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Wildfire activity is increasing globally. The resulting smoke plumes can travel hundreds to thousands of kilometers, reflecting or scattering sunlight and depositing particles within ecosystems. Several key physical, chemical, and biological processes in lakes are controlled by factors affected by smoke. The spatial and temporal scales of lake exposure to smoke are extensive and under-recognized. We introduce the concept of the lake smoke-day, or the number of days any given lake is exposed to smoke in any given fire season, and quantify the total lake smoke-day exposure in North America from 2019 to 2021. Because smoke can be transported at continental to intercontinental scales, even regions that may not typically experience direct burning of landscapes by wildfire are at risk of smoke exposure. We found that 99.3% of North America was covered by smoke, affecting a total of 1,333,687 lakes ≥10 ha. An incredible 98.9% of lakes experienced at least 10 smoke-days a year, with 89.6% of lakes receiving over 30 lake smoke-days, and lakes in some regions experiencing up to 4 months of cumulative smoke-days. Herein we review the mechanisms through which smoke and ash can affect lakes by altering the amount and spectral composition of incoming solar radiation and depositing carbon, nutrients, or toxic compounds that could alter chemical conditions and impact biota. We develop a conceptual framework that synthesizes known and theoretical impacts of smoke on lakes to guide future research. Finally, we identify emerging research priorities that can help us better understand how lakes will be affected by smoke as wildfire activity increases due to climate change and other anthropogenic activities., (© 2024 Oak Ridge National Laboratory and The Author(s). Global Change Biology published by John Wiley & Sons Ltd.)

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

An adequate supply of food sources with high levels (i.e., weight proportion of total fatty acids) and contents (i.e., absolute amount per mass) of long chain polyunsaturated fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are important for ecosystems. Therefore, the supply of EPA and DHA from basal food sources is a useful indicator of ecosystem health. To determine whether EPA and DHA levels and contents in fish can be used as indicators of EPA and DHA supply in lakes, five dominant species of fish and basal food sources (seston and sediment) were collected monthly from June to November from 2016 to 2021 from Lake Hachiro, Japan. Seston and Hypomesus nipponensis were collected from 12 lakes (one collection per lake) with varying seston contents in EPA and DHA. The trends of EPA and DHA in all fish species were similar to those of the basal food sources. Correlation analysis showed that the EPA levels were strongly correlated between fish and seston; moreover, the correlation coefficient increased when a 1- or 2-month moving average was applied to the basal food sources, suggesting that fish represent a time-integrated supply of EPA and DHA. EPA levels of H. nipponensis had the highest correlation coefficients with seston among all fish species. EPA levels of H. nipponensis were significantly correlated with those of seston among lakes. The results of this study suggest that H. nipponensis is a useful indicator of EPA and DHA supplies in lake ecosystems., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

This study is based on biological trait analysis (BTA), which provides a link between the distribution and biological characteristics of species. The paper investigates differences in the structure and functional diversity of benthic fauna in terms of seven biological traits (mobility, habitat, feeding type, habitat modification, body form, body size and feeding apparatus) in nine Baltic coastal lakes whose salinity ranged from 0.1 to 7.3 PSU. Mobile organisms were more common in lakes with higher salinity, while sessile and semi-mobile species preferred low-salinity or freshwater environments. There were also noticeable differences connected with feeding type: collectors and scrapers were more common in brackish lakes, and collectors were significantly dominant in freshwater and transitional ones. This indicates that Baltic coastal lakes are inhabited by similar species of benthic fauna, but that certain biological traits occur with different frequencies. We therefore identified features that may affect the functioning of coastal lakes with a relatively narrow salinity gradient (0.1-7.3 PSU). It seems to confirm the possibility of using BTA methods to determine key characteristics that are helpful for understanding the differences between aquatic ecosystems. The results may provide a basis for further research on changes in the functional diversity of lakes along the southern coast of the Baltic Sea, particularly in view of climate change, given their being small, shallow and less resilient lakes., (© 2022. The Author(s).)

Studying ecosystem dynamics is critical to monitoring and managing linked systems of humans and nature. Due to the growth of tools and techniques for collecting data, information on the condition of these systems is more widely available. While there are a variety of approaches for mining and assessing data, there is a need for methods to detect latent characteristics in ecosystems linked to temporal and spatial patterns of change. Resilience-based approaches have been effective at not only identifying environmental change but also providing warning in advance of critical transitions in social-ecological systems (SES). In this study, we examine the usefulness of one such method, Fisher Information (FI) for spatiotemporal analysis. FI is used to assess patterns in data and has been established as an effective tool for capturing complex system dynamics to include regimes and regime shifts. We employed FI to assess the biophysical condition of eighty-five Swedish lakes from 1996-2018. Results showed that FI captured spatiotemporal changes in the Swedish lakes and identified distinct spatial patterns above and below the Limes Norrlandicus, a hard ecotone boundary which separates northern and southern ecoregions in Sweden. Further, it revealed that spatial variance changed approaching this boundary. Our results demonstrate the utility of this resilience-based approach for spatiotemporal and spatial regimes analyses linked to monitoring and managing critical watersheds and waterbodies impacted by accelerating environmental change., Competing Interests: The authors have declared that no competing interests exist.

