Alluvial fans are common fan-shaped depositional landforms that develop at the outlets of mountain rivers or gullies. Mature and stable alluvial fans are important areas for both human habitation and production in mountainous regions, but they also pose potential hazards associated with flash floods and debris flows. Research on alluvial fans enhances our understanding of regional environmental dynamics and geomorphic evolution, as well as contributes to the mitigation of flood and debris-flow hazards. Therefore, it holds significant scientific value and practical importance. Although considerable research has been conducted on alluvial fans, both domestically and internationally, in recent decades, much of it has focused on geomorphology (morphometry), sedimentary history and characteristics, and historical environmental reconstruction (or inversion). Investigations into the mechanisms of fan development and their geomorphic effects remain relatively underexplored. This review systematically summarizes the key advancements in the research on the dynamic processes, mechanisms, and morphodynamics of alluvial fan development. We first provide an overview of current technical approaches applied in the study of alluvial fans, including field investigations and model experiments. Then, we summarize four critical aspects of fan dynamics processes and development mechanisms: primary and secondary processes; mechanisms of flow channel avulsion; interactions between tributary and main rivers; and the impact of alluvial fan development on sediment production, transport, and geomorphic processes. Finally, we discuss several areas that require further attention in future research. Currently, field observations and monitoring of the dynamic processes of alluvial fan development are inadequate. As an essential complement to post-event field surveys and experimental model research, there is an urgent need to enhance field observations in order to expand and deepen our understanding of alluvial fan development mechanisms. This will promote scientific insights into sediment dynamics and geomorphic processes within regional river systems.

The spatial disparities in resource endowments and industrial development levels across provincial-level regions in China lead to diverse water resource pressures. Economic trade redistributes water resources, causing spatial shifts in water demand. Water scarcity poses a significant bottleneck to regional development. Thus, examining water resource pressure distributions, patterns, and their drivers within economic supply and demand chains is crucial for sustainable development and ecological conservation. This research explores spatiotemporal changes in inter-provincial water resource pressure transfers and their drivers in China from 2007 to 2017. It analyzes the dynamics of scarce blue and grey water flows among 30 provincial-level regions (excluding Xizang, Hong Kong, Macao, and Taiwan due to the lack of data) and their impacts on inter-provincial transfers. Key drivers such as technological advancements, environmental pressures, industrial structures, and urban-rural consumer demand are decomposed to assess their contributions to water resource pressure. Results show an upward trend in water pressure transfers driven by final demand. Southwest and southeast regions, experiencing lower local water pressures, transfer significant pressures to other areas. Northwest region emerges as major exporters of scarce blue water, while central provinces shift from exporters to importers. This study provides insights into inter-provincial water resource pressure transfers, aiding water security strategies and sustainable development planning in China.

The riparian zone is a key area that affects river water quality, while the impacts of the riparian landscape pattern on water quality at various spatial scales is still controversial. Quantifying the spatial scale effects of riparian landscape patterns on water quality and determining key landscape indicators that affected water quality at various spatial scales were crucial for effectively improving river water quality. The Recursive Feature Elimination-Random Forest (RFE-RF) algorithm and Redundancy Analysis (RDA) were employed to analyze the response relationship between river water quality and riparian landscape patterns across different spatial scales in the Miyun Reservoir Basin, based on data collected from January 2022 to June 2023. Total nitrogen (TN) was the primary pollutant affecting the water quality of rivers in the study area. The riparian buffer zone scales with the strongest impact of landscape pattern on TN, total phosphorus (TP), ammonia nitrogen (NH₃-N), chemical oxygen demand (COD), and permanganate index (COD_Mn) were 100 m, 800 m, 200 m, 25 m, and 400 m, respectively. The riparian landscape patterns had the stronger interpretability for TN, TP, NH₃-N, and COD, while the interpretability of the riparian landscape pattern of COD_Mn was relatively weak. With the increase of the riparian spatial scale, there were significant fluctuations in the overall interpretability of landscape indicators on river water quality: The riparian landscape patterns at 25 m and 100 m had higher interpretabilities for the overall water quality, reaching 64.8% and 58.9%, respectively. The proportion of forest landscape, the average fractal dimension of grassland, and the patches density of bare land were the most important landscape indicators that influenced river water quality at the riparian spatial scales of 25-100 m, 200 m, and 400-800 m, respectively. This study helps to understand the impact mechanism of landscape patterns on water quality at various riparian spatial scales, and provided scientific basis for effective protection of river water quality.

The mixing of saline-fresh water masses is an important hydrological phenomenon in the Yangtze River Estuary (hereafter Yangtze Estuary), which influences the regional ecological security. Here we use historical local gazetteer, historical records of salt industry, traditional maps and historical charts to establish the relationship between anthropogenic salt-making, reclamation activities and the saline water distribution patterns. Meanwhile, on the basis of a combination of quantitative and qualitative analysis, we attempt to reveal the spatio-temporal water mixing pattern and identify the evolution mechanism of the mixing zone of saline-fresh waters in the Yangtze Estuary from the 16th to the 20th century. Furthermore, the causes and effects of the above evolution process were discussed based on the principles of estuarine hydrology and geomorphology. The results show that: (1) Since the 16th century, in response to the seaward expansion of the Yangtze Estuary, the bifurcation and the narrowing of the Estuary have promoted the continuous downward movement of the salt and fresh water mixing zone, with differences between the northern and southern branches. (2) The upper boundary of saline-fresh water mixing zone in the southern branch was located at the line dividing Shiqiao Estuary and Wusongkou during the Longqing and Wanli periods (1569-1574) of the Ming Dynasty, and this line moved down to Tongsha Shoal during the Daoguang period (1842) of the Qing Dynasty, with an annual downward rate of 285.7 m/a. (3) Since the 16th century, the isohaline in the nearshore section of the Yangtze Estuary moved inwards within the northern branch and downward within the southern branch, with its main axis rotating counterclockwise from S-N to SE-NW, and a total reversal of 54° from 1569 to 1980. (4) The continuous migration of saline-fresh water of the Yangtze Estuary since the 16th century is a naturally driven evolution process. Since the late 20th century, with the driving of the engineering, the geomorphology change of the estuary has accelerated the natural trend of the change of the saline-fresh water mixed zone. The artificial control based on the natural estuarine trend is the main driving factor for the evolution of the saline-fresh water mixing in the future. (5) Reducing and eliminating the effect of the northern branch salt tide on the fresh water resources and environment of the Yangtze Estuary is the primary goal of the ecological regulation of the Estuary. Facing the situation of sediment supply reduction and sea level rise in the Yangtze Estuary, the geometric change of the estuary driven by human coastal engineering projects will become the main factor affecting the change of saline and fresh water mixing.

