyton Se concentrations used in the models. At Vulture Lake, Se concentrations in northern pike muscle estimated using the grab sample data (17.3 ± 11.5 µg/g DW), but not the artificial substrates (34.5 ± 1.2 µg/g DW), were comparable with the observed mean concentration (19.0 ± 1.4 µg/g DW) in this species. At McClean Lake, Se body burdens in forage fish estimated using data from both sampling methods were comparable with measured data. Significantly lower mean whole-body Se concentrations were estimated for all fish species in winter (1.0 ± 0.3 µg/g DW) relative to summer (4.8 ± 1.6 µg/g DW). Further investigation is necessary to understand how potential seasonal shifts in dietary Se exposure relate to fish reproduction and early life stages., (© 2023 Society of Environmental Toxicology & Chemistry (SETAC).)

Methane (CH 4 ) inputs to lakes through lacustrine groundwater discharge (LGD-derived CH 4 ) represent a potentially important but often overlooked source of lake methane emissions. Although great efforts have been made to quantify LGD-derived CH 4 fluxes and their spatial variablity, the underlying mechanisms controlling seasonal LGD-derived CH 4 fluxes and their influence on lake CH 4 emissions remain poorly understood, particularly in humid inland areas. To address this gap, we applied the 222 Rn mass balance model, as well as hydrological, isotopic and microbial methods to assess seasonal LGD-derived CH 4 fluxes and their influence on the seasonal variability of lake methane emissions in a typical oxbow lake, central Yangtze River. The results revealed wide seasonal differences in LGD-derived CH 4 fluxes, which were controlled by hydrological and biogeochemical processes. During the dry season, although more intense methane oxidation and weaker methanogenesis occurred in groundwater, the much higher LGD rate (51.71 mm/d) produced a higher LGD-derived CH 4 flux (16.41 mmol/m 2 /d). During the wet season, methanogenesis was more active and methane oxidation was weaker, but a lower LGD rate (12.16 mm/d) led to a lower LGD-derived CH 4 flux (5.33 mmol/m 2 /d). Furthermore, higher LGD-derived CH 4 flux in the dry season resulted in higher CH 4 emissions from the lake and diminished the extent of methane oxidation in the lake. In comparison to other regions, the differences in LGD-derived CH 4 fluxes and their seasonal variations were found to be controlled by climatic conditions and lake types in different global regions. Higher LGD-derived CH 4 fluxes and more pronounced seasonal variations could be associated with higher temperature, larger water depth and more intense water level fluctuations. This study provides a novel perspective and broader implications for the comprehension and evaluation of seasonal methane emissions and understanding the carbon cycle in global lake ecosystems in humid areas with intense water level fluctuations., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Regulating internal and external phosphorus (P) holds a predominant position in eutrophication management of lakes and other water bodies, with less emphasis on controlling nitrogen (N) due to the presence of N 2 -fixing cyanobacteria. Nonetheless, external N influxes may stimulate the proliferation of non-N 2 -fixing cyanobacteria, thereby fostering cyanobacteria blooms during summer seasons. To elucidate the significance of N regulation, a two-factor orthogonal experiment was performed to study the influences of external N input on the efficacy of lanthanum-modified bentonite (LMB), a sediment capping material for P immobilization. At the experimentation ends, the total suspended solids (TSS), organic suspended solids (OSS) concentrations and optical attenuation coefficient (K d ) in the LMB + N treatment were 7.34, 8.65 and 5.20 times higher, respectively, compared to the LMB treatment. The total nitrogen (TN), total phosphorus (TP) and soluble reactive phosphorus (SRP) concentrations in the LMB + N treatment were 3.02, 1.30 and 0.60 times higher, respectively, than those in the LMB treatment. However, TP and SRP in the LMB + N treatment were 46.98% and 54.93% lower, respectively, compared to N treatment. The chlorophyll a (Chl a) concentration of algae in the LMB + N treatment was observed to be 2.86 times higher compared to the LMB treatment, and 17.13% lower compared to the N treatment. The biomass of cyanobacteria accounted for more than 95% of algae in the LMB + N treatment and N treatment. Furthermore, the photosynthetic performance of algae in the N treatment increased significantly, compared to the LMB + N treatment. Our results indicated that external N influxes significantly reduce the efficacy of LMB to control P and algae. Thus, the implementation of more stringent N control policies holds great significance in the eutrophication control., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Under persistent hypoxic conditions in the bottom layer of a lake, phosphorus (P) can be released from benthic sediments, significantly impacting the lake ecosystem. Hypoxia reduces iron ions, leading to P release through biogeochemical reactions associated with organic matter degradation, which in turn depletes dissolved oxygen (DO) in the sediment. The application of bubble technology is beneficial, as microbubbles (MBs) effectively remove P and enhance DO levels in both the overlying water and sediment surface. To identify the optimal bubble size for application, we conducted a series of flotation experiments and P fractionation studies using MBs and nanobubbles (NBs). Results indicate that NBs achieved a flotation efficiency of 12 %, MBs reached 44 %, and the combined use of NBs and MBs attained the highest flotation efficiency at 62 %, confirming that a combination of bubble sizes can enhance flotation efficiency. Furthermore, the introduction of air bubbles to mitigate hypoxia in the overlying water increased DO concentrations from 1 to 5 mg/L, followed by a gradual decline. P release in the bubble-injected