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Using lake‐sediment cores to document past seismicity requires a comprehensive understanding of possible lateral variations in depositional processes. This study aims to reveal the lateral variations in earthquake‐induced event deposits throughout Lake Iznik, a large lake located on the middle strand of the North Anatolian Fault. Based on stratigraphic, sedimentological and geochemical analyses of 14 sediment cores from two subbasins across the lake, five different types of event deposits (T1–T5) were identified and characterised. One event deposit type (T5) is restricted to a delta mouth, characterised by the occurrence of authigenic Fe‐Mn carbonates and interpreted to result from flood events. The four other types of event deposits are characterised by their synchronicity between cores and their age consistency with historical earthquakes and are interpreted to be likely generated by earthquakes. The locally prominent 1065 CE historical earthquake that ruptured the sub‐lacustrine Iznik Fault produced at least three different types of event deposits. One deposit type (T2) is only observed for this very local earthquake, implying that the type of event deposit might also depend on ground‐motion parameters. At the lake scale, the occurrence of various event deposits depends on the flow distance from the source of sediment destabilisations to the coring site. [ABSTRACT FROM AUTHOR]

Lakes act as natural reservoirs for storing organic material, and comprehending how organic carbon (OC) and black carbon (BC) are deposited in lake sediments is crucial for understanding the global carbon cycle and its impact on climate and ecosystems. In this study, we examined changes in the deposition patterns of OC and BC in Yinjia Lake (YJL) over the past 110 years, using a 60 cm sediment core dated with 210Pb. Our aim was to discern how these changes relate to human activities and other influencing factors in the region of southeast Hubei, central China. Our findings revealed a consistent rise in total organic carbon (TOC) and total nitrogen (TN) concentrations, indicating a gradual increase from the bottom upwards. Analysis of C/N ratios and δ13C values showed that the OC in the sediment mainly originated from phytoplankton and terrestrial C3 plants. Over the past century, OC burial rates (OCBR) in the YJL core increased from 61.35 to 86.69 g m−2 yr−1, primarily due to increased primary production resulting from intensified local agriculture and urban growth. Temperature was found to influence OCBR, while precipitation had little impact on OCBR dynamics in sedimentary environments. BC burial rates in YJL ranged from 3.67 to 11.51 g m–2 yr–1, significantly exceeding those observed in other lakes worldwide. The fluctuations in BC burial rates correlated with shifts in local industrial practices and energy consumption. In recent years (post-2005), BC burial rates have declined, likely due to reduced pollutant emissions resulting from the implementation of emission-control policies in China. These results provide valuable insights into the interactions between human activities, climate variability, and carbon cycling in lacustrine environments, with implications for regional carbon budgets, ecosystem management, and climate-change mitigation strategies. [ABSTRACT FROM AUTHOR]

This is the first report on high pesticide tolerance displayed by the microbiota isolated from the sediments of two high-altitude lakes, located in the Singalila National Park, Singalila Ridge of the Himalayas. Given the remote location of these lakes, direct exposure to chemical pesticides is highly unlikely. However, the high tolerance to commonly used pesticides exhibited, i.e. up to 250 mg/ml, suggests repeated exposure and contamination of the lakes. Microbial growth in the presence of varying concentrations of the pesticides, namely, emamectin benzoate, thiamethoxam, quinalphos, deltamethrin, spiromesifen, flubendiamide, monocrotophos, fipronil, fenazaquin and phorate, was tested. Results showed resistance to all pesticides except fenazaquin and fipronil, up to 250 mg/ml. For the latter two, tolerance was displayed up to a concentration of 40 mg/ml. Tolerance may potentially result from the transport and deposition of pesticides from nearby locations, particularly the tea plantations of Darjeeling and Eastern Nepal. This may create great ecological risks as these lakes are an important water source for endemic wildlife of this protected area. They also hold great significance to the religious sentiment of the local tribes who worship these lakes as sacred. The study highlights the need for monitoring pesticide contamination in such pristine high-altitude environments and the mechanisms of long-range pollutant transport. [ABSTRACT FROM AUTHOR]

Abstract Using lake‐sediment cores to document past seismicity requires a comprehensive understanding of possible lateral variations in depositional processes. This study aims to reveal the lateral variations in earthquake‐induced event deposits throughout Lake Iznik, a large lake located on the middle strand of the North Anatolian Fault. Based on stratigraphic, sedimentological and geochemical analyses of 14 sediment cores from two subbasins across the lake, five different types of event deposits (T1–T5) were identified and characterised. One event deposit type (T5) is restricted to a delta mouth, characterised by the occurrence of authigenic Fe‐Mn carbonates and interpreted to result from flood events. The four other types of event deposits are characterised by their synchronicity between cores and their age consistency with historical earthquakes and are interpreted to be likely generated by earthquakes. The locally prominent 1065 CE historical earthquake that ruptured the sub‐lacustrine Iznik Fault produced at least three different types of event deposits. One deposit type (T2) is only observed for this very local earthquake, implying that the type of event deposit might also depend on ground‐motion parameters. At the lake scale, the occurrence of various event deposits depends on the flow distance from the source of sediment destabilisations to the coring site.

Chaohu Lake is a representative lake in China that suffers from severe eutrophication and algal blooms. Understanding the changes in the lake’s eutrophic condition over time is essential for its restoration and management under the background of global changes and regional sustainability. In this context, the compositions of carbon and nitrogen isotopes (δ 13Corg and δ 15N, respectively), total organic carbon (TOC), total nitrogen (TN), and carbon–nitrogen ratio (C/N) were analysed to depict the history of eutrophic state of Chaohu Lake, and its relationship with environmental changes. The result show that before the 1950s, the primary productivity of the lake was low. During the period from the 1950s to the 1970s, primary productivity increased substantially due to eutrophication. From the 1970s to the present, as a result of the construction of the Chaohu Floodgate Station, water replacement in the semi-closed Chaohu Lake gradually slowed and nutrients began to accumulate more rapidly. These conditions led to enhanced lake productivity and rapid eutrophication, mainly caused by intensified human activities and increased exogenous inputs. Our findings suggest that the geochemical records (δ 13Corg, δ 15N, TOC, TN, and C/N ratios) in sediment for Chaohu Lake are capable of recording important shifts in the temporal evolution of lake-water trophic state.

Abstract Background Microbial methane oxidation, methanotrophy, plays a crucial role in mitigating the release of the potent greenhouse gas methane from aquatic systems. While aerobic methanotrophy is a well-established process in oxygen-rich environments, emerging evidence suggests their activity in hypoxic conditions. However, the adaptability of these methanotrophs to such environments has remained poorly understood. Here, we explored the genetic adaptability of aerobic methanotrophs to hypoxia in the methanogenic sediments of Lake Kinneret (LK). These LK methanogenic sediments, situated below the oxidic and sulfidic zones, were previously characterized by methane oxidation coupled with iron reduction via the involvement of aerobic methanotrophs. Results In order to explore the adaptation of the methanotrophs to hypoxia, we conducted two experiments using LK sediments as inoculum: (i) an aerobic "classical" methanotrophic enrichment with ambient air employing DNA stable isotope probing (DNA-SIP) and (ii) hypoxic methanotrophic enrichment with repeated spiking of 1% oxygen. Analysis of 16S rRNA gene amplicons revealed the enrichment of Methylococcales methanotrophs, being up to a third of the enriched community. Methylobacter, Methylogaea, and Methylomonas were prominent in the aerobic experiment, while hypoxic conditions enriched primarily Methylomonas. Using metagenomics sequencing of DNA extracted from these experiments, we curated five Methylococcales metagenome-assembled genomes (MAGs) and evaluated the genetic basis for their survival in hypoxic environments. A comparative analysis with an additional 62 Methylococcales genomes from various environments highlighted several core genetic adaptations to hypoxia found in most examined Methylococcales genomes, including high-affinity cytochrome oxidases, oxygen-binding proteins, fermentation-based methane oxidation, motility, and glycogen use. We also found that some Methylococcales, including LK Methylococcales, may denitrify, while metals and humic substances may also serve as electron acceptors alternative to oxygen. Outer membrane multi-heme cytochromes and riboflavin were identified as potential mediators for the utilization of metals and humic material. These diverse mechanisms suggest the ability of methanotrophs to thrive in ecological niches previously thought inhospitable for their growth. Conclusions Our study sheds light on the ability of enriched Methylococcales methanotrophs from methanogenic LK sediments to survive under hypoxia. Genomic analysis revealed a spectrum of genetic capabilities, potentially enabling these methanotrophs to function. The identified mechanisms, such as those enabling the use of alternative electron acceptors, expand our understanding of methanotroph resilience in diverse ecological settings. These findings contribute to the broader knowledge of microbial methane oxidation and have implications for understanding and potential contribution methanotrophs may have in mitigating methane emissions in various environmental conditions.