Based on extensive and detailed field investigations in the Zoige Basin on the NE Tibetan Plateau, the Niangyiqu (NYQ-A) section was found on the second terrace of the Yellow River in the basin. Through systematic stratigraphic division and sample collection in the field, combined with laboratory analysis of grain size, geochemical elements, paleontology, and OSL/AMS ¹⁴C dating, different sedimentary layers in the section and its paleoenvironmental significance were identified. Furthermore, this study focuses on investigating the lake level changes of the Zoige paleolake recorded by the lacustrine deposits and their causes. The results show that: (1) The sedimentary stratigraphy of the section, from bottom to top, consists of the following layers: deep lacustrine deposits A, shallow lacustrine deposits A, deep lacustrine deposits B, shallow lacustrine deposits B, overbank flood deposits of the Yellow River, aeolian loess, and modern meadow soil. (2) The deep lacustrine deposits A, dating to 51.82±2.34 ka, records a deep lake environment of the Zoige paleolake during the (Marine isotope stages) MIS 3c period. During this period, warm and wet climate conditions led to high precipitation and glacial meltwater inflow, resulting in a high paleo-lake level. The shallow lacustrine deposits A formed between 51.01±2.19 and 39.54±1.72 ka, indicating a shallow lake environment of the Zoige paleolake during the MIS 3b period. During this period, cold and dry climate conditions caused a lowered paleo-lake level. The deep lacustrine deposits B accumulated between 39.18±2.03 and 36.77±1.66 ka, inferring a deep lake environment of the Zoige paleolake during the MIS (Marine isotope stages) 3a period. During this period, warm and wet climate conditions led to increased precipitation and glacial meltwater, raising the paleo-lake level once again. (3) Notably, shallow lacustrine deposits B records a sudden transition of the Zoige paleolake from a deep lake environment to a shallow marshy environment at 36.77±1.66 ka during the MIS 3a period. Based on the previous studies on the development and evolution of the Zoige paleolake, our results further confirm that under the influence of warm and humid climate and the strong tectonic activity of the eastern segment of the East Kunlun Fault, the headward erosion and downcutting of the paleo-Yellow River intensified. At ca. 37 ka, the paleo-Yellow River captured the Zoige paleolake, causing the continuous discharge of the paleolake water and the transition to warm shallow marshy environment. This environment created favorable living conditions for aquatic gastropods (Radix) and numerous mammals (such as the woolly rhinoceros and primitive cattle). These results are of significance in understanding the evolution of the river-lake system within the Zoige Basin.

Under the guidance of the ecological protection and high-quality development strategy for the Yellow River Basin, it is essential to comprehensively analyze the characteristics of soil erosion and changes in the water environment in order to identify the governance status and promote coordinated management in this region. This study collects comprehensive data on sediment transport, water quality monitoring, land use and socio-economic factors across the Yellow River Basin, and constructs a two-dimensional space of sediment transport modulus and water quality index. It identifies the characteristics of soil erosion and water environment and their influencing factors, and classifies the governance status of the main tributaries of the Yellow River and proposes relevant management strategies. The results show that: (1) The long-term average sediment transport modulus for 264 hydrological stations in the study area from 2011 to 2020 varies from 0 to 4893 t/km². Areas with high sediment transport modules are concentrated between the Toudaoguai and Tongguan sections. Of the 276 water quality monitoring sites, 173 sites (63%) have good or excellent water quality. (2) The sediment transport modulus is significantly positively correlated (p < 0.01) with factors such as the ratio of area covered by loess, the rate of vegetation restoration, the ratio of terraces and dam farmlands, and the proportion of farmland with slopes greater than 8°. The water quality index is significantly negatively correlated (p < 0.01) with factors such as the ratio of area covered by loess, the rate of vegetation restoration, the ratio of terraces and dam farmlands. (3) In the sediment transport modulus-water quality index space, 60 major tributaries of the Yellow River were classified into four types: ecologically clean type, erosion control dominant type, water quality improvement dominant type, and integrated erosion control and water quality management type. (4) An indicator system was developed based on three key indicators: the proportion of terraced farmland with slopes greater than 8°, the intensity of check dam construction and the vegetation restoration index. This indicator system determines the direction of soil erosion management for 16 tributaries with a sediment transport modulus greater than 500 t/(km² a). In 30 major tributaries with a water quality index below 80, total phosphorus and ammonia nitrogen were identified as the main pollutants and appropriate control measures were proposed. The results are expected to provide new insights into the coordinated management of water and sediment in the Yellow River and to offer policy suggestions for the implementation of the river basin management principles of "water conservation first, spatial balance, systematic management, and joint efforts of the government and the market".