In recent years, the tidal limit of the lower reaches of the Yangtze River has shifted upward, the construction of water-related projects has increased, and the intensity of river bank failure disasters has been on the rise. Previous researchers have found the existence of strong vertical-axial backflow in the bank failure section through field surveys, physical modeling, and numerical simulation, and that there is a strong vertical-axial backflow in the bank failure section; however, the hydrodynamic zone characteristics of the bank-channel interactive zone and the microgeomorphic adaptation mechanism have not been explored. Based on the Doppler acoustic current profiler (ADCP) in the frequent bank failure sections, multibeam system, combined with previous high-resolution underwater topographic data, it is found that the flow velocity and flow direction in the interactive zone of the bank-channel have significant zone characteristics, and according to the backflow strength \alpha, i.e., the longitudinal flow velocity u and its ratio to the transverse flow velocity v, |u/v|, the zone from the channel to the bank is identified into the main stream zone (α<1, u>0), the mixing zone (α≥1), and the near-bank backflow zone (α<1, u<0). The mainstream zone develops large and medium-sized dunes, scour grooves, and scour pits, the mixing zone develops accumulators and small dunes, and the backflow zone develops spines and small dunes; the main stream direct flushing in the mainstream zone and the backflow lateral erosion in the backflow zone are the main driving forces for the development of scouring microgeomorphic type and the development of bank failures, and the high flow velocity gradient in the mixing zone near the main stream zone generates scouring geomorphology, and the remaining part of mixing zone remains a low flow-velocity to make the sediment fall and silt to form the accumulation body. The findings can provide important references for the disaster remediation and near-shore engineering design and monitoring.

In order to depict the spatiotemporal patterns of EASM variations (EASM: East Asian Summer Monsoon) since the last deglaciation, we analyzed n-alkane compositions and sedimentological characteristics of a lacustrine-wetland section (namely ZWZ-1 section) in the Xingyang Basin of the Central China Plains. We also reconstructed the climatic and environmental changes since ~17.8 cal ka BP on the basis of the analytical results. The reconstruction displayed five-staged variations: (1) ~17.8-~11.7 cal ka BP was a period of loess-like sediment accumulation under a steppe-dominating environment; (2) ~11.7-~8.5 cal ka BP was a period of wetland deposition, during which the n-alkane-indicated forest and wetland expanded; (3) ~8.5-~2.8 cal ka BP was a period of lacustrine deposition and also a period of maximal woody and aquatic plant n-alkane components; (4) ~2.8-~2.4 cal ka BP was again a period of wetland deposition when the n-alkane components of bacteria, algae/microorganisms and submerged phytoplankton increased dramatically; (5) ~2.4-~1.1 cal ka BP was a loess deposition period under a steppe-dominating environment. We also compared the Holocene moisture sequences (ZWZ-1 section and MC-1 section) from the Central China Plains with those from the middle and lower reaches of the Yangtze River and also with those from northern China. The moisture sequence at ZWZ-1 section was based on the average chain length of long-chain n-alkanes (ACL_27-33) and C₂₇₊₂₉/C₃₁₊₃₃ ratio and the moisture sequence at MC-1 section was based on tree pollen (%) and Poaceae/(Artemisia+Chenopodiaceae) ratio. Our comparison shows that the mid-Holocene drought (~7.0-~4.0 cal ka BP or ~8.0-~5.0 cal ka BP) in the Central China Plains chronologically corresponded with the mid-Holocene drought in the middle and lower reaches of the Yangtze River. It seems that the mid-Holocene drought in the entire central China (including the middle and lower reaches of the Yangtze River and the Central China Plains) was causally associated with lowered El Niño-Southern Oscillation (ENSO) intensity and also with elevated Sea Surface Temperature (SST) in the western Tropical Pacific. This implies that the spatiotemporal patterns of the Holocene moisture variations in the entire central China were controlled by ENSO state and modulated by ENSO-dictated north-south shift of West Pacific Subtropical High (WPSH).