Microsporidia are obligate intracellular eukaryotic parasites known to parasitize many species of the animal kingdom as well as some protists. However, their diversity is underestimated, in part as a consequence of the failure of 'universal' primers to detect them in metabarcoding studies. Besides, due to the inconsistency between taxonomy and phylogenetic data, available databases may assign incorrectly sequences obtained with high-throughput sequencing. In this work, we developed a comprehensive reference database which positions microsporidian SSU rRNA gene sequences within a coherent ranked phylogenetic framework. We used this phylogenetic framework to study the microsporidian diversity in lacustrine ecosystems, focusing on < 150 μm planktonic size fractions. Our analysis shows a high diversity of Microsporidia, with the identification of 1531 OTUs distributed within seven clades, of which 76% were affiliated to clade IV2 and 20% to clade I (nomenclature presented hereby). About a quarter of the obtained sequences shared less than 85% identity to the closest known species, which might represent undescribed genera or families infecting small hosts. Variations in the abundance of Microsporidia were recorded between the two lakes sampled and across the sampling period, which might be explained by spatio-temporal variations of their potential hosts such as microeukaryotes and metazooplankton., (© 2021 Society for Applied Microbiology and John Wiley & Sons Ltd.)

In general, the elaboration of the synthesis of water quality in Romania is based on the processing of a large volume of information coming from primary analytical data collected with a constant frequency by the organisms with a specific role in water quality monitoring. This study proposes a novel methodology for multi-criteria analysis aiming to evaluate the degradation state of lake ecosystems. The cornerstone of the newly presented methodology is a geographic information system (GIS) automated tool, involving the assessment of potential degradation sources affecting the watershed that supply the lakes with water. The methodology was tested by performing an analysis on 30 lakes in Romania. The lakes belong to different geographical areas, owing various natural specific conditions and were selected to fit to various types and specific local conditions. The calculation of the WRASTIC-HI (Wastewater-Recreation-Agriculture-Size-Transportation-Industry-Cover-Hazard Index) revealed that, out of 30 lake ecosystems selected as the case study, two lakes were fully degraded, 24 lakes were semi-degraded, and four were in a natural state. The four lakes characterised by a natural state are located in mountainous regions or in the Danube Delta. The results obtained on the selected lakes proved that the proposed index calculation corresponded in all case studies to the real field situation, highlighting thus the accuracy of the assessing process and increased advantages of the assessment's automation.

Due to differential exploitation pressure, ecosystems along the urban to rural gradients often exhibit different status in ecological structure and function. This can be challenging for lake restoration, given the relative strengths, magnitudes and speed of the exploitation. In this paper, we reconstructed the ecological changes over the past century and identified the regime shifts based on subfossil aquatic biota (chironomid records) in three shallow lakes (Shahu, Yanxi and Futou Lake) along an urban-rural gradient in the Yangtze floodplain, China. Our results illustrated the differences among lakes in trajectories, timing of critical transition and current ecological status. Eutrophic chironomid taxa increased markedly and replaced macrophyte-related taxa in urban Shahu Lake and suburban Yanxi Lake, indicated by the shift from a stable, vegetation-dominated state to an alternative, algal-dominated state in 1963 CE and 1975 CE respectively. The ecological regime in rural Futou Lake transited around 1980 CE but it is still in a relatively clear water state with abundant macrophytes due to anthropogenic hydrological controls. The greatest variance of chironomid compositional changes in both Shahu and Yanxi Lake was captured by anthropogenic pollutants, and analyses show that when these pressures are high they may be further amplified by climate warming. Responses along the urban-rural gradient are exemplified by urban Shahu Lake having shifted to a fragile regime with weak resistance and resilience, while rural Futou Lake has stabilized in a new regime with improved ecological resilience. Suburban Yanxi Lake is still moving toward a new state, and as such is unstable, because the types and magnitudes of external stressors are changing with urbanization in the city. It is suggested that active and precise management strategies for lakes should be established along the urban-rural gradient given their distinct development trajectories, drivers and current status., 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 © 2020 Elsevier B.V. All rights reserved.)

Predators can have strong impacts on prey populations, with cascading effects on lower trophic levels. Although such effects are well known in aquatic ecosystems, few studies have explored the influence of predatory aquatic mammals, or whether the same predator has similar effects in contrasting systems. We investigated the effects of platypus (Monotremata: Ornithorhynchus anatinus) on its benthic invertebrate prey, and tested predictions that this voracious forager would more strongly affect invertebrates-and indirectly, epilithic algae-in a mesotrophic lake than in a dynamic stream ecosystem. Hypotheses were tested using novel manipulative experiments involving platypus-exclusion cages. Platypuses had strongly suppressive effects on invertebrate prey populations, especially detritivores and omnivores, but weaker or inconsistent effects on invertebrate taxon richness and composition. Contrary to expectation, predation effects were stronger in the stream than the lake; no effects were found on algae in either ecosystem due to weak effects of platypuses on herbivorous invertebrates. Platypuses did not cause redistribution of sediment via their foraging activities. Platypuses can clearly have both strong and subtle effects on aquatic food webs that may vary widely between ecosystems and locations, but further research is needed to replicate our experiments and understand the contextual drivers of this variation.

