Lake Sediments Research Articles

The global distribution of Isoprenoidal Glycerol Dialkyl Diethers (isoGDDs) is consistent with a predominant degradation origin

Glycerol dialkyl diethers (GDDs) are membrane lipids and a variation of the more commonly known glycerol dialkyl glycerol tetraethers (GDGTs). GDGTs include both archaeal and bacterial membrane lipids that are both frequently used for paleoclimate reconstruction in a range of terrestrial and aquatic environments. In contrast to GDGTs, GDDs lack one of the terminal glycerol moieties. Although both isoprenoidal (iso) and branched (br) GDDs have been found, this study focuses on isoGDDs. These lipids have been found in a few terrestrial and aquatic environments. However, the origin of isoGDDs is debated and the extent of their distribution across the surface of the Earth is poorly constrained. Based on a few single site studies, previous authors hypothesised that isoGDDs are degradation products of isoGDGTs, but more recent studies that isolated isoGDDs from cultured nitrososphaerota (formerly thaumarchaeota) proposed a biological source through direct archaeal biosynthesis. Here we compiled a global dataset of isoGDD and isoGDGT abundance in environmental samples to thoroughly investigate the distribution of isoGDDs and the correlation with isoGDGTs on a global scale and across a variety of environments (peat, mineral soils, lake sediments, and marine sediments). We find that isoGDDs are present in most samples that we analysed. Their abundance is strongly proportional to isoGDGT abundance (r2 = 0.85), dominated by the GDGT-crenarchaeol/GDD-crenarchaeol ratio (r2 = 0.94) and supported by individual compound isoGDGT/isoGDD ratios (r2 = 0.56–0.94). In addition, the degree of cyclisation of isoGDDs, reflected in the ring index, is positively correlated (r2 = 0.84) with that of isoGDGTs across all environments. We conclude that isoGDDs are abundant on the surface of the Earth and predominantly originate from the degradation of isoGDGTs.

Warming drives dissolved organic carbon export from pristine alpine soils

Despite decades of research, the influence of climate on the export of dissolved organic carbon (DOC) from soil remains poorly constrained, adding uncertainty to global carbon models. The limited temporal range of contemporary monitoring data, ongoing climate reorganisation and confounding anthropogenic activities muddy the waters further. Here, we reconstruct DOC leaching over the last ~14,000 years using alpine environmental archives (two speleothems and one lake sediment core) across 4° of latitude from Te Waipounamu/South Island of Aotearoa New Zealand. We selected broadly comparable palaeoenvironmental archives in mountainous catchments, free of anthropogenically-induced landscape changes prior to ~1200 C.E. We show that warmer temperatures resulted in increased allochthonous DOC export through the Holocene, most notably during the Holocene Climatic Optimum (HCO), which was some 1.5–2.5 °C warmer than the late pre-industrial period—then decreased during the cooler mid-Holocene. We propose that temperature exerted the key control on the observed doubling to tripling of soil DOC export during the HCO, presumably via temperature-mediated changes in vegetative soil C inputs and microbial degradation rates. Future warming may accelerate DOC export from mountainous catchments, with implications for the global carbon cycle and water quality.

Relation between Central European Climate Change and Eifel Volcanism during the Last 130,000 Years: The ELSA-23-Tephra-Stack

The analysis of tephra layers in maar lake sediments of the Eifel shows 14 well-visible tephra during the last glacial cycle from the Holocene to the Eemian (0–130,000 yr b2k). These tephra were analyzed for their petrographic composition, which allows us to connect several tephra to eruption sites. All tephra were dated by application of the ELSA-20 chronology, developed using the late Pleistocene infilled maar lake of Auel and the Holocene lake Holzmaar (0–60,000 yr b2k). We extend the ELSA-20 chronology with this paper for the millennia of 60,000–130,000 yr b2k (ELSA-23 chronology), which is based on the infilled maar lake records from Dehner, Hoher List, and Jungferweiher. The evaluation of the tephra from the entire last glacial cycle shows that all 14 tephra were close to interstadial warming of the North Atlantic sea surface temperatures. In particular, phreatomagmatic maar eruptions were systematically associated with Heinrich events or C-events. These events represent times of warming of the Southern Hemisphere, global sea level rise, and CO2 increase, which predate the abrupt interstadial warming events of the Northern Hemisphere. This synchroneity indicates a physical relationship between endogenic and exogenic processes. Changes in the lithospheric stress field in response to changes in continental ice loads have already been suggested as a potential candidate to explain the exogenic forcing of endogenic processes. The chronology of volcanic activity in the Eifel demonstrates that intraplate mantle plumes are also affected by the exogenic forcing of endogenic processes.

