[Objective] The Emeizhou braided channel in the lower section of Anqing is situated in the lower reaches of the Yangtze River. Due to the significant variations in scouring and silting in the braided channel of the Anqing section, the variations in diversion ratio exhibit certain periodicity under the new water-sediment regime. This study aims to investigate the variations in the diversion ratio of the left branch and the stability of the main navigation channel conditions under the new water-sediment regime, as well as the potential impacts on water-related projects in the Mawo area of the left branch that may arise from near-bank siltation at the confluence of the braided channels in the near future. [Methods] By integrating a two-dimensional hydrodynamic model and utilizing the latest field observation data on water and sediment, this study tracked and analyzed the periodic evolution characteristics, influencing factors, and flow characteristics of this braided channel. Additionally, recommendations for the future management direction of the Anqing section were proposed. [Results] In recent decades, the thalweg swing amplitude in the Emeizhou braided channel was relatively small overall, and the river regime remained relatively stable, except for areas near the diversion point of Emeizhou, the head of the right branch, and certain localized river sections of the middle branch. After the impoundment of the Three Gorges Reservoir, the left branch of Emeizhou has experienced slight scouring, while the right branch was expected to maintain a shrinking trend for some time. Numerical simulation results of the flow characteristics of the braided channel showed that from 1998 to 2006, the middle branch developed rapidly, characterized by increased flow velocity and a shift of the main flow towards the Emeizhou on the right bank, while the flow velocities in the left and right branches decreased slightly. From 2006 to 2021, under the guidance and regulation of river (navigation) channel engineering, the diversion ratio of the Emeizhou braided channel remained basically stable, the development of the middle branch slowed down, and changes in flow velocity were mainly concentrated in the lower section of the middle branch. [Conclusion] We recommend to closely monitor the effectiveness of the existing river regulation projects in the Anqing section and to implement relevant measures when necessary.
[Objective] Submerged dams, as an important component of waterway regulation projects, can prevent from river and coastal erosion and also alter river flow patterns and improve river habitat environments. This study selects juvenile crucian carp as the target species to investigate the effects of W-shaped submerged dams with different particle size compositions on flow velocity distribution and the aggregation of target fish. It aims to clarify the habitat improvement effectiveness of W-shaped submerged dams and provide a theoretical basis for the construction of ecological conservation zones in cut-off river sections. [Methods] Crucian carp, a dominant fish species in the Pinglu Canal, were selected as the experimental species. Experiments on the influence of W-shaped submerged dam groups on flow structure and typical fish aggregation behavior were conducted in an annular flume. The W-shaped submerged dams were set with three particle size compositions ([5,10] mm, [5,20] mm, [10,20] mm), and four flow rate conditions (0.03, 0.045, 0.06, 0.09 m3/s) were set up. Under each test condition, 30 juvenile experimental crucian carp were placed, and the entire experimental process was recorded using a Nikon D7500 camera. Tracker software was used to collect and record the positions, frequencies, and total time where the experimental fish stayed for more than 1 minute. The average fish aggregation rate was used to evaluate the attraction effect of the W-shaped submerged dams on fish, and the flow pattern diversity index was used to quantify changes in flow patterns. [Results] Under the action of W-shaped submerged dams of the same particle size, as the flow rate increased from 0.03 m3/s to 0.09 m3/s, the area and flow velocity of the backwater zone upstream of the weir in the study area continuously increased, while the area of the triangular recirculation zone formed downstream of the weir gradually decreased. Under the action of W-shaped submerged dams of different particle sizes, those composed of larger particle sizes (10-20 mm) exhibited better permeability, smaller velocity gradients compared to smaller particle size groups, and higher flow pattern diversity. Analysis of the influence of W-shaped submerged dam groups on the aggregation behavior of experimental fish showed that at a flow rate of 0.09 m3/s, the W-shaped submerged dams composed of 10-20 mm particle sizes had the highest number of stays in fish aggregation areas, reaching 85 times. These dams composed of larger particle sizes (10-20 mm) had high habitat diversity, providing better habitat and shelter for experimental fish. As the flow pattern diversity index increased, the average fish aggregation rate also showed an increasing trend. The river flow pattern diversity index and the average fish aggregation rate exhibited a linear relationship. [Conclusion] W-shaped submerged dams composed of larger particle sizes have high habitat diversity and can provide better habitat and shelter for experimental fish. In the construction of ecological conservation zones in cut-off river sections of artificial canals, it is recommended to select large-particle-size submerged dam schemes with better permeability effects. A good correlation is observed between the average fish aggregation degree and the flow pattern diversity index, enabling quantitative assessment of habitat diversity and providing theoretical support for research on river habitat heterogeneity and ecological optimization design. In the future, the long-term effects of different submerged dam design parameters on the ecosystems of target river sections can be further explored, and more influencing factors can be incorporated to investigate the ecological development of canals.
[Objective] This study aims to systematically characterize the spatiotemporal distribution patterns and ecological risk levels of persistent organic pollutants (POPs)—including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs)—in the Jiangsu section of the Beijing-Hangzhou Grand Canal. Seasonal variations between wet and dry periods were examined, and pollutants posing significant ecological threats were identified to support water quality assessment, pollution-control prioritization, and risk management in artificial canal systems. [Methods] Water samples were collected from designated monitoring sites during both wet and dry seasons to capture POPs’ spatial distribution under distinct hydrological conditions. After standardized pretreatment, concentrations of individual POPs were quantified using a 7890-5975C gas chromatography-triple quadrupole mass spectrometry system (GC-MS/MS). Pollution loads and longitudinal variation trends were subsequently analyzed. Ecological risks of PAHs, PCBs, and OCPs were evaluated using the risk quotient method, enabling the identification of high-risk pollutants at both category and compound levels. [Results] During wet season, total concentrations of 16 PAHs ranged from 44.34-56.01 ng/L (median: 45.92 ng/L), increasing substantially to 99.05-198.04 ng/L (median: 128.08 ng/L) in the dry season, nearly tripling and indicating a pronounced seasonal accumulation effect. Total concentrations of 18 PCBs exhibited a similar pattern, increasing from 94.06-123.04 ng/L (median: 95.09 ng/L) during the wet season to 120.75-137.79 ng/L (median: 124.66 ng/L) in the dry season. For OCPs, total concentrations ranged from 417.86-676.68 ng/L (median: 453.74 ng/L) in the wet season and increased to 560.39-673.11 ng/L (median: 617.21 ng/L) in the dry season, indicating comparatively higher and persistent contamination relative to PAHs and PCBs. Despite the relatively narrow longitudinal variation along the canal, pronounced seasonal differences were observed. The recurrent elevation of pollutant concentrations in the dry season suggests that hydrological regulation is a key driver of POPs dynamics in the artificial canal system. Reduced river discharge weakens dilution capacity, resulting in the concentration and retention of hydrophobic pollutants in the water column. Lower water levels and intensified sediment-water interactions during the dry season may enhance sediment resuspension, further releasing historically deposited POPs into the overlying water. Additionally, lower winter temperatures inhibit photolytic and microbial degradation, prolonging the environmental persistence of POPs. Reduced hydrodynamic dispersion in the dry season also limits downstream transport, promoting local accumulation of pollutants. Anthropogenic activities, such as increased domestic heating and industrial energy demand during colder months, may also contribute additional pollutant inputs to the system. Comparison with other rivers globally revealed distinct contamination profiles for different POP categories. PAH concentrations in the study area were generally lower than those reported for many industrialized or highly urbanized rivers, reflecting limited direct emissions from combustion sources in the region. PCB concentrations fell within the intermediate range reported internationally, indicating residual sources associated with economically developed regions, intensive industrial activities (e.g., textile, electronics), and historical industrial zones along the Jiangsu section of the canal, which likely contribute to elevated PCB levels. In contrast, OCP concentrations were relatively high compared with both domestic and international rivers, likely due to Jiangsu Province being a major agricultural production area, where fertilizers and livestock wastewater carry OCP residues. Collectively, these findings indicate that the aquatic ecosystem of the canal remains under non-negligible environmental pressure. Ecological risk assessment revealed an overall moderate risk level, yet significant differences existed across compound classes and seasons. A total of 15 PAHs, 11 PCBs, and 15 OCPs exhibited moderate-to-high ecological risk during at least one sampling period. The number of high-risk compounds increased during the dry season, consistent with the observed elevation in pollutant concentrations. Among all detected compounds, benzo[b]fluoranthene, PCB180, PCB189, and endosulfan I contributed disproportionately to the total ecological risk. These compounds share characteristics of strong hydrophobicity, high chemical stability, resistance to degradation, and high bioaccumulation potential, collectively making them the primary drivers of ecological risk. [Conclusion] This study provides a comprehensive assessment of POP pollution characteristics, seasonal dynamics, and ecological risk profiles within an artificial canal system. The identification of key risk pollutants and the elucidation of hydrological control mechanisms offer valuable guidance for water quality assessment, pollution control prioritization, and ecological risk mitigation in artificial waterways, while providing a transferable framework for POP risk management in similar engineered systems.