groups was up to three times lower than in the control group. Water quality profiling of P distribution in sediments revealed a significant increase of approximately 10 % in iron-bound P under aerobic conditions, highlighting its critical role in regulating P release. Our findings suggest that utilizing a combination of bubble sizes, including NBs, enhances P removal efficiency and improves the anaerobic conditions of the lake's bottom layer, thereby further reducing P release from sediments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Cyanobacterial Harmful Algal Bloom (CyanoHAB) is a global aquatic environmental issue, posing considerable eco-environmental challenges in freshwater lakes. Comprehensive monitoring and accurate prediction of CyanoHABs are essential for their scientific management. Nevertheless, traditional satellite-based monitoring and process-oriented prediction methods of CyanoHABs failed to satisfy this demand due to the limited spatiotemporal resolutions of both monitoring data and prediction results. To address this issue, this paper proposes an upgraded framework for comprehensive monitoring and accurate prediction of CyanoHABs. A collaborative CyanoHAB monitoring network was firstly constructed by integrating space, aerial, and ground-based monitoring means. As a result, CyanoHAB conditions were assessed frequently covering the entire lake, its key areas, and core positions. Furthermore, by overcoming technical limitations associated with high-precision simulation of the growth-drift-accumulation process of CyanoHABs, such as the unclear drifting process of CyanoHABs and the mechanism of its coastal accumulation, the multi-scale CyanoHAB prediction was realized interconnecting the entire lake and its nearshore areas. The implemented framework has been applied in Lake Chaohu for over three years. It provided high-frequency and high-spatial-resolution CyanoHAB monitoring, as well as its multi-scale and accurate simulation. The application of this framework in Lake Chaohu had significantly improved the accuracies of CyanoHAB monitoring, simulation, and early warning. This advancement holds significant scientific value and offers potential for CyanoHAB prevention and control in eutrophic lakes., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Yinguo Qiu reports financial support was provided by Nanjing Institute of Geography and LimnologyChinese Academy of Sciences. Yinguo Qiu reports a relationship with Nanjing Institute of Geography and Limnology Chinese Academy of Sciences that includes: employment. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Impacts of the acid mine drainage (AMD) remediation are investigated on the largest gold mine in Latin America, located in the Dominican Republic. Geochemical analysis of suspended matter in water performed in 2022 on water bodies located downstream to the mine, namely, the Margajita River and Lake Hatillo, are compared with analyses made in 2007, before the AMD remediation. The results for the Margajita River show a strong decrease in heavy metal and metalloid concentrations in the dissolved phase for Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Sb, and Pb (between 89.1 and 99.9%) which is correlated with a pH neutralization (from a pH of 2 to 7.5). However, the concentrations of Cd and sulfate in the dissolved fraction remain higher than their environmental standard values, and a high concentration of K is also observed. High contributions in terms of mass are identified for Cs, Tl, Cd, and Li in the Margajita River. Concentrations of Al, Fe, Ni, Zn, and As in suspended sediments are higher than the environmental standard values in 2022. Modeling of the chemical speciation shows that the higher pH leads to the formation of suspended particles in the form of hydroxides and sulfates. The concentrations in suspended sediments are highly correlated between Margajita River and Lake Hatillo in 2022 for Fe, Cd, Li, and Ca (R 2 between 0.9 and 0.99 with p ≤ 0.05). In Lake Hatillo, principal component analysis shows that invariant elements Fe, P, Ti, Zr, and Al are correlated, as they precipitate between the inlet and outlet of the lake., Competing Interests: Declarations. Conflict of interest: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

CO 2 fixation (i.e. primary production) is a key function of all ecosystems, providing the carbon and energy that fuel the entire food web. It also plays an important role in mitigating climate change as CO 2 is the most important greenhouse gas. While photosynthesis is regarded as the most important carbon fixation pathway, prokaryotes able to fix carbon in the absence of light (chemolithoautotrophs) can also be a significant source of energy in a light-limited ecosystem. Boreal lakes, notoriously colored and stratified with respect to oxygen and nutrients, present ideal conditions for this so-called dark carbon fixation by the chemolithoautotrophs. However, the prevalence of dark carbon fixation in boreal lakes remains unknown. Here, we measured dark carbon fixation in Swedish lakes from the boreal and boreo-nemoral zones, during summer stratification. We detected dark carbon fixation in 16 out of the 17 lakes studied, and concluded that dark fixation is a widespread phenomenon in boreal lakes. Moreover, the average dark primary production ranged from 18.5 % in the epilimnion to 81.4 % in the hypolimnion of all tested lakes. Our data further suggests that chemolithoautotrophic activity is mostly driven by iron-oxidizing bacteria. The chemolithoautotrophic guild is diverse and seems to be composed of both ubiquitous bacteria, like Gallionellaceae or Chromatiaceae, and endemic taxa, such as Ferrovaceae, which appears to be favored by a low pH. These results are particularly exciting as they suggest that dark carbon fixation could partly compensate for the low photosynthetic capacity in lakes with dark-colored water., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier B.V.)