Lake sediment, as a solid waste, can be disposed harmlessly through combustion. The ash melting temperature is an important factor affecting boiler coking and restricting its safe and stable operation. Determining the ash melting temperature after mixing lake sediment with coal is of great significance for achieving the resource utilization of lake sediment. This paper takes the Yunnan Xiaolongtan lignite and the Dianchi Lake sediment as the research objects. The Dianchi Lake sediment is a high moisture solid waste with high nitrogen content and rich heavy metal elements. The Yunnan Dianchi Lake sediment has a large residual stock, mainly generated by a large amount of sediment entering the Dianchi Lake with river water and rainwater. It is the main source of pollution in the Dianchi Lake. However, the Xiaolongtan lignite has problems such as high production, poor coal quality, and high transportation costs, which seriously affect its utilization rate, if the local conditions can be adapted and the problems of high production, difficult treatment, and insufficient efficiency of local sediment can be solved through mixed combustion, in addition to achieving an efficient utilization of lignite, it can also alleviate the local disposal pressure. However, there is currently little research on the blending of lignite with sediment. Through experiments on the ash melting characteristics, the deformation, softening, hemisphere, and flow temperature of ash at a 5%−15% mixing ratio were determined, and the variation law of ash melting point was derived. The mineral composition, oxide, and elemental composition were obtained through XRD, XRF, and SEM-EDS detection and analysis. The crystal structure and mineral composition in the ash were confirmed, and a ternary phase diagram was constructed for thermochemical calculations. The results show that when 5% sediment is mixed, the melting temperature of the ash decreases sharply, and then the downward trend tends to be gentle. The acid-base ratio and silicon aluminum ratio are positively correlated with the downward trend. The oxides of Fe+2, Fe+3, and Ca+2 play a main role in reducing the melting point of the ash, and these oxides are prone to react with refractory minerals to form fluxing minerals such as anorthite and calcium iron pyroxene. During the low temperature stage, Ca oxides mainly promote melting, while during the high temperature stage, Fe oxides act.

Copyright of Environmental Science & Technology (10036504) is the property of Editorial Board of Environmental Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Endorheic river basins and their terminal lakes are highly sensitive to climate change and human activities. Based on chemical and pollen indicators, lake level, and erosion/accumulation rates of rivers, we explore the phasing of the evolution of the river system in the Hexi Corridor during the Holocene. The results suggest that climate change dominated the evolution of the river system during the early-Mid-Holocene. Entering the historical period, humans began to have an impact on runoff, water resources, and lake evolution, and since 1000 BP, anthropogenic perturbations recorded by regional proxies increased and humans dominated the migrations of river. In addition, we discuss the widespread erosion of rivers in the global endorheic zone and the impact of human activities in this context and found the timing of human influence on river evolution is not the same in different regions. [ABSTRACT FROM AUTHOR]

The grain‐size distributions of sediments can yield important information about sediment provenance and sedimentary processes; however, grain‐size distributions are frequently polymodal, rendering analyses difficult. To improve analyses of polymodal grain‐size data, the present study decomposed the grain‐size distributions of bottom surface sediments from Lake Kitaura, a shallow lake in Japan, into lognormal distributions and performed logratio analysis of their mixing proportions. The polymodal grain‐size distributions of the studied samples were separated into four common components at most sites. This logratio analysis revealed clear differences in the characteristics of the spatial distributions of the separated grain‐size components. The logratio values indicated that the three finer components were uniformly deposited within the lake, whereas the coarsest component was spatially diverse, reflecting differences in their sources and sedimentary processes. These results demonstrate the effectiveness of decomposition and logratio analysis of polymodal grain‐size distributions for estimating sedimentary processes. This method can be applied to modern sediments and for palaeoenvironmental reconstructions using sediment cores. [ABSTRACT FROM AUTHOR]

Currently available numerical models that describe the fecal contamination of aquatic environments using Escherichia coli as an indicator bacterium did not consider its survival in sediments. We conducted a series of comparative experiments to reveal the independent and interactive effects of sediment factors, including temperature, pH, water-extractable total dissolved solids (TDSs), coexisting microbes, and sampling sites, in lake environments on E. coli survival. In experiments, E. coli survival was observed by controlling any two factors at a time. Consequently, the decrease in pH and presence of coexisting microbes enhanced E. coli die-off, whereas the addition of water-extractable TDSs promoted its growth. To select factors to be considered for modelling E. coli survival in sediments, the independent effects of each factor and the interaction effect of the two factors were statistically compared based on their effect sizes (η2). As a result, pH (η2 = 59.5–89.0%) affected E. coli survival most significantly, followed by coexisting microbes (1.7–48.4%). Among the interactions affecting E. coli survival, including pH or coexisting microbes—which had larger independent effects—relatively larger statistically significant interactions were observed between pH and coexisting microbes (31.1%), coexisting microbes and water-extractable TDSs (85.4%), and coexisting microbes and temperature (26.4%). [ABSTRACT FROM AUTHOR]

Phosphorus (P) is critical for food production. However, it has been managed unsustainably for decades and geopolitical challenges complicate its availability. While accessible P-rock deposits are linearly exploited, excessive fertilization practices lead to P loss from land to water, and thus, eutrophication. The release of legacy P from sediments to the water column, i.e. internal P loading, sustains global eutrophication issues. Sediment removal and its subsequent reuse as soil amendment can simultaneously lower internal P loadings and create a new P resource. However, the plant bioavailability of sedimentary P, especially Fe-P, is rather controversial. In this study, the direct P fertilizer effect of fresh lake sediment, lake sediment after Fe-P removal, amorphous Fe-P, and the reduced Fe-P mineral vivianite on barley was investigated and compared to the conventional mineral P fertilizer triple superphosphate (TSP). Fresh sediment, amorphous Fe-P, and vivianite fertilization significantly increased biomass and P uptake compared to the 0-control, while the Fe-P removal from the sediment reduced both effects. The P use efficiency was generally lower than for TSP and decreased in the order amorphous Fe-P > fresh sediment > vivianite > sediment after Fe-P removal. In a parallel soil incubation without barley growth P diffusion from the tested alternative substrates was not observed. We conclude that fresh lake sediment has P fertilizer potential with amorphous Fe-P as a significant contributor. Further, fertilization with fresh sediment and Fe-P can increase soil adsorptive capacities potentially reducing leaching but also creating dependency of plant P bioavailability on plant-soil interactive mechanisms.