Stratigraphy and OSL chronology of the Middle–Upper Pleistocene sedimentary sequence and vegetation history during Late MIS6–MIS5e in the Neva Lowland (St. Petersburg region, Russia)

ABSTRACTThe quarry of the Sverdlov (Etalon) Factory stands out as a unique site in the northwest of the East European Plain since it exposes an almost complete Upper Pleistocene stratigraphic succession. Previous investigations have revealed a sequence of marine sediments deposited during the whole Mikulino Interglacial [Eemian, Marine Isotope Stage (MIS)5e], but the chronology of the Late Pleistocene deposits remains incomplete and requires further update. We present a study of the Middle–Upper Pleistocene units exposed in the Sverdlov Factory quarry by using geological methods, optically stimulated luminescence (OSL) dating and pollen analysis. The lower part of the Sverdlov Factory section comprises glaciomarine/glaciolacustrine varves, which accumulated during degradation of the Late Moscow (Late Saalian, Late MIS6) glaciation and correspond to pollen zone M1 (lower peak of Picea). They are covered by interglacial marine clayey silt that includes all Mikulino regional pollen zones M2–M8. According to a Bayesian model based on K‐rich feldspar luminescence ages, the interglacial marine deposition started 133 ± 8 ka ago and ended 109 ± 7 ka ago. The marine sediments are overlain by lacustrine silt with a K‐rich feldspar age of 119 ± 7 ka, lacustrine/alluvial sand with plant detritus formed 47–41 ka ago, and lacustrine sand and silt without organic matter accumulated ~39 ka ago. The upper part of the section is composed of subglacial till formed during the Late Valdai (Late Weichselian, MIS2) under the Scandinavian Ice Sheet and glaciolacustrine varved deposits of the Baltic Ice Lake. Two ages were acquired using quartz OSL from these varves, 16.9 ± 1.6 and 15.7 ± 1.0 ka, which are assumed to slightly overestimate the true age.

Revisiting Zeribar lake sediments: Effects ofclimate change on human development in Zagros

Zeribar Lake, located in the west-central Zagros mountains, serves as a key record for understanding the environmental and climate history of West Asia. Studies beginning in the 1960s have examined the lake's sediments to explore how changes in the environment might have influenced major human developments, including the start of the Neolithic period and the formation of early societies. Early research, limited by less precise radiocarbon dating methods, suggested that environmental factors had little impact on the development of cultures. However, with improved dating techniques, a clear link has been established between environmental events and significant stages in human evolution. Analysis of pollen from Zeribar Lake has provided a detailed picture of the region's ecological past. The data shows a significant change from the sparse, cold conditions of the late Pleistocene and early Holocene to the rich oak forests that appeared in the mid-Holocene. This change, previously thought to be caused by more rain, is now understood to be the result of a considerable decrease in temperature, with glaciers once widespread in the area. Updated radiocarbon dating and new interpretations of pollen data suggest that agriculture began earlier than previously thought, around 14,000 years ago, indicating that shifts in the pollen record may reflect the beginnings of farming rather than changes in the climate. These climate changes, initially thought to be minor until 8,000 years ago and believed to involve only slight temperature variations, are now viewed from a different perspective. Despite these revelations, the debate continues among scholars regarding the extent of climate's role in shaping human progress. This article aims to weave together the multifaceted strands of Zeribar Lake's story, bridging paleoecology and archaeology to shed light on the complex dance between humanity and its environment in the Zagros region. It is an endeavor to bolster the bedrock of knowledge for future scholarly pursuits.

