Search Results (46)

Climate-driven hydrological extremes and anthropogenic interventions are increasingly altering streamflow regimes worldwide. While prior studies have explored climate or regulation effects separately, few have integrated multiple teleconnection indices and reservoir chronologies within a cross-basin comparative framework. This study addresses this gap by assessing long-term streamflow nonstationarity and its drivers at two key stations—Khabarovsk on the Amur River and Datong on the Yangtze River—representing distinct hydroclimatic settings. We utilized monthly discharge records, meteorological data, and large-scale climate indices to apply trend analysis, wavelet transform, percentile-based extreme diagnostics, lagged random forest regression, and slope-based attribution. The results show that Khabarovsk experienced an increase in winter baseflow from 513 to 1335 m³/s and a notable reduction in seasonal discharge contrast, primarily driven by temperature and cold-region reservoir regulation. In contrast, Datong displayed increased discharge extremes, with flood discharges increasing by +71.9 m³/s/year, equivalent to approximately 0.12% of the mean flood discharge annually, and low discharges by +24.2 m³/s/year in recent decades, shaped by both climate variability and large-scale hydropower infrastructure. Random forest models identified temperature and precipitation as short-term drivers, with ENSO-related indices showing lagged impacts on streamflow variability. Attribution analysis indicated that Khabarovsk is primarily shaped by cold-region reservoir operations in conjunction with temperature-driven snowmelt dynamics, while Datong reflects a combined influence of both climate variability and regulation. These insights may provide guidance for climate-responsive reservoir scheduling and basin-specific regulation strategies, supporting the development of integrated frameworks for adaptive water management under climate change. Full article

Elucidating the compositions, sources and mixing processes of dissolved organic matter (DOM) is crucial for a gaining deeper understanding of the coastal carbon cycle and global carbon budget. Hangzhou Bay (HZB), a vital estuary in China, receives freshwater inputs in the upper bay, borders the Changjiang River Estuary (CRE) to the north and is adjacent to Zhoushan Islands Region (ZIR) to the east. In HZB, the DOM sources and their compositions in estuaries remain unclear due to the complexity of this dynamic environment. In this study, we aimed to explore the chemical composition and sources of the DOM in the HZB and its adjacent coastal waters based on chromophoric DOM, fluorescent DOM indices and other hydrochemical parameters in the winter. The results showed that the DOM compositions in HZB have significant differences in the upper bay, middle bay and lower bay. The highest concentration of DOC was found in the CRE, close to the northern lower HZB, with high humification index (HIX), low biological index (BIX) and high proportion of humic-like fluorescent component (C1), indicating terrestrial inputs. In contrast, the DOM in the upper bay had high BIX and low HIX, being dominated by protein-like fluorescent components (C2 and C3), indicating an autochthonous source. The DOM in the middle bay showed mixed composition characteristics indicated by the chromophoric DOM (CDOM) and fluorescent DOM (FDOM) indices. Moreover, the terrestrial DOM transported via CDW intrusion accounted for a large proportion of the DOM in Northern HZB. Our study shows that, even in coastal estuaries with very strong hydrodynamics, the DOM composition can still retain its unique source signal, which, in turn, affects its migration and transformation processes. The results of this study provide supplement insights into the global carbon cycle and carbon budget estimation. Full article

Multi-driver interactions shape estuarine wetland evolution, yet the intricate evolution patterns and their controlling factors their spatiotemporal dynamics remain inadequately understood. This study employs high-resolution satellite data (1985–2020) and 3S technology (overall classification accuracy: 92.44%, Kappa coefficient: 0.9132) to reveal the development of tidal creeks and vegetation evolution patterns of the Dongtan wetland. Our findings indicate a transition in the development of tidal creeks and vegetation from a natural stage to an artificial intervention stage. Northern regions exhibited severe degradation of both vegetation and tidal creeks influenced by reclamation, contrasting with southern recovery post-restoration. This disparity highlights the varied responses to human activities across different areas of the Dongtan wetland. Notably, the introduction of the invasive species Spartina alterniflora has negatively impacted the habitat of native vegetation. The interaction mechanism between vegetation and tidal creeks manifest as: vegetation constrains tidal creek development through substrate stabilization, wave dissipation, and sediment retention, while tidal creeks modulate physicochemical properties of the substrate hydrological connectivity and seed dispersal, affecting vegetation zonation and community structures. Human activities exert dual modulation effects on the Dongtan wetland, driving its phase transition from natural to artificial landscapes, with artificial landscapes exhibiting the most dynamic landscape type through reclamation and ecological restoration projects. Our findings enhance the understanding of the mechanisms underlying estuarine wetland development and inform strategies for restoring healthy estuarine wetland ecosystems. Full article