Only a few palaeo-records extend beyond the Holocene in Yakutia, eastern Siberia, since most of the lakes in the region are of Holocene thermokarst origin. Thus, we have a poor understanding of the long-term interactions between terrestrial and aquatic ecosystems and their response to climate change. The Lake Khamra region in southwestern Yakutia is of particular interest because it is in the transition zones from discontinuous to sporadic permafrost and from summergreen to evergreen boreal forests. Our multiproxy study of Lake Khamra sediments reaching back to the Last Glacial Maximum 21 cal ka BP, includes analyses of organic carbon, nitrogen, XRF-derived elements, sedimentary ancient DNA amplicon sequencing of aquatic and terrestrial plants and diatoms, as well as classical counting of pollen and non-pollen palynomorphs (NPP). The palaeogenetic approach revealed 45 diatom, 191 terrestrial plant, and 65 aquatic macrophyte taxa. Pollen analyses identified 34 pollen taxa and 28 NPP taxa. The inferred terrestrial ecosystem of the Last Glacial comprises tundra vegetation dominated by forbs and grasses, likely inhabited by megaherbivores. By 18.4 cal ka BP a lake had developed with a high abundance of macrophytes and dominant fragilarioid diatoms, while shrubs expanded around the lake. In the Bolling-Allerod at 14.7 cal ka BP both the terrestrial and aquatic systems reflect climate amelioration, alongside lake water-level rise and woodland establishment, which was curbed by the Younger Dryas cooling. In the Early Holocene warmer and wetter climate led to taiga development and lake waterlevel rise, reflected by diatom composition turnover from only epiphytic to planktonic diatoms. In the Mid-Holocene the lake water level decreased at ca. 8.2 cal ka BP and increased again at ca. 6.5 cal ka BP. At the same time mixed evergreen-summergreen forest expanded. In the Late Holocene, at ca. 4 cal ka BP, vegetation cover similar to modern conditions established. This study reveals the long-term shifts in aquatic and terrestrial ecosystems and a comprehensive understanding of lake development and catchment history of the Lake Khamra region. [ABSTRACT FROM AUTHOR]

The response of aquatic ecosystems in the Sierra Nevada (California, USA) to late Quaternary hydroclimate changes remains mostly unknown. Mono Lake, a large endorheic lake just east of the Sierra Nevada, contains an expanded archive of laminated sediments that can be used to examine the response of benthos to environmental changes. Fossil ostracodes from a radiocarbon‐dated core were used to examine paleoecologic changes from ~16.6 to 4.3k cal a bp. Seven species were identified, with the co‐occurrence of Limnocythere ceriotuberosa and Limnocythere staplini indicating a large SO42−‐rich lake in the Pleistocene. The Younger Dryas was complex, with Fabaeformiscandona caudata reflecting a cold and deep lake ~13.0–12.2k cal a bp, followed by an interval of extensive littoral habitat from ~12.2–11.6k cal a bp. Ostracode diversity, valves g–1 and the ratio of adult:juvenile valves declined after ~10.7k cal a bp due to regression, altered hydrochemistry and seasonal anoxia. Strong seasonality during the Early Holocene is suggested by the presence of reworked ostracodes and macrocharcoal, delivered to Mono Lake by erosion of ancient lake beds in the basin. A depauperate ostracode fauna in the Middle Holocene suggests a strong sensitivity to drought in this ecosystem, which has implications for biodiversity in the future. [ABSTRACT FROM AUTHOR]

Copyright of Advances in Earth Science (1001-8166) is the property of Advances in Earth Science Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Situated in the middle reaches of the Yangtze River, Sanshan Lake represents a typical rural-urban junction lake. In May 2019, sediment core samples were gathered from five distinct sites within the lake to assess contamination levels and potential health hazards stemming from organochlorine pesticides (OCPs). The OCPs scrutinized included p,p’-DDE, α-HCH, γ-HCH, β-HCH, and δ-HCH, with concentrations of ∑DDTs and ∑HCHs ranging from 0.03 to 1.49 mg/kg and from 0.03 to 1.42 mg/kg, respectively. Average DDT and HCH residues stood at 0.04 ± 0.03 and 0.51 ± 0.41 mg/kg, respectively. This study unveiled substantial OCP contamination in Sanshan Lake, notably with remarkably elevated HCH residue levels compared to other analyzed compounds. The predominant OCP detected was β-HCH, prevalent across all samples. Moreover, the average HCH residue concentrations were an order of magnitude higher than those found in soils of the United States and Italy. At some sampling points, DDT residue levels surpassed both the ecological screening benchmark for soil DDT established by the U.S. Environmental Protection Agency (0.0025 mg/kg) and China’s primary standard as per soil environmental quality regulations (GB15618–2008, 0.05 mg/kg). Source analysis indicated that historical agricultural practices primarily contributed to DDT contamination, while technical blends accounted for HCH pollution. Carcinogenic risk assessments conducted on HCH exposure through ingestion, inhalation, and dermal contact revealed higher non-carcinogenic risks for children, with α-HCH posing the most significant carcinogenic risk among the various homologues studied. Conversely, the associated carcinogenic and non-carcinogenic risks linked with DDT residue exposure were minimal or negligible. [ABSTRACT FROM AUTHOR]

Changes in land-use practices have been a central element of human adaptation to Holocene climate change. Many practices that result in the short-term stabilization of socio-natural systems, however, have longer-term, unanticipated consequences that present cascading challenges for human subsistence strategies and opportunities for subsequent adaptations. Investigating complex sequences of interaction between climate change and human land-use in the past—rather than short-term causes and effects—is therefore essential for understanding processes of adaptation and change, but this approach has been stymied by a lack of suitably-scaled paleoecological data. Through a high-resolution paleoecological analysis, we provide a 7000-year history of changing climate and land management around Lake Acopia in the Andes of southern Peru. We identify evidence of the onset of pastoralism, maize cultivation, and possibly cultivation of quinoa and potatoes to form a complex agrarian landscape by c. 4300 years ago. Cumulative interactive climate-cultivation effects resulting in erosion ended abruptly c. 2300 years ago. After this time, reduced sedimentation rates are attributed to the construction and use of agricultural terraces within the catchment of the lake. These results provide new insights into the role of humans in the manufacture of Andean landscapes and the incremental, adaptive processes through which land-use practices take shape. [ABSTRACT FROM AUTHOR]

The organic matter composition of lake sediments influences important in-lake biogeochemical processes and stores information on environmental changes. Extracting this information is notoriously difficult because of the complexity of the organic matter matrix, which routinely imposes trade-offs between high temporal and analytical detail in the selection of methods of analysis. Here, we demonstrate the potential of diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) for achieving both of these objectives using untreated bulk samples from two Holocene lake-sediment cores from central Sweden. We develop quantitative models for sediment total organic carbon (TOC) with the same predictive abilities as models based on samples diluted with KBr and qualitatively characterize the organic matter using a spectra processing-pipeline combined with principal component analysis. In the qualitative analysis we identified four organic matter sub-fractions and the interpretation of these is supported and further advanced with molecular data from pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Within these organic fractions, compound groups such as aromatics, lignin, aliphatics, proteins and polysaccharides were identified by means of DRIFTS and the analyses and processes outlined here enables rapid and detailed quantitative and qualitative analysis of sediment organic matter. The DRIFTS approach can be used as stand-alone method for OM characterization with high temporal resolution in Holocene sediment records. It may also function as a screening process for more specific analyses of sample subsets, such as when coupled with pyrolysis-GC/MS to further tease apart the OM composition, identify sources and determine degradation status. [ABSTRACT FROM AUTHOR]