The Distribution Characteristics and Risk Assessments of Organochlorine Pesticides in the Sediments of Sanshan Lake, China

ABSTRACT 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.

Postglacial vegetation and climate change in the Lake Onega region of eastern Fennoscandia derived from a radiocarbon-dated pollen record

With its numerous environmental archives stored in lake and peat sediments and relatively low human pressure, the Lake Onega region in eastern Fennoscandia is regarded as a particularly promising area for studying past changes in vegetation and climate since the Lateglacial period. The 885-cm-long sediment core RZ19 (62°27′53″N, 34°26′4″E) was collected from Razlomnoe Peat on the northern shore of Lake Onega in 2019, radiocarbon-dated and analysed for pollen and cryptogam spores. The age-depth model suggests continuous sedimentation since ca. 11,800 a BP (all ages given in years (a) or kiloyears (ka) before present (BP) with BP referring to 1950 CE). The results of pollen analysis and pollen-based biome reconstruction show rapid afforestation of the area in the Early Holocene, although the scores of the tundra biome remain relatively high prior to ca. 11,450 a BP, suggesting that the vegetation was likely more open than today. Between 8300 and 8000 a BP, Betula sect. Albae shows a marked increase in pollen percentage, while Pinus sylvestris experiences a marked decrease. These changes coinciding with the 8.2 ka BP cooling event indicate less favourable conditions for Scots pine while being beneficial for fast-growing birch. The transition from the Early to Middle Holocene (i.e. from Greenlandian to Northgrippian) is marked by an increase in pollen productivity, spread of Picea and further afforestation of the area. The decrease in arboreal and Picea pollen percentages and the abrupt increase in landscape openness after ca. 4000 a BP mark the onset of the Late Holocene (i.e. Northgrippian-Meghalayan transition) and likely reflect the combined effect of insolation-induced temperature decrease and associated paludification and forest retreat rather than a decrease in atmospheric precipitation and/or spread of Late Neolithic agriculture.

TP or Not TP? Successful Comparison of Two Independent Methods Validates Total Phosphorus Inference for Long-Term Eutrophication Studies.

Validating paleo total phosphorus (TP) inference methods over long time scales is essential for understanding historic changes in lake P supply and the processes leading up to the present-day global lake eutrophication crisis. Monitored lake water TP time series have enabled us to identify the drivers of eutrophication over recent decades. However, over longer time scales, the lack of reliable TP inference means our understanding of drivers is speculative. Validation of lake water TP reconstruction, therefore, remains the "ultimate aim" of eutrophication studies. Here, we present the first critical comparison of two fully independent paleo TP inference approaches: the well-established diatom method (DI-TP) and a recently developed sediment geochemical method (SI-TP). Using lake sediment records from a small eutrophic U.K. lake (Crose Mere), we find a statistically significant agreement between the two inferred TP records with greater than 60% shared variance. Both records show identical timings, with a 19th century acceleration in TP concentration and subsequent declines following a peak in 1930. This significant agreement establishes the validity of long-term paleo TP inference for the first time. With this, we can now test assumptions and paradigms that underpin understanding of catchment P sources and pathways over longer time scales.

Distribution of branched glycerol dialkyl glycerol tetraether (brGDGT) lipids from soils and sediments from the same watershed are distinct regionally (central Chile) but not globally

