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• Surface pollen spectra from different coastal wetlands in northwest Bohai Bay are compared. • Chenopodiaceae pollen can indicate variations in halophytes, salinity, and pH. • Pollen concentrations are related to vegetation coverage and sediment grain size. • Back-trajectory modelling can help estimate the potential source of arboreal pollen. • Remote sensing LUCC data are used to understand pollen-vegetation relationships. Understanding the relationship between modern pollen and vegetation in coastal wetlands is essential for reconstructing long-term land cover changes, and for determining the response of coastal wetland ecosystems to global changes. We selected 68 sampling sites in different types of coastal wetland in northwest Bohai Bay, North China, for palynological analysis, and hence to determine the relationships between pollen and environmental factors, such as soil grain size, salinity, and pH. A back-trajectory model and remote sensing LUCC data were used to reveal the pollen source area and the pollen representation for different land cover types. The results show that the pollen assemblages of these coastal wetlands are dominated by Chenopodiaceae and Poaceae. The pollen assemblages are significantly different between silty and sandy coastal wetlands, and they also reflect different vegetation landscapes. Chenopodiaceae pollen is a potential indicator of saline-alkali soil environments in coastal areas. In addition to the vegetation coverage and sedimentary environment, pollen concentrations are negatively correlated with the grain size of the surface soil. The pollen diversity is higher in areas with strong human influences (e.g., cultivated land, villages, roads), but lower in natural wetlands with a high vegetation coverage. The arboreal pollen is generally sourced from the northern and northwestern mountains, while the major dispersal area of halophyte and hygrophyte pollen is on a local scale, constrained by the local vegetation canopy and its settlement characteristics. Fern spores are mainly waterborne, carried by rivers and surface runoff from mountain areas. The arboreal and upland herbaceous pollen is over-represented for forest and grassland landscapes. Halophyte and hygrophyte pollen show a good correlation with the area of coastal wetland, and they can be used as an indicator of the extent of coastal wetland influenced by climate change and human activities. [ABSTRACT FROM AUTHOR]

Abstract Land use and land cover changes (LUCCs) have largely altered terrestrial ecosystems and landscapes during the Anthropocene. Reconstructing past LUCCs is necessary to better understand terrestrial ecosystem succession and human-environment interactions so that ecosystem services can be used conservatively and developed sustainably. In this paper, we reconstructed the LUCCs over the past century in a typical anthropogenic watershed based on a high-resolution pollen record from Changdang Lake, eastern China. The sediment core was 210Pb dated and constrained cluster analysis identified different periods of LUCCs associated with the 110-year pollen record. Multi-sedimentary proxies, historical records, and remote sensing LUCC maps were analyzed to complement the palynological results. Our results demonstrate that pollen records can accurately capture LUCCs during different historical periods. Extra-regional arboreal pollen, fern spores, and pollen concentration can record the hydrological variations of waterbodies under both climatic and anthropogenic impacts. Multiple agriculture-related pollen indicators, such as cereal, Cruciferae, and wetland taxa are significantly related to the corresponding vegetation cover and landscape variations. Specifically, the anthropochore taxa to wetland taxa ratio is a good indicator of agricultural intensity. Dominant arboreal pollen (Pinus and Quercus) and the arboreal taxa to non-arboreal taxa ratio reflects the forestry landscape changes. Urban greening arboreal pollen (including Platanus , Salix , and Ulmus) is found to be an indirect indicator of urbanization. In addition, agriculture and urbanization in the region are causing the pollen diversity to increase in lake sediments. This study from a shallow lake in eastern China contributes to our understanding of pollen-based LUCC studies in similar climatic and anthropogenic regions around the world. Graphical abstract Unlabelled Image Highlights • First investigation of high-resolution pollen-based LUCCs in eastern China • Different LUCCs could be indicated by corresponding pollen indicators. • Hydrological processes played a critical role on the representation of pollen records. • Agriculture and urbanization increased the pollen diversity in lake sediments. [ABSTRACT FROM AUTHOR]