Human impacts on lakes can lead to nutrient release, increased algal productivity and consequently low oxygen concentrations in deepwater environments. Here we report the unexpected and contrasting finding of a pronounced shift to chironomid and invertebrate assemblages suggesting oligotrophication and oxygen increase in Lac de Champex, a Swiss mountain lake, due to human activities during the Mediaeval period. Chironomid assemblages in the lower part of the lake sediment record show changes that agree with known climatic shifts during the Lateglacial period and early Holocene and a progressively stronger influence of peat development, and possibly humic conditions, from ca. 8500 calibrated 14C years BP (cal. BP) onwards. This resulted in low chironomid influx and assemblages with high abundances of Procladius and Chaoborus ca. 2000–3000 cal. BP. These assemblages resemble those found in relatively nutrient-rich, oxygen-poor lakes and may have developed due to natural, long-term development to more nutrient-rich and possibly humic conditions, and from the Bronze Age (ca. 4000 cal. BP) onwards, due to human activities such as pasturing. Ca. 1000 cal. BP, an abrupt increase in sediment accumulation, chironomid influx and distinct changes in the chironomid assemblage composition were observed, coinciding with evidence for local human activities from pollen data. A major transition in chironomid and invertebrate assemblages followed ca. 500 cal. BP with the disappearance of Chaoborus, a decrease in Procladius, and the increase or appearance of several chironomid taxa, including several rheophilous groups. We conclude that Late-Holocene human impact led to re-oligotrophication and increased oxygen availability for invertebrates in the lake. This reversal of the long-term Holocene trend was possibly promoted by increased erosion from the Mediaeval period onwards and from ca. 500 cal. BP likely by the construction of an irrigation canal (bisse), leading to inflow of clear, cool water which changed the lake's hydrological characteristics. [ABSTRACT FROM AUTHOR]

Shallow thermokarst lakes are important sources of greenhouse gases (GHGs) such as methane (CH4) and carbon dioxide (CO2) resulting from continuous permafrost thawing due to global warming. Concentrations of GHGs dissolved in water typically increase with decreasing lake size due to coastal abrasion and organic matter delivery. We hypothesized that (i) CH4 oxidation depends on the natural oxygenation gradient in the lake water and sediments and increases with lake size because of stronger wind‐induced water mixing; (ii) CO2 production increases with decreasing lake size, following the dissolved organic matter gradient; and (iii) both processes are more intensive in the upper than deeper sediments due to the in situ gradients of oxygen (O2) and bioavailable carbon. We estimated aerobic CH4 oxidation potentials and CO2 production based on the injection of 13C‐labeled CH4 in the 0–10 cm and 10–20 cm sediment depths of small (~300 m2), medium (~3000 m2), and large (~106 m2) shallow thermokarst lakes in the West Siberian Lowland. The CO2 production was 1.4–3.5 times stronger in the upper sediments than in the 10–20 cm depth and increased from large (158 ± 18 nmol CO2 g−1 sediment d.w. h−1) to medium and small (192 ± 17 nmol CO2 g−1 h−1) lakes. Methane oxidation in the upper sediments was similar in all lakes, while at depth, large lakes had 14‐ and 74‐fold faster oxidation rates (5.1 ± 0.5 nmol CH4‐derived CO2 g−1 h−1) than small and medium lakes, respectively. This was attributed to the higher O2 concentration in large lakes due to the more intense wind‐induced water turbulence and mixing than in smaller lakes. From a global perspective, the CH4 oxidation potential confirms the key role of thermokarst lakes as an important hotspot for GHG emissions, which increase with the decreasing lake size. [ABSTRACT FROM AUTHOR]

Plant environmental DNA extracted from lacustrine sediments (sedimentary DNA, sedDNA) has been increasingly used to investigate past vegetation changes and human impacts at a high taxonomic resolution. However, the representation of vegetation communities surrounding the lake is still unclear. In this study, we compared plant sedDNA metabarcoding and pollen assemblages from 27 lake surface-sediment samples collected from alpine meadow on the central-eastern Tibetan Plateau to investigate the representation of sedDNA data. In general, the identified components of sedDNA are consistent with the counted pollen taxa and local plant communities. Relative to pollen identification, sedDNA data have higher taxonomic resolution, thus providing a potential approach for reconstructing past plant diversity. The sedDNA signal is strongly influenced by local plants while rarely affected by exogenous plants. Because of the overrepresentation of local plants and PCR bias, the abundance of sedDNA sequence types is very variable among sites, and should be treated with caution when investigating past vegetation cover and climate based on sedDNA data. Our finding suggests that sedDNA analysis can be a complementary approach for investigating the presence/absence of past plants and history of human land-use with higher taxonomic resolution. [ABSTRACT FROM AUTHOR]

In slowly deforming tectonic settings (e.g., European Alps), large earthquakes occur too infrequently to be adequately represented in instrumental and historical records. This leads to uncertainties and inaccuracies of seismic hazard estimations. To extend the seismic record, lacustrine paleoseismologists usually resort to the sedimentary archive of large lakes where earthquakes can be recorded as mass-transport deposits and associated turbidites. The imprint of seismic shaking is generally more subtle and poorly understood in small lakes (

Only a few palaeo-records extend beyond the Holocene in Yakutia, eastern Siberia, since most of the lakes in the region are of Holocene thermokarst origin. Thus, we have a poor understanding of the long-term interactions between terrestrial and aquatic ecosystems and their response to climate change. The Lake Khamra region in southwestern Yakutia is of particular interest because it is in the transition zones from discontinuous to sporadic permafrost and from summergreen to evergreen boreal forests. Our multiproxy study of Lake Khamra sediments reaching back to the Last Glacial Maximum 21 cal ka BP, includes analyses of organic carbon, nitrogen, XRF-derived elements, sedimentary ancient DNA amplicon sequencing of aquatic and terrestrial plants and diatoms, as well as classical counting of pollen and non-pollen palynomorphs (NPP). The palaeogenetic approach revealed 45 diatom, 191 terrestrial plant, and 65 aquatic macrophyte taxa. Pollen analyses identified 34 pollen taxa and 28 NPP taxa. The inferred terrestrial ecosystem of the Last Glacial comprises tundra vegetation dominated by forbs and grasses, likely inhabited by megaherbivores. By 18.4 cal ka BP a lake had developed with a high abundance of macrophytes and dominant fragilarioid diatoms, while shrubs expanded around the lake. In the Bølling-Allerød at 14.7 cal ka BP both the terrestrial and aquatic systems reflect climate amelioration, alongside lake water-level rise and woodland establishment, which was curbed by the Younger Dryas cooling. In the Early Holocene warmer and wetter climate led to taiga development and lake water-level rise, reflected by diatom composition turnover from only epiphytic to planktonic diatoms. In the Mid-Holocene the lake water level decreased at ca. 8.2 cal ka BP and increased again at ca. 6.5 cal ka BP. At the same time mixed evergreen-summergreen forest expanded. In the Late Holocene, at ca. 4 cal ka BP, vegetation cover similar to modern conditions established. This study reveals the long-term shifts in aquatic and terrestrial ecosystems and a comprehensive understanding of lake development and catchment history of the Lake Khamra region.

Currently available numerical models that describe the fecal contamination of aquatic environments using Escherichia coli as an indicator bacterium did not consider its survival in sediments. We conducted a series of comparative experiments to reveal the independent and interactive effects of sediment factors, including temperature, pH, water-extractable total dissolved solids (TDSs), coexisting microbes, and sampling sites, in lake environments on E. coli survival. In experiments, E. coli survival was observed by controlling any two factors at a time. Consequently, the decrease in pH and presence of coexisting microbes enhanced E. coli die-off, whereas the addition of water-extractable TDSs promoted its growth. To select factors to be considered for modelling E. coli survival in sediments, the independent effects of each factor and the interaction effect of the two factors were statistically compared based on their effect sizes (η2). As a result, pH (η2 = 59.5–89.0%) affected E. coli survival most significantly, followed by coexisting microbes (1.7–48.4%). Among the interactions affecting E. coli survival, including pH or coexisting microbes—which had larger independent effects—relatively larger statistically significant interactions were observed between pH and coexisting microbes (31.1%), coexisting microbes and water-extractable TDSs (85.4%), and coexisting microbes and temperature (26.4%).