[Objective] To address the high cost and limited sustainability of conventional river-dredging techniques, this study proposes a novel, environmentally friendly, and energy-saving dredging approach—a pressure-difference-driven passive rotating flow turbulence device. It aims to clarify the mechanisms by which different blade types (curved, twisted, and flat) of the device affect local scouring and sediment transport, and to identify the blade type with the optimal scouring-silting performance, thereby providing an innovative technical method and structural optimization basis for targeted and directional river dredging. [Methods] The study was conducted through flume-based physical model experiments. Passive rotating flow turbulence devices with three blade types (curved, twisted, and flat) were designed and fabricated, with a single-pile device (without blades) as the control group. Tests were conducted under constant flow (13.62 L/s) and water depth conditions, with a movable bed paved using fine sand (median grain size d50=0.16 mm) having a gradation similar to the prototype sand of the Tarim River. Three-dimensional laser scanning technology was employed to accurately measure topography, and obtain the area, volume, and morphological characteristics of scouring and silting. An acoustic Doppler velocimeter (ADV) system was used to measure the time-averaged flow velocity and turbulence intensity distribution in the flow field around the device. By comparatively analyzing the scour hole development process, flow velocity field structure, turbulence characteristics, and final scouring-silting equilibrium state (with the scouring-silting ratio K as the core evaluation indicator), the dredging performance of devices under different blade types was assessed. [Results] The experimental results demonstrated that blade type significantly affected the device’s rotation characteristics, flow field disturbance capability, and ultimate scouring-silting performance. (1) Flow field characteristics: the curved-blade device achieved stable continuous rotation. Due to the Magnus effect, the main flow was noticeably deflected toward the side rotating with the current (right bank), with the bottom flow velocity at the right bank increasing by about 49.6% compared to the left bank, which effectively accelerated the initiation of bed sediments. The peak bottom turbulence intensity increased by about 89.47% compared to the flat-blade device, with the most intense flow field disturbance. The twisted-blade device rotated discontinuously, while the flat-blade device remained largely stationary. Both exhibited weaker flow field disturbance capability and less asymmetry than the curved type. (2) Scouring/silting morphology and performance: the curved-blade device yielded the highest scouring-silting ratio (K=94.6%), 48.5% and 16.3% greater than that of the twisted (K=46.1%) and flat (K=78.3%) types, respectively. The curved blade produced a distinctly asymmetric scour hole biased toward the right bank, with a large affected area and an interwoven pattern of scouring and silting zones, which facilitated downstream sediment transport. (3) Scour hole development: the scouring process could be divided into four stages: initial, transition, disturbance, and stabilization. The curved-blade device exhibited the fastest scour-depth development rate across all stages, particularly during the disturbance stage (device rotating continuously), efficiently disturbing bed sediments and enlarging the scour hole. [Conclusion] Among the passive rotating flow turbulence devices, the curved blade demonstrates the best comprehensive performance in scouring and sediment transport, owing to its ability to induce stable continuous rotation, produce a significant Magnus effect, and maximize the enhancement of bottom turbulence and flow velocity deflection, with a scouring-silting ratio significantly higher than other types. The device has a simple structure and requires no external power, offering a novel, environmentally friendly, and energy-saving approach for targeted river dredging. The findings clarify the critical influence of blade type, thereby providing a direct theoretical and experimental basis for further optimization of the device’s structural parameters and engineering deployment schemes.
[Objective] In recent years, excessive exploitation of groundwater resources has led to severe depletion of water resources in the Dusitu River Basin, limiting the healthy development of the local ecological environment and economy. Therefore, accurately acquiring the long-term spatiotemporal change characteristics of water storage is crucial for the sustainable utilization of water resources. [Methods] This study employed the Bayesian three-cornered hat method to integrate three GRACE Mascon products, combined with the soil water and snow water components simulated by the GLDAS model, to generate high-precision groundwater storage change results for the Dusitu River Basin. The results were validated for accuracy using measured groundwater level data from 2018 to 2021 and the water body area of Bulong Lake extracted from satellite remote sensing. The cross wavelet transform method was further introduced to analyze the synergistic effects of precipitation, temperature, and evapotranspiration factors on groundwater storage changes in the time-frequency domain. [Results] From 2003 to 2021, terrestrial water storage and groundwater storage in the Dusitu River Basin decreased significantly at rates of -6.71 mm/a and -7.88 mm/a, respectively. Spatially, the groundwater depletion trend intensified from west to east, with the declining rate increasing from -5.71 mm/a to -9.31 mm/a. After 2018, groundwater depletion accelerated, with the decline rate increasing from -7.37 mm/a to -9.52 mm/a. The trends and seasonal characteristics of measured groundwater levels were consistent with GRACE results, with an average correlation coefficient of 0.56. The area of Bulong Lake continuously decreased at a rate of approximately -2 698 m2/a, showing significant seasonal fluctuations, which was largely consistent with the trends of groundwater storage changes in the river basin. Cross wavelet analysis showed that precipitation and groundwater storage were significantly positively correlated at the 1-month scale, while temperature and evapotranspiration were significantly negatively correlated. [Conclusion] This study significantly improves the inversion accuracy of water storage changes through multi-source GRACE data fusion, clarifies the severe reality of continuous and intensifying groundwater over-exploitation in the Dusitu River Basin, and highlights regional water resources and ecological pressures. Furthermore, precipitation is the main source of groundwater recharge, while temperature and evapotranspiration exacerbate its consumption. The research findings provide reliable technical methods and data support for water resource management in the river basin.
The Three Gorges Reservoir (TGR) is located in the transitional zone between the upper and middle reaches of the mainstream Yangtze River and has strong storage regulation capacity. Since its operation, it has achieved significant comprehensive benefits and has played a prominent role in flood control, power generation, navigation, and water resources utilization in the basin. With the successive completion and operation of several giant reservoirs in the upper reaches of the Yangtze River and the in-depth implementation of the national high-quality development strategy, the operation of the TGR is facing a more complex hydrometeorological environment and higher multi-objective requirements. Meanwhile, the construction and operation of the upstream reservoir system have significantly altered the inflow and sediment regime of the TGR, increasing the complexity of its operation and regulation. This paper reviews the status and comprehensive utilization demands of water resources of the TGR, summarizes the achievements of water resources utilization optimization and operation practices over the years, and analyzes the comprehensive utilization benefits of water resources from the aspects of flood control, power generation, navigation, ecology, and water resources utilization. By integrating medium- and long-term hydrological forecasting results, promoting potential exploitation and efficiency enhancement of the TGR is an inevitable approach to further improving the comprehensive utilization benefits of water resources. Under the new requirements of adhering to the simultaneous prevention and control of droughts and floods and strengthening cross-regional allocation and regulation of water resources between wet and dry conditions, measures are proposed to further tap the potential and enhance efficiency of the TGR, including accelerating the construction of the “three lines of defense” for rainfall and flood monitoring and forecasting, strengthening research on the unified joint operation of key reservoir systems in the Yangtze River basin under extreme inflow conditions, and promoting the development of the Digital Twin Three Gorges system.
[Objective] Numerous influencing factors contribute to the imbalance between the calculated inflow and outflow discharges in the reach between the Three Gorges and Gezhouba Dams. Analyzing the significance of individual influencing factors and identifying the key drivers underlying this imbalance are of considerable importance for formulating power generation plans and conducting hydrological analysis of the Three Gorges-Gezhouba cascade hydropower stations. [Methods] Historical records of discharge and power output in the Three Gorges Reservoir Area were collected from 2018 to 2023. Based on the calculation logic of inflow and outflow discharges, 19 potential influencing factors that may affect the inflow-outflow imbalance in the reach between the two dams were selected. Grey relational analysis (GRA) and random forest (RF) model were employed to identify the key factors contributing to the inflow-outflow discharge imbalance between the Three Gorges and Gezhouba Dams. [Results] The results of GRA showed that the grey relational grade of the total power generation discharge of the Gezhouba Dam reached 0.696, ranking first. The grey correlation degree of the power generation flow of the Three Gorges Dam was 0.695, ranking second. The grey correlation degrees of the total active power of Gezhouba Dam, the total power generation flow of the Three Gorges Dam, and the total active power of the Three Gorges Dam were 0.661, 0.651, and 0.636, respectively, ranking third, fourth, and fifth. For RF model, two methods—rank assignment summation and normalization summation—were adopted to integrate the two indicators, namely %IncMSE (percentage increase in mean squared error) and IncNodePurity (increase in node purity). The results indicated that in both methods, the total power generation discharge of the Gezhouba Dam and the storage-release discharge of the Gezhouba Dam ranked first and second, respectively, in terms of importance. Specifically, the normalization summation method not only reflected the importance ranking of different influencing factors, but also demonstrated that the relative importance of each factor through specific indicator values. Among these factors, the total power generation discharge of the Gezhouba Dam scored the highest (1.25), followed by its storage-release discharge (1.22). In contrast, the total power generation discharge of the Three Gorges Hydropower Station, which ranked third, had a significantly lower score (0.61) than the storage-release discharge of the Gezhouba Dam, which ranked second. [Conclusion] The total power generation discharge of Gezhouba Dam is the key influencing factor causing the inflow-outflow discharge imbalance. This is mainly attributed to the following reasons: 1) the Gezhouba Dam launched its capacity expansion and renovation project in 2013, with the total installed capacity of its 19 generating units increasing by 475 000 kilowatts. However, the NHQ curve adopted for calculating the power generation discharge of the units still remains the original factory curve without any updates, which leads to calculation errors in power generation discharge. 2) The head loss of the Gezhouba Dam is derived from the calculation based on the inflow discharge, instead of being accurately determined for each individual unit, and this calculation method will also induce certain errors. 3) Due to the complex flow conditions in front of the Gezhouba Dam, there are often differences in water head between the left and right banks. Nevertheless, water-head data from a single monitoring station are applied uniformly in power generation discharge calculations, which may further contribute to calculation errors.