Sediment transport in Hangzhou Bay and the adjacent Changjiang Estuary is extremely complex due to the bathymetry and hydrodynamic conditions in this region. Using the particle tracing method based on the ROMS model, three-dimensional (3D) passive particle transport in Hangzhou Bay and the Changjiang Estuary was simulated. Ocean temperature, salinity, and circulation patterns before and during Severe Tropical Storm Ampil (2018) were reproduced by the model. The circulation in Hangzhou Bay is significantly influenced by the passing of the storm with an enhanced southeastward surface current. The along-front current offshore of the Changjiang Estuary, accompanied by the Changjiang River plume, is weakened by strong mixing under the storm. The transport of passive particles before and during the storm was also simulated based on the current fields of the model. The results show that the passing of the tropical storm enhances mass exchange in Hangzhou Bay by the storm-induced southeast circulation, while particle transport near the Changjiang Estuary decreases as the estuarine plume is weakened by the intense mixing of strong winds of the storm. Full article

The oceanic fronts play an important role in marine ecosystems and fisheries. This study investigates the seasonal variability of sea surface temperature (SST) fronts in Zhoushan and its adjacent seas for the period 1982–2021. The influences of various underlying dynamic processes on the fronts are also discussed. The horizontal gradient of SST is calculated as frontal intensity, and a threshold value of 0.03 °C/km is set to count the frontal frequency. The fronts in Zhoushan and its adjacent seas show significant seasonal variability, with high (0.1 °C/km and 60–90%) and low (0.03 °C/km and 30–60%) frontal activity in winter and summer, respectively. In summer, the fronts along Jiangsu and the north of the Changjiang River Estuary show higher frontal intensity and frequency, which is mainly influenced by the Changjiang diluted water and southerly wind, and fronts around Zhoushan Island are highly related with Zhoushan upwelling. In winter, the fronts strengthen into regular bands offshore and parallel to the coast, which are mainly influenced by coastal currents. Frontal intensity and frequency show a more significant long-term increasing trend in winter than in summer. Full article

Estuaries and deltas hold significant socioeconomic importance and immense ecological value due to their dynamic geomorphic processes and unique geographical advantages. However, in recent decades, delta recession and the instability of river regimes have become global challenges, driven by intensive human interventions in upstream river basins and local regions. This study examines the South Branch of the Changjiang Estuary as a typical case to investigate its morphological evolution over the past decades and project future trends, offering suitable solutions to enhance the river regime stability. Analysis of bathymetric data reveals substantial channel–shoal adjustments in the South Branch from 1958 to 2016, characterized by significant erosion and deposition on a decadal scale. After 1997, reduced fluvial sediment supply has led to widespread erosion in the South Branch. Further disturbances at the Baimao Shoal and Biandan Shoal have exacerbated the instability of the river regime. Numerical predictions indicate continued erosion in the South Branch over the next 20 years, accompanied by further channel–shoal pattern adjustments. Hydrodynamic modeling of proposed measures demonstrates an improved flow ratio for the North Baimao Shoal Channel, contributing to enhanced channel–shoal system stability. These integrated governance measures have been incorporated into the latest renovation plan for the Changjiang Estuary. The findings provide valuable scientific guidance for the comprehensive management of the Changjiang Estuary and offer insights applicable to other large estuaries facing similar challenges. Full article