Excessive nitrogen exported to water bodies affects the balance of ecosystem and poses a threat to human health. Although the concept of water purification service helps quantify nitrogen export, the impact of river transport remains unclear. This study focused on nitrogen as a pollutant by utilizing the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model to assess nitrogen export in the Dongting Lake Basin, taking into account both the processes of sub-basin nitrogen export and river transport. Additionally, the monthly variations within the year were further explored, together with the identification of the priority area of returning cropland to forest land. The results showed that in 2021, the total nitrogen load outside the Dongting Lake was 11.34 × 10 8 kg·year -1 , with the sub-basins retaining a total of 9.02 × 10 8 kg·year -1 , accounting for 79.57 % of the total nitrogen load. Notably, the total nitrogen retention by the river made up 16.87 % of the total nitrogen retention, up to 1.83 × 10 8 kg·year -1 . In view of monthly variation, water purification service based on the entire process was higher in winter and late autumn, and lower in summer and early autumn. The priority areas for ecological project were mainly distributed around the Dongting Lake, achieving an improvement of 58.15 % in water purification service with approximately 7.02 % of the total returnable cropland. This study proposed a new approach of water purification service assessment through integrating river transport processes and seasonal dynamics, aiming to assess watershed nitrogen export risk more accurately., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Lakes are rapidly losing ice under global warming, but little is known about ice structure changes. Ice structure is a key regulator of ice stability and thus safety, affecting activities on ice. Here, we analysed spatial and temporal variations in ice structure across 21 Swedish lakes, spanning from 55 to 69 °N, and over five decades. We found regional differences in ice structure, with fastest changes occurring in southern Sweden. The stable clear ice layer was particularly sensitive to warming, showing a rapid decline. The number of days when temperatures exceeded the freezing point during the ice cover period was identified as a strong driver for how ice was structured. Since there is a high risk for increased occurrences of unsafe ice conditions under predicted air temperature changes, we recommend re-establishing ice structure monitoring programmes, informing society on the increased risks of being on ice and including ice structure to safety guidelines., (© 2024. The Author(s).)

Large-scale water transport helps solve the imbalance in water resources. Studies on ecological benefits after long-term EWT mainly focus on vegetation restoration and increase in water surface. However, the maintenance of aquatic communities in the EWT context is a major challenge. This study studied the seasonal dynamics of phytoplankton communities during the interval period of 22nd and 23rd EWT in a newborn lake generated by long-term EWT in an extremely arid zone. The 22nd EWT was carried out from August 2021 to November 2021, and the 23rd EWT was implemented from July to September 2022. Our research indicates that during the interval period, water temperature (WT), pH, dissolved oxygen (DO), suspended solids (SS), turbidity, total nitrogen (TN), NO 3 -N, total phosphorus (TP), chemical oxygen demand (COD cr ), SO 4 2- showed seasonal dynamic changes. Meanwhile, the phytoplankton community also exhibits seasonal variations, including the succession of dominant phyla and dominant species, the decrease in density and α diversity, as well as the increased instability of functional groups and ecological networks. These phenomena are more pronounced in summer when the lake water evaporates and the water quality changes, suggesting that the phytoplankton community shows attenuation along with the changes of environmental factors during the interval period. Based on this, our study suggested that the coupling relationship between water quantity, water quality change and aquatic community succession should be considered for the precise control of EWT projects aiming at improving ecological benefits. Regular phytoplankton monitoring is recommended to track the evolution of aquatic ecosystems after long-term EWT., Competing Interests: Declaration of competing interest All authors declare that there are no competing financial interests associated with this work., (Copyright © 2024. Published by Elsevier B.V.)