Small lakes largely outnumber large lakes among the world's lentic ecosystems. Despite being common landscape elements, however, little is known about the value small lakes provide to recreationists. This paper presents results of an economic valuation study concerned with small gravel pits in Lower Saxony, Germany. Gravel pits are artificially created lake ecosystems that, particularly in Europe, are regularly used and managed by privately organized recreational anglers in an angling club context. A stated choice experiment provided insights into anglers' preferences for the abundance of target fish species, biodiversity of taxa other than fishes in the lakes as well as in the lake surroundings, and about the use of gravel pits by other recreationists for walking, swimming or boating. Latent class analysis identified five segments that varied in preferences. For the majority of anglers, the value of angling at gravel pit lakes was improved by an increase in the abundance of predatory fishes. Additionally, the presence of aquatic and terrestrial endangered species at the lakes increased the value of the ecosystems as perceived by the majority of anglers. By contrast, the presence of other recreational uses reduced the value of angling, with swimming being considered the most disturbing, while the degree of shoreline development had the least impact on the recorded choices. The results suggest that managing the gravel pit lakes for high biodiversity and the presence of desired game fish species maximizes the value for anglers. However, also two smaller segments with anglers revealing lexicographic preferences were identified. These anglers expressed either strong preferences against swimming in the lakes or strongly preferred the opportunity to use boats. Lake management may address the preference heterogeneity and the aversion against other recreational uses, such as swimming, by spatial zoning., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The discovery of microplastic (MP) being present in freshwaters has stimulated research on the impacts of MP on freshwater organisms. To date, research has focused on primary effects, leaving questions with respect to secondary effects at the level of freshwater food webs unanswered. Here, we use a theoretical modeling approach to investigate the hypothesis that MP imposes negative impacts on the level of freshwater shallow lake food webs. We find that increasing MP levels have the potential to affect the critical phosphorus loading (CPL), which is defined as the threshold for regime shifts between clear and turbid states of the water column. The possible occurrence of catastrophic cascades due to MP pollution is predominantly driven by the negative effects of MP on zooplankton. We explore the possible states of the food web by scenario analysis and show that the secondary effects of MP at current concentrations are likely to be negligible. However, at the current rate of MP production, a 20-40% reduction in the CPL would occur by the end of this century, suggesting a loss of resilience in shallow lakes that would be subject to abrupt changes in the food web under lower nutrient loading.

Lake biodiversity is an incomplete indicator of exogenous forcing insofar as it ignores underlying deformations of community structure. Here, we seek a proxy for deformation in a network of diatom assemblages comprising 452 species in 273 lakes across China. We test predictions from network theory that nodes of similar type will tend to self-organize in an unstressed system to a positively skewed frequency distribution of nodal degree. The empirical data reveal shifts in the frequency distributions of species associations across regions, from positive skew in lakes in west China with a history of low human impacts, to predominantly negative skew amongst lakes in highly disturbed regions in east China. Skew values relate strongly to nutrient loading from agricultural activity and urbanization, as measured by total phosphorus in lake water. Reconstructions through time show that positive skew reduces with temporal intensification of human impacts in the lake and surrounding catchments, and rises as lakes recover from disturbance. Our study illustrates how network parameters can track the loss of aquatic assemblage structure in lakes associated with human pressures., (© 2019 John Wiley & Sons Ltd.)

Persistent organic pollutants (POPs) are highly toxic organic chemicals. Lakes are one of the main sinks of POPs. POPs can be accumulated in multiple matrices in lake ecosystems and biomagnified through the food web, and thus pose a potential threat not only to lake ecosystems, but also to human health. Given their potential persistent risks, they have received much attention over the past decades. This review comprehensively summarizes the data on the levels and distributions of POPs in selected typical lake ecosystems in China and worldwide, involving water, sediments, organisms, and surrounding soils and atmosphere. It was found that current publications on POPs in Chinese lakes are mainly related to lakes in the developed eastern plain area, with only a few studies concerning the less-developed Qinghai-Tibet Plateau area. Similarly, around the world, there are more research on POPs in developed countries and less in relatively less-developed areas. Moreover, there are significant differences in the levels of POPs in different matrices in different lake ecosystems. Legacy POPs, such as polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and polybrominated diphenyl ethers (PBDEs), were commonly detected and reported in different lakes, while emerging POPs like perfluorinated compounds (PFCs), polychlorinated naphthalenes (PCNs), Tetrabromobisphenol A (TBBPA), and hexabromocyclododecane (HCBD) were relatively less detected or reported. A comprehensive summarization on the levels and distributions of traditional and emerging POPs in lake ecosystems could be significant for further understanding the behaviors and risks of POPs in lake ecosystems., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Eutrophication is one of the main causes of the degradation of lake ecosystems. Its intensification during the last decades has led the stakeholders to seek for water management and restoration solutions, including those based on modelling approaches. This paper presents a review of lake eutrophication modelling, on the basis of a scientific appraisal performed by researchers for the French ministries of Environment and Agriculture. After a brief introduction presenting the scientific context, a bibliography analysis is presented. Then the main results obtained with process-based models are summarized. A synthesis of the scientist recommendations in order to improve the lake eutrophication modelling is finally given before the conclusion., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The concentrations, sources, and risks of heavy metals (Fe, Al, Mn, Cr, Co, Ni, Cu, Zn, As, Cd, W, Pb, and Tl) in sediments in five river-lake ecosystems in the Poyang Lake region were studied. The concentrations of the heavy metals varied spatially, with most of the highest concentrations in the Raohe river-lake ecosystem (RH). All heavy metals except As, Cd, W, and Tl were enriched in sediments possessing high total organic carbon contents or in finer sediments. Based on enrichment factors and statistical methods, it was found that Cd in sediments in the Xiushui (XS), Ganjiang (GJ), Xinjiang (XJ) river-lake ecosystems, and RH; Mn in the XS, GJ, and RH; and W in the XS and GJ were greatly affected by anthropogenic inputs. Moreover, the origins of Cu, Zn, and As require more attention due to the high concentrations found. The high enrichment factor of Cd in the sediments indicated that this metal might cause significant pollution in the environment. The results of the modified potential ecological risk index revealed that the XS, GJ, RH, and XJ were at considerable ecological risk, while the sediments in the Fuhe river-lake ecosystem (FH) were at moderate ecological risk, with Cd contributing the highest proportion of risk. The hazard score fundamentally validated the modified potential ecological risk analysis and revealed a mean toxicity of 57.80% to the benthic organisms in the RH.