Abstract Aquatic plants in shallow freshwater lakes play a key role in stabilizing ecological function and providing valuable ecosystem services, yet they are severely degraded worldwide. An improved understanding of long-term aquatic plant succession is critical to investigate the potential driving mechanisms and to facilitate ecological restoration. In this paper, we reconstructed changes in the aquatic plant community over the past century based on palynological records from Changdang Lake, Middle and Lower Yangtze River Basin (MLYB), China. Our results reveal that aquatic plants in Changdang Lake have undergone three clear phases: emergent macrophytes dominated the aquatic vegetation in the 1900s–1970s, submerged macrophytes in the 1970s–1990s, and floating macrophytes increasingly after the 1990s. Significant changes in the aquatic plant communities were caused by increasing anthropogenic pressures, such as damming and nutrient loading from agriculture, aquaculture, and urbanization after the Chinese economic reform. We argue that Changdang Lake is currently in a transition phase between a macrophyte-dominated state and an algae-dominated state. Our palynological record is different from many contemporary studies, which suggest submerged plants dominated most lakes in this region before the 1950s. We suggest that the return of the aquatic plants to their 1970s–1980s state would be a realistic target for lake restoration. Our results show that palynological records can reveal long-term dynamics of macrophytes in shallow lakes for sustainable lake restoration and management. Graphical abstract Unlabelled Image Highlights • First attempt to reveal long-term aquatic plant succession in the MLYB based on palynology. • There was a low biomass of aquatic plants in Changdang Lake in the first half 20th century. • Changdang Lake is currently in a macrophyte-algae transition. • Hydrological condition and nutrient input are the main factors for succession of aquatic plants. • The 1970–1980s state of aquatic plants in Changdang Lake would be a realistic restoration target. [ABSTRACT FROM AUTHOR]

Vegetation reconstructions from palaeoecological records depend on adequate understanding of relationships between modern pollen, vegetation and climate. A key parameter for quantitative vegetation reconstructions is the Relative Pollen Productivity (RPP). Differences in both environmental and methodological factors are known to alter the RPP estimated significantly, making it difficult to determine whether the underlying pollen productivity does actually vary, and if so, why. In this paper, we present the results of a replication study for the Bashang steppe region, a typical steppe area in northern China, carried out in 2013 and 2014. In each year, 30 surface samples were collected for pollen analysis, with accompanying vegetation survey using the “Crackles Bequest Project” methodology. Sampling designs differed slightly between the two years: in 2013, sites were located completely randomly, whilst in 2014 sampling locations were constrained to be within a few km of roads. There is a strong inter-annual variability in both the pollen and the vegetation spectra therefore in RPPs, and annual precipitation may be a key influence on these variations. The pollen assemblages in both years are dominated by herbaceous taxa such as Artemisia , Amaranthaceae, Poaceae, Asteraceae, Cyperaceae, Fabaceae and Allium . Artemisia and Amaranthaceae pollen are significantly over-represented for their vegetation abundance. Poaceae, Cyperaceae and Fabaceae seem to have under-represented pollen for vegetation with correspondingly lower RPPs. Asteraceae seems to be well-represented, with moderate RPPs and less annual variation. Estimated Relevant Source Area of Pollen (RSAP) ranges from 2000 to 3000 m. Different sampling designs have an effect both on RSAP and RPPs and random sample selection may be the best strategy for obtaining robust estimates. Our results have implications for further pollen-vegetation relationship and quantitative vegetation reconstruction research in typical steppe areas and in other open habitats with strong inter-annual variation. [ABSTRACT FROM AUTHOR]

• Long-term environmental changes of Lake Baiyangdian are spatially heterogeneous. • Hydrological process and land use together lead to the spatial heterogeneities. • Major environmental transitions of the wetland occurred in the 1960 s and 1990 s. • Humulus pollen is a key indicator of anthropogenic impacts in populated wetland. Understanding long-term environmental changes and man-land interactions within wetlands is important for their ecological maintenance and restoration. However, there has been little focus on the spatial heterogeneity of environmental variations of wetlands, especially large agricultural wetlands, which hinders the development of targeted management programs for specific areas. We conducted a multi-proxy study of the sediments of a typical agricultural wetland, Lake Baiyangdian in North China, to assess the spatial heterogeneity of environmental changes over the past 70 years. The results reveal that the environmental changes in Lake Baiyangdian were spatially heterogeneous, mainly reflected by the response to hydrological variations before the 1970 s, and by changes in trophic level and land cover transitions since the 1990 s, which are strongly linked to changes in agricultural land use. Pollen and grain-size analyses revealed the large-scale spatial heterogeneity of changes in the sedimentary environment. Areas with greater openness, shallower water depths, and proximity to inflowing rivers were generally more sensitive to hydrological processes and provided regional records of environmental change. In contrast, populated areas far from inflows tended to capture more local changes related to anthropogenic impacts. Intensive agricultural activity has led to a continuous increase in nutrient enrichment and significant land cover transitions in Lake Baiyangdian, mainly the loss of natural wetland. Variations in Humulus pollen were a key indicator of these anthropogenic impacts. Hydrological processes and land use changes were together responsible for the spatial heterogeneity of the environmental variations in Lake Baiyangdian over the last 70 years, indicating the dominant role of human impacts on the spatio-temporal pattern of the evolution of this wetland ecosystem, and the complexity of its environmental management. [ABSTRACT FROM AUTHOR]