The Bacillus velezensis strain NBNZ-0060 was isolated from the bottom sediment samples of the lake Jin in Wuhan, China. This strain is an aerobic denitrifying bacterium and able to promote growth of submerged macrophytes. The 3,929,784 bp entire genome contains 3,781 coding sequences (CDS), 27 rRNAs, 85 tRNAs, 5 ncRNAs, with an average G + C content of 46.5%. The average nucleotide identity and digital DNA-DNA values between strain NBNZ-0060 and Bacillus velezensis NRRL B-41580T were 98.28% and 84.5%, respectively. The genome data have been deposited in NCBI with the accession number CP133277.1.

We present oxygen isotope and charcoal accumulation records from two lakes in eastern Washington that have sufficient temporal resolution to quantitatively compare with tree‐ring records and meteorological data. Hydroclimate reconstructions from tree‐rings and lake sediments show close correspondence after accounting for seasonal‐ to centennial‐ scale temporal sensitivities. Carbonate δ18O measurements from Castor and Round lakes reveal that the Medieval Climate Anomaly (MCA) experienced wetter November‐March conditions than the Little Ice Age (LIA). Charcoal records from Castor, Round, and nearby lakes show elevated fire activity during the LIA compared to the MCA. Increased multidecadal hydroclimate variability after 1250 CE is evident in proxy records throughout western North America. In the Upper Columbia River Basin, multidecadal wet periods during the LIA may have enhanced fuel loads that burned in subsequent dry periods. A notable decline in biomass burning occurred with Euro‐American settlement in the late nineteenth century. Plain Language Summary: Paleoclimate reconstructions are based on proxy records that are sensitive to particular aspects of the climate system. We compare high‐resolution lake sediment records with nearby tree‐ring chronologies and instrumental data to explore hypotheses about climate variability. Here, we confirm that lake‐sediment oxygen isotope ratios in the Upper Columbia River Basin are primarily sensitive to cool‐season precipitation, whereas many tree‐ring records are primarily sensitive to warm‐season conditions. When lake records are compared with winter‐sensitive tree‐ring width chronologies, the reconstructions are similar. Oxygen isotopes indicate wet and stable winter conditions during the Medieval Climate Anomaly (900–1250 CE) and variable but generally dry conditions during the Little Ice Age (1450–1850 CE). Wet periods of fuel buildup, followed by drought, may have driven greater fire activity during the LIA. An abrupt decline in fire begins occurred Euro‐American settlement, after the 1850s, and is attributed to loss of fuel connectivity and less ignition. Key Points: Sediment δ18O records show heightened hydroclimate variability during the Little Ice AgeDiscrepancies between tree rings and lake sediments from the Pacific Northwest stem from different seasonal and temporal sensitivitiesCharcoal records in the region indicate enhanced fire activity during periods of higher multi‐decadal hydroclimate variability [ABSTRACT FROM AUTHOR]

Major shifts in hydroclimate have been documented during the last deglacial period and the Holocene in south‐central Alaska. Rare freshwater calcium carbonate (marl) deposits in lakes on the Kenai Peninsula can be used to reconstruct past changes in hydroclimate, including the influence of groundwater inflow to lakes. Here, the postglacial sediment sequence from groundwater‐fed Kelly Lake (60.514°N, 150.374°W) was analyzed for multiple proxies including isotopes of carbon and oxygen in marl calcite (δ13Cmarl and δ18Omarl), and isotopes of carbon (ẟ13COM) and abundances of C and N in organic matter. Bulk sediment analyses include organic matter and calcium carbonate (CaCO3) contents, visual stratigraphy and sediment flux. These analyses extend those of a previous paleoenvironmental reconstruction from Kelly Lake, which focused on sedimentary diatom oxygen isotopes and mass balance modeling over the past 10 000 years. Here, we show that Kelly Lake was deglaciated prior to 14.6 ka, and that by 14.0 ka marl dominated the sediments, with CaCO3 precipitation probably driven by groundwater input and mediated by shallow‐water charophytes. Marl accumulation decreased as organic and clastic inputs increased between ~12.2 and 11.5 ka. This shift, together with an increase in both δ13Cmarl and δ18Omarl values and a decrease in CaCO3 content, indicates an increase in the influence of meteoric water on the hydrologic budget under wet conditions, possibly driven by a strengthened Aleutian Low atmospheric pressure cell. A shift to lower δ13Cmarl and δ18Omarl values at ~11.5 ka is interpreted as an increase in the proportion of groundwater relative to meteoric water in the lake. Beginning around 9 ka, the proportion of meteoric water input continued to increase, the surrounding coniferous forest was established, and by 8 ka, CaCO3 accumulation ended. Our results elucidate the environmental conditions under which marl was deposited during the Lateglacial and early Holocene in this part of Alaska, and demonstrate how a variety of synoptic‐ and local‐scale climatic variables can converge to influence sedimentation in a groundwater‐fed lake. [ABSTRACT FROM AUTHOR]

Lake‐based studies can provide seasonal‐ to millennial‐scale records of sediment yield to improve our understanding of catchment‐scale sediment transfer and complement shorter fluvial‐based sediment transport studies. In this study, sediment accumulation rates at 40 coring locations in Lake Peters, Brooks Range, Alaska, over ca. 42 years, calculated using fallout radionuclides and sediment density patterns, were spatially modelled based on distance from the primary inflow and lake water depth. We estimated mean interdecadal specific sediment yield (Mg km−2 year−1) using the spatially modelled sediment accumulation rates and compared that result to fluvial‐based sediment delivery for 2015–2016 open‐channel seasons, as well as to yields reported for other Arctic catchments. Using the lake‐based method, mean yield to Lake Peters between ca. 1973 and 2015 was 52 ± 12 Mg km−2 year−1, which is comparable with fluvial‐based modelling results of 33 (20–60) Mg km−2 year−1 in 2015 and 79 (50–140) Mg km−2 year−1 in 2016 (95% confidence intervals), respectively. Although 2016 was a year of above average sedimentation, the last extreme depositional event probably occurred between ca. 1970 and 1976 when a basal layer of fine sand was deposited in a broadly distributed, relatively thick and coarse bed, which we used for lake‐wide correlation. The dual lacustrine–fluvial method approach permits study of within‐lake and catchment‐scale processes. Within Lake Peters, sedimentation patterns show decreasing fluxes down‐lake, sediment bypassing near the primary inflow, the influence of secondary inflows and littoral redistribution, and a focusing effect in the deep proximal basin. At the watershed scale, sediment yield is largely driven by intense summer rainfall and strong seasonal hydroclimatic variability. This research informs paleo‐environmental reconstruction and environmental system modelling in Arctic lake catchments. [ABSTRACT FROM AUTHOR]

The disposal of lake sediment is a major problem in dredging and lakeside construction projects. Due to its poor mechanical properties and contamination, sediment is difficult to use directly in resource applications. Previous research has found that alkali-activated reactions can improve the mechanical properties of silicon- and aluminum–rich solid waste. In this study, the basic physical and mechanical properties of dried sediment from a lake in Wuhan, China, were analyzed. Orthogonal tests, compressive strength measurements, and X-ray diffraction spectrum and scanning electron microscope analyses were used to investigate the solidification effects of three types of alkaline materials used alone or in combination with the lake sediment: straw ash, calcium lime, and sodium silicate. In the single-doped samples, calcium lime had the best curing effect, with a maximum seven-day compressive strength of 1.31 MPa (190 psi). When the compound-doped samples were cured to seven days, the maximum compressive strength was 7.18 MPa (1040 psi). Furthermore, with the compound-doped materials, sediment solidification was aided by suitably alkaline conditions and large quantities of active silicon-calcium components. As a result, the microstructures of the cured compound-doped samples were more compact and their overall mechanical properties were greatly improved. [ABSTRACT FROM AUTHOR]