Permafrost is highly sensitive to global changes, and it is important to reveal climate and environmental changes in permafrost regions using vegetation succession. Based on palynological evidence and AMS¹⁴C dating from a sediment core, vegetation succession and climate history in the Late Pleistocene of the Mohe Basin (MHB) in the Greater Hinggan Mountain permafrost region was reconstructed. The response of vegetation to environmental changes was further investigated. Results showed that pollen assemblages effectively reflect the vegetation composition in the MHB and surrounding mountainous areas. Based on the relationship between key regional vegetation and climate indicators, vegetation has undergone significant historical changes: from 30.0 to 27.1 ka BP, a meadow wetland landscape showed a cold and humid climate; from 27.1 to 20.5 ka BP, a coniferous forest-grassland landscape indicated a relatively cold and arid climate; from 20.5 to 11.3 ka BP, there was a transition from coniferous forest wetlands to mixed coniferous-broadleaved forest wetlands, indicating the beginning of a warming although the climate remained cold and humid; from 11.3 to 1.9 ka BP, a mixed coniferous-broadleaved forest wetland landscape demonstrated a warm and humid climate; from 1.9 ka BP to the present, a coniferous forest wetland landscape revealed a cool and humid climate. A comparative analysis showed that factors influencing vegetation succession include not only climate conditions related to latitude and land-sea location but also regional factors caused by permafrost itself. Vegetation succession exhibited different response mechanisms to permafrost changes during glacial and interglacial periods. During the Last Glacial Maximum, permafrost expansion benefited the growth of cold and drought-resistant terrestrial herbs with shallow roots such as Artemisia and Chenopodiaceae, leading to the expansion of arid grasslands. During the Holocene Megathermal Period, permafrost degradation provided favorable habitats for vegetation, and also facilitated the formation and expansion of wetlands, promoting the extensive proliferation of aquatic plants, ferns, mosses, and trees, forming a forest wetland landscape. Therefore, permafrost presence enhances the effects of water and heat under different climate conditions on vegetation, making vegetation more sensitive to environmental changes in permafrost regions.

The northern part of the Kumtagh Desert exhibits a dark surface color, ranging from brown black to grayish brown. Additionally, certain feather-like dunes often display contrasting patches of light and dark hues on their surfaces, which has emerged as one of the distinctive characteristics defining this desert. The origin of light and dark spots in sand grains was investigated by conducting field surveys from 45 geomorphic sampling sites in the northern Kumtagh Desertin late September to early October 2020 and 2021,75 groups of grain size analysis, 39 groups of color grains (434 grain size samples) were identified visually, as well as 157 samples of sediment chroma were determined by colorimeter. The findings demonstrate a robust linear relationship between the visual colorimetric index (CI) and the measured luminance L^* as well as yellowness b^*, indicating their interchangeability in expressing both color and brightness levels of sediment. CI and L^* exhibit close associations with particle color and size. The presence of black, gray, and brown hues can be attributed to the primary lithology of clasts and weathered attachments show a strong correlation with coarse rock debris, resulting in high chromaticity but low brightness. On the other hand, yellow and white tones primarily originate from light-colored rocks and minerals that are closely linked to fine particle sizes, leading to low chroma yet high brightness. The desert has obvious sedimentary stratification, in which parallel bedding is characterized by the largest particle size at the top and gradually decreasing downward, and has a major influence on the chromaticity of the dune surface. The variation in surface chroma of sand dunes is the outcome of peristaltic accumulation of coarse-grained rock debris and wind erosion transport of fine-grained minerals during the movement of sand particles. A slight relative change, ranging from 5% to 10%, in very coarse sand with high chroma -1.0~0 Φ or a mixture of very coarse sand and coarse sand -1.0~0.5 Φ can result in different shades of color spots appearing on adjacent areas of the dune surface. The present study can offer experimental models and data references to elucidate the origin and formation mechanism of surface color in sand dunes within the Kumtagh Desert and similar desert environments.