This paper presents the results of pollen trapping studies designed to quantify the pollen assemblages carried in the winds of the Loess Plateau in Luochuan and Hunyuan. The one-year-collection samples analysis results show that pollen assemblages can be more sensitive to the change of climate than the vegetation composition, because of the change of pollen production. The analysis results of pollen traps in different weather regimes indicate that the pollen influx coming from dust weather contribute more to the total pollen influx than that coming from non-dust weather. The wind speed is the most important influenced factor to pollen assemblages, then the mean temperature and the mean relative humidity, the wind direction also contributes some. Strong wind coming from dust direction can make the percent and influx of Artemisia and Chenopodiaceae increase obviously with averagely higher than over 2.7 times in dust weather than in non-dust samples. The influences of wind speed and wind direction are not serious to some arboreal pollen such as Rosaceae, Quercus , Betula , Pinus and Ostryopsis , which are mainly influenced by temperature or the relative humidity such as Salix , Hippophae , Carpinus , Brassicaceae, Cupressaceae, Fabaceae. [ABSTRACT FROM AUTHOR]

• A 150-year environmental change of a populated wetland was reconstructed. • Agriculture and hydrological process variations altered the wetland landscape. • Nutrient and pollution inputs caused negative effects on aquatic plant succession. • Effective protection was helpful to maintain the resilience of wetland ecosystem. Lakes and wetlands in populated areas have become very vulnerable to pollution and habitat degradation, seriously threatening regional ecological security and socio-economic development. Exploring long-term environmental changes in these systems is essential to reveal the interactions of human activities and catchments, and further to provide valuable reference for current restoration. In this paper, we present paleolimnological data from a short sedimentary core from Liangzi Lake, a typical wetland nature reserve in the middle and lower Yangtze River Basin, China. Multiple sedimentary proxies (principally pollen but also geochemistry and grain size data) combined with historical records were used to establish environmental changes of Liangzi Lake, in both terrestrial and lacustrine aspects, over the last 150 years. Despite the influence of hydrological processes to some extent, our results indicate that the anthropogenic effects (negative and positive) are well recorded by the sedimentary records. The landscape changes of the wider Liangzi Lake wetland can be placed into four stages: less disturbed background (before the 1950s), hydrological regulation (1950s–1960s), intensive reclamation (1970s–1990s), and wetland restoration (starting in the late 1990s). Agriculture and hydrological control were the most important factors in transforming the wetland landscapes, as well as the aquatic ecosystem. The changes in the lake itself could be divided into three main stages: low nutrient levels and unstable hydrologic condition with dominant emergent plants (before the 1960s), rising nutrient levels and a stable water environment with increasing submerged plants (1960s–1990s), and high nutrient and pollution levels with the subsequent adjustment and restoration (after the late 1990s). Our study provides a comprehensive history of environmental changes of a typical inland lake and its surrounding wetland, and may contribute to future wetland conservation in similar regions, as well as pollen-based environmental reconstruction studies. [ABSTRACT FROM AUTHOR]