Quantitative reconstructions of past continental climates are vital for understanding contemporary and past climate change. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are unique bacterial lipids that have been proposed as universal paleothermometers due to their correlation with temperature in modern settings. Thus, brGDGTs may serve as a crucial paleotemperature proxy for understanding past climate variations and improving regional climate projections, especially in critical but under constrained regions. That said, complications can arise in their application due to varying source contributions (e.g., soils vs. peats vs. lacustrine). As such, this study investigates brGDGT distributions in Chilean lake surface sediments and corresponding watershed soils to determine the source of brGDGTs to lake sediments. Global datasets of brGDGTs in lake sediments and soils were additionally compiled for comparison. Distinct brGDGT distributions in Chilean lakes and soils indicate minimal bias from soil inputs to the lacustrine sediments as well as in situ lacustrine production of brGDGTs, which supports the use of brGDGTs in lake sediments as reliable paleotemperature proxies in the region. The ΣIIIa/ΣIIa ratio, initially promising as a brGDGT source indicator in marine settings, shows global complexities in lacustrine settings, challenging the establishment of universal thresholds for source apportionment. That said, we show that the ratio can be successfully applied in Chilean lake surface sediments. Direct comparisons with watershed soils and further research are crucial for discerning brGDGT sources in lake sediments and improving paleotemperature reconstructions on regional and global scales moving forward. Overall, this study contributes valuable insights into brGDGT variability, essential for accurate paleoreconstructions.

Dynamics of antibiotic resistance genes in the sediments of a water-diversion lake and its human exposure risk behaviour

The dynamics and exposure risk behaviours of antibiotic resistance genes (ARGs) in the sediments of water-diversion lakes remain poorly understood. In this study, spatiotemporal investigations of ARG profiles in sediments targeting non-water (NWDP) and water diversion periods (WDP) were conducted in Luoma Lake, a typical water-diversion lake, and an innovative dynamics-based risk assessment framework was constructed to evaluate ARG exposure risks to local residents. ARGs in sediments were significantly more abundant in the WDP than in the NWDP, but there was no significant variation in their spatial distribution in either period. Moreover, the pattern of ARG dissemination in sediments was unchanged between the WDP and NWDP, with horizontal gene transfer (HGT) and vertical gene transfer (VGT) contributing to ARG dissemination in both periods. However, water diversion altered the pattern in lake water, with HGT and VGT in the NWDP but only HGT in the WDP, which were critical pathways for the dissemination of ARGs. The significantly lower ARG sediment-water partition coefficient in the WDP indicated that water diversion could shift the fate of ARGs and facilitate their aqueous partitioning. Risk assessment showed that all age groups faced a higher human exposure risk of ARGs (HERA) in the WDP than in the NWDP, with the 45–59 age group having the highest risk. Furthermore, HERA increased overall with the bacterial carrying capacity in the local environment and peaked when the carrying capacity reached three (NWDP) or four (WDP) orders of magnitude higher than the observed bacterial population. HGT and VGT promoted, whereas ODF covering gene mutation and loss mainly reduced HERA in the lake. As the carrying capacity increased, the relative contribution of ODF to HERA remained relatively stable, whereas the dominant mechanism of HERA development shifted from HGT to VGT.

A marine incursion during the onset of T-OAE in Sichuan Basin, China: Evidence from green clay minerals and carbonate concretions

A high-amplitude global sea level rose rapidly during the early Toarcian (Early Jurassic), making the transgression deposits potential stratigraphic correlation markers of marine and terrestrial successions. Green clay minerals (i.e., glauconite and chamosite), carbonate concretions, and geochemical database associated with the early Toarcian global transgression are archived in the Lower Jurassic Da'anzhai Member (the Early Toarcian age) in the Sichuan Basin of China, a mega lake along the Tethys Ocean. The fine-grained glauconites with high Al and low Si contents suggested that they were transported from offshore to the lake by marine incursion and were oxidized during the transport processes. The green authigenic chamosite cement and redeposited chamosite grains with high Mg/Fe and low Al/Si ratios were diagenetically transformed from berthierine formed in the brackish water caused by marine incursion. The chemically impure siderite concretions with low 87Sr/86Sr ratios and high δ13C values suggested that the lake water and sediment pore waters were mixed with seawater. Coeval calcareous concretions have low 87Sr/86Sr ratios and high δ13C values, indicating the mixing of lake water with seawater. Combining the stratigraphic low 87Sr/86Sr values, we suggested that there was a marine incursion into the Sichuan Basin. According to the organic carbon isotopic stratigraphy correlation, the marine incursion occurred during the onset of T-OAE. The rapid and high-amplitude global sea-level rise may have caused this marine incursion.