In cave environments, the temperature and relative humidity are considered the important factors in the formation of stalagmites. In this study, we introduced a contribution of 43-month duration monitoring records with hourly resolution on temperature and relative humidity, within the Shihua Cave in Beijing, aiming to discern the interplay between these environmental variables and understand their interrelation with the cave dynamics. The observation results are as follows: (1) Cave temperature and relative humidity show the characteristics of low in winter and spring and high in summer and autumn. Notably, the temperature dynamics within the cave exhibited a temporal lag behind surface temperature changes, ranging between 1 to 3 months. This lag contained a gradual response to warming trends and a relatively fast response to cooling trends. Additionally, the response characteristics differ across various monitoring points. In the cold season, both the temperature and humidity at the XHT (Xiuhuatai) and XMG (Xiaomogu) displayed a declining trend and a notable positive correlation. In contrast, the relative humidity levels at the PL (Panlong) remained essentially saturated throughout the year and demonstrated no significant correlation with temperature fluctuations. (2) There are notable seasonal differences in the daily fluctuations of temperature and relative humidity in the cave. In the cold season, the temperature patterns at the PL and XMG monitoring points exhibit a stark contrast to the daily temperature variations on the surface and the relative humidity levels at the XHT and XMG points correspond to the daily fluctuations in surface relative humidity, whereas the XHT points align with the surface temperature trends. In the warm season, the temperature fluctuations at the cave's monitoring points mirror the daily temperature changes on the surface. The significant spatial distribution pattern of temperature and relative humidity in the cave reflects the seasonal differences in airflow activity, influenced by the unique "floor-type" structure of the Shihua Cave, and tourism activities. Airflow activity in the winter mainly affects temperature and humidity changes in the cave. During peak periods and at the attraction, the influence of tourism activities is significant. The findings of this study advanced our understanding of airflow dynamics under the cave setting and established a solid foundation for the cave stalagmite deposition interpretations and their paleoclimate mechanism. Furthermore, this research can serve as valuable guidance for the conservation of tourist cave landscapes.

This study focuses on the Lower Yellow River (LYR), which has experienced continuous erosion since the operation of Xiaolangdi Reservoir in 1999, and its complex spatio-temporal variation process. Using the single-step mode of the Delayed Response Model (DRM), we derive a calculation formula for the accumulated erosion and deposition volume in the LYR. The coefficient of determination R² between the simulated and observed values from 2000 to 2020 is 0.99. Currently, the LYR is undergoing continuous erosion, but the erosion rate is gradually slowing down, and the difference between the equilibrium value and the calculated value of accumulated erosion and deposition volume gradually decreases, which means that the riverbed erosion is approaching equilibrium. Additionally, we derive a formula for the spatial distribution of main channel accumulated erosion volume per unit river length in the LYR based on the non-equilibrium suspended sediment transport equation. The coefficient of determination between the fitted value and observed value from 2003 to 2015 is about 0.98-0.99, with a relative error of approximately 6.2%. Our findings suggest that under the current conditions of decreasing sediment inflow and continuous scouring, it takes around 3.0 years for the riverbed to achieve half of the erosion and deposition adjustment and approximately 13.0 years to achieve 95% of the adjustment. Moreover, the spatial distribution of accumulated erosion volume in the LYR tends to become more uniform with the continuous development of erosion. These results provide valuable reference for analyzing the complex spatio-temporal variation process of the LYR.