[Objective] Minimum ecological flow (e-flow) targets are increasingly used as enforceable constraints in basin management, but their spatiotemporal reliability and ecological representativeness remain insufficiently evaluated at large scales. This study aims to quantify e-flow compliance across the Yangtze River Basin (YRB), identify the drivers of noncompliance and spatial heterogeneity, examine how compliance aligns with river ecological environment conditions, and propose targeted recommendations for improving goal setting, monitoring, and assessment. [Methods] The daily e-flow compliance records were compiled for 114 key control cross-sections from the Yangtze River Water Resources Commission’s monthly monitoring bulletins between January 2023 and July 2024. Compliance was summarized as (i) whether each cross-section met the minimum target throughout the full study period, and (ii) the number of noncompliant days at each cross-section and by month. For ecological environment linkage, 40 e-flow cross-sections were matched with nearby national automated surface-water quality stations, and dissolved oxygen, permanganate index, total nitrogen, total phosphorus, and water-quality class were examined. Subsequently, a four-quadrant diagnostic framework was constructed using mean noncompliance days and the mean share of days classified as Class Ⅳ to Inferior Ⅴ. [Results] Throughout the study period, 71 of 114 cross-sections (62%) fully met the minimum e-flow targets, whereas 43 cross-sections (38%) experienced noncompliance ranging from 1 to 170 days (mean 25.8 d; median 5.0 d). Compliance exhibited a pronounced seasonal unimodal pattern, with lower performance in winter and spring and higher performance in summer and autumn. Specifically, 901 noncompliance days occurred from January to March and from November to December, compared to only 118 days from April to October. Notably, all cross-sections met targets in August. Interannual variability was substantial. From January to July, the number of noncompliance days decreased from 814 in 2023 to 335 in 2024, and the monthly average number of noncompliant cross-sections declined from 18.8 to 10.5. Spatially, heterogeneity was strong among secondary basins, and the left bank outperformed the right bank. Mechanistically, major contributors included seasonal unevenness in precipitation and runoff, differences in dam regulation, reduced mainstream-to-lake diversion affecting the Dongting system, intensive agricultural withdrawals in lake-dominated right-bank regions, and governance and measurement challenges in cross-province water allocation. For the 40 paired sites, pollutant indicators showed no significant monotonic relationship with e-flow compliance, and the total phosphorus could even appear lower in low-flow and noncompliant months due to particulate phosphorus dynamics. The quadrant analysis indicated that 60% of sites fell into high-match zones, but 16 sites showed notable mismatches, suggesting that e-flow compliance was a necessary but insufficient condition for good ecological environment status and that relying solely on flow as a warning indicator remained uncertain. [Conclusion] Large-scale e-flow compliance in the YRB is generally favorable but exhibits strong seasonal, interannual, and governance-linked spatial heterogeneity. To improve ecological relevance and management effectiveness, the following recommendations are proposed: (i) shifting from fixed single-value targets to higher time-resolution, multi-objective, and adaptively updated e-flow targets; (ii) optimizing monitoring networks to better cover ecological hotspots (e.g., key spawning habitats), implementing flexible temporal resolution, and conducting emergency monitoring during rapid ecological events; (iii) transitioning from flow-only, section-based assessment toward integrated basin-scale evaluation that couples flow, water quality, habitat, and biodiversity outcomes.
[Objective] Heavy metal pollution in sediments is a major factor contributing to the deterioration of lake water quality. To accurately assess the sources and potential ecological risks of heavy metals in lake sediments, it is necessary to conduct source analysis and risk assessment at the watershed scale. [Methods] Concentrations of Cr, Ni, Cu, Zn, As, Cd, and Pb in soil and sediments were measured at the small watershed scale in the western lake area of Taihu Lake, and a comprehensive ecological risk evaluation of heavy metals was performed using the enrichment factor (EF), geoaccumulation index (Igeo), and potential ecological risk index. [Results] The heavy metal contents in sediments were generally higher than those in soil. Moreover, the heavy metal contents in sediments from the northern lake area were higher than those in the central and southern lake areas. About 88.4% of the increase in heavy metal content in sediments came from exogenous inputs such as terrestrial rivers and runoff discharged into the lake. Additionally, the EF and Igeo demonstrated that the sediments experienced various degrees of heavy metal accumulation and pollution. The ecological risk values of Cr, Ni, Cu, and Zn were significantly higher than those of the corresponding elements in soil, indicating a relatively high potential ecological risk. Finally, the assessment using the potential ecological risk index showed that Cd exhibited a relatively high ecological risk value, and the sediments exhibited moderate to high comprehensive ecological risks. [Conclusion] Overall, the potential ecological risks of heavy metals in sediments from the western lake area of Taihu Lake are attributed to terrestrial inputs, including surface soil erosion. By coupling comparative analysis of exogenous and endogenous pollution levels of heavy metals at the small watershed scale of the lake, this study provides important management information and a scientific basis for heavy metal control in the Taihu Lake watershed.
[Objective] Identifying the key landscape pattern factors that affect water quality is of great significance for integrated watershed water quality management. [Methods] Based on the water quality data from January 2014 to August 2024, redundancy analysis (RDA) and Pearson correlation analysis were applied to investigate the relationship between landscape pattern indices and ammonium nitrogen concentration in the Gaoguan Reservoir Basin during the wet and non-flood periods. RDA was used to identify the key landscape pattern indices,and Pearson correlation analysis was used to quantify the intensity and significance of correlation coefficients between ammonium nitrogen concentration and landscape pattern indices. [Results] The results were as follows: (1) In the Gaoguan Reservoir Basin,the area of forest land was the largest,accounting for more than 84.9% of the whole area and significantly contributing to the improvement of water quality. (2) The absolute values of correlation coefficients between landscape pattern indices and ammonium nitrogen concentration in the non-flood period were always higher than those in the wet period,and the same trend was observed for landscape composition and land-use areas. (3) In the wet and non-flood periods,with the increase of landscape diversity,splitting degree,and degree of fragmentation,the risk of surface runoff carrying pollutants into water bodies increased and aggravated the ammonium nitrogen pollution. Largest Patch Index (LPI) presented a negative correlation with ammonia nitrogen content in wet period, but a positive correlation in level period. Conversely, Contagion (CONTAG) exhibited a opposite relationship with ammonia nitrogen content, and a significant positive correlation in the non-flood period; in other words,the better integrity of the landscape and the lower degree of fragmentation can reduce the output of ammonium nitrogen during the flood period. During the non-flood period,the closer the pollution-source landscape type was to the water body,the more severe the impact on water quality due to its proximity. [Conclusion] Overall,forest land exhibits a more pronounced effect on water quality improvement in the Gaoguan Reservoir watershed compared with other land-use types.During the non-flood period,landscape pattern indices demonstrate a more significant capacity to regulate and influence water quality relative to the wet period. However,in general,water quality in the reservoir is primarily governed by landscape integrity during the wet period,whereas during the non-flood period,it is mainly controlled by pollution-source patches located closer to the water body.The results will be of great significance for the integrated watershed management and water quality improvement of the Gaoguan Reservoir in the future.