Elevated environmental pressures negatively affect the bacterial community structure. However, little knowledge about the nonlinear responses of spatially related environmental variable across multiple plateau lake ecosystems on bacterioplankton communities has been gathered. Here, we used 454 pyrosequencing of 16S rRNA genes to study the associations of bacterial communities in terms of environmental characteristics as well as the potentially ecological threshold-inducing shifts of the bacterial community structure along the key environmental variables based on hypothesized structural equation models and the SEGMENTED method in 21 plateau lakes. Our results showed that water transparency was the major driving force and that total nitrogen was more significant than total phosphorus in determining the taxon composition of the bacterioplankton community. Significant community threshold estimates for bacterioplankton were observed at 7.36 for pH and 25.6% for the percentage of the agricultural area, while the remarkable change point of the cyanobacteria community structure responding to pH was at 7.74. Furthermore, the findings indicated that increasing nutrient loads can induce a distinct shift in dominance from Proteobacteria to Cyanobacteria, as well as a sharp decrease and adjacent increase when crossing the change point for Actinobacteria and Bacteroidetes along the gradient of the agricultural area., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The conducted research is aimed at assessing the current state of the tourist and recreational potential of the lake system in the region of North Kazakhstan (Kazakhstan). The research included the relationship between the distribution and natural diversity of reservoirs and landscapes and the density of the transport network of the studied region in the administrative division of the region. The aim of the research undertaken is to indicate the spatial differentiation of the conditions for t he development of tourism in relation to the degree of lake density and transport accessibility. The quantitative and qualitative characteristics of the lakes in terms of spatial diversity and transport accessibility in the region were presented. The anal ysis of the natural and recreational potential, with the use of statistical methods, satellite images, comparative analysis and field studies, made it possible to identify lake ecosystems that are already used or recommended for use as objects in tourism, as well as i n the national economy. The analysis of the road network allows to conclude that its density, despite the higher indicators than the national average, does not fully allow the use of the region's tourist potential and may constitute a barrier to its development.

Inferring ecosystem functioning and ecosystem services through inspections of the species inventory is a major aspect of ecological field studies. Ecosystem functions are often stable despite considerable species turnover. Using metatranscriptome analyses, we analyse a thus-far unparalleled freshwater data set which comprises 21 mainland European freshwater lakes from the Sierra Nevada (Spain) to the Carpathian Mountains (Romania) and from northern Germany to the Apennines (Italy) and covers an altitudinal range from 38 m above sea level (a.s.l) to 3110 m a.s.l. The dominant taxa were Chlorophyta and streptophytic algae, Ciliophora, Bacillariophyta and Chrysophyta. Metatranscriptomics provided insights into differences in community composition and into functional diversity via the relative share of taxa to the overall read abundance of distinct functional genes on the ecosystem level. The dominant metabolic pathways in terms of the fraction of expressed sequences in the cDNA libraries were affiliated with primary metabolism, specifically oxidative phosphorylation, photosynthesis and the TCA cycle. Our analyses indicate that community composition is a good first proxy for the analysis of ecosystem functions. However, differential gene regulation modifies the relative importance of taxa in distinct pathways. Whereas taxon composition varies considerably between lakes, the relative importance of distinct metabolic pathways is much more stable, indicating that ecosystem functioning is buffered against shifts in community composition through a functional redundancy of taxa., (© 2016 The Authors. Molecular Ecology Published by John Wiley & Sons Ltd.)

Primary producers form the base of food webs but also affect other ecosystem characteristics, such as habitat structure, light availability, and microclimate. Here, we examine changes caused by 5-30+ years of nutrient addition and resulting increases in net primary productivity (NPP) in tundra, streams, and lakes in northern Alaska. The Arctic provides an important opportunity to examine how ecosystems characterized by low diversity and low productivity respond to release from nutrient limitation. We review how responses of algae and plants affect light availability, perennial biotic structures available for consumers, oxygen levels, and temperature. Sometimes, responses were similar across all three ecosystems; e.g., increased NPP significantly reduced light to the substrate following fertilization. Perennial biotic structures increased in tundra and streams but not in lakes, and provided important new habitat niches for consumers as well as other producers. Oxygen and temperature responses also differed. Life history traits (e.g., longevity) of the primary producers along with the fate of detritus drove the responses and recovery. As global change persists and nutrients become more available in the Arctic and elsewhere, incorporating these factors as response variables will enable better prediction of ecosystem changes and feedbacks in this biome and others.

Permafrost thaw ponds of the warming Eastern Canadian Arctic are major landscape constituents and often display high levels of methylmercury (MeHg). We examined photodegradation potentials in high-dissolved organic matter (DOC) thaw ponds on Bylot Island (BYL) and a low-DOC oligotrophic lake on Cornwallis Island (Char Lake). In BYL, the ambient MeHg photodemethylation (PD) rate over 48 h of solar exposure was 6.1 × 10(-3) m(2) E(-1), and the rate in MeHg amended samples was 9.3 × 10(-3) m(2) E(-1). In contrast, in low-DOC Char Lake, PD was only observed in the first 12 h, which suggests that PD may not be an important loss process in polar desert lakes. Thioglycolic acid addition slowed PD, while glutathione and chlorides did not impact northern PD rates. During an ecosystem-wide experiment conducted in a covered BYL pond, there was neither net MeHg increase in the dark nor loss attributable to PD following re-exposure to sunlight. We propose that high-DOC Arctic thaw ponds are more prone to MeHg PD than nearby oligotrophic lakes, likely through photoproduction of reactive species rather than via thiol complexation. However, at the ecosystem level, these ponds, which are widespread through the Arctic, remain likely sources of MeHg for neighboring systems.