• Pollen assemblages reflect well the vegetation types at different altitudes. • The RSAP in the mountain area in the Taihang Mountains is about 600 m. • The RPPs can be well estimated in the human influenced Taihang Mountains. • Implications for land cover reconstruction in the North China Plain are discussed. Pollen-based land cover reconstructions are important for understanding the history of regional environmental responses to natural and anthropogenic factors, and for managing the ecological environment. The vegetation in the mountain landscape of North China has been significantly influenced by human activities, and evaluating the pollen-vegetation relationship for the region is important for reconstructing anthropogenic land-cover changes in the North China Plain. In this study, 35 sampling sites were randomly selected in representative vegetation zones of the Taihang Mountains in North China. Based on a detailed vegetation survey (field work combined with the analysis of remote sensing images), we evaluated the pollen-vegetation relationships in the area. In addition, the relevant pollen source area (RSAP) of the sampling sites and the relative pollen productivity (RPP) of the major plant taxa were estimated using ERV (Extended R-Value) models. The results show that the pollen spectra in the Taihang Mountains reliably reflect the vegetation landscape of different altitudinal zones. The estimated RSAP in the Taihang Mountains is ~ 600 m. Using Poaceae as a reference taxon (RPP = 1), the RPPs of the dominant plant taxa in the Taihang Mountains can be ordered as follows: Pinus > Hippophae > Caryophyllaceae > Betula > Quercus > Rhododendron > Artemisia > Asteraceae > Cyperaceae. Our results suggest the importance and complexity of RPP estimates in the Taihang Mountains, and provide valuable implications for improving the accuracy of reconstructions of land-cover changes in the North China Plain. [ABSTRACT FROM AUTHOR]

• A new study on the modern pollen-vegetation relationships in southeastern China. • Pollen signals are compared with LUCC data in different categories and distances. • Hydrologic process plays a key role in pollen dispersal and deposition. • Human activities deeply impact the pollen-vegetation relationships in the YHRB. • The p/v ratios have potential value for the reconstruction study in the YHRB. Fossil pollen, as a key indicator of vegetation landscapes, can provide abundant information of long-term land use dynamics. However, pollen-vegetation relationships are complex, and the relevant studies are rare in the large sedimentary basins associated with strong human disturbances. This study aims to investigate the pollen-vegetation/land use relationships at a large regional scale, and to supplement reference for more accurate paleoenvironmental reconstruction in the future. A total of 124 modern pollen samples were collected from 66 lakes in the Yangtze-Huaihe River Basin (YHRB), southeastern China. We conducted a contrastive analysis of both pollen and land use data in different spatial extents and categories. Our results reveal that the pollen assemblages of the YHRB are dominated by both arboreal and herbaceous taxa, such as Pinus , Quercus , Pterocarya , Juglans , Poaceae, Artemisia , Cruciferae, Chenopodiaceae, Compositae, and Humulus. The spatial differences of pollen assemblages in the YHRB are obvious, resulted from the confounded effects of natural environment and human disturbance. Hydrologic process plays a key role in pollen dispersal and deposition in the YHRB. Waterborne pollen is an important component of the lacustrine pollen assemblages, and fern spores and total pollen concentration can be used to indicate the degree of hydrologic process. The main source of lacustrine pollen here generally derives from sub-basins, and the source area is about 80 km. Anthropogenic impact is another significant factor determining the pollen-vegetation relationships in the YHRB. Cereal and anthropochore pollen as well as pollen diversity indexes are ideal indicators of agricultural activities. We suggest that the 4 types of estimated pollen/land-use ratios in this study, covering forest, farmland, rural land, and wetland could be used as a reference for reconstructing past land cover. Our study also demonstrates the existing problems and the potential improvements for the further studies on pollen-based paleoenvironmental reconstruction. [ABSTRACT FROM AUTHOR]

Bohai Bay is a typical area of global change research in East Asia, due to its unique geographical location and shallow water environment. In this paper, we present the results of a study of grain-size, geochemistry, pollen and algae of a middle to late Holocene sediment core from Haixing wetland, which located on the west coast of Bohai Bay. The results show that: 1) Prior to 6700 cal a B.P., the content of Cl, Sr/Ca ratio were the highest, end-member analysis of grain size suggested EM2 were dominant, which is characteristic of marine sediment and the concentrations of Pediastrum and Typha (indicating a freshwater environment) pollen were lowest, overall indicating the maximum of relative sea level; 2) During 6700–5000 cal a B.P., and the Ti and K contents, EM1 (lacustrine sedimentary component) increased substantially, EM2 decreased, and EM3 (fluvial sedimentary component) began to appear. The concentrations of Pediastrum , Dinophyceae and Typha pollen began to increase. All these indicating that the relative sea level began to fall and the study area became a lagoon environment; 3) During 5000–3500 cal a B.P. the Ti and K content increased further; EM1 was dominant, EM2 was rare, indicating that the relative sea level decreased further and the lagoon gradually became enclosed; 4) After 3500 cal a B.P., the Ti content reached its maximum and the Cl content and Sr/Ca ratio decreased to their lowest levels. EM1 was dominant and EM2 was virtually absent; dinoflagellate cysts almost disappeared and there was large increase of Typha pollen, indicating the complete exclusion of a marine influence during most of this period. However, during 2500–2000 cal a B.P. the Cl and the Sr/Ca ratio increased slightly once again, indicating a transient transgression. [ABSTRACT FROM AUTHOR]