[Objective] As a vital ecological barrier in Northwest China, the river ecosystem health of Zhangye City is of critical importance to regional ecological security. This study aims to provide a comprehensive understanding of the aquatic ecological health of rivers in Zhangye City across different seasons. [Methods] A survey of benthic macroinvertebrates was conducted in 2023 at 136 sampling sites along seven rivers in Zhangye City. The benthic macroinvertebrate-based index of biological integrity (B-IBI) system for rivers in Zhangye City was constructed by selecting 23 candidate biological parameters from five categories that increased in sensitivity with the level of disturbance. B-IBI values of each river were then calculated for different seasons to evaluate their ecological health. [Results] A total of 159 benthic species were identified across both the wet and dry seasons. These species belonged to 5 phyla, 8 classes, 17 orders, and 51 families. Arthropods were the dominant taxa in both seasons, particularly Baetis sp. and Orthocladius sp. The analysis revealed significant differences in benthic macroinvertebrate communities between the dry and wet seasons across rivers in Zhangye City (r=0.09,p<0.05). The B-IBI results indicated that the overall ecological health of the rivers was satisfactory, with minimal seasonal variation. The proportion of sites classified as “healthy” during the dry and wet seasons was 42.39% and 42.71%, respectively. [Conclusion] Despite the currently favorable state of aquatic ecological health in Zhangye City, ecological degradation remains a risk due to ongoing climate change and human activities. To enhance the stability and health of the river ecosystem, it is necessary to strengthen monitoring and management efforts, optimize water resource allocation, and conduct further research on the long-term adaptability of benthic macroinvertebrate communities to extreme weather events and human activities.
[Objective] The eastern Gansu Province is an important ecological transition zone and a fragile area on the Loess Plateau, and understanding the dynamic variation mechanisms of vegetation NDVI (Normalized Difference Vegetation Index) provides a crucial basis for regional ecological restoration. [Methods] This study investigated the response of vegetation NDVI to climate change and human activities in the eastern Gansu based on MODIS NDVI, climate, and land use data from 2000 to 2024, using methods including Theil-Sen trend analysis and the Hurst exponent. [Results] (1) Vegetation NDVI in the eastern Gansu exhibited a spatial pattern of “high in the southeast and low in the northwest”, and areas with significant improvement accounted for 54.74%. However, the Hurst exponent (0.35-0.65) indicated that the future improvement trend had weak persistence. (2) Human activities were the dominant driver, with a contribution rate exceeding 80% in 57.53% of the area, mainly influenced by the Grain for Green program (2 248 km2 of cropland converted to grassland) and urbanization (an increase of 35.14% in the urbanization rate). The contribution rate of climate change was mainly in the 0%-20% range (45.04% of the area), and improved hydrothermal conditions (precipitation increased by 180.95 mm) provided essential support for vegetation growth. (3) A total of 86.68% of the area was jointly driven by climate and human activities, forming a distribution pattern characterized by “human activities as the primary driver and climate as the supporting factor”. [Conclusion] From 2000 to 2024, vegetation NDVI in the eastern Gansu showed a significant improving trend, but with obvious spatial differentiation. The improvement is mainly attributed to the strong driving effect of human activities. However, its rapid intervention leads to weak future sustainability of the ecosystem, posing a significant risk of “degradation after greening”.
[Objective] As a hotspot region of soil respiration and carbon pool dynamics, the Three Gorges Reservoir area is most extensively covered by Pinus massoniana forests, whose soil organic carbon storage is the largest among all forest types. Therefore, investigating soil carbon release is particularly important. Soil carbon emissions are mainly regulated by microbial decomposition of aboveground litter, organic matter substrates, and root exudates; however, studies on the coupling relationship between soil respiration and microorganisms in Pinus massoniana forests in the Three Gorges Reservoir area are scarce, which affects the accurate quantification of the reservoir-area carbon pool. [Methods] This study used a Li-8100 automated soil CO2 flux system (Li-Cor Inc., Lincoln, NE, USA) and the chloroform fumigation-extraction method (FE) to monitor soil respiration rates and microbial biomass carbon and nitrogen in two Pinus massoniana forest types (a Pinus massoniana pure forest and a Pinus massoniana-Quercus acutissima mixed forest) across spring, summer, autumn, and winter. The trenching method was further used to determine the contributions of autotrophic and heterotrophic respiration components, and one-way analysis of variance was used to analyze differences. [Results] Both total respiration and heterotrophic respiration rates in the mixed forest were higher than those in the pure forest. Under both forest types, heterotrophic respiration accounted for an average of 88%, while autotrophic respiration accounted for an average of 12%, which was also a consequence of Pinus massoniana being the main constructive or dominant species in the Three Gorges Reservoir area. The proportions of autotrophic and heterotrophic respiration exhibited significant seasonal variation: the contribution of heterotrophic respiration first decreased and then increased with season, whereas autotrophic respiration first increased and then decreased. Autotrophic respiration contributed approximately 3%-25% to total soil carbon release. In the pure forest, heterotrophic respiration contributed 75%-97% of total soil carbon release, while in the mixed forest, heterotrophic respiration accounted for 82%-98% of total soil respiration. During the growing season (May-October), the average rates of all respiration components were higher and reached their maximum in summer. Microbial biomass carbon and nitrogen contents in the mixed forest were higher than those in the pure forest, reaching 259.54 and 20.25 mg/kg, respectively. After root exclusion treatment, microbial biomass carbon and nitrogen only decreased by 30.53% and 34.56%, respectively. The microbial biomass C to N ratio was 15.70 in the pure forest and 12.82 in the mixed forest. Both microbial biomass carbon and the C to N ratio drove soil carbon release. [Conclusion] In both Pinus massoniana pure and mixed forests, the contribution of heterotrophic respiration is much higher than that of autotrophic respiration, indicating that heterotrophic respiration is the main pathway of soil carbon release in the Three Gorges Reservoir area. After root exclusion treatment, the decreases in microbial biomass carbon and nitrogen are relatively small, suggesting that microorganisms mainly release carbon by decomposing litter and organic matter substrates rather than root exudates. Soil respiration, in both pure and mixed forests, is significantly positively correlated with microbial biomass carbon and the C to N ratio (P<0.05), but is not correlated with microbial biomass nitrogen. The positive correlation and similar patterns between microbial biomass carbon and soil respiration can directly reflect soil carbon release. Microbial biomass in the mixed forest is higher than that in the pure forest both before and after root exclusion, resulting in greater soil carbon emissions. In the absence of roots and their exudates, the C to N ratio in the mixed forest increases to facilitate the decomposition of more recalcitrant substrates. The findings of this study provide an important reference for research on carbon cycling and ecological construction in the Three Gorges Reservoir area.
[Objective] Drought-flood abrupt alternation (DFAA), characterized by high suddenness, strong complexity, and great destructive power, has emerged as a significant risk source threatening regional ecological security and social sustainable development. This study aims to systematically review the progress of DFAA research, clarify its development trajectory, research hotspots, and knowledge structure, identify existing research gaps, and provide scientific guidance for future research directions. [Methods] Based on Web of Science (WOS) Core Collection and China National Knowledge Infrastructure (CNKI) database, Chinese and English publications related to drought-flood abrupt alternation (DFAA) between 2005 and 2024 are systematically retrieved. The bibliometric analysis tool CiteSpace software is utilized to visually analyze annual publication trends, keyword co-occurrences, and keyword bursts. On this basis, existing research is summarized and compared from three dimensions—identification methods, causal mechanisms, and disaster impacts—and, accordingly, optimization pathways for future research are proposed. [Results] (1) From 2005 to 2024, a total of 322 DFAA-related publications were issued globally, with China accounting for 53.2%. The development of CNKI literature went through three stages: preliminary exploration (2005-2010), rapid development (2011-2018), and stable development (2019-2024). Publications in the WOS have accelerated since 2018 and reached a peak in 2023, reflecting a rapid increase in international attention. (2) Domestic research focuses on the spatiotemporal evolution patterns and atmospheric circulation mechanisms of DFAA, with keyword bursts concentrated in trend analysis, spatiotemporal characteristics, and low-frequency oscillations. International research places greater emphasis on the long-term changes of DFAA and its ecological impacts in the context of climate change, with hotspot keywords including the Yangtze River, vegetation, and climate change. (3) First, there is a lack of a unified, multi-scale coupled DFAA identification system, as existing indices are mostly limited to a single temporal scale and consider limited factors in index construction. Second, causal analysis relies excessively on meteorological factors, with insufficient consideration of underlying surface changes and human activities. Third, impact assessment focuses on agricultural yield reduction and vegetation response, while research on the long-term impacts on urban resilience, water resource security, socio-economic systems, and ecosystem service functions remains inadequate. [Conclusion] Research on DFAA is currently at a critical stage of transitioning from phenomenon description to mechanism analysis and comprehensive impact assessment. Future research should focus on constructing a comprehensive identification indicator system that integrates multiple temporal scales and considers regional heterogeneity, while integrating multi-source data such as precipitation, soil moisture, temperature, topography, and vegetation to improve the accuracy and applicability of event identification. Future efforts are needed to deepen investigations into the formation mechanisms of DFAA and to strengthen regional comparisons and global-scale correlation analysis. In addition, the dimensions of impact research should be expanded to systematically assess the compound effects of DFAA on urban infrastructure, water resource allocation, ecological service functions, and socio-economic resilience, and to establish long-term monitoring networks that can provide scientific support for disaster risk management and climate adaptation policy formulation.
