Lakes are considered as one of the most important natural sources of methane. However, there are few lacustrine records tracing the history of methane production far back in time in the geological record. Here, we utilize two indices based on isoprenoid glycerol dialkyl glycerol tetraethers, the GDGT-0/Cren and the Methane Index (MI), to reconstruct the methane production in Sihailongwan Maar Lake (Lake SHL) in northeastern China since the last deglaciation (similar to 15.5 kyr BP). The results show that methane production was at a relatively low level from similar to 15.5 to 11.7 kyr BP, with an increase during the Bolling-Allerod interstadial and a decrease during the Younger Dryas cold event. In the Holocene, the methane production shows a fast increase from 12.0 to 11.0 kyr BP, then remains stable until 2.0 kyr BP, and a decrease after 2.0 kyr BP. Changes in methane production of Lake SHL were roughly coupled with variations in mean lake water temperature and regional precipitation, suggesting that warm and humid climate could facilitate methane production. Further studies indicate that an increase in the availability of organic matter under humid conditions, primarily due to increased nutrient supply (nitrogen), and that an expansion of the anoxic zone triggered by the thermal stratification of the lake under warm and humid conditions, could prompt methane production. Moreover, the elevated metabolic rates stemming from increased enzyme activity could also stimulate methane production in the warmer climate. This study provides a record of methane production in a mid-latitude freshwater lake, and is helpful for understanding variations in methane productions from different natural sources.

Two diatom samples collected from two freshwater habitats in Hunan Province, China, were studied using light microscopy and scanning electron microscopy. Three Tryblionella species were found; one was identified as T. calida (Grunow) Stroganov et al., and the other two species are established here as new species: T. dongtingensis sp. nov . and T. hunanensis sp. nov . These two new species are morphologically allied to T. calida because they possess the following unique combination of characters: 1) a more or less undulate valve face from side to side; 2) transapical ribs; 3) uniseriate striae with rounded, rimmed inner openings of areolae; 4) a longitudinal row of bar-like ribs connecting the raphe canal wall on both the valve side and the distal mantle side; 5) a marginal ridge; and 6) squat, sometimes apically elongated fibulae. This group around T. calida is different from the group around T. apiculata W. Gregory, which possesses an axial sternum and different stria and areola structures. Additional details of the complex marginal ridges in Tryblionella are revealed and discussed in this paper. Whether the group around T. calida is a monophyletic group and possesses a synapomorphy cannot currently be resolved, and further investigations are needed.

To elucidate the relative influences of different-scale forcing factors on climate change, in particular on relative aridity, we developed a 40,000-year-long record of lake-level fluctuations using the high-resolution sedimentary archive from Huguangyan Maar Lake (HML) in the Leizhou Peninsula, southern China. Analyses on grain size and total organic matter revealed that lake levels were the lowest during the Last Glacial Maximum (LGM), while minor variations occurred during Heinrich events, and more pronounced oscillations characterized the Younger Dryas (YD). Following the YD, lake levels gradually recovered, peaking around 8000 years ago before declining to present-day levels. Our data unequivocally demonstrate that the lake-level decline during the LGM was the most extreme observed throughout the 40,000-year long record, exceeding the magnitude of other millennial-scale climate events. Crucially, despite orbital forcing imposing two distinct periods of both minimum and maximum solar insolation over the 40,000 year-long intervals, the drastic hydrological changes—total desiccation and peak water levels—each occurred only once. Total desiccation uniquely coincided with the LGM, while peak water levels were confined to the early-middle Holocene. These findings suggest that while variations in solar insolation and the Atlantic Meridional Overturning Circulation (AMOC) modulate monsoon rainfall, the extensive glacial expansion during the LGM played a significant role in southern China's extreme aridity. The LGM thus represents the driest period in southern China over the past 40,000 years, indicating that this pronounced aridity resulted from the synergistic interplay of large ice volume and low solar insolation.