Evapotranspiration (ET) is one of the key components of the terrestrial water cycle, and its long-term changes directly affect the spatiotemporal pattern of regional water availability. In recent decades, China has experienced significant changes in climate and land surface characteristics. However, how these changes affected the spatiotemporal pattern of terrestrial ET was still poorly understood. In this study, we quantified the contributions of five factors related to climate and vegetation (precipitation, wind speed, vapor pressure deficit, net radiation, and leaf area index) to ET trends across China using the Penman-Monteith-Leuning model and a forcing variable detrending experiment. The results showed that nationwide annual ET increased significantly (p < 0.05) from 1982 to 2019, with a trend of 1.25 mm a^-1. Vapor pressure deficit, leaf area index and precipitation dominated the national ET changes, and their contributions to ET trends are 42% (0.54 mm a^-1), 29% (0.36 mm a^-1), and 27% (0.31 mm a^-1), respectively. Spatially, the dominant factors of ET changes show clear regional differences. Changes in ET are dominated by precipitation in the arid and semi-arid regions of northwestern China, and by vapor pressure deficit in humid regions such as the Yangtze River basin and the northern part of northeastern China. Leaf area index dominates ET changes in areas with a significant greening such as the Loess Plateau, North China Plain and parts of Northeast China. The findings are expected to provide guidance for national water resources management and planning under climate change.

As an important strategic resource in the arid inland region of Northwest China, water resources are related to the sustainable development of the regional economy and society. As important regional water resources, inland river basins are highly sensitive to global climate change. In this study, we studied the typical inland river basins in the Qilian Mountains, Tianshan Mountains, and Kunlun Mountains. The regional runoff composition and its relationships with the main environmental factors were analyzed based on long-term runoff monitoring and water chemical isotope analysis data of precipitation, meltwater, river water, groundwater, and other water bodies. The results showed that: (1) Except for the Shiyang River, the annual runoff of most rivers in the study area showed an upward trend in recent decades; (2) Most of the water bodies in the study area were alkaline, and the dominant anion and cation of each water body were HCO₃^-, and Ca²⁺ and Na⁺, respectively. The hydrochemical type was mostly HCO₃^--Ca²⁺, which is strongly affected by rock weathering. The TDS of river water showed a similar seasonal trend, being low in summer and autumn, but high in winter and spring. Meanwhile, the seasonal differences of each ion are relatively prominent. (3) Except for the Hutubi River, the variation trend for δ¹⁸O was relatively consistent, showing the seasonal variation of low in summer and autumn while high in winter and spring throughout the year. (4) The average annual contributions of groundwater, precipitation, and glacier/snow meltwater to regional streamflow in the study area were 42.6%, 34.4%, and 23.0%, respectively, with spatial heterogeneity in regional runoff composition. (5) In the context of climate change, regional temperature variability will increase the risk of runoff changes in the Aksu, Hotan, and Shiyang rivers, whereas fluctuations in precipitation may pose potential risks to runoff processes in the Tizinafu and Shule river basins, and there are potential water quality risks in the Hotan River. The results of this study have strong implications for the sustainable use of regional water resources.

Sedimentary DNA has been widely used in the studies of climate change, ecological function, and environmental archaeology, because it can provide biological dynamic information with temporal dimension in geographical environment. However, the surface processes and impact factors of sedimentary DNA within the catchments are still not fully understood, which limits the accuracy of sedimentary DNA data interpretation. In this study, topsoil DNA concentrations at the Buha River catchment in northwest Qinghai Lake, which was suitable for DNA preservation, were firstly measured based on domestic new sedimentary DNA laboratory. Meanwhile, soil physical and chemical compositions, including grain size, elements, loss on ignition and TOC, were determined. Subsequently, the abiotic factors which had impact on spatial distribution of topsoil DNA concentration were analyzed by combing the status related with climate, vegetation cover, and land use at the Buha River catchment. The results showed that the average concentration of topsoil DNA at the whole catchment was 0.91 μg/g, with the higher values in the middle reaches of the Buha River and its tributary Jilmon River, while the lower ones in the lower reaches near the Qinghai Lake. In addition, topsoil DNA concentrations at the catchment were positively correlated with the contents of clay and organic matter, but negatively correlated with sand content and the intensity of weathering and leaching. Besides, high vegetation cover and frequent grazing activities contributed to the enrichment of the topsoil DNA, while strong weathering and leaching under warm and wet environment, river transportation and crop cultivation reduced the concentration of the topsoil DNA. All the above results provide a scientific basis for an understanding of the deposition processes of sedimentary DNA and their impact factors in the Buha River catchment, which are helpful for revealing sedimentary DNA compositions and evolution processes of ecological environment and human-environment relationship in regions west of the Qinghai Lake.