Although it has been demonstrated that atmospheric reactive nitrogen (i.e., Nr mainly including NH 3 , NH 4 + , NO x , NO 3 - and etc.) deposition has substantial impacts on nitrogen pools in remote and/or sensitive lakes, there is a scarcity of systematic evaluations regarding the impact on nitrogen burden in eutrophic lakes with riverine input as primary nitrogen source. Utilizing a regional atmospheric chemical transport model, combined with observation-based estimates of atmospheric nitrogen deposition fluxes and riverine nitrogen inputs, we investigate the contribution of atmospheric Nr deposition to the fifth largest freshwater lake located in eastern China, i.e., the Chaohu Lake which is facing frequent outbreaks of algal bloom. The results indicate that in the studied year of 2022, riverine total nitrogen (TN) input to the lake was 11553.3 t N yr -1 and atmospheric TN deposition was 2326.0 t N yr -1 . For Nr species which are directly available for the biosphere supporting algae and plant growth, riverine NH 4 + input was 1856.1 t N yr -1 and atmospheric NH x (NH 3 and NH 4 + ) deposition was 824.5 t N yr -1 . The latter accounts for 30.8% of total NH x input to the lake. For NO y (HNO 3 and NO 3 - ), riverine NO 3 - input was estimated as 2621.7 t N yr -1 , while atmospheric NO y deposition was 629.3 t N yr -1 , accounting for 19.4%. In all, atmospheric Nr deposition accounts for 24.5 % of total Nr input to the lake. Our results suggest that even in regions with dense human activities with primary riverine N input, atmospheric deposition of Nr could also contribute significantly to the bio-available nitrogen in lake systems, and addressing eutrophication in Lake Chaohu and other eutrophic lakes will also need to consider the influence of atmospheric Nr deposition which is related to NH 3 and NO x (i.e., NO + NO 2 , the precursor of NO y ) emissions, in addition to the mitigation of riverine N input., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

In the 1980s, liming became a large-scale, governmentally supported restoration program implemented by many countries to mitigate the effects of acidification of freshwaters. Despite some 50 years of liming of thousands of lakes and streams, its efficacy remains largely debated. This study is the first of its kind to use paleolimnological reconstructions using both subfossil chironomid assemblages and their carbon stable isotopic composition to compare the ecological trajectories of limed and control (unlimed) lakes over the last 100 years in order to unravel the effects of liming on Scandinavian lakes. Our study revealed strong effects of liming on lake water chemistry and sedimentary characteristics of limed lakes. Overall, higher present-day pH values were observed in lake water of the limed lakes (average pH of 6.7 ± 0.2) than in control lakes (average pH of 5.9 ± 0.5), and the pH variability was much lower among limed lakes. A decrease in the dissimilarity of the chironomid assemblages among limed lakes was also observed as liming progressed, and the degree of dissimilarity after liming was largely lower than pre-acidified levels. This pattern suggests that liming favoured the selection of similar chironomid taxa in limed lakes, thus providing complementary empirical evidences about the effects of liming on aquatic communities through taxonomic homogenization of chironomid assemblages. As the ecological trajectories of limed and control lakes strongly differed, our study also questions the impact of liming on the resilience of Scandinavian lakes and, importantly, their ability to cope with ongoing and future climatic and environmental changes. Finally, isotope-based results indicated that liming masks potential complex effects on carbon flows at the base of the food web by shifting algal carbon isotopic baselines. The use of carbon stable isotope analysis of chironomid head capsules to study the effects of liming on energy flows within lake food webs is, therefore, not suitable., Competing Interests: Declaration of competing interest There is no conflict of interest., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The presence of antibiotics in the environment is of significant concern due to their adverse effects on aquatic ecosystems. This study provides an assessment of potential ecological risks (RQ) associated with the concentrations of eight antibiotics and antiparasitics (amoxicillin-AMO, azithromycin-AZI, ciprofloxacine-CIP, ofloxacine-OFL, oxfendazole-OXF, lincomycin-LIN, sulfacetamide-SCE and sulfamethoxazole-SME) in the surface water of 13 urban lakes in Hanoi city, Vietnam during the period 2021-2023. The findings revealed considerable variations in the total concentrations of these 8 substances (T AB ), ranging from below the method detection limit (< MDL) to 2240 ng L -1 with an average of 330.4 ng L -1 . Among the 8 antibiotics and antiparasitics examined, OXF, AMO, and SCE were undetectable, while the others were present at a range of concentrations (in ng L -1 ): OFL: 129 (< MDL-1530); CIP: 87.1 (< MDL-608); LIN: 72.7 (< MDL-676); SME: 41.5 (< MDL-504); AZI: 0.03 (< MDL-1). The calculated RQ values for these antibiotics in the Hanoi lakes