The North China Plain is a region where the natural vegetation was increasingly influenced by human activities from ∼3000 cal yr B.P. (Zhang et al., 2017; Peng, 2019). We used pollen, charcoal and sediments from the Dacaozhuang Holocene profile in Ningjinpo, central North China Plain, in combination estimates of relative pollen productivity, to quantitatively reconstruct vegetation changes over the last 3000 years using the REVEALS model. Our aims were to study the combined effects of climate change and human activities on the zonal vegetation. The principal findings are as follows. 1) During 3000–2600 cal yr B.P., the study area was strongly influenced by the Yellow River, leading to a complex pollen source area, which is inappropriate for REVEALS models. Since 2600 cal yr B.P., the sediments were mainly supplied by rivers originating in the Taihang Mountains, and the reconstructed tree coverage was generally less than 20%, while that of herbaceous plants such as Artemisia , Poaceae and Asteraceae was more than 50%. This indicates that the study area was predominantly grassland with trees sparsely distributed in the mountains. 2) Crop plants (Poaceae≥35 μm, and Fagopyrum), and the occurrence of synanthropic plants like Brassicaceae and Urtica/Humulus , together with a high sedimentary content of coarse charcoal particles (>100 μm), indicate substantial disturbance of the natural vegetation by human activities from 2600 cal yr B.P. 3) During the Medieval Warm Period (1300–600 cal yr B.P.), the concentration of charcoal and the proportion of synanthropic plants were relatively high, indicating strong human activity. Nevertheless, the proportion of trees, dominated by Pinus and Quercus , was substantially higher (increasing to more than 19%) compared with the previous interval, indicating an increase in forest vegetation and thus a strong climatic influence on the vegetation. 4) During the periods of the Ming and Qing Dynasties (after 500 cal yr B.P.), the concentration of charcoal and crop plants reached a maximum and the tree coverage decreased substantially (to 4.8%), indicating the highest level of human influence on the vegetation. The shift to a cool and dry climate may also have contributed to the reduction of trees within the landscape. [ABSTRACT FROM AUTHOR]

It is widely recognized that the climate of the Little Ice Age (LIA) was generally cold. However, there are differences in the climate response of the vegetation in different regions during the LIA, and high-resolution quantitative research is lacking. Here, we present a high-resolution pollen analysis and the Landscape Reconstruction Algorithm (LRA) based on relative pollen productivity, combined with AMS 14C dating, to quantitatively reconstruct the vegetation response to climate and sea level change on the western coast of Bohai Sea. The main findings are as follows: (1) The coverage of the main plant taxa reconstructed using estimates of relative pollen productivity was closer to the actual vegetation conditions than that based on pollen percentages. (2) Since ∼1250 A.D., the study area was occupied by temperate deciduous broadleaved forest, dominated by Quercus , with a smaller proportion of Pinus forest. The regional vegetation types did not change significantly, but the forest cover decreased gradually from ∼60% in the Middle Warm Period (MWP, 1250–1310 A.D.) to ∼40% in the LIA (1310–1610 A.D.), due to the combined influences of climate and human activities. (3) The composition of herbaceous plants changed substantially during the LIA. In the early LIA (1310–1450 A.D.), the climate became cold and dry and the sea level began to fall, resulting in a substantial increase in the proportion of Poaceae (∼10%). In the middle of the LIA (1450–1610 A.D.), the climate became colder and drier, the sea level fell further, and the lagoon shrank. In response, there was an increase in drought and salt-tolerant Chenopodiaceae (∼10%) and Artemisia (∼5%), a substantial increase in Selaginella sinensis supplied by fluvial processes. [ABSTRACT FROM AUTHOR]