Terrestrial ecosystems export large amounts of organic carbon (t-OC) but the net effect of this OC on the productivity of recipient aquatic ecosystems is largely unknown. In this study of boreal lakes, we show that the relative contribution of t-OC to individual top consumer (fish) biomass production, and to most of their potential prey organisms, increased with the concentration of dissolved organic carbon (DOC; dominated by t-OC sources) in water. However, the biomass and production of top consumers decreased with increasing concentration of DOC, despite their substantial use (up to 60%) of t-OC. Thus, the results suggest that although t-OC supports individual consumer growth in lakes to a large extent, t-OC input suppresses rather than subsidizes population biomass production.

Silver nanoparticles (AgNPs) are currently the most commonly used nanoparticles in consumer products, yet their environmental fate in natural waters is poorly understood. In the present study, we investigated the persistence, transformations and distribution of polyvinylpyrrolidone (PVP) and citrate (CT) coated AgNPs in boreal lake mesocosms dosed either with a 6-week chronic regimen or a one-time pulse treatment at environmentally relevant dosing levels. In the chronic treatments, total Ag (TAg) concentrations reached ∼40% of target concentrations by the end of the experiment, and in the pulsed mesocosms, TAg dissipated slowly, with a half-life of ∼20 days. Sediments and periphyton on the mesocosm walls were an important sink for Ag. We found little effect of AgNP loading and surface coating on the persistence of TAg. There were also no differences between treatments in the degree of agglomeration of AgNPs, as indicated by the accumulation and distribution of Ag in the particulate and colloidal fractions. The low ionic strength and relatively high dissolved organic carbon concentrations in the lake water likely contributed to the relative stability of AgNP in the water column. The low concentrations of dissolved Ag (<1 μg L(-1)) in the size fraction <3 kDaA reflect the importance of natural ligands in controlling the concentrations of Ag released by dissolution of AgNPs. Overall, these data indicate that AgNPs are relatively stable in the tested lake environment and appear to result in quantities of highly toxic ionic Ag(+) that are below our limit of detection.

Although competing species are expected to exhibit compensatory dynamics (negative temporal covariation), empirical work has demonstrated that competitive communities often exhibit synchronous dynamics (positive temporal covariation). This has led to the suggestion that environmental forcing dominates species dynamics; however, synchronous and compensatory dynamics may appear at different length scales and/or at different times, making it challenging to identify their relative importance. We compiled 58 long-term datasets of zooplankton abundance in north-temperate and sub-tropical lakes and used wavelet analysis to quantify general patterns in the times and scales at which synchronous/compensatory dynamics dominated zooplankton communities in different regions and across the entire dataset. Synchronous dynamics were far more prevalent at all scales and times and were ubiquitous at the annual scale. Although we found compensatory dynamics in approximately 14% of all combinations of time period/scale/lake, there were no consistent scales or time periods during which compensatory dynamics were apparent across different regions. Our results suggest that the processes driving compensatory dynamics may be local in their extent, while those generating synchronous dynamics operate at much larger scales. This highlights an important gap in our understanding of the interaction between environmental and biotic forces that structure communities., (© 2014 The Author(s) Published by the Royal Society. All rights reserved.)

Long implicated in the invasion process, live-bait anglers are highly mobile species vectors with frequent overland transport of fishes. To test hypotheses about the role of anglers in propagule transport, we developed a social-ecological model quantifying the opportunity for species transport beyond the invaded range resulting from bycatch during commercial bait operations, incidental transport, and release to lake ecosystems by anglers. We combined a gravity model with a stochastic, agent-based simulation, representing a 1-yr iteration of live-bait angling and the dynamics of propagule transport at fine spatiotemporal scales (i.e., probability of introducing n propagules per lake per year). A baseline scenario involving round goby (Neogobius melanostomus) indicated that most angling trips were benign; irrespective of lake visitation, anglers failed to purchase and transport propagules (benign trips, median probability P = 0.99912). However, given the large number of probability trials (4.2 million live-bait angling events per year), even the rarest sequence of events (uptake, movement, and deposition of propagules) is anticipated to occur. Risky trips (modal P = 0.00088 trips per year; approximately 1 in 1136) were sufficient to introduce a substantial number of propagules (modal values, Poisson model = 3715 propagules among 1288 lakes per year; zero-inflated negative binomial model = 6722 propagules among 1292 lakes per year). Two patterns of lake-specific introduction risk emerged. Large lakes supporting substantial angling activity experienced propagule pressure likely to surpass demographic barriers to establishment (top 2.5% of lakes with modal outcomes of five to 76 propagules per year; 303 high-risk lakes with three or more propagules, per year). Small or remote lakes were less likely to receive propagules; however, most risk distributions were leptokurtic with a long right tail, indicating the rare occurrence of high propagule loads to most waterbodies. Infestation simulations indicated that the number of high-risk waterbodies could be as great as 1318 (zero-inflated negative binomial), whereas a 90% reduction in bycatch from baseline would reduce the modal number of high risk lakes to zero. Results indicate that the combination of invasive bycatch and live-bait anglers warrants management concern as a species vector, but that risk is confined to a subset of individuals and recipient sites that may be effectively managed with targeted strategies.

Fires are the major natural disturbance in the boreal forest, and their frequency and intensity will likely increase as the climate warms. Terrestrial nutrients released by fires may be transported to boreal lakes, stimulating increased primary productivity, which may radiate through multiple trophic levels. Using a before-after-control-impact (BACI) design, with pre- and postfire data from burned and unburned areas, we examined effects of a natural fire across several trophic levels of boreal lakes, from nutrient and chlorophyll levels, to macroinvertebrates, to waterbirds. Concentrations of total nitrogen and phosphorus were not affected by the fire. Chlorophyll a levels were also unaffected, likely reflecting the stable nutrient concentrations. For aquatic invertebrates, we found that densities of three functional feeding groups did not respond to the fire (filterers, gatherers, scrapers), while two groups increased (shredders, predators). Amphipods accounted for 98% of shredder numbers, and we hypothesize that fire-mediated habitat changes may have favored their generalist feeding and habitat ecology. This increase in amphipods may, in turn, have driven increased predator densities, as amphipods were the most numerous invertebrate in our lakes and are commonly taken as prey. Finally, abundance of waterbird young, which feed primarily on aquatic invertebrates, was not affected by the fire. Overall, ecosystems of our study lakes were largely resilient to forest fires, likely due to their high initial nutrient concentrations and small catchment sizes. Moreover, this resilience spanned multiple trophic levels, a significant result for ecologically similar boreal regions, especially given the high potential for increased fires with future climate change.

