Si-Yi Zhang

The Beijiang River Basin is an important ecological security protection area and water source supply area in Guangdong Province. This study assesses the spatiotemporal distribution characteristics of watershed water quality based on on-site monitoring data and multivariate statistical analysis. The results indicate that PO₄³⁻P concentrations peak during the flood season, whereas pH, NO₃⁻-N, and total nitrogen (TN) reach their highest levels during the autumn normal-flow period. Spatially, water quality follows a gradient of upstream > downstream > midstream, with the midstream region identified as the primary zone of water quality degradation. Future non-point source (NPS) pollution characteristics in the Beijiang River Basin are influenced by land use/cover change (LUCC) and climate change, showing significant variation across Shared Socioeconomic Pathway (SSP) scenarios. Under SSP126, precipitation increases at the slowest rate, with a peak annual value of 1599.77 mm during 2031–2040 and an average basin temperature of 19.61 °C. In contrast, SSP245 exhibits a marked increase in precipitation, reaching 1802.92 mm by 2061–2070. Under SSP585, annual precipitation rises to 2200.04 mm, with temperatures approximately 0.5 °C higher than those under SSP126. Simulations based on the improved ESP-PLUS model indicate that, under the natural development scenario (NDS), expansion of construction land increases urban runoff pollution by 32.97%. Under the economic development scenario (EDS), 1023 km² of ecological land is lost, significantly weakening pollution interception capacity, while construction land increases by 26.01%. In contrast, the coordinated development scenario (CDS) reduces ecological land loss by more than 60% compared to EDS through balanced development and conservation, thereby maintaining the basin’s pollutant purification function. Overall, future nitrogen and phosphorus loads in the watershed are projected to first decrease and then increase. Accordingly, differentiated management strategies are recommended, emphasizing the coordinated development of economic growth and ecological protection, and providing a scientific basis for controlling NPS pollution under changing climatic conditions.

This study takes the Beijiang River Basin in Guangdong Province as an example, examining the changes in land usage throughout time and space between 1980 and 2020. Using multidimensional ecosystem service functions and the loop theory, this study constructs ecological constraints (ES) for the Beijiang River Basin. Based on these ecological constraints, an ES-PLUS model is developed to simulate future land cover changes under multiple scenarios in the Beijiang River Basin by 2050. The results indicate the following: (1) Currently, the major land use types in the Beijiang River Basin are forest, cropland, and grassland, accounting for over 95% of the area. Significant changes in land use were observed between 1980 and 2020, including the severe degradation of forests and grasslands, a notable expansion of construction land, intense human–land conflicts, and the highest single land use dynamic degree for unused land at 5.67%, with a comprehensive land use dynamic degree of 0.18%. (2) In the four development scenarios of the Beijiang River Basin in 2050, construction land increased by 32.97%, 74.75%, 26.01%, and 45.50%, respectively, suggesting that ecological constraints as flexible constraint spaces can effectively control the disorderly expansion of construction land. Therefore, formulating ecological protection policies, optimizing the land use structure in the Beijiang River Basin, and constructing ecological sources and corridors in line with the distribution of urban areas, roads, and railroads in the basin may offer direction for the best use of land resources, the preservation of the environment, and sustainable growth in the Beijiang River Basin.

Soil structure is an important factor interacting with soil erosion and sediment processes. However, few studies have focused on the relationship between soil macroporosity and soil erosion across different terrains. The aim of this study was to quantify and compare soil properties and macroporosity characteristics in collapsing gully areas and to explore their impact on the formation and development of collapsing gullies. Soil cores were excavated at different positions of a typical collapsing gully and then scanned to analyze soil macropores. Soil properties and saturated hydraulic conductivity were also investigated. The results showed that the contents of sand, silt, and clay, the mean weight diameter of aggregates, and the infiltrate rates varied at different positions. The valley had the greatest macroporosity (1.09% ± 0.33%), the number (5919 ± 703), volume (1468 ± 194 mm ³ ), and surface area (10.4 ± 2.6 m ² ) of macropores, as well as the mean volume (16.8 ± 7.4 mm ³ ) of macropores >1 mm ³ , whereas these indices were lowest at the slope (0.15% ± 0.14%, 1189 ± 747, 266 ± 188 mm ³ , 1.7 ± 1.4 m ² , and 10.6 ± 2.9 mm ³ , respectively). The macroporosity and the number of macropore decreased with increasing depth but were also influenced by the erosion and sediment processes. The processes of sediment and the roots of vegetation also influenced the orientation of the macropores. Macropore characteristics at different sites of the collapsing gullies affected the soil water infiltration and hydraulic conductivity and further affected the processes of water erosion and mass erosion.