Natural- and human-induced environmental changes lead to structure shifts in phytoplankton communities, impacting the resilience, functioning, and ecosystem services of lakes. Given the scarcity of long-term monitoring data, particularly in the tropical region, our understanding of phytoplankton communities (cyanobacteria and eukaryotic micro-algae) and their triggering factors remains limited over decadal scales. We determined whether shifts in phytoplankton community within Huguangyan Maar Lake, a tropical lake, are linked to climate warming and assessed whether the observed changes resemble those documented in temperate or arctic regions. We applied 23S rRNA gene metabarcoding to 43 sediment samples covering the past similar to 140 years, and explored how the phytoplankton community respond to multiple environmental stresses. Phytoplankton diversity exhibited a marked increase beginning in the 1940s, followed by a distinct decline in the 1980s. Notably, a significant shift in community composition emerged toward the late 1980s, characterized by a rise in the relative abundance of diatoms (Aulacoseiraceae) and a concurrent decrease in rhodophytes (Bangiaceae) and cyanobacteria (Synechococcaceae). This pattern contrasted sharply with trends observed in other lakes, where cyanobacteria have maintained dominance in recent decades.Through integrated application of Mantel tests and random forest multivariate modeling, nutrient loading emerged as the predominant driver of community restructuring outweighing climatic factors. Concurrently, anthropogenic combustion signatures, such as polycyclic aromatic hydrocarbons, demonstrated significant covariance with phytoplankton assemblage reconstructing. This study highlights the dual impact of anthropogenic nutrients input and pollutants on phytoplankton communities in tropical lakes and provides important implication for future pollution and nutrient control.

Abstract Aquatic ecosystems have changed dramatically, but the relative roles of external forcings and internal atmospheric variability remain unclear. Here, using Tibetan lake ecological reconstructions and Earth system simulations, we reveal how shared external forcings shaped Tibetan Plateau limnoecology over the past millennium through two distinct pathways. In the temperature-centric pathway, cooling episodes driven by volcanic activity and internal variability likely regulated preindustrial lake conditions. This baseline was disrupted as recent forced warming has shortened lake ice-cover and increased meltwater input, altering lake resources and triggering unprecedented diatom shifts. In the freshening-centric pathway, salinity-tolerant diatoms tracked monsoon-driven precipitation changes and lake freshening, both governed by shifts in the intertropical convergence zone. Preindustrial shifts likely reflected hemispherically asymmetric orbital and volcanic forcings, whereas modern changes have been altered remarkably by Northern Hemisphere industrial aerosol fluctuations and warming-induced meltwater. As multifaceted stressors intensify, Tibetan lake ecosystems may continue diverging from their natural variability.

The B & oslash;lling-Aller & oslash;d (B-A) interstadial (similar to 14.7-12.85 cal ka BP), the most important warming event of the last deglaciation in the northern hemisphere, is a key time window to study how precipitation changes under the background of rapid warming. However, the relationship between precipitation changes and rapid warming during the B-A interstadial in Northeast (NE) China has remained unclear. Here, we present a multiproxy record spanning the interval 20-10 cal ka BP from a small volcanic lake in NE China and compare it with other records from the same region to clarify the hydroclimatological history of the last deglaciation in NE China. The results suggest that precipitation lagged behind temperature increase during the B-A interstadial in NE China. We attribute this lag to the different forcings at play on the evolution of precipitation and temperature during the B-A, in which the temperature changes were forced by the recovery of the Atlantic Meridional Overturning Circulation and the triggered release of stored heat in the North Atlantic from the high latitudes while the precipitation changes were controlled by increasing sea surface temperatures in the low latitudes.

Paleotemperature changes since the last deglaciation provide key insights for understanding gradual and abrupt paleoclimate changes and their forcing factors in different climatic backgrounds. However, there are notable discrepancies between different temperature time series. Here we report a high-resolution temperature reconstruction based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) from annually laminated sediments of the Sihailongwan maar lake in northeastern China and compare it with temperature records from pollen and long-chain alkenones. The brGDGTs-based mean lake water temperature reconstruction shows a mean temperature of 6.1 degrees C for the Older Dryas, followed by an increase of 2.6 degrees C until the peak of the B & oslash;lling-Aller & oslash;d, a decrease to 7.8 degrees C during the Younger Dryas, and a warming from the beginning of the Holocene until 6 ka BP, and finally a gradual decrease until modern times. Although seasonal biases and interpretations differ in different proxy-based reconstructions, all records show broadly similar temperature changes since the last deglaciation. The results suggest that the temperature variations recorded in Sihailongwan maar lake are coupled with high latitude ice-sheet dynamics through atmosphere-ocean circulation systems. The gradual temperature changes could be mainly associated with the ice-volume, while the abrupt variations of the temperature could be related to the Atlantic Meridional Overturning Circulation, the intensity of the East Asian winter monsoon and solar activity.