Recent attention regarding the impacts of oil and gas development and exploitation has focused on the unintentional release of hydrocarbons into the environment, whilst the potential negative effects of other possible avenues of environmental contamination are less well documented. In the hydrocarbon-rich and ecologically sensitive Mackenzie Delta region (NT, Canada), saline wastes associated with hydrocarbon exploration have typically been disposed of in drilling sumps (i.e., large pits excavated into the permafrost) that were believed to be a permanent containment solution. However, failure of permafrost as a waste containment medium may cause impacts to lakes in this sensitive environment. Here, we examine the effects of degrading drilling sumps on water quality by combining paleolimnological approaches with the analysis of an extensive present-day water chemistry dataset. This dataset includes lakes believed to have been impacted by saline drilling fluids leaching from drilling sumps, lakes with no visible disturbances, and lakes impacted by significant, naturally occurring permafrost thaw in the form of retrogressive thaw slumps. We show that lakes impacted by compromised drilling sumps have significantly elevated lakewater conductivity levels compared to control sites. Chloride levels are particularly elevated in sump-impacted lakes relative to all other lakes included in the survey. Paleolimnological analyses showed that invertebrate assemblages appear to have responded to the leaching of drilling wastes by a discernible increase in a taxon known to be tolerant of elevated conductivity coincident with the timing of sump construction. This suggests construction and abandonment techniques at, or soon after, sump establishment may result in impacts to downstream aquatic ecosystems. With hydrocarbon development in the north predicted to expand in the coming decades, the use of sumps must be examined in light of the threat of accelerated permafrost thaw, and the potential for these industrial wastes to impact sensitive Arctic ecosystems.

Animals can be important in nutrient cycling through a variety of direct and indirect pathways. A high biomass of animals often represents a large pool of nutrients, leading some ecologists to argue that animal assemblages can represent nutrient sinks within ecosystems. The role of animals as sources vs. sinks of nutrients has been debated particularly extensively for freshwater fishes. We argue that a large pool size does not equate to a nutrient sink; rather, animals can be nutrient sinks when their biomass increases, when emigration rates are high, and/or when nutrients in animal carcasses are not remineralized. To further explore these ideas, we use a simple model to evaluate the conditions under which fish are phosphorus (P) sources or sinks at the ecosystem (lake) level, and at the habitat level (benthic and water column habitats). Our simulations suggest that, under most conditions, fish are sinks for benthic P but are net P sources to the water column. However, P source and sink strengths depend on fish feeding habits (proportion of P consumed from the benthos and water column), migration patterns, and especially the fate of carcass P. Of particular importance is the rate at which carcasses are mineralized and the relative importance of benthic vs. pelagic primary producers in taking up mineralized P (and excreted P). Higher proportional uptake of P by benthic primary producers increases the likelihood that fish are sinks for water column P. Carcass bones and scales are relatively recalcitrant and can represent a P sink even if fish biomass does not change over time. Thus, there is a need for better documentation of the fraction of carcass P that is remineralized, and the fate of this P, under natural conditions. We urge a more holistic perspective regarding the role of animals in nutrient cycling, with a focus on quantifying the rates at which animals consume, store, release, and transport nutrients under various conditions.

The absence of well-executed environmental monitoring in the Athabasca oil sands (Alberta, Canada) has necessitated the use of indirect approaches to determine background conditions of freshwater ecosystems before development of one of the Earth's largest energy deposits. Here, we use highly resolved lake sediment records to provide ecological context to ∼50 y of oil sands development and other environmental changes affecting lake ecosystems in the region. We show that polycyclic aromatic hydrocarbons (PAHs) within lake sediments, particularly C1-C4-alkylated PAHs, increased significantly after development of the bitumen resource began, followed by significant increases in dibenzothiophenes. Total PAH fluxes in the modern sediments of our six study lakes, including one site ∼90 km northwest of the major development area, are now ∼2.5-23 times greater than ∼1960 levels. PAH ratios indicate temporal shifts from primarily wood combustion to petrogenic sources that coincide with greater oil sands development. Canadian interim sediment quality guidelines for PAHs have been exceeded since the mid-1980s at the most impacted site. A paleoecological assessment of Daphnia shows that this sentinel zooplankter has not yet been negatively impacted by decades of high atmospheric PAH deposition. Rather, coincident with increases in PAHs, climate-induced shifts in aquatic primary production related to warmer and drier conditions are the primary environmental drivers producing marked daphniid shifts after ∼1960 to 1970. Because of the striking increase in PAHs, elevated primary production, and zooplankton changes, these oil sands lake ecosystems have entered new ecological states completely distinct from those of previous centuries.