To reveal the characteristics and environmental indications for the combination of the grain size and magnetic susceptibility of coastal sediments, we provided a necessary basis for further study on their genetic mechanisms. Based on the data of grain size and magnetic susceptibility of the 36.10 m long core 07SR01 sediments in the Xiyang tidal channel of western South Yellow Sea, we analyzed their variations and correlations and further revealed their environmental indications and corresponding regional sedimentary evolution via the combination of the aforementioned analysis results, the reinterpretation results of the sedimentary sequence and the age of core 07SR01 and shallow seismic profiles, and the findings of climate and glacial–eustatic cycles during Late Quaternary. The three stages of the sedimentary evolution of the Xiyang tidal channel between marine isotope stage (MIS) 7 and MIS 5 were summarized as follows: First is the stage of marginal bank and riverbed developments in the tidal estuary under a relatively high sea level and strong hydrodynamic conditions during MIS 7 (core section: 36.10–26.65 m). The sediments deposited in this stage were mainly affected by the paleo-Changjiang River and characterized by a coarse grain size (mean: 4.02 Φ) and relatively high magnetic susceptibilities (mean: 27.06 × 10⁻⁸ m³·kg⁻¹), with small fluctuations which were strongly and positively correlated with the sand component. Second is the stage dominated by fluviolacustrine and littoral environments with the weak hydrodynamics during MIS 6–5, in which the climate changed from cold and dry to warm and humid as the sea level rose after a drop (core section: 26.65–15.77 m). The sediments deposited in this stage were characterized by a fine grain size (mean: 5.27 Φ) and low magnetic susceptibilities with minor variations (mean: 10.83 × 10⁻⁸ m³·kg⁻¹) which were weakly and positively correlated with the coarse silt component. Third is the stage of delta front in the tidal estuary with a relatively high sea level and strong hydrodynamics during MIS 5 (core section: 15.77–0 m). The sediments deposited in this stage were strongly influenced by the paleo-Yellow River and characterized by a relatively coarse grain size (mean: 4.86 Φ), and high magnetic susceptibilities (mean: 37.15 × 10⁻⁸ m³·kg⁻¹) with large fluctuations which were weakly and positively correlated with the sand and coarse silt components. Full article

Marine heatwave (MHW) events have significant consequences for marine ecosystems and human society. This paper investigates a MHW’s spatial–temporal characteristics in the Changjiang River Estuary and its surrounding coastal regions (CRESs), as well as analyzes the drivers, using satellite and reanalysis data spanning from 1982–2021. The findings show that, during the last 40 years, all four of the MHW indicators have increased. The summer MHW is more severe than other seasons, showing a rising pattern from southeast to northwest. The rise of MHWs can be attributed to the increase in sea surface heat flux, weak wind speed, and powerful El Niño events. Additionally, two special MHW events were detected during the entire study period: Event A lasted for 191 days from 9 October 2006 to 17 April 2007; Event B had an average intensity of 4.93 °C from 5 July 1994 to 1 August 1994. For locations so close to each other, the characteristics of MHWs can also vary, and the mechanisms behind them are highly complex. Full article

The continuous operation of the Three Gorges Reservoir since 2003 has altered the annual runoff into the Changjiang River Estuary, significantly affecting patterns of saltwater intrusion. This has become more pronounced with the development of the East Route of the South-to-North Water Transfer Project, which has changed the runoff distribution and saltwater dynamics once again. Recognizing the critical need to understand these changes, this study employs numerical simulations to investigate the impact of the East Route of the South-to-North Water Transfer Project’s water abstraction on saltwater intrusion in the Changjiang River Estuary post-2003. It assesses intrusion distances, freshwater availability, and periods when water intake might be compromised due to high salinity. Our findings indicate that the East Route of the South-to-North Water Transfer Project markedly influences intrusion patterns. By modeling various runoff scenarios, the study delineates the correlation between average monthly runoff at the Datong Hydrological Survey Station and estuary salinity. It then suggests optimal ecological discharge levels to manage saltwater intrusion effectively. This research provides insights which are necessary for informed water management and ecological protection in the region. Full article