indicated a high ecological risk for OFL and CIP to bacteria, a medium to high risk for SME for phytoplankton, a high risk for LIN to phytoplankton, while the risk for invertebrates was deemed negligible for all antibiotics across all lakes. The strong, positive correlation between T AB concentrations and different microbial and environmental variables (Escherichia coli, ammonium, phosphate, and chemical oxygen demand) suggests that untreated domestic wastewater is the primary pollution source in these Hanoi lakes. These results should be used to raise public awareness and to encourage the implementation of strategies targeted at managing antibiotic use. They also underscore the need to reduce inputs of untreated, antibiotic-containing wastewater into urban lakes, such as those in Hanoi and advocate for the establishment of national limits for antibiotic concentrations in surface water., Competing Interests: Declarations. Ethics approval: Not applicable. Consent to participate: Not applicable. Consent for publication: All authors have given consent for publication. Conflict of interest: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

To inhibit eutrophication caused by endogenous pollutants release, the experiment explored the efficiency and mechanism of the synchronous control of nitrogen (N) and phosphorus (P) release from sediments in shallow lakes under wind disturbance by modified Ca/Al-based sludge (MS) and modified zeolite (MZ). High-temperature calcination and NaCl impregnation increased the pore volume of MS and Na + content of MZ, and the adsorption capacity of MS for PO 4 3- -P and MZ for NH 4 + -N was as high as 42.01 and 20.28 mg g -1 . The results of a 90-day incubation experiment showed that the addition of MS and MZ increased the abundance of Thauera, Nitrospira, Denitratisoma, and Clostridium, while decreasing the proportion of Proteus Hauser and Saccharimonadales, thereby reducing the active N and P contents in sediments through microbial transformation. At the same time, the efficient adsorption performance of the MS and MZ resulted in a significant decrease in pollutants in the interstitial water and sediments. In addition, sediment resuspension caused by wind disturbance increased the contact between sediments and remediation agents, resulting in the action depth of covering materials exceeding 100 mm. Compared to adding MS or MZ alone, the combination of the two (MSZG) could synchronously, efficiently, and stably inhibit N and P release. Under the coupling effects of physical interception, physicochemical adsorption, and biotransformation, the average TN, NH 4 + -N, TP, and PO 4 3- -P in the overlying water of the MSZG decreased by 72.13%, 88.92%, 69.28%, and 81.26%, respectively, compared to Control, which satisfying the Class III standard for surface water. Therefore, this study could provide reference for controlling endogenous release, improving eutrophication in shallow lakes under wind disturbance, and recycling residual sludge from sewage plants., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Per- and polyfluoroalkyl substances (PFAS) have been detected in lake ecosystems globally, even in remote areas at high altitudes. Compared to plain lakes with short water change cycles and significant human influence, plateau lakes are primarily tectonic closed or semi-closed lakes with steep terrain. Their long water change cycles lead to an obvious cumulative effect on pollutants. In this study, a targeted screening method for 74 PFAS in aquatic environment was established. The contamination characteristics of PFAS in surface water samples (0.5 m below the water surface) and bottom samples (0.5 m above the lake bottom) of plateau Lake Yangzonghai were studied and compared to a reference site in Dianchi Lake which has been severely affected by anthropogenic sources. Results showed that 32 PFAS were detected in Lake Yangzonghai with the total concentration (∑ 32 PFAS) ranging from 14.95 to 26.42 ng L -1 . Among the 27 PFAS with available standards for accurate quantification, 22 PFAS were detected, with the concentration of ∑ 22 PFAS ranging from 13.27 to 20.17 ng L -1 . Significant differences (p < 0.05) in PFAS concentrations were observed between surface water (22.12 ng L -1 ) and bottom water (18.18 ng L -1 ), demonstrating a stratification phenomenon. The spatial differences in PFAS concentrations in surface water were minimal, indicating that the surface water was uniformly mixed with limited local disturbance from human pollution. The main PFAS monomers were perfluorooctanoic acid (PFOA), 8-3 fluorotelomer carboxylic acid (8-3 FTCA), perfluoroheptanoic acid (PFHpA) and 2H-perfluoro-2-decenoic acid (8-2 FTUCA), while PFBA was not detected. This distribution remarkably differed from many other plain lakes and the reference lake. Source apportionment analysis showed that PFAS primarily originated from atmospheric transport and precursor degradation. The results provide a background pollution level of PFAS in the plateau lake near the city and will benefit for formulating control policies., Competing Interests: Declarations. Competing interests: The authors declare no competing interests. Consent