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

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

Development of magnetic matrix solid phase dispersion method for the extraction of crystal violet and rhodamine B from sediments based on magnetic ZIF-8 and a deep eutectic solvent

A magnetic matrix solid phase dispersion (MSPD) method based on magnetic ZIF-8 (SDS@MZIF-8) and a deep eutectic solvent was developed and used to the extraction of crystal violet and rhodamine B in lake sediments. SDS@MZIF-8 was prepared and used as the extraction sorbent and dispersant in MSPD. The magnetic property of MZIF-8 facilitated the recovery of the extraction sorbent after the blending step. Hydrophilic deep eutectic solvents were prepared and used as efficient green dispersing solvents in MSPD. The use of magnetic sorbent in MSPD is simple and fast, eliminating some additional steps commonly used in the classical MSPD and shortening the extraction time. The parameters influencing the extraction efficiency were investigated and optimized. Under the optimized conditions, the intra- and inter-day relative standard deviations were less than 4.9 %. The linearity ranged from 2-400 µg g−1 with coefficients of determination higher than 0.9943. The detection and quantification limits of RB and CV varied between 0.3–0.5 μg g−1 and 1.0–1.8 μg g−1, respectively. Finally, the developed method was applied to the analysis of RB and CV in the sediment samples. The recoveries ranged from 93.2 to 107.3 % and the relative standard deviations ranged from 0.8 to 4.9 %. The results suggest a high potential use of the proposed method to determine the organic pollutants in solid samples. Compared with the conventional MSPD extraction technique, the developed method considerably reduced the sample and solvent consumption, offering important environmental benefits.

Chelativorans salis sp. nov., a slightly halophilic bacterium isolated from an enrichment system with saline lake sediment.

A Gram-stain-negative, non-motile, and slightly halophilic alphaproteobacterium, designated strain EGI FJ00035T, was isolated from enrichment sediment samples of a saline lake in Xinjiang Uygur Autonomous Region, PR China. The taxonomic position of the isolate was determined using the polyphasic taxonomic and phylogenomic analyses. Phylogenetic analysis based on the 16S rRNA gene sequences indicated that strain EGI FJ00035T formed a distinct clade with 'Chelativorans alearense' UJN715 and 'Chelativorans xinjiangense' lm93 with sequence similarities of 98.44 and 98.22 %, respectively, while sharing less than 96.7 % with other valid type strains. The novel isolate could be distinguished from other species of the genus Chelativorans by its distinct phenotypic, physiological, and genotypic characteristics. Optimal growth of strain EGI FJ00035T occurred on marine agar 2216 at pH 7.0 and 30 °C. The major respiratory quinone was Q-10, while the major fatty acids (>5 %) were C19 : 0 cyclo ω8c, summed feature 8 (C17 : 1 ω6c and/or C17 : 1 ω7c), C16 : 0, C18 : 0, and iso-C17 : 0. The detected polar lipids included diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, unidentified aminophospholipids, unidentified glycolipids, and an unidentified lipid. Based on its genome sequence, the G+C content of strain EGI FJ00035T was 63.2 mol%. The average nucleotide identity, average amino acid identity, and digital DNA-DNA hybridization values of strain EGI FJ00035T against related members of the genus Chelativorans were below the thresholds for delineation of a novel species. According our polyphasic taxonomic data, strain EGI FJ00035T represents a new species of the genus Chelativorans, for which the name Chelativorans salis sp. nov. is proposed. The type strain of the proposed novel isolate is EGI FJ00035T (=KCTC 92251T=CGMCC 1.19480T).