Changes in land-use practices have been a central element of human adaptation to Holocene climate change. Many practices that result in the short-term stabilization of socio-natural systems, however, have longer-term, unanticipated consequences that present cascading challenges for human subsistence strategies and opportunities for subsequent adaptations. Investigating complex sequences of interaction between climate change and human land-use in the past—rather than short-term causes and effects—is therefore essential for understanding processes of adaptation and change, but this approach has been stymied by a lack of suitably-scaled paleoecological data. Through a high-resolution paleoecological analysis, we provide a 7000-year history of changing climate and land management around Lake Acopia in the Andes of southern Peru. We identify evidence of the onset of pastoralism, maize cultivation, and possibly cultivation of quinoa and potatoes to form a complex agrarian landscape by c. 4300 years ago. Cumulative interactive climate-cultivation effects resulting in erosion ended abruptly c. 2300 years ago. After this time, reduced sedimentation rates are attributed to the construction and use of agricultural terraces within the catchment of the lake. These results provide new insights into the role of humans in the manufacture of Andean landscapes and the incremental, adaptive processes through which land-use practices take shape.

Abstract We present oxygen isotope and charcoal accumulation records from two lakes in eastern Washington that have sufficient temporal resolution to quantitatively compare with tree‐ring records and meteorological data. Hydroclimate reconstructions from tree‐rings and lake sediments show close correspondence after accounting for seasonal‐ to centennial‐ scale temporal sensitivities. Carbonate δ18O measurements from Castor and Round lakes reveal that the Medieval Climate Anomaly (MCA) experienced wetter November‐March conditions than the Little Ice Age (LIA). Charcoal records from Castor, Round, and nearby lakes show elevated fire activity during the LIA compared to the MCA. Increased multidecadal hydroclimate variability after 1250 CE is evident in proxy records throughout western North America. In the Upper Columbia River Basin, multidecadal wet periods during the LIA may have enhanced fuel loads that burned in subsequent dry periods. A notable decline in biomass burning occurred with Euro‐American settlement in the late nineteenth century.

As the Arctic continues to warm, woody shrubs are expected to expand northward. This process, known as ‘shrubification,’ has important implications for regional biodiversity, food web structure, and high-latitude temperature amplification. While the future rate of shrubification remains poorly constrained, past records of plant immigration to newly deglaciated landscapes in the Arctic may serve as useful analogs. We provide one new postglacial Holocene sedimentary ancient DNA (sedaDNA) record of vascular plants from Iceland and place a second Iceland postglacial sedaDNA record on an improved geochronology; both show Salicaceae present shortly after deglaciation, whereas Betulaceae first appears more than 1000 y later. We find a similar pattern of delayed Betulaceae colonization in eight previously published postglacial sedaDNA records from across the glaciated circum North Atlantic. In nearly all cases, we find that Salicaceae colonizes earlier than Betulaceae and that Betulaceae colonization is increasingly delayed for locations farther from glacial-age woody plant refugia. These trends in Salicaceae and Betulaceae colonization are consistent with the plant families’ environmental tolerances, species diversity, reproductive strategies, seed sizes, and soil preferences. As these reconstructions capture the efficiency of postglacial vascular plant migration during a past period of high-latitude warming, a similarly slow response of some woody shrubs to current warming in glaciated regions, and possibly non-glaciated tundra, may delay Arctic shrubification and future changes in the structure of tundra ecosystems and temperature amplification.

Reliable records of past volcanic activities are essential for assessing future eruption probabilities and establishing effective volcanic disaster mitigation plans. We integrated the lacustrine and terrestrial sequences of tephra deposits at the northeastern foot of Mt. Fuji based on high-resolution radiocarbon (14C) dating to elucidate its eruptive history over the past 8000 years. Accurate chronologies of 29 tephra layers in the Lake Yamanaka sediments (core YA-1) were determined using the age-depth model of the 14C of bulk organic matter after variability correction of lake reservoir ages. The following ages were compared to those of major tephra deposits in the proximal trench section (MF20-01) and in the literature. From ∼7300 to ∼3200 cal yr BP, four tephra layers in core YA-1 (i.e., YA-T1, 2, 7, and 10) were likely correlated with the scoria fall deposits S-3, 5, 6, and 10 respectively, as reported in the outcrops near the lake. The core also features six undetected eruptions from ∼5050 to ∼3900 cal yr BP, demonstrating the advantages of lake sediments proximal to the volcano in identifying previously undetected eruptions. After ∼3200 cal yr BP, five tephra layers in core YA-1, ranging from ∼2900 to ∼1600 cal yr BP (YA-T11, 12, 14, 20, and 22), showed similar age ranges as the major tephra layers in MF20-01 (IY5, 8, 11, 25, and 26), with identical lithological characteristics and stratigraphic orders. This suggests that the tephra sequence in the trench section positively reflects the major eruptive events over the past 2900 years, providing a basis for the comprehensive reconstruction of volcanic eruption histories in the region.

Megaturbidites are commonly used to reconstruct the seismic history (palaeoseismology) of areas where large earthquakes occur. However, the depositional mechanisms and sedimentary characteristics of these deposits are not yet fully understood. This study unravels the sequence of sediment deposition that occurred in Lake Lucerne (Vitznau Basin) following the 1601 ce earthquake in central Switzerland. During this event, slope failures were triggered, generating mass flows and turbidity currents that led to the formation of mass‐transport deposits and a megaturbidite. These deposits are sampled in 28 sediment cores, which are examined with X‐ray computed tomography scans (medical and μCT), grain‐size analysis and natural remanent magnetisation. This suite of analyses allows a detailed reconstruction of turbidite stacking and amalgamation in the centre of the basin, followed by settling of finer sediments influenced by a lake seiche. Initial deposition of mass‐transport deposits is followed by sandy turbidites reaching the depocentre. Some of these turbidite sands can be linked to their source areas, and evidence is found of some turbidites being overridden by mass flows in the peripheral parts of the megaturbidite deposit. Hereafter, sedimentation becomes controlled by seiche‐induced currents, which rework fine sediments upon deposition, leading to subtle grain‐size variations at the base of the seiche‐influenced sub‐unit and a ponded geometry of the megaturbidite. As the seiche movement dampens, a relatively muddy, homogeneous sub‐unit is deposited that drapes the basin plain. Overall, this study provides the first highly detailed sedimentological analysis of megaturbidite deposition in a lake, demonstrating the distinct sedimentological imprint of lake seiching and turbidite amalgamation/stacking. This will improve the recognition and interpretation of earthquake‐induced megaturbidites in other lake records or isolated basins, and demonstrates the value of using (μ)CT scans in combination with traditional sedimentological parameters to reconstruct the depositional processes of megaturbidites. [ABSTRACT FROM AUTHOR]