Lake surface water-heat exchange and its climatic attribution critically influence the evaporation mechanism and water balance in alpine lakes in a warming climate. Based on the eddy covariance turbulent flux observation of Yamzhog Yumco, an alpine lake in Tibet, this paper explored the characteristics of the hourly, daily, and monthly variations of the lake surface water-heat flux and their correlations with meteorological factors during the non-freezing period in 2016 and 2017. We found that the average latent heat flux was much higher than the sensible heat flux on the lake surface from April to December. Moreover, the water-heat flux exhibited remarkable seasonal variation, and the higher air temperature and humidity in summer jointly controlled the lake-air energy exchange over the lake surface. First, the lake-air temperature difference was the most significant meteorological factor related to sensible heat flux on half-hourly, daily, and monthly scales. Second, the latent heat flux was strongly positively correlated with wind speed and the synergies of wind speed and water vapor pressure deficit on the daily and half-hourly scales. Third, the lake surface water-heat flux was significantly negatively correlated with the net radiation flux on the daily and monthly scales, which was attributed to the seasonal variation of the water surface net radiation and the phase difference of the water-heat flux intensity change due to the lake-air temperature difference and heat capacity contrast. The results revealed the differences of the main controlling meteorological factors in the variation of water-heat flux in the alpine lakes in south Tibet on different timescales. The work will hopefully improve our understanding of the mechanisms of energy exchange and evaporation over alpine lakes in the future projected climate conditions.

Wind is the second largest fluid shaping the earth's landscape besides water. The aeolian landform formed by wind is widely distributed in the global arid regions, and more than 40% of the land area is affected by the aeolian process in the world. Owing to a close relationship with the human's living environment, aeolian geomorphology has received continuous attention from the international academia since the end of the 19th century. Although aeolian landforms are widely distributed in arid and semi-arid regions of China, the relevant study started in the late 1950s. This paper summarizes the development of aeolian geomorphology during the past 70 years in China, which has experienced three stages: the initial stage before reform and opening-up; the development stage between the reform and opening-up to the end of the 20th century; and international stage since the beginning of the 21st century, even partially beyond the international standard nowadays. There are many influential achievements in China, including dunes movement, regional comprehensive study on aeolian landforms, formation and evolution process of unique aeolian landforms, Gobi, the secondary flow around dunes and the exploration of extraterrestrial planets. Aeolian research in China has the potential to lead the international aeolian research in the future, but the aeolian geomorphologists must have following strategic thinking on meta-synthesis, the guidance of the earth system science, the global view and development of the outer space era.

Based on the comprehensive analyses of 18 core profiles' sedimentary sequences and lithological characteristics in Jianghan-Dongting Basin of the middle reaches of Yangtze River and the spatial-temporal distribution of archeological sites in this area, we reconstructed the Holocene hydro-environmental evolution of the research area, and its relationship with human activities. The comparison reveals that in 11.5-5.5 ka BP, the water level of rivers and lakes in the middle Yangtze River presented a rising trend, concurrently, under the development of Neolithic culture and rice agricultural activities, human occupation extended from piedmont plain to inner basin plain in the research area. The water level fell in 5.5-4.0 ka BP, meanwhile, the number of human settlements of Qujialing-Shijiahe culture rapidly increased, especially in the inner basin plain. The water level rose again around 4.0 ka BP, and floods spread massively in this period, which led to the decline of Shijiahe culture. The main causes of hydro-environmental evolution in the research area are the fluctuation of sea level and the aggradation of fluvio-lacustrine sediments.