Shrub encroachment has been a worldwide phenomenon, but the interactions between the surface hydrological cycle and the shrub‐encroached landscape at different hillslope positions remain poorly investigated. The present study was undertaken to explore the interactions between the water infiltration patterns affected by shrub encroachment. At four slope positions of a hillslope encroached by Caragana microphylla Lam, soil water content and temperature were continuously measured at 10‐min intervals at four or five depths in both the presence (shrub patches) and absence (grass matrix) of shrubs. Then, the infiltration of rainfall and meltwater was estimated based on analyses of the above data. The rainfall infiltration ratios (IRs) of grass matrix were as high as 0.78 ± 0.08, except at the lower site, which had a value of only 0.47. The IRs of shrub patches increased from 0.38 at the top site to 0.77 at the lower site. In snowy years, snow and ice were blown upward by wind and accumulated in the shrub patches and their leeward areas, which resulted in higher water input for the shrub patches than for the grass matrix. Shrub encroachment changed the microtopography and soil properties of the hillslope and further affected the surface hydrological processes. The feedbacks between shrub encroachment and water infiltration varied among sites of the hillslope, which may in turn have affected the development of shrub patches.

Vegetation canopy interception (Ic) of precipitation is a considerable component of the global hydrological cycles. Although the measurement and modeling of canopy interception have been explored worldwide at the individual, stand or ecosystem scale, it is still unclear how to recognize this process at the regional or global scales within the context of global climate change. In this study, a revised Gash model was employed to estimate canopy interception based on remote sensing and meteorological data. The spatial and temporal variations in Ic were investigated and the main environmental factors were explored in China for the 2000–2018 period. The results showed that the revised Gash model performed well in modeling canopy interception at the regional scale compared with the PML_V2 dataset product and the in-situ measurements. The average annual Ic in China from 2000 to 2018 was 166.55 mm, with a significant decreasing spatial pattern from the Southeastern to the Northwestern regions. The ratio of canopy interception to precipitation (Ir) displayed a similar spatial pattern, with an average value of 22.30%. At the temporal scale, the mean annual Ic significantly increased at a rate of 1.79 mm yr⁻¹ (p < 0.01) during the study period, and the increasing trend was more pronounced during the 2000–2009 period, at a rate of 3.34 mm yr⁻¹ (p < 0.01). In most vegetation types, except for the deciduous broad-leaved forest and temperate desert, canopy interception showed a significant increasing trend (p < 0.01). Precipitation, temperature, and the normalized differential vegetation index (NDVI) were considered to be the main factors affecting the variations of Ic in China during the last two decades, with specific dominant factors varying in different areas. Specifically, precipitation was considered to control the variations of Ic in the Northwestern regions, temperature mainly influenced the Southern regions, and the NDVI was identified as the main factor in regions where significant ecological conservation projects are established, such as the Loess Plateau. Our findings are expected to not only contribute to the understanding of regional ecohydrological cycle but also provide valuable insights into the methodology of interception modeling at the regional and global scales.