[Objective] Existing grouting theories and engineering experience are mostly based on hydrostatic or weakly flowing water conditions, making it difficult to accurately describe the diffusion and evolution characteristics of grout under dynamic water-flow environments. It is necessary to systematically reveal the diffusion mechanisms of grout in water-flowing fractures so as to provide theoretical support for grouting design under complex water inrush conditions in water-sealed caverns. In response to engineering conditions involving stable flowing water in a single fracture, this study aims to: (1) reveal the influence mechanisms of fracture geometric characteristics and construction parameters on grout diffusion behavior; (2) quantitatively analyze the controlling effects of key factors on grout diffusion distance, diffusion time, and sealing efficiency; and (3) clarify the relative importance of different influencing factors in the grouting of water-flowing fractures, thereby providing a basis for optimization of grouting parameters and construction decision-making for water-sealed caverns. [Methods] Based on the grout-water two-phase flow theory, a numerical model of grouting in a single fracture with flowing water was established using the finite element method. Variations in water flow velocity within the fracture and the driving effect of grouting pressure were comprehensively considered, and the diffusion, advection, and deposition processes of grout within the fracture were simulated. Through parametric comparative analysis, the effects of fracture aperture, fracture inclination, grouting pressure, flowing water velocity, and fracture boundary extent on the evolution of grout diffusion were systematically investigated. On this basis, a sealing efficiency index was introduced to comprehensively evaluate the grouting performance under different working conditions. [Results] Under flowing water conditions, the grout diffusion pattern, stabilization time, and final sealing performance within fractures were jointly controlled by multiple coupled factors. (1) Fracture inclination had a significant inhibiting effect on grout diffusion. As the fracture inclination increased, the coupling between the gravitational component and the flowing water direction was enhanced, causing the grout to more easily deviate along the down-dip direction. As a result, the ability of grout to migrate against the water flow was weakened, and the diffusion range was markedly restricted. (2) The time required for grout diffusion to reach a stable state increased significantly with an increase in the extent of the fracture domain, because a larger boundary extent provided a greater seepage space for grout diffusion. In contrast, increasing grouting pressure effectively accelerated the advance of the grout diffusion front and shortened the stabilization time, exhibiting a pronounced accelerating effect. (3) In terms of diffusion distance, the effective diffusion distance of grout was inversely proportional to fracture boundary extent and flowing water velocity. Higher flowing water velocity resulted in stronger scouring and transport effects on the grout, thereby reducing its retention capacity within the fracture. Conversely, increases in fracture aperture and grouting pressure facilitated the grout in overcoming water flow resistance, enabling longer diffusion distances and more sufficient fracture filling. (4) Comparative analysis of the influence degrees of various factors indicated that fracture aperture had the most significant effect on grout sealing efficiency, followed in descending order by flowing water velocity, grouting pressure, and fracture boundary extent. This demonstrated that fracture geometric characteristics and hydrodynamic conditions were the key factors controlling the success or failure of grouting under flowing water conditions. [Conclusion] Overall, in strong flowing water environments, relying solely on increasing grouting pressure does not significantly improve grouting performance, and comprehensive design must be carried out by jointly considering fracture aperture characteristics and groundwater hydrodynamic conditions. For areas with larger fracture apertures and higher flowing water velocities, measures such as staged grouting or advance water reduction should be preferentially adopted to enhance grout retention and sealing capacity within fractures.
[Objective] This study aims to investigate the influence of super-large-diameter double-circular pipe jacking construction on the settlement deformation of underground pipelines. Taking the water quality assurance project of Tiegang-Shiyan Reservoir in Shenzhen as the background, and based on the modified Peck formula, this study uses a combination of numerical simulation and field monitoring to systematically analyze the effects of multiple factors such as pipeline burial depth, material, pipe diameter, pipe jacking spacing, and spatial position. [Methods] The variable normalization method was used to analyze the influence degree of each factor on the pipeline, and the safety performance of the pipeline was evaluated. [Results] When the jacking pipes vertically crossed under the pipeline, the induced settlement range was the smallest, indicating a relatively reasonable construction method. When the pipeline burial depth, material, or pipe diameter was changed, the stratum displacement field ultimately showed a “V”-shaped distribution. However, when the spacing between the two jacking pipes increased to 1.5 times the jacking pipe diameter (i.e., 6 m), the displacement field shape transformed into a “W”-shaped pattern, and the influence range of pipeline deformation significantly expanded. Sensitivity analysis showed that the spacing between the two jacking pipes was the most significant factor affecting pipeline settlement (sensitivity=0.54), while pipeline diameter had the least influence (sensitivity=0.06), and pipeline burial depth had a moderate influence (sensitivity=0.40). Furthermore, the safety state of the sewage pipeline was evaluated using the allowable joint rotation angle. The calculated joint rotation angle under field monitoring conditions was 0.54°, which was lower than the standard control value of 1.15°, indicating that the pipeline joints remained in a safe state during construction and did not suffer damage due to uneven settlement. [Conclusion] Currently, there is considerable research on settlement deformation of underground pipelines caused by single-line pipe jacking construction, but research on the influence of super-large-diameter double-line pipe jacking with shallow burial depth is limited. This study clarifies the influencing mechanisms of key construction parameters, providing theoretical basis and data support for engineering practices involving large-diameter pipe jacking undercrossing existing pipelines.
[Objective] In recent years, the increasing number of buildings constructed on soft ground has made the treatment of soft soil foundations particularly important. Investigating the strength variation characteristics of silt foundations under different types of stabilizing agents and curing ages,as well as exploring a preliminary method for identifying the strength level of non-standard soil samples obtained in the field,is of great practical significance for engineering applications. [Methods] Representative silty soil layers from the Zhongshan area were selected. Cement-only mixing tests were first conducted to optimize cement content (ratio of cement mass to the mass of treated wet soil). Subsequently,silt was stabilized using lignosulfonate acid (LA),triethanolamine (TEA),and alkali-activated sodium silicate (AS) as stabilizing agents,respectively. Scanning electron microscopy (SEM) tests were then carried out to analyze the microstructures and stabilization mechanisms of untreated and stabilized soils. Finally,ArcGIS was used to construct independent elevation models from the SEM images of untreated and stabilized soils and to process them into three-dimensional images. Scatter plots were plotted in double-logarithmic coordinates,and the soil porosity and particle fractal dimension were further calculated and analyzed. [Results] 1) Using the unconfined compressive strength of specimens as the evaluation index,under the same curing age, the cement content was positively correlated with the unconfined compressive strength. Before a curing age of 7 days, the unconfined compressive strength increased rapidly; during 7-14 days, the growth rate slowed down; and from 14 to 28 days, the unconfined compressive strength continued to increase. Considering economic cost and code requirements, the optimal cement content was 18% of the wet soil mass. 2) At certain mixing ratios, single incorporation of LA, TEA, and AS all enhanced the strength of cement-stabilized soil and could be used as stabilizing agents. Based on the optimal contents of the three stabilizers, ternary mixing stabilization tests were conducted. The results showed that single incorporation of AS exhibited better stabilization performance than the other single-additive groups and the ternary mixing group. When the cement content was 18% and the AS content was 0.9%, the unconfined compressive strength of the stabilized soil reached a maximum value of 2.39 MPa. 3) SEM tests indicated that the specimens of the 18S blank group failed to generate sufficient gel-like hydration products (C-S-H) and needle-like Aft crystals. As a result, limited cementitious material existed between soil particles, and numerous pores were observed. After stabilization with 18S-0.9AS, a large amount of gel-like C-S-H hydration products and needle-like Aft crystals were rapidly generated, which interwove to form a large-area spatial network structure and initially formed a skeleton. This process led to particle bonding and aggregation and filled the interparticle pores. Overall, the 18S-0.9AS group exhibited the best stabilization effect. 4) Three-dimensional SEM images of untreated and stabilized soils were constructed and processed using ArcGIS. Data calculation and analysis showed that the untreated soil had 97 663 226.34 pore pixels, accounting for 53.22% of the total image pixels (porosity), with a fractal dimension of 1.399 8. The 18S-0.9AS stabilized soil had 50 153 642.75 pore pixels, accounting for 27.27% of the total image pixels (porosity), decreased by 25.95 percentage points compared with the untreated soil. The fractal dimension of this group was 1.853 5, and the unconfined compressive strength reached the maximum value of 2.39 MPa. [Conclusion] 1) The larger the particle fractal dimension of a specimen, the more complex the particle structure, the higher the surface roughness, the lower the porosity, and the higher the compressive strength. 2) The porosity of specimens and the compressive strength exhibit a nonlinear decreasing relationship, whereas the particle fractal dimension and the compressive strength exhibit a nonlinear increasing relationship. 3) When standard specimens cannot be obtained at construction sites, the compressive strength of specimens can be preliminarily inferred by using the porosity and particle fractal dimension of non-standard specimens, based on the physical significance and correlations of fractal dimensions among different specimens.