Acidification is a major ecological problem in a large number of lakes around the world. In recent decades, research has primarily focused on the effects of human-induced acid deposition on lake ecosystems. However, there has been relatively little research on how changes in the natural environment influence the acid-base balance of lakes. In this study, we tracked the changes of lake acidity in the past similar to 10,000 years by using the records of sedimentary diatoms in Buteha Lake, a volcanic lake in northeast China. We also compare the historical changes in lake acidity with variations in vegetation and aeolian activity recorded in the same core and regional data to evaluate the relationships among lake acidity, vegetation changes, and dust deposition. The diatom results show that during the mid-Holocene (8200-4500 cal yr BP), acid-tolerant diatoms (Eunotia species) were very abundant. This pattern was followed by a gradual decline during the late Holocene, with a slight increase observed in recent decades. Proliferation of acid-tolerant diatoms indicate that severe lake acidification occurred during the mid-Holocene. The trend of lake acidification closely resembles the regional vegetation changes, contrasting with the intensity of aeolian activity. Our results suggest that lake acidification in the mid-Holocene was not directly linked to change in temperature and/or precipitation, but rather was driven by the balance between acidic and alkaline substance inputs. Specifically, climate warming and stronger monsoons enhanced terrestrial vegetation, increasing acidic humic substance inputs to the lake, while decreased alkaline dust deposition synergistically exacerbated acidification. This study provides a scientific basis for predicting the future development of lake environment in northeast China, and offers valuable insights for environmental research on natural lakes acidification globally. We predict that if global warming continues and precipitation increases in the future, more lakes, especially those that depend on dust inputs to maintain their acid neutralizing capacity, may experience acidification due to the decrease of alkaline dust deposition and the increase of acidic humic substances input caused by vegetation expansion.

In this study on diatoms, which are unicellular microalgae with a siliceous cell wall, images obtained by electron microscopy were used to compare three taxa from East Asia that were referred as Cyclotella hubeiana, Discostella guiyangensis and “Cyclotella fottii” in the original studies. Morphometrical and morphological analyses indicate that these three taxa are conspecific. The distinctive morphological features of this species are the following: one rimoportula located on the valve mantle within the ring of marginal fultoportulae, marginal fultoportulae situated on costae with internally two satellite pores positioned circumferentially (laterally) and externally long tubular opening, biseriate striae and branching costae. A comparison of these morphological features with those of Discostella and Cyclotella species and a re-assessment of the existing molecular data suggest that this species could be separated from both these genera. On this basis, we describe the new genus Discocyclus gen. nov. with Discocyclus hubeianus comb. nov. as the type species.

The Tibetan Plateau formation, resulting from the collision between India and Eurasia, is accompanied by significant seismic activity. Along its SE margin, the sinistral Xianshuihe fault is one of the most active faults in China. To understand the seismic cycle and estimate subsequent hazards, long-term records extending beyond historical archives are required. In Kangding's restraining bend, fault partitioning leads to seismic activity being distributed across four branches, exposing significant population and critical infrastructures to seismic hazards. To document the long-term patterns of fault activity, we identified seismically-triggered event deposits in three mountain lakes near the fault, using a multiproxy approach, including CT scanning, grain-size analysis, and XRF core scanning, associated with chronology based on palaeomagnetism, short-lived radionuclides, and radiocarbon ages. Our investigation across three sites (Yari Acuo, Yalatuo, Mugecuo) distributed over 30 km of the fault, revealed varying sensitivities to seismic events over the past ~300 years. Based on these different sensitivities to record earthquakes, this multi-site approach allowed us to relocate historical earthquakes based on sediment core evidence. However, the high frequency of events and the uncertainties in age models limit our ability to unambiguously attribute the oldest deposits to specific events. The recently retrieved 3.6 m-long core from Lake Yalatuo, on which we will apply similar analyses, appears more promising to reconstruct the long-term regional palaeoseismological record and discuss the Xianshuihe fault seismic cycle.