for publication: The paper submitted with the mutual consent of authors for publication in Environmental Geochemistry and Health., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Chlorophyll-a (Chla) is recognized as a key indicator of water quality and ecological health in aquatic ecosystems, offering valuable insights into ecosystem dynamics and changes over time. This study aimed to to develop and validate a robust ML model for estimating Chla using Landsat data, produce a time series of Chl a maps, and analyze the spatiotemporal variability of Chla in Chilika Lagoon, Asia's largest brackish water lagoon. Nine ML regression models, including Extreme Gradient Boost, Support Vector Regression, Random Forest, and Bagging Regression, were evaluated using Landsat imagery and field data. After extensive hyperparameter tuning, the Bagging Regression model achieved the highest estimation accuracy, with an R 2 of 0.8776 and a Root Mean Square Error of 0.9190 µg/L. This optimized model was subsequently applied to generate a time series of Chla maps for Chilika Lagoon from 2014 to 2023, revealing notable seasonal and spatial variability. Chla concentrations peaked during summer months and were generally higher in the lagoon's northwestern region, gradually decreasing towards the southern area. This approach holds promise for precise Chla monitoring in diverse lagoon environments and may aid in the assessment and management of similar coastal and inland lake ecosystems worldwide., Competing Interests: Declarations. All authors have read, understood, and have complied as applicable with the statement on "Ethical responsibilities of Authors" as found in the Instructions for Authors. Conflict of interest: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Freshwater ecosystems, including high-altitude lakes, can be affected by trace metal pollution derived from a mix of natural sources and anthropogenic activities. These pollutants often collect in surface sediments, with notable concentrations in the deeper areas of lakes. To evaluate the environmental risk associated with metal contaminated sediment in Rara Lake, southern Himalaya, surface sediment samples were systematically collected in November 2018, with a subsequent specific emphasis on determinations of trace element concentrations. Subsequent analysis revealed nine elements exhibiting a descending mean concentrations order: iron (Fe) > manganese (Mn) > chromium (Cr) > rubidium (Rb) > nickel (Ni) > strontium (Sr) > cobalt (Co) > copper (Cu) > cadmium (Cd), of 7205.55 mg kg -1 , 2290.34 mg kg -1 , 176.29 mg kg -1 , 153.78 mg kg -1 , 51.86 mg kg -1 , 44.61 mg kg -1 , 38.89 mg kg -1 , 29.11 mg kg -1 , and 0.10 mg kg -1 , respectively. Comparisons to sediment quality guidelines highlight that Mn, Cr, Cu, and Cd as significant threats to the aquatic ecosystem in Rara Lake. To assess the impact of metal pollution, enrichment factor (EF), geo-accumulation index (I geo ), pollution load index (PLI), and contamination factor (CF) were computed. All metals (except Cd) had I geo value exceeding 5, displaying strong contamination. EF values for Mn, Cr, Co, and Ni metals were > 10, indicating severe effects of anthropogenic influences. CF and PLI values also indicated significant pollution for most of the investigated sites. Elevated trace element concentrations have the potential to adversely affect water, sediment, and aquatic life, also potentially impacting nutrient cycling and microbial activity. This study enhances our understanding of the metal compositions within Rara Lake sediments and provides a basis for more effective lake management and pollution control strategies. Urgent action by regional governing bodies is crucial to address the early stages of metals pollution, including identification and controlling of pollution sources, by appropriate regulations, optimizing industrial practices, and remediating existing pollution to prevent further contamination and protect the lake ecosystem., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Poyang Lake is the largest freshwater lake in China. In recent years, the stability of the lake's ecosystem has been challenged by climate change and human activities. It is important to study changes in the lake to understand how to maintain the health of the lake ecosystem. To date, individual factors have been used to support studies of the lake's stability. However, these studies are inadequate because they fail to provide quantitative information for multiple factors. In this study, we innovatively proposed a method for quantifying the lake stability that considered multiple habitat and biotic factors, thereby advancing our understanding of the drivers influencing changes in lake stability. We analyzed monitoring data from Poyang Lake for long-term changes in the stability and used structural equation modeling to quantitatively assess the main influences on the lake stability. Our results showed that the ecosystem stability index of Poyang Lake decreased by 12.3 % from 2013 to 2023, which indicates that the stability of the lake gradually declined. We further found that zooplankton, phytoplankton, and ammonium nitrogen were the main