[Objective] Microwave-assisted rock breaking technology shows promising application potential in hard rock tunneling. The effectiveness of microwave irradiation on rocks is significantly influenced by their microstructure, particularly the mineral particle size distribution. Existing studies mostly focus on single mineral components or simple binary combinations, whereas systematic investigations into how the heterogeneity of complex mineral particle size distributions in natural rocks affects the microwave rock breaking remain limited. This study aims to quantify the heterogeneity of mineral particle size distribution through experiments and numerical simulations, and to reveal its influence mechanisms on the thermal-physical response, damage evolution, and mechanical property degradation of rocks. [Methods] Seven groups of standard granite specimens (Φ50 mm × 100 mm) with different mineral particle size heterogeneity coefficients were selected and subjected to microwave irradiation tests. Surface temperature variations of the specimens during irradiation were monitored, longitudinal wave velocities before and after irradiation were measured, and the peak strengths were obtained through uniaxial compression tests. Image processing techniques were used to extract the surface mineral distributions of the specimens, and quantitative indicators characterizing the heterogeneity of particle size distributions were defined and calculated. Using COMSOL software, a multi-physics numerical model coupling electromagnetic fields, heat conduction, and solid mechanics was established. The model precisely reconstructed the real mineral distributions with different heterogeneity coefficients, and simulated and analyzed the dynamic evolution process of the temperature fields, stress fields, and plastic damage zones of the specimens under microwave irradiation. [Results] (1) Thermal response: under identical irradiation conditions, the heterogeneity of mineral particle size distribution significantly affected the thermal response of the specimens. With the increase of heterogeneity, the temperature rise of the rock became more pronounced. The specimen with the highest heterogeneity (H=0.78) exhibited a final temperature approximately 44 ℃ higher than that of the most homogeneous specimen (H=0.34).(2) Damage and weakening: with increasing heterogeneity coefficient, the number of microwave-induced surface microcracks increased significantly. The reduction in longitudinal wave velocity intensified, with a maximum difference reaching 30%. The uniaxial compressive strength loss rate increased from 11.2% to 29.6%, with a maximum difference of 18.4%. These results indicated that the more heterogeneous the mineral distribution was, the more severe the internal damage induced by microwaves and the more significant the weakening effect on macroscopic mechanical performance became.(3) Mechanism: stronger heterogeneity led to more intense temperature gradients and thermal stress concentrations at the interface between strong microwave-absorbing minerals (such as potassium feldspar) and weak microwave-absorbing minerals (such as quartz). This was because specimens with higher heterogeneity contained larger potassium feldspar particles, which had stronger microwave absorption capacity, resulting in a rapid local temperature rise. Both the area proportion of the critical tensile stress zones (>15 MPa) and the area proportion of the plastic zones increased monotonically with the increase of the heterogeneity coefficient. The plastic zones first appeared at the contact interface between potassium feldspar and quartz and expanded over time. [Conclusion] The heterogeneity of mineral particle size distribution is a key microstructural factor controlling the effectiveness of microwave-assisted rock breaking. The defined quantitative heterogeneity coefficient can effectively predict the outcomes of microwave irradiation: rocks with higher heterogeneity are more likely to experience uneven heat accumulation and large interfacial thermal stresses under microwave irradiation, thereby leading to more extensive microcrack initiation, more significant wave velocity reduction, and more significant strength loss. This study identifies the potassium feldspar-quartz interface as the preferential site for damage initiation.
Deformation is the comprehensive reflection of the structural behavior of high arch dam bodies and their foundations. To ensure the safe service of such projects, it is of utmost importance to study and propose scientific theories for deformation behavior analysis and safety monitoring of high arch dams. This study reviews the current research progress on deformation behavior analysis, monitoring models, and early warning criteria for the deformation behavior of high arch dams, providing a new perspective for intelligent monitoring, characteristic analysis, and safety monitoring of dam deformation. Three key scientific issues that need to be addressed urgently are emphasized, namely, the mutual feedback mechanism of time-varying effects of deformation between high arch dams and adjacent dam abutments, the mutual feedback mechanism of progressive failure process of deformation between the two, and the buckling instability modes and corresponding early warning criteria for the deformation behavior of high arch dams. In future research and practice, the following aspects should be given due attention. First, research on the deformation mechanisms of high arch dams and adjacent dam abutments under complex environmental conditions should be strengthened, with particular emphasis on the impact of cold waves, freeze-thaw cycles, dissolution, and carbonation in cold regions, along with their coupled effects, to refine theoretical models. Second, interdisciplinary integration should be advanced by leveraging emerging technologies, such as artificial intelligence, the Internet of Things, and blockchain, to enable in-depth mining and intelligent analysis of deformation characteristics of high arch dams and adjacent dam abutments. Furthermore, a comprehensive monitoring database and shared platform should be established for deformation of high arch dams and adjacent dam abutments to facilitate efficient management and utilization of monitoring data, thereby providing scientific evidence and technical support for the safe operation, performance improvement, and service life extension of high arch dam projects.
[Objective] To investigate the influence of mainshock-aftershock sequences on seismic performance of hollow gravity dams, the nonlinear seismic response of one overflow dam section in a hollow gravity dam in China is investigated. [Methods] Real mainshock and aftershock records were selected from the PEER (Pacific Earthquake Engineering Research Center) earthquake database. Three mainshock-aftershock sequences, Mammoth Lakes, Chalfant Valley, and Whittier Narrows, were constructed based on aftershock decay characteristics. Taking one overflow dam section of a hollow gravity dam in China as the research object, the 3D finite element model of the dam-foundation system of the overflow dam section was built. The concrete damaged plasticity model was adopted to simulate the nonlinear characteristics of the concrete material of the dam body. The massless foundation was used to simulate the dynamic interaction between the structure and the foundation. The hydrodynamic pressure of the reservoir was simulated by the added mass method. The influence of the mainshock-aftershock sequences on the nonlinear seismic response of the hollow gravity dam was analyzed based on the development of cumulative macroscopic failure areas, the residual deformation of the dam crest, and the cumulative damage dissipation energy. [Results] (1) The failure area of the hollow gravity dam caused by aftershocks usually continued to expand along the failure areas caused by the mainshocks. The aftershocks significantly increased the range and depth of the failure area caused by the mainshocks. In some areas, such as the dam heel and the reverse arc area, when the damage caused by the mainshock was relatively deep, aftershocks could directly lead to a through-going failure of the dam body. (2) Aftershocks could cause a significant increase in the residual deformation at the dam crest and the damage dissipation energy of the dam body. The residual deformations caused by the three mainshocks were 2.13, 2.83,2.12 cm, respectively. When the aftershock coefficient was 0.852 6, the proportion of residual deformation caused by aftershocks was 24.2%, 24.1%, and 26.4%, respectively. The damage dissipation energy caused by the three mainshocks was 131, 121,108 kJ, respectively. When the aftershock coefficient was 0.852 6, the proportion of the dam damage dissipation energy caused by the three aftershocks was 38.8%, 49.6%, and 47.1%, respectively. (3) When the aftershock coefficient was small, it also significantly increased the distribution of failure areas in the dam body. In some regions, non-through failure caused by the mainshock could further develop into through-going failure under aftershocks. When the aftershock coefficient was 0.6, the proportion of residual deformation at the dam crest caused by three aftershocks was 18.4%, 18.2%, and 19.4%, respectively. The proportion of the damage dissipation energy caused by the three aftershocks was 29.9%, 40.1%, and 37.5%, respectively. [Conclusion] The innovation of this paper lies primarily in revealing the influence of mainshock-aftershock sequences on the nonlinear seismic response of the hollow gravity dam. The results indicate that the failure areas caused by aftershocks usually continue to expand along the failure areas caused by the mainshocks. The aftershocks may significantly increase the range and depth of the failure areas caused by the mainshocks. The aftershocks may cause a significant increase in the residual deformation at the dam crest and the damage dissipation energy of the dam body. In the seismic safety evaluation of the hollow gravity dam exposed to earthquake hazards, the influence of aftershocks is non-negligible.