Poyang Lake is the largest freshwater in China. Continual monitoring on its hydrologic changes can supply basic data for ecological environment researches and is favorable for studying the exchange between the Poyang Lake and the Yangtze River or other rivers in the watershed. Hydrologic changes of Poyang Lake are essential to land-surface process studies and water resources management. Altimeter data and high-frequency MODIS images were used in this paper to obtain water levels, inundation extents and lake storage changes of Poyang Lake during 2000-2015. Then water exchange between Poyang Lake and Yangtze River was estimated based on water balance equation. The results showed that lake inundation presented a large fluctuation and an obvious seasonality. The maximum area was 3600 km ², approximately 7.5 times of the minimum (482 km ²). Areas in the years 2004, 2007, 2009 and 2011 were smaller and the situation improved after 2012. The extent shrunk to less than 500 km ² in dry season (January, February and December) when water level at Hukou Station was only 4.71 m. At that time, the water surface inclined from south to north, and the water level difference between south and north could reach 2.59 m. The increase of lake storage in dry season was 3 km ³ relative to the minimum during the study period. Surface extent was usually greater than 2670 km ² in wet season (June-September) when water level was higher than 15 m and the surface was almost flat. The increase of lake storage in wet season was 12 km ³ relative to the minimum during 2000-2015. Water exchange between Poyang Lake and Yangtze River was from 7 km ³ to 40.66 km ³ during the research period and water from the lake to the river occurred in 93.33% time of the year. The flow water volume had obvious seasonality. Usually, the exchanged volume in May and June was more than that of July and August when precipitation increased in the upper-middle reaches of Yangtze River, thus more volume of the main stream and water was hindered to flow from Poyang Lake to Yangtze River.

Sediment from the Yellow River is the main material source in the formation of several landform types in the lower reaches of the Yellow River. This sediment deposition changes the surface soil structure and its organic carbon content. Here, the distribution characteristics of soil organic carbon components and their influencing factors were analyzed in the Kaifeng and Zhoukou areas based on field investigations, laboratory experiments and spatial analyses. The statistical results showed that the TOC, AOC and NOC contents were 0.05-30.03 g/kg, 0.01-8.86 g/kg and 0.02-23.36 g/kg, respectively. Contents were higher in the surface (0-20 cm) layer than those in the lower (20-100 cm) layer, and the sequence of change from high to low content in a single layer was TOC, AOC and NOC. The NOC content contributed to TOC more than AOC did. The geostatistical characteristics obtained by using the GS+ software showed that the nugget coefficients of TOC, AOC and NOC were between 0.50 and 0.67, with a moderate degree of spatial correlation. This indicates that structural and random factors commonly influence variations in TOC, AOC and NOC, and that the action intensity between them is similar. The overall trend in all areas was that the contents of TOC, AOC and NOC were relatively consistent with those from the 0-20 cm to the 20-100 cm layer, although a transition from high-value region to low-value region was obvious. The spatial distribution and the statistical characteristics of TOC, AOC and NOC contents indicates that the high-value region is located in the area less affected by sediment, and the low-value region is located in the area which the Yellow River floods. The old riverway of the Yellow River has a value somewhere in between. In flooded areas, the TOC, AOC and NOC contents were the lowest in the burst place, and then contents gradually increased in the direction of water flow and passed area. Spatial variation in the NOC and AOC contents reflected the regions of TOC spatial variation and accumulation well. Throughout history, the banks of the Yellow River have been overflowed, causing river realignment and serious flooding. The resulting sediment deposition changed the surface particulate matter composition and soil organic matter content. It was found that the distribution of deposited sediment in the flooded area and old riverway of the Yellow River, the farming process and the cultivation history were all important factors affecting SOC composition content and spatial distribution. In addition, the organic matter input, soil particle composition and their dynamic relationship were the key factors affecting soil structure and organic carbon components. In short, increasing organic matter content and improving soil structure are effective ways to improve soil quality and to achieve sustainable regional agricultural development.