causes of the decline in the lake stability. The method utilized in this study can assist lake managers in analyzing the effects of environmental changes on lake stability, facilitate the rapid identification of key factors influencing stability variations, and provide a scientific basis for assessing the ecological health of lake waters., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Nitrous oxide (N 2 O) emission from lake systems could be affected via intrusion of terrestrial organic matter, causing impairment in biogeochemical cycling. The sources and mechanisms by which DOM (Dissolved organic matter) alters emissions of N 2 O are poorly understood. Here, we simulate different terrestrial DOM (anthropogenic sources, natural sources, and surface runoff) to assess the mechanisms affecting N 2 O emissions with variations of DOM. We used a combination of absorption spectroscopy, excitation-emission matrix fluorescence, and Fourier transform ion cyclotron resonance mass spectrometry to characterize DOM comprehensively. For the characterization of DOM, a combination of absorption spectroscopy, excitation-emission matrix fluorescence, and Fourier transform ion cyclotron resonance mass spectrometry was used. Microbial analysis was conducted to identify the potential microbial mechanisms. Different terrestrial DOM inputs primarily impact N 2 O emissions through the denitrification process (14.52 %, p < 0.05), with significant effects on the abundance of narG (12.97 %, p < 0.05) and nir K+S (10.13 %, p < 0.05). The biodegradable components in sediments directly promote N 2 O emissions, while in aquatic systems, the labile components (proteins, sugars, and lipids-like) were preferentially metabolized, producing reluctant derivatives. The biodegradable components (i.e., protein-like) from anthropogenic sources rapidly facilitate N 2 O production. Natural and surface runoff sources were the significant drivers for the continuous release and metabolism of DOM. N 2 O Loss emissions are negatively influenced by the regulation of carbon and nitrogen metabolism by nitrifiers and denitrifies in the sediment (p < 0.001). Metabolism of carbon and nitrogen regulated by nitrifier and denitrifies in the sediments negatively influences N 2 O flux (p < 0.001). N 2 O emissions were mainly influenced by bioavailability of inputs: DOM and varying terrestrial conditions. The results provide a theoretical base for the management of greenhouse gas emissions from lakes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Per- and polyfluoroalkyl substances (PFAS) are widespread, highly persistent, and bio-accumulative compounds that are increasingly found in the sediments of aquatic systems. Given this accumulation and concerns regarding the environmental impacts of PFAS, their influence on sedimentary bacterial communities remains inadequately studied. Here, we investigated the concentrations of 17 PFAS in sediments from six urban lakes in Nanjing, China, and assessed their effects on the diversity, composition, potential interactions, and assembly mechanisms of sedimentary bacterial communities. Sediment concentrations of PFAS ranged from 4.70 to 5.28 ng·g -1 dry weight. The high concentrations of the short-chain perfluorobutanesulfonic acid (PFBS) suggested its substitution for the long-chain perfluorooctanesulfonic acid (PFOS). As alternatives to long-chain PFAS, short-chain PFAS had similar effects on bacterial communities. The short-chain perfluoropentanoic acid (PFPeA) and the long-chain perfluorotridecanoic acid (PFTrDA) were the most important PFAS related to the ecological patterns of the co-occurrence network and may alter the composition of the sedimentary bacterial communities in the urban lakes. The Anaerolineaceae family represented as keystone bacteria within the PFAS-affected bacterial co-occurrence network. Deterministic processes (65.9 %), particularly homogeneous selection (63.2 %), were the dominant process driving bacterial community assembly. PFAS promoted the phylogenetic clustering and influenced the community dispersal capabilities to shape bacterial community assembly. This study provides a comprehensive analysis of PFAS distribution in sediments across six urban lakes in Nanjing and provides novel insights into the effects of PFAS on sedimentary bacterial communities. Further research is required to elucidate the mechanisms underlying the impacts of PFAS on microbial communities and to evaluate their broader ecological consequences., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Great Salt Lake is a critical habitat for migratory birds that is threatened by elevated metal concentrations, including mercury (Hg) and lead (Pb), and is subject to severe hydrologic changes, such as declining lake level. When assessing metal profiles recorded in Great Salt Lake sediment, a large data gap exists regarding the sources of metals within the system, which is complicated by various source inputs to the lake and complex biogeochemistry. Here, we leverage Hg and Pb stable isotopes to track relative changes in metal source contributions to Great Salt Lake over time. Mercury and Pb concentrations increase in sediments deposited