Lakes, as integral social-ecological systems, are hotspots for exploring climatic and anthropogenic impacts, with crucial pathways revealed by continuous sediment records. However, the response of multi-proxies in large shallow lakes to typical abrupt events and sustained drivers since the Anthropocene remains unclear. Here, we explored the driver-identification relationships between multi-proxy peaks and natural and anthropogenic events as well as the attribution of short-term perturbations and long-term pressures. To this end, sediment core records, socio-ecological data, and documented events from official records were integrated into a large shallow lake (Dongting Lake, China). Significant causal cascades and path effects (goodness-of-fit: 0.488; total effect: -1.10; p < .001) were observed among catchment environmental proxies, lake biogenic proxies, and mixed-source proxies. The peak-event identification rate (PEIR) and event-peak driving rate were proposed, and values of 28.57%-46.43% and 50%-81.25% were obtained, respectively. The incomplete accuracy of depicting event perturbations using sediment proxies was caused by various information filters both inside and outside the lake. PEIRs for compound events were 1.41 (±0.72) and 1.09 (±0.46) times greater than those for anthropogenic-dominated and natural-dominated events, respectively. Furthermore, socio-economic activity, hydrologic dynamics, land-use changes, and agriculture exerted significant and persistent pressures, cumulatively contributing 55.3%-80.9% to alterations in sediment proxies. Relatively synergistic or antagonistic trends in temporal contributions of these forces were observed after 2000, which were primarily attributed to the "Grain for Green" project and the Three Gorges Dam. This study represents one of the few investigations to distinguish the driver-response relationship of multiple proxies in large shallow lakes under typical event perturbations and long-term sustained pressures since the Anthropocene. The findings will help policymakers and managers address ecological perturbations triggered by climate change and human activities over long-term periods., (© 2024 John Wiley & Sons Ltd.)

This study analyzes proteolytic enzyme persistence and the role of dead (or metabolically inactive) aquatic bacteria in organic matter cycling. Samples from four lakes of different trophic status were used. Irrespective of the trophic status of the examined lakes, bacterial aminopeptidases remained active even 72 h after the death of the bacteria that produced them. The total pool of proteolytic enzymes in natural lake water samples was also stable. We found that the rates of amino acid enzymatic release from proteinaceous matter added to preserved lake water sample were constant for at least 96 h (r(2)  = 0.99, n = 17, P ≤ 0.0001, V(max)  = 84.6 nM h(-1) ). We also observed that proteases built into bacterial cell debris fragments remained active for a long time, even after the total destruction of cells. Moreover, during 24 h of incubation time, about 20% of these enzymatically active fragments adsorbed onto natural seston particles, becoming a part of the 'attached enzymes system' that is regarded as the 'hot-spot' of protein degradation in aquatic ecosystems., (© 2011 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.)

Gravel excavation often bears conflicts with the use of drinking water as under-water-table mining can directly impact groundwater quality downstream of the open gravel pit lake due to exposure of the groundwater aquifer to the atmosphere and to human activities. To assess this potential impact of GPLs on groundwater, we assessed the mass balance for nitrate (NO(3)) and phosphate (PO(4)) and whole-ecosystem metabolism of five post-excavation GPLs in Austria. GPLs differed in both age and residence time of lake water. We found that GPLs significantly reduced the concentration of NO(3) and PO(4) as groundwater passes through the lake ecosystem, which in most cases acted as a net sink for these nutrients. Groundwater-derived nutrients enhanced both epilithic and pelagic net primary production in the GPLs, which ultimately leads to biomass accrual. Our data also suggest that this biomass accrual may induce, at least in part, clogging of the GPLs and their successive hydrodynamic isolation from the adjacent groundwater. Despite continuous biomass build-up and elevated concentrations of dissolved organic carbon (DOC) in the lake water compared to the inflowing groundwater, DOC export into the outflowing groundwater remained low. Our data suggest that GPLs could contribute to groundwater amelioration where agricultural land use increases nutrient concentrations in the groundwater given a proper management of these man-made ecosystems., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The atmospheric concentration of methane (CH(4)), a major greenhouse gas, is mainly controlled by the activities of methane-producing (methanogens) and methane-consuming (methanotrophs) microorganisms. Freshwater lakes are identified as one of the main CH(4) sources, as it was estimated that they contribute to 6-16% of natural CH(4) emissions. It is therefore critical to better understanding the biogeochemical cycling of CH(4) in these ecosystems. In this paper, the effects of environmental factors on methanogenic and methanotrophic rates are reviewed and an inventory of the methanogens and methanotrophs at the genus/species level in freshwater lakes is given. We focus on the anaerobic oxidation of methane, which is a still poorly known process but increasingly reported in freshwater lakes., (Copyright © 2011 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.)