Coastal wetlands provide valuable ecosystem services and understanding their response to past climatic changes may help predict their possible future responses. In this paper, we obtained records of pollen, algae, sediment grain-size, and other environmental proxies, from a late Holocene sediment core (CFD-E) from the Caofeidian area, on the northwest coast of the Bay of Bohai, China. Our results indicate three major stages of environmental change. During Stage I (3500–2800 cal yr BP), arboreal pollen content was high (mostly >60%), especially for Pinus and Quercus , and the PCA sample scores on Axis 1 were negative indicating that regional vegetation was temperate broadleaved forest and the climate was wet. During Stage II (2800–2350 cal yr BP), the arboreal pollen content decreased substantially (mostly <40%), and the PCA Axis 1 sample scores were positive indicating a decrease in forest vegetation, grassland expansion, and a drier climate. During Stage III (2350–1400 cal yr BP), the arboreal pollen content increased again (mostly >40%), although it remained lower than during Stage I, indicating that forests expanded under a relatively humid climate while the wetland area decreased slightly. Our results also record the 2.8 ka and 2.4 ka events of monsoon weakening, which were characterized by increases in herbaceous pollen (indicating grassland expansion) and the drying of the regional climate. There are several differences in the regional expression of these two climatic events. During the 2.4 ka event, Chenopodiaceae pollen increased substantially (average of 42.0%), indicating the expansion of halophytes; whereas during the 2.8 ka event, an increase in Artemisia indicates the occurrence of a dry climate throughout the region. We suggest that the aridity during the 2.8 ka event was triggered by decreased solar activity and the resulting changes in the El Niño-Southern Oscillation, which weakened the East Asian summer monsoon. However, we suggest that the 2.4 ka event was driven by the weakening of the Atlantic Meridional Overturning Circulation. • Significant increase in halophytic vegetation during 3500–1400 cal yr BP • The 2.8 ka and 2.4 ka events were characterized by climate drying lasting ∼150 years. • During these two events the area of forest decreased and grassland expanded. [ABSTRACT FROM AUTHOR]

• Climate and sea-level changes together influenced the Bohai coastal region. • Qilihai Lagoon sensitively responded to DACP and the 1.4 ka cold event. • Fossil pollen spectra well reflected the variations of lagoon-wetland environment. • End-member analysis can be used to identify the sediment source of lagoon. Lagoons are sensitive to the interaction between marine and terrestrial environments, and their evolution is also closely related to climate and sea level changes. Bohai Bay is a representative area of global change research in East Asia, due to its unique geographical location and shallow water environment. Here, we present the results of a study of pollen, algae, and grain-size of a late Holocene sediment core from Qilihai Lagoon in Bohai Bay, which is the largest lagoon in North China. The results show that the Qilihai Lagoon area experienced three stages of environmental change in 3,100–1,000 cal yr BP: during 3,100–1,800 cal yr BP the regional vegetation was broadleaved forest dominated by Quercus with a small amount of Pinus , indicating that the regional climate was warm and wet. The level of the Bohai Sea was high, and the sampling site was a shallow bay environment. During 1,800–1,400 cal yr BP, corresponding to the Dark Ages Cold Period (DACP), coniferous trees and grassland expanded. The sedimentary environment of the sampling area was greatly influenced by terrestrial sediment sources as the sea level fell and sandbars were exposed. We speculate that the modern Qilihai Lagoon formed at ∼ 1,800 cal yr BP. The lagoon shrank during the coldest interval of the DACP, and an extensive area of coastal wetland developed around the lagoon. During 1,400–1,000 cal yr BP the regional climate warmed, however, there was little change in the terrestrial vegetation. The lagoon became closed and the sedimentary environment was unstable due to the encroachment of coastal dunes driven. The coastal wetland began to decrease due to the expansion of the lagoon. Our study provides an important supplement for the environmental response research in the East Asian coastal areas, as well as other regions of the world. [ABSTRACT FROM AUTHOR]

The lower Yellow River is characterized by frequent channel avulsion and flooding during the late Holocene, which not only shaped the geomorphic landscape of the North China Plain, but also modified the preexisting drainage network and affected human settlement pattern. The channel evolution of the lower Yellow River during historical periods of China has been well known from documentary records. However, it is still unclear about the drainage pathway of the river during the archaic period of Chinese history. Here we show sedimentary evidence for a dramatic channel displacement of the lower Yellow River about 3000–2600 years ago. Our multi-proxy analyses indicate that the first prehistoric diversion of the Yellow River occurred around 3000 yr B.P. and the river flowed northward into the Bohai Sea through the foreland depression along the eastern foothill of the Taihang Mountains. Frequent floods thereafter not only led to the widespread infilling of depressions in the lower reaches of the Yellow River and thus accelerated the formation of the North China Plain, but also drove humans to migrate from the piedmont area of the Taihang Mountains to the hinterland of the central North China Plain. • Sedimentary evidence of Yellow River flow into Bohai Sea via Taihang Mountains. • Between 3 and 2.6 kyr BP, Yellow River Flowed through Taihang Mountains' Front Basin. • After 3 kyr BP, Yellow River course changes accelerated North China Plain Formation. [ABSTRACT FROM AUTHOR]