Occupation of land and damage to the surrounding ecosystem may occur due to the accumulation of dredged lake sediments. In order to solve the large amount of dredged lake sediments, industrial wastes (slag, desulfurization gypsum) and urban construction waste were used to solidify the lake substrate, obtained a new construction material. Water content, volumetric shrinkage, unconfined compressive strength and flexural strength parameters and hydraulic conductivity coefficients of the solidified sediment were obtained from water content determination tests, volumetric shrinkage tests, unconfined compressive strength tests, flexural tests and permeation tests. Mineralogical composition and microstructural characterization of the solidified sediment using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were obtained. The solidification mechanism of lake sediment under the coupling of industrial waste and urban construction waste was revealed. The water content of the specimens decreased rapidly, and shrinkage deformation occurred in curing for 7 d. The volumetric shrinkage of 28 d was eventually maintained at 1.27–5.19%. The trend of specimen strength changed with the extension of time in the overall increase state, the compressive strength and flexural strength within 28 d were 3.15–10.96 MPa and 0.64–2.69 MPa, respectively. The solidified sediment material showed excellent anti-seepage performance, the hydraulic conductivity reached stability at 1.22 × 10−8–55.4 × 10−8 cm/s. Gismondine, gypsum, calcite, scawtite and fibrous C-S-H phases were generated in the solidified material. [ABSTRACT FROM AUTHOR]

Our knowledge about the interaction between human activities and the environment in the middle-late Holocene remains incomplete. Core C1 in Lake Chaohu from the middle and lower reaches of Yangtze River (MLYR), eastern China, provides an opportunity to investigate vegetation and climate changes, human activities, and East Asian summer monsoon (EASM) evolution since 5100 cal. yr BP. These variables are assessed based on radiocarbon dating, pollen and charcoal records, and magnetic susceptibility (χlf), median grain size and TP. Results reveal a hiatus in sedimentation between 2080 and 730 cal. yr BP in the western part of Lake Chaohu, which is common in most lakes in the MLYR. Evergreen and deciduous broadleaved mixed forest retreated gradually after 3650 cal. yr BP, and was replaced by secondary Pinus forest after at least 730 cal. yr BP. Intense agricultural activities and vegetation clearance are first detected at 2520 cal. yr BP. Human settlements expanded from the lake front wetlands (during the period 2520–2080 cal. yr BP) to remote high-altitude areas (2080–100 cal. yr BP), and then returned to the lake front to reclaim the wetlands and lake (after 400 cal. yr BP). A gradual trend of recessional EASM strength from 4300 cal. yr BP and centennial-scale variations of EASM during the period 5100–3650 cal. yr BP are revealed. The reduction of summer insolation, southward shift of the ITCZ, and El Niño Southern Oscillation may control the intensity of EASM and climate on a large regional scale. [ABSTRACT FROM AUTHOR]

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Abstract Fungi are crucial organisms in most ecosystems as they exert ecological key functions and are closely associated with land plants. Fungal community changes may, therefore, help reveal biodiversity changes in past ecosystems. Lake sediments contain the DNA of organisms in the catchment area, which allows reconstructing past biodiversity by using metabarcoding of ancient sedimentary DNA. We re‐evaluated various commonly used metabarcoding primers, and we developed a novel PCR primer combination for fungal metabarcoding to produce a short amplicon, thus accounting for amplification bias due to the degradation of ancient DNA. In silico PCRs showed higher diversity using this new primer combination, compared with previously established fungal metabarcoding primers. We analyzed data from sediment cores from four artic and one boreal lake in Siberia. These cores had been stored for 2–22 years after coring; we, therefore, examined the degradation effects of ancient DNA and storage time‐related bias affecting fungal communities. Amplicon lengths showed considerable variation within and between the major divisions of fungi, for example, amplicons of Basidiomycota were significantly longer than those of Mucoromycota; however, we observed no significant effect of sample age on amplicon length and GC content, suggesting the robustness of our results. We also found no indication of post‐coring fungal growth during storage regarding the proportions of common mold taxa, which would otherwise distort conclusions on past fungal communities. Terrestrial soil fungi, including mycorrhizal fungi and saprotrophs, were predominant in all lakes, whereas typical aquatic taxa were only represented to a negligible extent, which supports the use of lake sedimentary ancient DNA for reconstructing terrestrial communities.

Priming effect (PE) is a key biogeochemical process regulating organic carbon mineralization. However, the impacts of climate change-related factors on PE remain largely unclear in lakes with a large salinity range. The patterns of PE induced by algal (13C-labeled Chlorella vulgaris) and terrestrial grass (13C-labeled Festuca ovina) organic matter (OM) at 8 °C and 18 °C were investigated in lake sediments with a salinity range from 0.7 to 376.3 g L−1. The results showed that the intensities of early (7th day) and late (42nd day) PEs in the studied lake sediments ranged −51.0%–3833.7% and −55.2%–1874.5% of basal respiration, respectively; positive PE predominated over negative PE. Climate-related factors (e.g., salinity, temperature, OM types) exhibited significant influences on the intensity and/or direction of PE. Positive PE was more likely to occur in the sediments of hypersaline lakes than in freshwater/saline lakes, while negative PE showed an inverse trend. PE intensity induced by algal OM was significantly different at 8 °C and 18 °C, but no temperature influence was observed for that induced by grass OM. The effect of temperature increase on PE induced by algal OM was negative and positive in the early and late stages of incubation, respectively. The types of OM (algal OM vs. grass OM) supply significantly (P < 0.05) affected PE intensity except for the late PE intensity at 8 °C. Overall, these results suggest that organic carbon mineralization in lake sediments may be enhanced by positive PEs induced by the increased input of both allochthonous and autochthonous OM, and the autochthonous OM-induced PE is more susceptible to climate warming than that by allochthonous OM. These results help understand the carbon cycle in lakes under global climate change. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau has ∼1,200 lakes larger than 1 km2 with a total area of ~46,000 km2. The annual mean air temperature of the Tibetan Plateau has increased 2.5°C over the past 60 years. Lakes in this region are extremely responsive to climate changes as a result of their low biodiversity and simple food webs. However, it is unclear whether the current anthropogenic warming will benefit or threaten the aquatic ecosystems in this region.We assessed patterns of change associated with climate change in a shallow, freshwater lake (Genggahai Lake) on the NE Tibetan Plateau over the past ~1,600 years based on diverse aquatic fossils (macrophytes, molluscs, cladocerans and diatoms), total organic carbon (TOC) and total nitrogen (TN) of a sediment core.The abundances of macrophytes, molluscs and cladocerans, and the concentrations of TOC and TN in the sediments were high during the Mediaeval Warm Period (MWP, ~940–1,410 CE) but low during the Dark Ages Cold Period (DACP, ~390–940 CE) and the Little Ice Age (LIA, ~1,410–1970 CE), suggesting that modest natural warming was associated with the biomass of macrophytes and consumers in the food web. By contrast, low abundance of macrophytes and high abundance of planktonic diatoms were recorded in the sediments during the Current Warm Period (CWP, ~1970–2020 CE). Current anthropogenic warming has resulted in significantly higher temperatures than during the MWP, associated with the development of planktonic algae rather than macrophytes.Our findings show that the current anthropogenic warming, coupled with increased atmospheric nitrogen deposition and activated nutrients from thawed permafrost, is associated with phytoplankton dominance in lakes on the Tibetan Plateau, and may lead to significant reductions in ecosystem services provided by the lakes. [ABSTRACT FROM AUTHOR]

Chronologies generated from core profiles to apply dates to environmental changes commonly use the measurement of the activity of radionuclides deposited and stratified with physical environmental material. The most commonly reported nuclide to define chronologies covering the last 150 years is Pb-210, for which accepted data processing methodologies in the literature have focussed on the constant rate of supply (CRS) model and the more recently published Bayesian Plum model. This short communication describes a validation approach using defined sediment layers referred to as 'varve' counting, which provide known points of reference to account for uncertainty between generated dates from each model using published Pb-210 measurements. A significant improvement in the chronologies was observed when applying reference date corrections to the models. This was shown to be essential in providing confidence in reported datasets and accuracy of predicted chronologies, which will better inform the interpretation of environmental change, e.g. sedimentation rates, climate change, pollution pathways and land degradation. Generated chronologies from both the CRS and Plum methods showed good agreement with the established varve dates (typically < 4-year difference). [ABSTRACT FROM AUTHOR]