The study was carried out in the Phewa Lake of Pokhara Metropolitan City, Gandaki Province, Nepal, for geochemical assessment and characterization of the lake water quality. A total of 28 water samples were collected in each season from the different zones of the lake in March 2022 (pre-monsoon) and November 2022 (post-monsoon). The lake exhibited elevated levels of PO 4 3- , NO 3 , indicating that anthropogenic activities are interfering the lake water. The significant differences in many monitored physicochemical parameters between the pre- and post-monsoon visualize dilution effect in the lake during post-monsoon. Piper diagram illustrates that the majority of water samples in the lake are of Ca-HCO - , and NH 3 , indicating that anthropogenic activities are interfering the lake water. The significant differences in many monitored physicochemical parameters between the pre- and post-monsoon visualize dilution effect in the lake during post-monsoon. Piper diagram illustrates that the majority of water samples in the lake are of Ca-HCO 3 type. Additionally, Piper diagram, Gibbs diagram, and Mixing plot illustrate that carbonate weathering is dominant in both seasons. Principal component analysis (PCA) reveals significant correlations among NO 3 - , demonstrating that pollution in the lake water is attributed to agricultural activities and domestic effluents. In the majority of samples, water quality index (WQI) depicts that the lake water quality is very poor to poor in the pre-monsoon and poor to good in the post-monsoon. Sodium absorption ratio (SAR), % Na (percent sodium), electrical conductivity (EC), cation ratio of soil structural stability (CROSS), and United States Salinity Laboratory (USSL) diagram illustrate that the lake water is suitable for irrigation.4 2- , Na + , and Cl - , demonstrating that pollution in the lake water is attributed to agricultural activities and domestic effluents. In the majority of samples, water quality index (WQI) depicts that the lake water quality is very poor to poor in the pre-monsoon and poor to good in the post-monsoon. Sodium absorption ratio (SAR), % Na (percent sodium), electrical conductivity (EC), cation ratio of soil structural stability (CROSS), and United States Salinity Laboratory (USSL) diagram illustrate that the lake water is suitable for irrigation., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Historical changes of sediment characteristics and levels of inorganic and organic contaminants were studied in dated sediment cores from the Visovac Lake, situated in the Krka National Park, Croatia, to identify the main sources of anthropogenic pressures on this highly protected system. Depth distributions of lithogenic elements showed a steady decrease of terrigenous inputs due to the reduction in agricultural activities in the area, which was particularly pronounced during the 1991-1995 war in Croatia. Vertical and longitudinal distributions of Cd and Zn indicated that they are predominately of anthropogenic origin. The historical profiles of these toxic metals coincide well with the recorded production of metal industry in the upper reach of the Krka River with a sharp decrease reflecting the interruption by the war and slow recovery afterwards. By contrast, the recovery of the tourist industry in Krka NP after the war was accompanied by increasing contamination by elements characteristic of boat and car traffic (Sn, Cu, Pb) as well as oil pollution. The contamination with polycyclic aromatic hydrocarbons and polychlorinated biphenyls was only moderate. Although levels of metallic and organic contamination can be considered relatively low, the observed shift from industrial to tourism-related sources indicated that touristic activities should also be regarded as a possible threat for this vulnerable karst aquatic ecosystem., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Shrinking saline lakes provide irreplaceable habitat for waterbird species globally. Disentangling the effects of wetland habitat loss from other drivers of waterbird population dynamics is critical for protecting these species in the face of unprecedented changes to saline lake ecosystems, ideally through decision-making frameworks that identify effective management options and their potential outcomes. Here, we develop a framework to assess the effects of hypothesized population drivers and identify potential future outcomes of plausible management scenarios on a saline lake-reliant waterbird species. We use 36 years of monitoring data to quantify the effects of environmental conditions on the population size of a regionally important breeding colony of American white pelicans (Pelecanus erythrorhynchos) at Great Salt Lake, Utah, US, then forecast colony abundance under various management scenarios. We found that low lake levels, which allow terrestrial predators access to the colony, are probable drivers of recent colony declines. Without local management efforts, we predicted colony abundance could likely decline approximately 37.3% by 2040, although recent colony observations suggest population declines may be more extreme than predicted. Results from our population projection scenarios suggested that proactive approaches to preventing predator colony access and reversing saline lake declines are crucial for the persistence of the Great Salt Lake pelican colony. Increasing wetland habitat and preventing predator access to the colony together provided the most effective protection, increasing abundance 145.4% above projections where no management actions are taken, according to our population projection scenarios. Given the importance of water levels to the persistence of island-nesting colonial species, proactive approaches to reversing saline lake declines could likely benefit pelicans as well as other avian species reliant on these unique ecosystems., (© 2024 The Ecological Society of America. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.)

The use of organisms like macroinvertebrates in developing bioassessment tools, such as multimetric indices (MMIs), is gaining global recognition in monitoring the health status of lakes. The transition from traditional methods of physico-chemical parameters is due to the financial and time costs involved in their analysis while failing to provide accurate early warning signals on ecosystem conditions. Currently, there is scanty information on the use of MMIs in the conservation and management of lakes in Nigeria. This study aimed at developing a macroinvertebrate-based MMI to assess the ecological status of lakes in North Central Nigeria. The study was conducted on Tagwai and Old Gawu Lakes, from April to October 2022. Sampling sites were clustered based on organic pollution and categorized into reference (four) and impaired (four) sites. Out of 54 macroinvertebrate-based candidate metrics, only five were selected after discriminatory, stability, and redundancy tests (performed using R software). The final metrics were abundance of Ephemeroptera + Trichoptera; abundance of Coleoptera + Ephemeroptera; Gastropoda richness; Shannon Wiener index; and percentages of shredders + predators + scrapers, hereafter referred to as North Central Nigeria-Lakes Multimetric Index (NCN-LMMI). The NCN-LMMI values ranged as follows: 21-25, 16-20, 11-15, and 5-10 corresponding to categories I, II, III, and IV for water quality, as indications of good, fair, poor, and very poor ecological status of the lake, respectively. The developed NCN-LMMI will be a useful tool for aquatic resource managers and environmentalists to assess the ecological condition of lakes, mainly the North Central Nigeria municipal lakes., (© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Although competing species are expected to exhibit compensatory dynamics (negative temporal covariation), empirical work has demonstrated that competitive communities often exhibit synchronous dynamics (positive temporal covariation). This has led to the suggestion that environmental forcing dominates species dynamics; however, synchronous and compensatory dynamics may appear at different length scales and/or at different times, making it challenging to identify their relative importance. We compiled 58 long-term datasets of zooplankton abundance in north-temperate and sub-tropical lakes and used wavelet analysis to quantify general patterns in the times and scales at which synchronous/compensatory dynamics dominated zooplankton communities in different regions and across the entire dataset. Synchronous dynamics were far more prevalent at all scales and times and were ubiquitous at the annual scale. Although we found compensatory dynamics in approximately 14% of all combinations of time period/scale/lake, there were no consistent scales or time periods during which compensatory dynamics were apparent across different regions. Our results suggest that the processes driving compensatory dynamics may be local in their extent, while those generating synchronous dynamics operate at much larger scales. This highlights an important gap in our understanding of the interaction between environmental and biotic forces that structure communities.