A new species, Fragilaria longwania sp. nov. from Sihailongwan Maar Lake in northeastern China is described on the basis of observations made using light microscopy (LM) and scanning electron microscopy (SEM) that reveal the distinctive features that separate this new taxon from the other species currently placed in the genus Fragilaria. Fragilaria longwania sp. nov. has relatively short valve length, high stria density, spindle-shaped valves with a swollen, and sometimes deformed central area and capitate valve apices, short spines and weakly developed apical pore fields. This combination of character was found to be unique when the new species was compared with morphologically similar taxa. This species was found in various samples collected from Sihailongwan Maar Lake between 2003 and 2017. The analysis of the diatom assemblages collected in the sediment trap samples allowed an assessment of the cell size variation, seasonal occurrences and ecological requirements of this species. Fragilaria longwania appears to be a planktonic diatom most often associated with the spring season.

Three Tryblionella species found at the same locality in Lake Qinghai, the largest inland saline water lake of China, are studied by using light and scanning electron microscope. One species is proposed as new to science and named Tryblionella qinghainensis sp. nov. The other two species are identified as T. apiculata W. Gregory and T. levidensis W. Smith. Tryblionella qinghainensis sp. nov. is characterized by its linear-lanceolate valve outline, broad axial sternum, a stria density to fibula density ratio of ca. 1.9:1, alveolate striae, and a simple standing lamella-like marginal ridge unperforated. Several ultrastructural details for T. apiculata and T. levidensis are revealed for the first time, especially the ultrastructure of their marginal ridges. The structure and shape of the marginal ridge in these three Tryblionella species are different, and the ultrastructure at the junction between the marginal ridge and the distal mantle can also vary for each individual species. The ultrastructure of the marginal ridge and distal mantle may be used as important diagnostic characters for the species of the genus Tryblionella.

Three Surirella species found at the same locality in Lake Qinghai, northwestern China, are studied using light and scanning electron microscope observations. Two species are proposed as new to science and named S. ectorii sp. nov. and S. qinghainensis sp. nov. The third species is identified as S. brightwellii W. Smith. Both S. brightwellii and S. qinghainensis have valves with an ovate outline and a broadly rounded headpole and cuneate footpole, whereas S. ectorii has valves with a nearly elliptical outline and an almost isopolar headpole and footpole. Both S. ectorii and S. qinghainensis produce a marginal row of costae on the wall of the raphe canal, whereas S. brightwellii does not possess this feature. This study provides further insights into the diversity of endemic diatom species inhabiting the ancient Lake Qinghai and illustrates the variability of valve ultrastructure in the genus Surirella.

Since its description by Chen and Zhu in 1985 from samples collected in a river and reservoir from Hubei Province (Central China), Cyclotella hubeiana has been reported from several sites in central and southern China. Only line drawings were provided with the original description and the same drawings were used in the subsequent diatom floras from China. The more recent reports of this species come from limnological studies which generally do not provide illustrations. There is therefore a need to better illustrate this taxon. As the type material could not be retrieved, new material was collected from the type locality (Xionghe Reservoir) to elucidate its ultrastructure using light and electron microscopy. The figures published by Chen and Zhu in 1985 are designed as lectotype and the new material as epitype to the lectotype. Characteristics of the valve such as the position of the rimoportula (on a costa, within the ring of marginal fultoportulae) and the absence of central fultoportulae on the valve face suggest that this species is best placed within the genus Cyclotella as presently defined. Its morphology is compared with similar species of Cyclotella and Pantocsekiella. In addition, in a study on Qiandao Lake, a reservoir from Zhejiang Province (eastern China), a large population of this taxon was found in down-core assemblages within 20 years of the reservoir being impounded. This abundant material allowed a better assessment of the size range and morphological variability of this species. Besides emending the description and validating the taxonomic status of this species, this study also discusses its ecology and distribution.