Estuarine projects can quickly change the estuarine topography and influence the hydrodynamics and saltwater intrusion. The Changjiang Estuary is a multiple-bifurcation megaestuary, and the outstanding feature of the saltwater intrusion is the saltwater spillover from the North Branch (NB) into the South Branch (SB). In this study, the improved ECOM-si model was adopted to numerically experiment with the impact of the sluices that are planned for construction in the upper, middle, and lower reaches of the NB on the saltwater intrusion and freshwater resources. The simulation results show that, on the one hand, sluice construction can eliminate the saltwater spillover from the NB into the SB; on the other hand, sluice construction makes water enter the NB from the SB, and the runoff discharging into the sea in the SB decreases. The water intake time of the Qingcaosha Reservoir (QCSR) increases by 3.2 days for sluice construction in the upper reaches of the NB and decreases by 0.97 and 0.94 days for sluice construction in the middle and lower reaches of the NB, respectively. Considering the impact of sluice construction in the NB on the saltwater intrusion and freshwater resources, the construction of sluices in the upper reaches of the NB is recommended. Full article

The Sheyang estuary is located on the northern Jiangsu muddy coast, in the western South Yellow Sea, and in the transition area between the eroded coast of the abandoned Yellow River delta and the silted coast of the central Jiangsu. This area is also one of the key areas of interactions between the paleo-Yellow River and paleo-Changjiang River during the late Quaternary. In order to investigate deeply the late Quaternary sedimentary sequence models of coasts and continental shelves under the interactions of the above two large rivers, the sedimentary sequence and age of the core NTCJ1 drilled at the Sheyang estuary were re-examined and re-interpreted recently, based on the existing data on lithology, grain size, ostracods, foraminifera, clay minerals, geochemical elements, and Electron Spin Resonance (ESR) dating, together with other adjacent key cores and shallow seismic profiles. The three new perspectives were summarized as follows: Firstly, the 22.00 m-long core NTCJ1 recorded the evolution of the sedimentary environments since Marine Isotope Stage 5 (MIS 5), and the first continental facies layer formed in MIS 4-2 is supposed to be missing; therefore, the MIS 1 marine facies layer directly overlays on the MIS 5 marine facies layer. Furthermore, the second continental facies layer formed in MIS 6 and/or the stage of the relatively low sea-level of MIS 5 has not been drilled yet. Secondarily, the middle-upper part of the NTCJ1 core sediments (0.00–17.95 m) are characterized by a finer grain, with a predominantly silty texture and dark yellow tone, and from bottom to top it shows a change from fine to coarse and then to fine in grain size, which could be substantially interpreted as the abandoned Yellow River deltaic deposits mainly formed in 1128–1855 CE, and may contain a small amount of Holocene coastal-shallow marine deposits at the bottom; however, it is difficult to identify them currently. Thirdly, the lower part of the NTCJ1 core sediments (17.95–22.00 m) have not yet been drilled through and are characterized by a coarser grain, with a predominantly fine sandy texture and dark grey tone, which could be interpreted as a delta front deposit in the MIS 5 tidal estuary and were obviously influenced by the paleo-Yellow River. Full article

The study used the SCHISM ocean model combined with the WWM III wind wave model to quantify the interaction between wind waves and tides in the coastal zone of the Changjiang River Estuary and its adjacent areas. The wave and storm surge during Typhoon Ampil, which made landfall in July 2018 in Shanghai, were simulated by using the Climate Forecast System Version 2 (CFSv2) and Medium-Range Weather Forecasts (ECMWF) latest reanalysis (ERA5) wind dataset from 1 July to 31 July. Model results with CFSv2 forcing show better performance in terms of significant wave height and storm surge than those with ERA5 forcing. To investigate the interactions between waves, water levels, currents, and their combined effects on significant wave and surge variations, six numerical sensitivity experiments were designed according to the different coupling methods between SCHISM and WWMIII. The research shows that in coastal areas with water depths of less than 10 m, waves are affected by water levels and currents. The differences in the effect on significant wave height between wave-tide coupling and one-way coupling with water levels and currents are negligible. Wave setup is an important physical term which cannot be ignored during the variations of storm surge caused by Typhoon Ampil. The contributions of wave set up were concentrated in coastal areas with water depths less than 10 m. The peak wave setup occurred in the Changjiang River Estuary, reaching 0.15 m. In Xiangshan Bay and Sanmen Bay, wave radiation stress makes the proportion of wave setup to the total surge reached more than 30%. The consideration of wave-tide interaction can effectively improve the accuracy of numerical wave and storm surge simulations, which can provide more accurate hindcasts of wave and storm surge variations in the Changjiang River Estuary and its adjacent coastal areas. Full article