after 1920 and peak between 1965 and 1995, following closure of several local smelters and the onset of increased emission controls. The nominal associations above are confirmed via Hg stable isotopes in pre-1920 background sediments, which reflect atmospheric inputs from regional and global origin, whereas Hg and Pb stable isotopes together indicate that elevated metal concentrations in mid-late 20th century sediments reflect increased mining/smelting inputs. The observed minimal rebound towards pre-1920 Pb isotope signatures in 21st century sediments indicates that mining/smelting inputs, though reduced, remain a primary source of Pb to Great Salt Lake. In contrast, the more pronounced rebound of Hg stable isotope signatures to pre-1920 values indicate a greater contribution of atmospheric inputs of regional/global origin to current Hg inputs, though Hg concentrations are ∼10 times greater than pre-1920 background values due to global increases in atmospheric Hg concentrations or possibly slow recovery from local contamination. The importance of regional/global Hg sources to the system suggests that reductions in Hg bioaccumulation in the open water food webs of Great Salt Lake are more dependent on national and global reductions in Hg emissions and management strategies to limit methylmercury production within system. This work highlights the utility of using coupled Hg and Pb stable isotope values to assess trace metal pollution sources and pathways in aquatic systems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Investigations into the repercussions of human activities on global climate and the ecological environment have received widespread attention. Over the past century, research has primarily focused on the impact of heavy metals and nutrients on lake ecosystems, along with their links to human activities. However, there is a noticeable dearth in explorations of historical variations in sulfur (S), an element that also has complex adverse effects on the environment and ecosystems. Here, we present an approximately 1800-year record of the total S (TS) content of sediments in Lake Nvshan, central-eastern China. The results provide evidence to indicate that high (low) TS contents in Lake Nvshan sediments are associated with strong (weak) volcanism in the Northern Hemisphere on multi-century scales. We also observed significant enhancement of TS content at 1750 and 1900 CE, which corresponded to a significant increase in the regional population at these times. We thus infer that elevations in TS levels prior to the increase in human activities likely resulted from increased volcanisms that led to greater inputs of sulfate from the stratosphere into the lake. Subsequently, the increases in TS contents could be attributed to intensified human industrial activities. Our findings revealed that volcanically derived sulfates have been supplanted by anthropogenically driven increases in the levels of sulfides as the primary factor influencing sediment TS contents in Lake Nvshan. These findings could elucidate how human activities have steered lake systems away from their natural baseline, thereby augmenting our understanding of their broader environmental impact., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Zebra mussels (Dreissena polymorpha) are invasive species that alter ecosystems and food webs with the potential to affect aquatic mercury cycling and bioaccumulation in fishes, although the effect of zebra mussels on fish tissue mercury has not been tested in inland lakes. We assessed differences in fish tissue mercury concentrations and food webs in Minnesota lakes with and without zebra mussels while controlling for other lake and watershed characteristics. Mercury concentrations in adult walleye (Sander vitreus) and yellow perch (Perca flavescens) were 72 % and 157 % higher, respectively, in lakes containing zebra mussels compared to uninvaded lakes. Mercury in young of year (age-0) fish was also elevated, with mercury concentrations 97 % and 82 % higher in age-0 walleye and yellow perch, respectively, in zebra mussel lakes. Walleye mercury concentrations exceeded 0.22 ppm - a threshold triggering more restrictive human consumption advisories for sensitive populations - at a 23 % smaller size, and average-sized walleye (420 mm) exceeded this threshold at a rate of 77 % in invaded lakes, compared to 35 % in uninvaded lakes. Walleye and yellow perch relied more on littoral resources in lakes with zebra mussels but did not feed at meaningfully higher trophic levels. Increased fish tissue mercury in lakes invaded by zebra mussels have consequential implications for fisheries and human health., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Gretchen Hansen reports financial support was provided by Minnesota Environment and Natural Resources Trust Fund as recommended by the Minnesota Aquatic Invasive Species Research Center (MAISRC) and the Legislative-Citizen Commission on Minnesota Resources (LCCMR). Gretchen Hansen reports financial support was provided by the U.S. Geological Survey (USGS) in cooperation with the National Institutes for Water Resources. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)