More than 1100 lakes covering an area greater than 4500 km² are located on the Tibetan Plateau, and these lakes are important regulators of several large and famous rivers in Asia. The determination of hydrological changes that have occurred in these lakes can reflect climate change and supply scientific data to plateau environmental research. Data from high frequency (moderate-resolution imaging spectro-radiometer) MODIS images, altimetry, and the Hydroweb database collected during 2000–2015 were integrated in this study to delineate the detailed hydrological changes of 15 lakes in three basins—Inner Basin, Indus Basin, and Brahmaputra Basin—on the southern Tibetan Plateau. Seven of the 10 lakes in the Inner Basin presented increasing trends with various intensities, and the increasing rates in the area of four lakes (Nam Co, Selin Co, Zhari-namco, and Ngangze) were 1.62, 28.81, 2.27, and 3.70 km²/yr, respectively. The yearly increases in volume of the four lakes were 3.6, 9.44, 6, and 2.36 km³, respectively. A water balance equation was established for the four lakes based on lake volume changes to illustrate the contributions of precipitation, ground runoff, evaporation, and other factors. The results revealed that surface runoff was the major contributor to expansion, and lake surface evaporation was almost 2.76–3.86 times that of lake surface precipitation. The two lakes in Indus Basin, Rakshastal and Mapam Yumco, presented a slight retreat. As a representative of Brahmaputra Basin, Yamzho Yumco underwent a retreat of –3.49 km²/yr in area, –0.39 m/yr in level, and –0.19 km³/yr in volume. Decreasing precipitation, increasing evaporation, and the operation of a hydrological project were the main causes of its constant retreat.

Soil water conditions play an important role in the formation of a collapsing gully, but we are still at the early stages of understanding how the soil water changes on the slope after different rainfall events due to a lack of high-frequency continuous field observations. This study aimed to reveal the response of soil water dynamics to rainfall events for different slope aspects and positions based on continuous multi-depth observations of soil water on a typical collapsing gully slope from 2017 to 2019 in Wuhua County, Guangdong Province, China. The vegetation characteristics and soil properties were investigated, and the storage of soil water was also calculated. The results showed that the dynamics and storage of soil water varied with the slope aspect, slope position and vegetation cover. The response time of the soil water to intensive rainfall events on the sunny slope was shorter than that on the shady slope, while soil water storage in the sunny slope was significantly lower than in the shady slope (p < 0.01). For the different slope positions, the soil water response time to the intensive rainfall events on the upper slope was shorter than that in the middle slope, while the soil water storage in the middle slope was significantly higher than on the upper slope. This was mainly due to the redistribution runoff from the upper slope to middle slope, delaying the process by which rainwater infiltrated into the soil layers. Moreover, vegetation significantly allayed the response of soil water dynamics to an intensive rainfall event but increased the storage of soil water, owing to the protection of soil surface from rain and conservation of high soil clay content. The bare area in the middle position of the sunny slope was speculated to be the potential source of the collapsing gully because it lacked the cover of vegetation. Our findings highlight the importance of soil water dynamics on the formation of a collapsing gully and provided valuable insights for the optimization of soil conservation and management practices for collapsing erosion.

Background: The amyloid cascade hypothesis of Alzheimer’s disease (AD) posits that amyloid-β (Aβ) protein accumulation underlies the pathogenesis of the disease by leading to the formation of amyloid plaques, a pathologic hallmark of AD. Aβ is a proteolytic product of amyloid-β protein precursor (AβPP; APP), which is expressed in both neurons and astrocytes. Although considerable evidence shows that astrocytes may play critical roles in the pathogenesis of AD, the longitudinal changes of amyloid plaques in relationship to AβPP expression in astrocytes and cellular consequences are largely unknown. Objective: Here, we aimed to investigate astrocyte-related pathological changes of Aβ and AβPP using immunohistochemistry and biochemical studies in both animal and cell models. Methods/Results: We utilized 5XFAD transgenic mice and found age-dependent upregulation of AβPP in astrocytes demonstrated with astrocytic reactive properties, which followed appearance of amyloid plaques in the brain. We also observed that AβPP proteins presented well-defined punctate immuno reactivity in young animals, whereas AβPP staining showed disrupted structures surrounding amyloid plaques in older mice. Moreover, we utilized astrocyte cell models and showed that pretreatment of Aβ ₄₂ resulted in downstream astrocyte autonomous changes, including up regulation in AβPP and BACE1 levels, as well as prolonged amyloidogenesis that could be reduced by pharmacological inhibition of BACE1. Conclusion: Collectively, our results show that age-dependent AβPP up regulation in astrocytes is a key feature in AD, which will not only provide novel insights for understanding AD progression, but also may offer new therapeutic strategies for treating AD.