Dongting Lake is China’s second largest freshwater lake; some new diatom species have been described from this lake recently. The current study describes a new diatom species from this lake, Gyrosigma dongtingense sp. nov. Gyrosigma dongtingense sp. nov. belongs to the section Strigiles sensu H. Peragallo and it is characterized by: 1) its large cell size (valves are 161–218 μm long and 24–29 μm wide), 2) having two curvatures for each half of its raphe sternum, 3) the transverse stria density (12–14 in 10 μm) lower than the longitudinal stria density (16–18 in 10 μm), 4) both the external proximal raphe fissures deflecting towards the convex side of each corresponding half-valve, 5) T-shaped internal proximal raphe fissures, and 6) a prominent axial costa presents along the primary side of the raphe sternum. The isomorphism and dimorphism of the external proximal raphe fissures are reviewed, and similar taxa are discussed.

A new species, Ctenophora hunanensis Bing Liu & Rioual, sp. nov., found in the Yongle River, a tributary of the Xiang River (Hunan Province, southern China) is described on the basis of morphological observations made under light and scanning electron microscopes. Ctenophora hunanensis is distinguished from other Ctenophora taxa by a unique combination of characters that includes its lanceolate valve outline with rostrate apices, sternum gradually becoming wider from valve apices to center, and a greater valve width than the other members of the genus. Ctenophora hunanensis inhabits the epilithic community in the headwaters of a freshwater river. Many abnormal valves of C. hunanensis were observed in the samples investigated and the most frequent morphological abnormalities consisted in a lack of symmetry relative to the apical axis caused by a unilateral incising in the middle part of the valve.

The Xianshuihe fault, located in the southeastern Tibetan Plateau, stands as one of the most active faults in China. As assessing earthquake hazard relies on access to long-term paleoseismological archives, this paper seeks to optimize the interpretation of paleoseismological records. We retrieved nine sediment cores from three lakes over a 30 km fault segment. Earthquake-related deposits were identified through grain-size analysis, XRF core scanning, and SEM observations of thin sections. Age models based on short-lived radionuclides correlate these events with historical earthquakes, which are recorded with varying sensitivities to seismic intensity across the three lakes. We developed a code that evaluates the plausibility of rupture scenarios against sedimentary evidence: Each site is used as a binary paleoseismometer, indicating whether or not an earthquake reached a local intensity threshold. The combined evidence from the three sites allows to evaluate rupture scenarios on the Xianshuihe fault, according to rupture length-magnitude scaling laws and intensity prediction equations. The most probable scenarios allow to discriminate the rupture area and magnitude range providing a good agreement with historical reconstructions. Our work demonstrates the potential of combining earthquake records to infer the magnitude and rupture zone of paleo-earthquakes, even with a limited data set. Our approach, applicable across diverse geological settings and timescales, offers enhanced precision in understanding long-term paleoseismology covering multiple earthquake cycles. However, establishing the synchronicity of events in such an active area-where earthquake return times are typically <100 years-demands highly accurate age models, which remains challenging.

A new species, Ulnaria shun-biseriatasp. nov., was found in the Shun River of Hunan Province, southern China, and its morphology was described based on light and scannning electron microscope obervations. Ulnaria shun-biseriata is characterized by its lanceolate valve outline, apiculate valve apices, slightly undulate valve margins, mostly biseriate striae, variable central area, and closed valvocopula. Many abnormal valves of U. shun-biseriata were observed in the samples investigated and the most frequent morphological abnormalities consisted of a lack of symmetry relative to the apical axis caused by a unilateral expansion in the middle part of the valve.

This study describes a new species of Pinnularia, P. hupingensis sp. nov., on the basis of light and scanning electron microscope images. Pinnularia hupingensis sp. nov. is characterised by its linear valve outline, extremely divergent striae, and very large hexagonal central area occupying ca. 1/5–1/8 of the valve length. The primary and secondary sides of the valve and the internal proximal raphe fissures are discussed. The new species is compared to similar taxa of the genus Pinnularia.