Multi-proxy temperature and environmental reconstruction during the Late Glacial and Early Holocene in the Bohemian Forest, Central Europe

Multi-proxy temperature reconstructions can provide robust insights into past environmental conditions. By combining different proxies we can disentangle the temperature signal from the indirect climate effects on the environment. This study uses a multi-proxy approach to reconstruct temperature and palaeoenvironmental conditions during the Late Glacial and Early Holocene (13.5–8 cal. ka BP) in the Bohemian Forest, Central Europe. We assessed the similarity of the temperature signal based on chironomids, isoprenoid glycerol dialkyl glycerol tetraether lipids (isoGDGTs), and pollen within a comparison with locally modeled temperature data generated by the CHELSA_Trace21k dataset. Pollen, macroscopic charcoal remains, and geochemistry were further used to reconstruct past environmental conditions such as vegetation dynamics, fire activity, the input of lithogenic material (Titanium), nutrient content (Total Nitrogen) and the sources of organic matter (C/N and δ13Corg). All temperature reconstructions based on independent proxies were positively correlated and followed the same long-term trend. However, results also showed that chironomids-inferred July temperature had lower amplitude variations compared to the other temperature curves. IsoGDGTs showed the most pronounced decrease in temperature values at the onset of the Younger Dryas (YD), corroborating that this cooling event was more marked during winter than summer. However, a decrease of less than 1 °C during summer and two short-term warm events at 12.6 and 12.2 cal ka BP provoked a modest and asynchronous response of the vegetation to the onset of the YD. Nevertheless, isoGDGTs appeared to react to changes in both temperature and organic carbon sources, particularly between 11.2 and 10.6 cal yr BP. These environmental changes, characterized by high values of the GDGT-0/crenarchaeol ratio, recorded an increase in methanogenic activity in the lake sediments, which likely altered the recorded climatic signal. The corresponding anoxic episodes in the lake sediments might be caused by an increasing input of organic carbon from the catchment, related to the development of the vegetation and catchment soils at the beginning of the Holocene. Finally, pollen-based temperature reconstruction showed a lag in the response to major climatic events, such as the onset of YD and Holocene. Our study increases the understanding of the climate-vegetation-environmental feedback during the Late Glacial and Early Holocene in the Bohemian Forest, Central Europe.

Distribution Patterns of Sediment Organic Carbon Stocks in Shallow Lakes and the Significance for Sustainable Lake Management: Chaohu Lake in Eastern China as a Case Study

Shallow lake sediments have huge potential for carbon storage, but they are vulnerable to various environmental changes and are highly susceptible to becoming a source of carbon emissions. Understanding the amount of sediment carbon storage can provide information about the potential of shallow lakes in mitigating climate change. In this study, sediment sampling was conducted at 12 study sites in Chaohu Lake, China, and sediment water content, grain size, bulk density, and sediments organic carbon (SOC) content were examined in five layers along the vertical direction, respectively, and the distribution and storage of SOC were estimated. The results showed that the surface sediments in the west lake area of Chaohu Lake would release 66,300 t of SOC to the overlying water body in the future. The sediments in the middle lake area and the east lake area will absorb another 15,900 t and 17,300 t of TOC from the water body in the future, respectively. Overall, the lake-wide sediments will release 33,100 t of SOC into the water body in the future. In addition, the results of the study also indicate that human activities are another major influence on the change in organic carbon stocks in lake sediments, and therefore, proactive measures for the restoration and protection of lake sediments are essential because increasing the SOC stocks in the sediments and maintaining the lakes in a sustainable manner can contribute to the crucial role they play in mitigating climate change.

Unveiling unique microbial nitrogen cycling and nitrification driver in coastal Antarctica