[Objective] The adhesion problem between acidic aggregates and asphalt is a key issue in the application of acidic aggregates in hydraulic asphalt concrete. For hydraulic structures, the mix design of hydraulic asphalt concrete incorporating acidic aggregates modified with anti-stripping agents is not entirely the same as that used in road engineering. This study aims to investigate, under a constant gradation index, the individual effects of the proportion of coarse and fine aggregates, as well as their interaction effects with asphalt-aggregate ratio and filler content, on the performance of anti-stripping-agent-modified hydraulic asphalt concrete with granite aggregates, and to optimize the mix proportion design of granite aggregate hydraulic asphalt concrete. [Methods] A Box-Behnken response surface methodology was employed for experimental design. Air voids, flow value, and stability were selected as response variables to establish response surface regression models. The effects of asphalt-aggregate ratio, filler content, and sand ratio, as well as their single and interaction effects on the response values, were analyzed to determine the optimal mix proportion. Meanwhile, water stability tests were conducted to verify the performance. [Results] (1) The mix proportion design of granite hydraulic asphalt concrete was optimized using response surface methodology, and the established quadratic regression equations were able to well describe the relationships among sand ratio, asphalt-aggregate ratio, filler content, and air voids, stability, and flow value. Analysis of variance and significance tests indicated that the model was effective and reliable, with high credibility. (2) Response surface analysis showed that the order of influence on the air voids of granite hydraulic asphalt concrete was asphalt-aggregate ratio>sand ratio>filler content; the order of influence on stability was sand ratio > asphalt-aggregate ratio > filler content; and the order of influence on flow value was sand ratio > asphalt-aggregate ratio > filler content. (3) The three-dimensional distribution of the water stability coefficient indicated that a relatively high water stability coefficient was obtained in the region where the sand ratio ≤ 36%, filler content ≤13.5%, and asphalt-aggregate ratio ≥6.8%. (4) The optimized mix design parameters of granite hydraulic asphalt concrete were a sand ratio of 33%, an asphalt-aggregate ratio of 7.1%, and a filler content of 12.5%. [Conclusion] The experimental results confirm that this mix proportion exhibits good performance and can provide a reference for the optimization design of granite hydraulic asphalt concrete mix proportions in practical engineering.
[Objective] This study addresses the numerical modeling of nonlinear steady-state heat conduction processes where the thermal conductivity varies with temperature. The governing equation for such problems is a second-order quasi-linear partial differential equation, whose nonlinear nature makes analytical solutions extremely challenging, thus necessitating efficient numerical approaches. This work employs the Numerical Manifold Method (NMM) based on quadrilateral mesh covers to analyze and solve two-dimensional nonlinear steady-state heat conduction problems. [Methods] Within the NMM over traditional methods framework, a discrete formulation suitable for nonlinear steady-state heat conduction was established by incorporating three typical boundary conditions: Dirichlet, Neumann, and Robin. The classical Newton-Raphson iterative algorithm was adopted to solve the resulting nonlinear system of equations. A complete numerical solution procedure was implemented on the MATLAB platform to ensure algorithm stability and computational efficiency. To systematically verify the accuracy and robustness of the proposed NMM in handling nonlinear heat conduction, a series of representative numerical examples were designed and conducted. These examples covered various scenarios, including continuous homogeneous materials, discontinuous media containing circular holes, and heterogeneous materials. The simulation results were compared against analytical solutions, existing literature data, or Finite Element Method (FEM) solutions. [Results] 1) Compared to the traditional Finite Element Method (FEM), NMM demonstrates significant theoretical and practical advantages when simulating problem domains with complex geometries or internal discontinuities. This advantage primarily stems from its distinctive numerical characteristics: in NMM, the interpolation subdomains are independent of the subdomains used for numerical integration, whereas in FEM they coincide entirely on the same mesh. Furthermore, FEM is prone to mesh distortion when handling complex boundaries, which can degrade accuracy and impair computational efficiency. Leveraging its physical cover system, NMM can accurately describe complex geometric boundaries. At material interfaces, the different heat conduction behaviors across materials are naturally captured through physical covers and local functions without introducing additional interface conditions, thereby simplifying the computational process and enhancing efficiency. 2) The proposed NMM not only achieves high accuracy in temperature field and heat flux distribution across all examples but also exhibits excellent stability and convergence when dealing with discontinuous interfaces and complex geometries, fully validating the method’s effectiveness and reliability for nonlinear steady-state heat conduction problems. [Conclusion] This study successfully applies NMM to solve two-dimensional nonlinear steady-state heat conduction problems. Through comprehensive comparative analysis and numerical validation, the unique advantages of this method in handling complex engineering thermal problems are highlighted. It provides a novel solution for the numerical simulation of nonlinear heat conduction problems and extends the application scope of NMM in the field of computational thermal physics.
[Objective] To systematically review the development trends in terrestrial carbon sink research, this paper employs bibliometric methods to analyze Chinese and English literature from 1994 to 2024, aiming to reveal its evolution, research hotspot shifts, distribution of core research entities, and future directions, thereby providing a reference for grasping field frontiers and supporting relevant decision-making. [Methods] Data were sourced from the Web of Science Core Collection (SCI-E) and the China National Knowledge Infrastructure (CNKI) database, retrieving 8 431 relevant publications on terrestrial carbon sinks from 1994 to 2024 (4 727 in English, 3 704 in Chinese). Using CiteSpace software, knowledge graphs including literature co-citation, author collaboration, and keyword timeline maps were constructed. Combined with the burst detection algorithm, the analysis covered the temporal, disciplinary, journal, and country distributions of publications, identified high-impact institutions, prolific authors, high-centrality and highly-cited literature, and investigated the evolutionary stages and frontier hotspots of keywords. [Results] (1) Publication trends: The number of publications showed significant growth over the past three decades, with an average annual increase of approximately 12% after 2008 and 15% after 2019. The development process could be divided into three stages: slow inception (1994-2008), steady development (2008-2019), and rapid advancement (post-2019). (2) Distribution by country, journal, and discipline: China published the most papers (2 149 in WOS, 3 704 in CNKI), followed by the United States and Germany. Key journals included Global Change Biology, Science of the Total Environment, Agricultural and Forest Meteorology, Acta Ecologica Sinica, and Ecological Economy. Environmental science and technology and resources science and technology were core disciplines. Chinese literature emphasized forestry and agricultural economics, while English literature focused on ecology and geosciences. (3) Core research entities: The Chinese Academy of Sciences was the most prolific institution (832 papers), followed by the University of Chinese Academy of Sciences and the French National Centre for Scientific Research (CNRS). High-centrality and highly-cited literature concentrated on three areas: the dynamics of terrestrial carbon sinks, carbon flux monitoring models, and the coupling between climate change and carbon sinks. (4) Evolution of research hotspots: Keyword burst detection revealed three distinct stages. Stage 1 (1994-2008): focused on fundamental carbon cycle theory, with keywords such as “carbon cycle”,“carbon balance”, and “eddy covariance”. Stage 2 (2008-2019): research expanded to socio-economic dimensions, featuring keywords like “net primary production”,“low-carbon economy”, and “ecological compensation”. Stage 3 (2019-2024): closely aligned with global carbon reduction goals and ecosystem value realization, highlighted by keywords including “carbon neutrality”, “carbon peak”,“carbon emissions”, “temperature sensitivity”, “ecological product accounting”, and “carbon trading”. [Conclusion] This bibliometric analysis indicates that terrestrial carbon sink research is developing rapidly, with China being a major contributor. Research hotspots have evolved from fundamental mechanisms to socio-economic integration, and further toward a trajectory driven by carbon neutrality goals and market mechanisms. Future research directions mainly include: enhancing carbon sink monitoring, accounting, and assessment accuracy; studying carbon process mechanisms in coupled multiple ecosystems; evaluating regional emission reduction and sink enhancement potential along with technological applications; developing economic valuation and market trading mechanisms for carbon sinks; and strengthening international cooperation and data sharing. The findings can provide a basis for understanding the field’s development trajectory, predicting future trends, and supporting policies related to China’s “Dual Carbon” goals.