Skeletonema potamos is a freshwater diatom that has been widely distributed in North America, Europe, and Australia since the 1980s. However, there have been few previous reports of S. potamos in China. Only recently has S. potamos been frequently found in our extensive ecological surveys in China, and it has sometimes even been the dominant species. This study clarified the morphology, distribution, and origin of S. potamos, as well as the underlying mechanism contributing to its dominance. We examined the samples collected from the Changjiang River (Yangtze River) Basin during 2016–2022 and determined their geographical distribution. Genetic distance analysis indicated that S. potamos strains in China might have been transported by ships and ballast water from the USA or Japan through the East Sea into the Yangtze River Estuary. Cargo ships possibly contribute to its dispersal. An analysis of the ecological factors affecting the occurrence and distribution of S. potamos in China indicated that many waterbodies provide environments suitable for S. potamos. The suitable environment, small size, and rapid reproduction of S. potamos are the reasons for its dominance in the Yangtze River Basin. We predict that S. potamos is likely to form “blooms” in China in the future. Full article

Based on a high-resolution unstructured SWAN model and GFS forecast wind, an operational wave forecasting system is conducted for the Changjiang River Estuary (CRE). The performance of the wave forecasting system is evaluated by comparing it with the altimeter observations and in situ wave buoys. The present operational system shows good accuracy in reproducing the seasonal and the synoptic-scale wave characteristics over the CRE. The forecasting capability in three different horizons, including 24 h, 48 h, and 72 h forecasts, is evaluated. Waves over the CRE exhibit distinct seasonal variability. Larger waves occur in both the summer and winter when typhoons and cold weather events affect the CRE. In contrast, waves with longer wave periods take place mainly in the wind transition seasons, i.e., the spring and fall, and the wave directions are more dispersed in these seasons. A seasonal varied forecasting capability is also revealed: better in the winter and spring than in the summer and fall and better during cold weather events than during typhoons. A cross comparison with the model analysis suggests that there is a systematic difference between wave measurements by Jason-3 and Sentinel-3A/3B. The significant wave height from Jason-3 compares best with the model analysis and forecasts and is systematically lower than Sentinel-3A/3B in lower wave conditions (<4 m) in the East China Sea. Substantial discrepancies exist among the three altimeters when the significant wave height exceeds 4 m, and further efforts are needed to discern their merits. Full article

More and more attention has been paid to the study of the impact of extreme climatic events on the ecological environment off the Changjiang River Estuary. In this study, the relationship between the chlorophyll concentration and ENSO (El Niño Southern Oscillation) events was studied. Several potential physical mechanisms between the ENSO and chlorophyll concentration were analyzed using observation and sensitivity experiments from a high-resolution ROMS-CoSiNE coupled model (Regional Ocean Modeling System-Carbon, Oxygen, Silicon, Nitrogen and Ecosystem) off the Changjiang River Estuary. Our results indicated that the April to August averaged chlorophyll concentration off the Changjiang River Estuary was significantly correlated with the December to February averaged ENSO indices in the previous winter. The 10 m wind speed and SST (Sea Surface Temperature) affected by an ENSO event had little effect on the chlorophyll concentration, while the discharge had a significant effect on the chlorophyll concentration off the Changjiang River Estuary, and the discharge was significantly and positively correlated with the ENSO indices. We tested the effect of interannual variations of the discharge and nutrients carried by discharge on the interannual variation in the chlorophyll concentration in the ENSO events. Two sensitivity experiments showed that when the nutrients in the freshwater discharge were kept as a constant seasonal cycle, the composite differences in the chlorophyll concentration between the positive and negative ENSO phases off the Changjiang River Estuary were reduced. When there were no nutrients in the freshwater discharge, the composite differences in the chlorophyll concentration between the positive and negative ENSO phases off the Changjiang River Estuary were reduced by one order of magnitude. The discharge can modify the stratification off the Changjiang River Estuary, and the nutrients carried by the discharge play a dominant role in determining the interannual variation of the chlorophyll concentration associated with the ENSO cycles. Full article