Largely removed from anthropogenic delivery of nitrogen (N), Antarctica has notably low levels of nitrogen. Though our understanding of biological sources of ammonia have been elucidated, the microbial drivers of nitrate (NO3−) cycling in coastal Antarctica remains poorly understood. Here, we explore microbial N cycling in coastal Antarctica, unraveling the biological origin of NO3− via oxygen isotopes in soil and lake sediment, and through the reconstruction of 1968 metagenome-assembled genomes from 29 microbial phyla. Our analysis reveals the metabolic potential for microbial N2 fixation, nitrification, and denitrification, but not for anaerobic ammonium oxidation, signifying a unique microbial N-cycling dynamic. We identify the predominance of complete ammonia oxidizing (comammox) Nitrospira, capable of performing the entire nitrification process. Their adaptive strategies to the Antarctic environment likely include synthesis of trehalose for cold stress, high substrate affinity for resource utilization, and alternate metabolic pathways for nutrient-scarce conditions. We confirm the significant role of comammox Nitrospira in the autotrophic, nitrification process via 13C-DNA-based stable isotope probing. This research highlights the crucial contribution of nitrification to the N budget in coastal Antarctica, identifying comammox Nitrospira clade B as a nitrification driver.

Seasonal impact of constructed wetlands on nitrogen and phosphorus in sediments of flood control lakes with pollution assessment.

The primary drivers of eutrophication in lakes following the reduction of external nutrient inputs are the release of N and P from sediments. Constructed wetlands play a pivotal role in ameliorating N, P, and other biogenic element levels. However, the presence of large vegetation in these wetlands also substantially contributes to nutrient accumulation in sediments, a phenomenon influenced by seasonal variations. In this study, a typical constructed wetland was selected as the research site. The research aimed to analyze the forms of N and P in sediments during both summer and winter. Simultaneously, a comprehensive pollution assessment and analysis were conducted within the study area. The findings indicate that elevated summer temperatures, together with the presence of wetland vegetation, promote the release of N through the nitrification process. Additionally, seasonal variations exert a significant impact on the distribution of P storage. Furthermore, the role of constructed wetlands in the absorption and release of N and P is primarily controlled by the influence of organic matter on nitrate-nitrogen, nitrite-nitrogen, and available phosphorus, and is also subject to seasonal fluctuations. In summary, under the comprehensive influence of constructed wetlands, vegetation types, and seasons, sediments within the lake generally exhibit a state of mild or moderate pollution. Therefore, targeted measures should be adopted to optimally adjust vegetation types, and human intervention is necessary, involving timely sediment harvesting during the summer to reduce N and P loads, and enhancing sediment adsorption and retention capacity for N and P during the winter.

Sedimentological characterization of earthquake-generated turbidites in fault-proximal glacial lakes: a case study from Jenny Lake, Teton range, Wyoming

Lakes in seismically active regions preserve valuable sedimentary archives of paleoseismic activity within their catchment and beyond. A series of glacially-excavated lakes positioned directly along the surface trace of the Teton normal fault at the base of the Teton Range, WY, are ideally situated to record past fault activity since their formation approximately 15,000 years ago. Here, we focus on the sediment fill contained in Jenny Lake (5 km2; approximately 73 m max depth) located at the bottom of Cascade Canyon, in the central Tetons, where postglacial slip rates are greatest. Past earthquakes that generated slope failures in and around Jenny Lake are expressed stratigraphically as coseismic turbidite deposits. These deposits were previously identified and dated in sub-bottom profiles and in sediment cores taken from multiple locations around the basin. In this study, we focus on the six thickest turbidites (ranging from 6 to 34 cm thick) present in multiple cores recovered from the central depositional basin and analyze them at sub-centimeter resolution for changes in physical, biological, and geochemical parameters, including sediment density, magnetic susceptibility, grain size distributions, organic content, and elemental composition. Results reveal each deposit contains a well-defined, three-component sedimentary sequence composed of a relatively homogenous and thick basal sandy unit with a sharp bottom contact, a similarly thick silt-rich middle unit, and a thin top unit of very fine-grained sediments. The characteristics of these components and their similarity between individual deposits suggest consistent sediment sources and transport pathways during successive earthquake events. Based on our analyses and the unique local geomorphic setting, we create a mechanistic model of coseismic turbidite formation in Jenny Lake, which may provide an improved framework for identifying, characterizing, and correlating earthquake-generated disturbance deposits in other Teton lakes and lakes in similar tectonic-geomorphological settings, for example, in the Basin and Range Province, USA or beyond.

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

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