Microbial communities in freshwater lake sediments exhibit a distinct depthdependent variability. Further exploration is required to understand their biodiversity pattern and microbial interactions in vertical sediments. In this study, sediment cores from two freshwater lakes, Mugecuo (MGC) and Cuopu (CP), on the Tibetan plateau were sampled and subsequently sliced into layers at a depth of every centimeter or half a centimeter. Amplicon sequencing was used to analyze the composition, diversity, and interaction of microbial communities. Results showed that sediment samples of both lakes could be clustered into two groups at a sediment depth of about 20 cm, with obvious shifts in microbial community compositions. In lake MGC, the richness component dominated β-diversity and increased with depth, indicating that the microbial communities in the deep layer of MGC was selected from the surface layer. Conversely, the replacement component dominated β-diversity in CP, implying a high turnover rate in the surface layer and inactive seed banks with a high variety in the deep layer. A co-occurrence network analysis showed that negative microbial interactions were prevalent in the surface layers with high nutrient concentrations, while positive microbial interactions were more common in the deep layers with low nutrient concentrations, suggesting that microbial interactions are influenced by nutrient conditions in the vertical sediments. Additionally, the results highlight the significant contributions of abundant and rare taxa to microbial interactions and vertical fluctuations of β-diversity, respectively. Overall, this work deepens our understanding of patterns of microbial interactions and vertical fluctuation in β-diversity in lake sediment columns, particularly in freshwater lake sediments from the Tibetan plateau. [ABSTRACT FROM AUTHOR]

Anthropogenic activities, especially due to agricultural practices, tourism, and other land-use forms, have resulted in serious pollution of Bukit Merah reservoir (BMR), the oldest artificial reservoir in Malaysia since the 1980s. This study assessed the past ecological conditions of the reservoir using 210Pb, dating techniques, selected metals, and physicochemical analysis of the sediment core to better manage the reservoir. 210Pb results indicated 34 years of human impact on the reservoir, with arsenic recording the least concentrations in the 1980s and the highest concentrations in 2016 and 2018. The minimum and maximum concentrations of lead and cadmium were found in 1990 and 2009. Whereas Copper and Zinc, concentrations peaked in 2012. The mean EF values of metals in the sediment core were above 1 (EF>1), indicating anthropogenic sources. The Igeo values of Arsenic and Cadmium ranged from uncontaminated to strongly contaminated, uncontaminated to moderately contaminated for Lead, Zinc, and Copper. Overall, the dated sediment of BMR revealed that human population growth and increasing economic and agricultural activities coupled with poor land-use forms at the catchment area are the main source of pollution to the reservoir. Therefore, regular monitoring and the enforcement of relevant environmental laws are needed to manage the reservoir. [ABSTRACT FROM AUTHOR]

Algal communities act as sensitive indicators of past and present climate effects on northern lakes, but their responses can vary considerably between ecosystems. Functional trait-based approaches may help us better understand the nature of the diverse biotic responses and their underlying ecosystem changes. We explored patterns in diatom (Bacillariophyceae) growth forms and species composition during the Neoglacial in two shallow lakes typical of subarctic regions, including a dark-colored woodland lake and a clear tundra lake. Sediment carbon and nitrogen elemental and isotope biogeochemistry and spectral indices were used to track broadscale changes in lake productivity, the inflow of organic carbon from land, and benthic substratum over the past three millennia. The biogeochemical indices tracked declines in land-lake connectivity as well as lake-water and sediment organic enrichment above and below the subarctic treeline driven by Neoglacial cooling. This broadscale environmental transition was intercepted by periods of elevated primary production associated with transient Neoglacial warm anomalies and, in particular, the twentieth century warming. Although the Neoglacial development of the lakes showed conspicuous similarities, diatom functional and taxonomic responses were not uniform between the lakes pointing to intrinsic differences in the development of benthic habitats and underwater-light regimes. Many of the observed biotic shifts aligned with expectations based on earlier research linking diatom functional traits to changing light and organic levels but the results also point to further research needs, particularly to better differentiate the individual and interactive effects of substratum and light. Despite distinct anthropogenic imprints in the biogeochemical record, the scale of human impact on the lakes' biota has not, as yet, been profound, but the changes are nonetheless clear when compared to the previous three millennia of natural lake development. [ABSTRACT FROM AUTHOR]

The risk posed by heavy metals makes it difficult to dispose of sediment contaminants from dredging lakes in China. Black soldier fly (Hermetia illucens) can convert organic waste, such as restaurant waste and lake sediment, to high-value-added protein feed and fertilizer. Experimental groups were formed in this study to explore the conversion of heavy metals present in the mixture of restaurant waste and lake sediment by black soldier fly larvae (BSFL). The results demonstrated that BSFL could survive in pure sediment with an 84.76% survival rate. Relative to the substrate, BSFL could accumulate 70-90% zinc (Zn), chromium (Cr), copper (Cu), and 20-40% cadmium (Cd) and lead (Pb). The experimental group 2:3, with 40% lake sediment and 60% restaurant waste, was the best group after conversion for 15 days, which showed a 95.24% survival rate of BFSL, 82.20 mg average weight of BFSL, 8.92 mm average length of BFSL, with varying content of heavy metals such as Cu (43.22 mg/kg), Zn (193.31 mg/kg), Cd (1.58 mg/kg), Cr (25.30 mg/kg) Cr, and Pb (38.59 mg/kg) in BSFL. Furthermore, the conversion residue conforms to the relevant standards of organic fertilizer in China and can be used as organic fertilizer. Overall, the present study shows that black soldier flies can improve the resource utilization of lake sediment, especially by reducing the effect of heavy metals.

Indian monsoon circulation is the primary driver of the long‐range transboundary mercury (Hg) pollution from South Asia to the Himalayas and Tibet Plateau region, yet the northward extent of this transport remains unknown. In this study, a strong δ202Hg signature overlapping was found between Lake Gokyo and Indian anthropogenic sources, which is an indicative of the Hg source regions from South Asia. Most of the sediment samples were characterized with relatively large positive Δ199Hg values (mean = 0.07‰–0.44‰) and small positive Δ200Hg values (mean = 0.03‰–0.08‰). Notably, the Δ199Hg values in the lake sediments progressively increased from southwest to northeast. Moreover, the Δ199Hg values peaked at Lake Tanglha (mean = 0.44‰ ± 0.04‰) before decreased at Lake Qinghai that is under the influence of the westerlies. Our results suggest that transboundary atmospheric transport could transport Hg from South Asia northwards to at least the Tanglha Mountains in the northern Himalaya‐Tibet. Plain Language Summary: The fragile ecosystems of the Himalayas and Tibet Plateau region have been suffering transboundary Hg pollution from South Asia. However, the northward extent of this transport of atmospheric Hg pollution remains poorly understood. In our study, sediment core Hg isotope compositions from four lakes (Gokyo, Namco, and Tanglha in the south of the Tanglha Mountains and Qinghai in the north) along a southwest‐northeast transect in the region were combined to constrain the northward extent of transboundary Hg pollution by examining both mass‐dependent and mass‐independent fractionations. Our results suggest that transboundary atmospheric transport could transport Hg from South Asia northwards to at least the Tanglha Mountains in the northern Himalaya‐Tibet. Key Points: The δ202Hg signatures among the three lakes in the north are indistinguishable without spatial distribution differencesMost of sediment samples were characterized by positive Δ199Hg and Δ200Hg valuesThe northward extent of atmospheric mercury transboundary transport could be anchored by progressive shifts of Δ199Hg signatures [ABSTRACT FROM AUTHOR]