[Objective] To address the challenges of incomplete remote sensing imagery and insufficient measured terrain data in large-scale river numerical simulations, this study proposes a novel method for river channel terrain reconstruction that integrates Copernicus DEM 30 data with limited measured data, aiming to solve the problem of constructing large-scale river channel DEMs in data-scarce areas and to verify its applicability in MIKE 21 hydrodynamic-sediment numerical simulations. [Methods] This study took the Alar-Xinquman river section of the Tarim River as the study area and utilized relevant hydrological data and measured terrain elevation data from 2011 as the basic dataset. The specific reconstruction process was as follows: (1) Using ArcGIS software, combined with Google Earth historical imagery and Copernicus DEM 30, the inner and outer bank lines of the river channel were delineated by scaling overlapping imagery proportionally to determine the main channel boundary.(2) The river DEM was corrected stepwise. First, the quadratic interpolation method was applied to densify the elevation data of the main channel cross-sections. Second, the mean difference method was used to calculate the deviations in elevation between measured points and the Copernicus DEM at corresponding locations, enabling an overall vertical correction of the Copernicus DEM data. Next, a locally weighted regression (LOESS) algorithm was introduced to correct the longitudinal cross-section elevations of the main channel, smoothing the riverbed terrain and generating the main channel DEM. Finally, the main channel and floodplain DEM data were merged to construct the complete river channel DEM.(3) The reconstructed DEM was imported into the MIKE 21 hydrodynamic-sediment module. Measured data such as water level, flow, and sediment concentration were selected as boundary conditions for numerical simulation. The accuracy and reliability of the reconstructed DEM were evaluated by comparing the errors between the simulated and measured values. [Results] Comparison between numerical simulation results and measured data revealed that the results for flow velocity, flow-stage relationships, and river channel erosion-deposition tests all met the allowable deviation requirements specified in relevant technical standards. This indicated that the river channel DEM constructed in this study was reasonably suitable for two-dimensional hydrodynamic-sediment numerical simulations. [Conclusion] (1) The river channel terrain reconstruction method proposed in this study, integrating Copernicus DEM 30, quadratic interpolation, mean difference method, and locally weighted regression (LOESS) algorithm, can effectively address the lack of measured underwater terrain data for large-scale rivers. It demonstrates superior continuity and accuracy compared to traditional single-interpolation methods.(2) The hydrodynamic model established based on the reconstructed DEM achieves simulation accuracy within the allowable deviation limits specified by relevant technical standards. This method is characterized by low cost, high efficiency, and strong applicability, providing a practical new approach and technical support for the numerical simulation of large-scale rivers with scarce data, such as the Tarim River.
[Objective] We constructed an evaluation system for Happy Rivers tailored to the characteristics of small and medium-sized rivers in Jiangxi Province, and quantitatively evaluated the happiness level of Yishui River from 2019 to 2023 using an innovative comprehensive evaluation model. The study aims to provide a scientific basis for the construction of Happy Rivers and Lakes in Yishui River and similar river basins in Jiangxi Province, while verifying the applicability of the combined evaluation model for assessing the water environment of small and medium-sized rivers. [Methods] Guided by the framework for constructing Happy Rivers and Lakes in Jiangxi Province, we developed a three-layer system of “target layer - criterion layer - indicator layer” and selected 18 indicators, such as the compliance rate of flood control standard and the satisfaction degree of ecological base flow. The independence of the indicators was verified using correlation principal component analysis. To overcome the limitations of single weighting methods, the “BWM-EWM-minimum entropy” combined weighting method was employed to balance theoretical importance and actual data contribution. Integrating the advantage of GRA in describing dynamic trends with the comparative strength of TOPSIS in defining ideal states, this study calculated the Euclidean distance and grey correlation coefficient between samples and both the positive and negative ideal solutions to obtain the relative closeness and classify happiness levels. [Results] The relative closeness of the criterion layers for Yishui River was 0.418 9, 0.491 1, 0.547 3, 0.602 4 and 0.713 6 for the years 2019 to 2023, respectively, with an average annual growth rate of 14.04%. Compared to 2019, the relative closeness in 2023 increased by 1.7035 times, and the comprehensive happiness level improved from the qualified level of grade III in 2019 to the excellent level of grade I in 2023. These results indicated that Yishui River has achieved significant progress under the planning and construction of Happy Rivers and Lakes. From the perspective of each criterion layer, except for “enriching the people”, the relative closeness and happiness level of the other five criterion layers showed an increasing trend each year. The overall level of “enriching the people” exhibited an upward trend, improving from the qualified level of grade III in 2019 to the good level of grade II in 2023. “Enriching the people” emerged as the primary aspect affecting the happiness level of Yishui, and the development and utilization rate of water resources and water use per 10 000 yuan GDP were identified as key factors. [Conclusion] The construction of the Yishui Happy River and Lake has achieved remarkable results, but the dimension of “enriching the people” remains a bottleneck. Future efforts should focus on overcoming this bottleneck by strengthening water-saving management, developing water-related characteristic industries, and promoting regional cooperation. As the research data cannot reflect long-term change patterns, future studies should extend the monitoring period and improve the indicator system by incorporating county-level statistical data.
[Objective] The Yangtze River is the most important east-west axis for the development of territorial space and provides a foundation for urban agglomeration planning, industrial development, and transportation in Jiangsu Province. Implementing protection and utilization planning of the Yangtze River shoreline is a practical measure to promote the high-quality development of the Yangtze River Economic Belt and to support integrated development of the Yangtze River Delta. Given the high intensity and complexity of Yangtze River shoreline utilization in Jiangsu Province, this study conducts an implementation evaluation of protection and utilization planning in Jiangyin City. [Methods] From different perspectives such as shoreline utilization project types, shoreline functional zones, and the “production-living-ecological” utilization types, the status of shoreline utilization in Jiangyin City was reviewed and analyzed for the base year (2018) and the recent level year (2025). Changes, characteristics, and key problems of shoreline utilization were identified, and the phased planning outcomes and their implementation under protection and utilization planning were evaluated for the recent level year. [Results] The results showed that protection and utilization planning of the Yangtze River shoreline provided important guidance and that current utilization reached the main planning goals. Specifically, they mainly included: (1) the number of shoreline utilization projects decreased from 104 to 92 since 2018, and utilization rate of the shoreline declined from 80.1% to 66.0%. Across the 92 shoreline utilization projects, the overall proportion of shoreline length in the “production-living-ecological” types was 40∶5∶55. The production shoreline length of Xiagang Street had the highest proportion compared to other streets, reaching 73.3%, while Shengang Street had the highest proportion of living shoreline length (8.5%), and Chengjiang Street had the highest proportion of ecological shoreline length (90.5%), consistent with the functional distribution across streets. (2) Three stages of shoreline utilization were identified: rapid development and intensified utilization from 2000 to 2015, a shift toward governance and protection from 2016 to 2020, and improved efficiency of intensive utilization since 2021. The proportions of the three categories tended to stabilize, and the ecological environment along the Yangtze River in Jiangyin City improved substantially. However, increasing the retention rate of natural shoreline remained challenging. (3) The planned proportions of the three types were 46∶18∶36 for the recent level year (2025), and 42∶18∶40 for the long-term level year (2035). Following the implementation of the plan and related actions for the management and protection of rivers and lakes, the proportion of production shoreline was reduced to below the planned requirement for the long-term level year (2035), while the proportion of ecological shoreline was increased to above the planned requirement. Nevertheless, there are still risks in implementing certain specific arrangements of the plan, and dismantling some utilization projects in Jiangyin City continues to be difficult. [Conclusion] This study proposes targeted countermeasures to support the management and protection of rivers and lakes in Jiangyin City, including improving coordination among plans, continuously enhancing the efficiency of shoreline utilization, and strengthening process supervision of shoreline utilization projects. Accordingly, the shoreline protection and utilization planning in Jiangyin City can serve as a representative reference for the other seven cities along the Yangtze River in Jiangsu Province. Meanwhile, the planning review and evaluation study represents an innovative approach for river and lake management in the Yangtze River Basin. At the beginning of the 15th Five-Year Plan period, the study can also serve as a summative evaluation example for other special water conservancy plans from the 14th Five-Year Plan period, as well as a reference for planning during the 15th Five-Year Plan period.
[Objective] Data sharing serves as the foundation and guarantee for transboundary river cooperation, and its effectiveness largely depends on the degree of support from the external institutional environment. This study aims to address the current gap in research on transboundary river data sharing and provide theoretical support for the ongoing water resources data sharing under Lancang-Mekong cooperation led by China. [Methods] Based on the institutional collective action (ICA) framework, this study revealed the mechanisms through which structural external environments influenced cooperation risks. Furthermore, utilizing this framework, the study analyzed the characteristics of the external environment for data sharing within the Mekong River Commission (MRC), the structure of cooperation risks faced by participating parties, and the impact of these risks on data sharing behaviors and outcomes. [Results] (1) The data sharing system of the MRC was characterized by weak authorization relationships, multiple and complex tasks, and high heterogeneity in the preferences of the participating parties. (2) Cooperation risk was the core driver of the collective action dilemma in data sharing. Different data-sharing tasks are subject to various types of collaboration risks. (3) The decentralization reform of the MRC increased cooperation risks and further decreased the effectiveness of data sharing. [Conclusion] Based on the findings, it is recommended that future data sharing under the Lancang-Mekong water resources cooperation should: (1) begin with relatively simple tasks that involve low cooperation risks, focusing on low-risk, high-consensus tasks to advance data sharing progressively; (2) adhere to the principle of “software before hardware,” prioritizing soft infrastructure development tasks such as unifying monitoring standards, enhancing data management capabilities, and coordinating perceptions on sharing, and then gradually transition to constructing a unified data cooperation platform and a cross-border station network system; and (3) fully consider the compatibility between cooperation benefits and transaction costs, adopt a bottom-up institution construction model, promote the implementation of data sharing tasks through the approach of “pilot projects first, item-by-item negotiation,” and gradually construct a data sharing institutional framework for the entire river basin.