The 4.2 ka event was an important climatic event during the mid–late Holocene, with significant effects on the ecological environment and climatic evolution of different regions. Coastal wetlands, as a transitional ecosystem between land and sea, are sensitive to changes in climate and sea level; hence, research on coastal wetlands is important for reconstructing past climate and sea-level changes and for predicting future changes. However, little research has been conducted on the characteristics of the 4.2 ka event on the western coast of Bohai Bay in China. We analyzed the pollen assemblages (214 samples), grain size, and geochemical element contents of a mid–late Holocene sedimentary sequence from the Nandagang (NDG) wetland on Bohai Bay, with the chronology based on 13 AMS 14C dates. The results revealed the history of climate and sea-level changes on the western coast of Bohai Bay during the interval of 5000–3600 cal yr BP. High sedimentary arboreal pollen concentrations indicated that the NDG area had a relatively dense cover and humid climate during 5000–4450 cal yr BP. During the 380-year interval of 4450–4070 cal yr BP, corresponding to the 4.2 ka event, the decreased representation of arboreal pollen indicated a decrease in the regional forest cover and an arid climate. The internal structure of the 4.2 ka event recorded in core NDG showed a dry-wet-dry temporal structure during the intervals of 4450–4290 cal yr BP, 4290–4170 cal yr BP, and 4170–4070 cal yr BP, respectively, together with a relatively low sea level. Comparison of the relative sea level (RSL) record of the NDG wetland with similar records from other coastal regions in East Asia during the 4.2 ka event revealed contrasting trends. During 4070–3600 cal yr BP, the tree pollen concentration increased again, indicating that the forest vegetation coverage increased and the climate became wetter. Overall, our results suggest that the 4.2 ka event, as recorded in Bohai Bay, was related to the reduced influence of the western Pacific Ocean Warm Pool and the more frequent occurrence of the El Niño–Southern Oscillation. • High-resolution multi-index records of coastal wetlands. • Secondary fluctuations in climate and sea level of 4.2 ka event in coastal wetlands. • Causes and responses of coastal wetlands 4.2 events. [ABSTRACT FROM AUTHOR]

The Xiashagou fauna is one of the most abundant and representative faunas in East Asia and can be directly compared to the Olivola fauna of early Late Villafranchian age in Europe. Therefore, it is of great significance for understanding the evolution of the Quaternary faunas and environment of East Asia. We conducted pollen analyses of 163 fossil samples and 1045 surface samples, combining the results from the NHA drill core to characterize the patterns of vegetation and climate change in the Early Pleistocene and the early stage of the Xiashagou fauna. The results enable the definition of three cold periods (2.6–2.58 Ma, 2.55–2.34 Ma, 2.20–2.14 Ma) and two warm periods (2.58–2.55 Ma, 2.34–2.20 Ma). The pollen assemblages are dominated by Picea or Artemisia , Amaranthaceae and Poaceae during the cold periods, while dominated by Pinus and broadleaved trees during the warm periods. The annual average temperature (Tann) decreased by ∼2 °C (up to ∼10 °C), and average annual precipitation (Pann) decreased by ∼200 mm (up to ∼500 mm) during the cold period. The Xiashagou fauna emerged at the beginning of the third cold period (∼2.20 Ma) with Tann decreased by 3–4 °C and Pann by 100–200 mm, when the pollen spectra are dominated by Artemisia , Amaranthaceae and Poaceae (>80%), indicating that the vegetation was predominantly grassland. From 2.19 to 2.18 Ma, the climate became slightly warm and humid, with increased Pinus and Ulmus representation, which resulted in the development of forest; after 2.18 Ma the climate became colder and drier again. • Three cold periods and two warm periods can be divided from 2.6 to 2.1Ma. • Picea, Artemisia and Amaranthaceae dominated pollen assemblages in cold periods. • Pinus and broadleaved trees dominated pollen assemblages during the warm periods. • It decreased by ∼2 °C for Tann and by ∼200 mm for Pann during the cold periods. • The Xiashagou fauna emerged at ∼2.20 Ma, at the beginning of the third cold period. [ABSTRACT FROM AUTHOR]