China’s 10-year fishing moratorium in the Changjiang River Basin, implemented in 2021, provides an important context for evaluating early habitat responses of estuarine fishes under reduced fishing pressure. We compared seasonal distribution, habitat suitability, and niche differentiation of two sympatric anchovies, Coilia nasus and Coilia mystus, in the Changjiang River Estuary and adjacent East China Sea. Bottom-trawl surveys were conducted at 55 fixed stations in spring, summer, and autumn of 2024, and four species distribution modelling algorithms were evaluated; an independent 2025 survey at the same stations and seasons was used to assess temporal transferability. Random Forest performed best [mean area under the receiver operating characteristic curve (AUC) = 0.837–0.860] and was used for spatial prediction. The two species showed contrasting habitat dynamics. Coilia nasus had relatively broad environmental tolerance, with high-suitability habitat covering 50.0
The Mariana arc is considered a typical intra-oceanic arc system in the western Pacific, however, the southwestern tip of the Mariana arc with a narrow forearc zone and the Caroline plateau as subducting plate remains enigmatic in tectonic and magmatic history. In this study, new geochemical and geochronological results from metagabbro in the southwestern Mariana forearc provide insights into subduction initiation and tectonic evolution processes. The protoliths of these metagabbros have forearc basalt (FAB)-type geochemical affinity, and were formed at ca. 49.3 Ma (zircon U-Pb age), indicating subduction initiation occurred simultaneously across the entire Izu-Bonin-Mariana arc system. The titanite U-Pb ages indicate that amphibolite metamorphism occurred at ca. 23.3 Ma, which we interpret as resulting from plateau-arc collision. Interactions of the incoming young Caroline plateau have induced a slow subduction rate and, thus, impeded the maturation of the southwestern Mariana arc, and played a crucial role in the tectonic evolution of the Parece Vela Basin and Mariana Trough.
Understanding the impacts of navigation channel construction on saltwater dynamics is essential for effective water resource management and ecosystem protection in estuaries. In this study, we investigated how canal construction altered saltwater intrusion in the Qinjiang River Estuary using a well-calibrated three-dimensional numerical model. The results show that canal construction increased the intrusion length under all combinations of river discharge and tidal conditions. Prior to canal construction, tidal currents exhibited larger amplitudes, resulting in pronounced intratidal variability in salinity and intrusion length. During spring tides, the combination of strong velocity and salinity fluctuations, along with their phase offset, produced a substantial tidal oscillatory salt flux, which served as the primary mechanism for landward salt transport. While during neap tides, the tidal oscillatory salt flux decreased, and the increase in the steady shear flux could not offset the seaward advective salt flux. Consequently, the net salinity flux was directed seaward, leading to a shortened saltwater intrusion length. After construction, tidal current amplitudes decreased due to the enlarged channel cross-section, resulting in weaker intratidal variability in salinity and intrusion length, as well as reduced tidal oscillatory salt flux. Channel deepening promoted more persistent stratification and enhanced estuarine circulation, causing steady shear transport to dominate landward salt flux during both spring and neap tides. As a result, salt tended to be retained within the estuary, and intrusion length showed reduced fortnightly variability. The potential implications of this shift in saltwater intrusion regime for estuarine functions warrant further investigation.
The coastal waters of the Zhujiang (Pearl) River Estuary (CWPRE) represent a typical region with high terrestrial nutrient inputs, where anthropogenic activities have significantly perturbed coastal carbon cycling processes. Understanding the biogeochemical response of carbon dynamics to changes in nutrient inputs is critical for advancing knowledge of coastal carbon cycling. This study utilizes a coupled physical-biogeochemical model, validated against observational and remote sensing data, to investigate the response of seawater partial pressure of carbon dioxide (pCO2) and air-sea CO2 flux (FCO2) in the CWPRE under three nutrient reduction scenarios (energy management, fertilizer management, and integrated management strategies). In winter, changes in dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) were accompanied by variations in phytoplankton growth, whereas in summer, a reduction in DIP limited net primary productivity (NPP), leading to a significant increase in pCO2. However, the most significant pCO2 changes occurred in May, when declines in NPP rates elevated dissolved inorganic carbon (DIC) concentrations, resulting in a distinct peak in pCO2 variability. In September, although the decline in NPP reached its maximum, the associated rise in DIC was offset by weakened vertical mixing and enhanced advection, thereby limiting variability in DIC concentrations and minimal changes in seawater pCO2. The peak change in FCO2 occurs in June, with its deviation from the pCO2 peak mainly attributed to fluctuations in wind speed. These findings demonstrate the high sensitivity of coastal carbon cycling to nutrient variations, underscoring the importance of modeling and scenario-based analysis in capturing ecosystem responses and providing quantitative insights into nutrient–carbon interactions to support ecological management under anthropogenic pressures. While nutrient reduction enhances the carbon sink capacity in estuaries, it may conversely reduce carbon uptake in coastal waters, underscoring the contrasting responses of these two systems.
Seagrass-coral reef seascapes are critical for larval recruitment of coastal fish, yet how monsoons shape larval dynamics and seagrass retention remains poorly understood. This study investigated larval fish assemblages throughout one year in the tropical seascape of Gaolong Bay, Wenchang City, Hainan Island, China. Our findings revealed exceptional diversity, identifying 213 species/taxa across 62 families. Larval density and species richness peaked in March–April during the northeast-to-southwest monsoon transition, remaining elevated through August (southwest monsoon period). Seasonal analysis revealed three distinct assemblage clusters: the spring–summer (March–August) cluster was dominated by seagrass-coral reef associated species, the autumn (October–November) cluster by estuarine-mangrove taxa, and the winter (December–February) cluster by cold-tolerant species. These assemblage patterns were structured primarily by water temperature (optimal at ∼26°C) and wind speed (favorable at 3–5 m/s). Seagrass meadows hosted peak larval abundance (306.20 ind./100 m3), which was six times greater than that of fore-reef waters, and retained larger larval sizes (e.g., Gerres oyena), confirming their critical retention function and connectivity to fore-reef spawning grounds potentially via tidal flows. These findings highlight that monsoon-induced oceanography drives spawning strategies, that seagrass structural complexity enhances retention, and that seascape heterogeneity supports high diversity. Management implications include advancing the summer fishing moratorium to March to protect spawning adults and thereby enhance larval supply, and preserving connected seagrass-coral reef habitats to ensure the persistence of diverse larval community.
Life-history traits and their variation are an important part of research on marine fish and their ecosystems. A clear understanding of basic life-history information at the individual level is a fundamental basis for fishery management and conservation. We compile data on six key life-history traits for 105 fish species in the Northwest Pacific, and analyze them using Pearson’s correlation analysis, principal component analysis (PCA), and K-means clustering. Correlation analysis showed that life-history traits did not occur independently, and several significant relationships were found among them. PCA indicated a clear three-endpoint pattern in the life histories of species in the Northwest Pacific. However, rather than clustering strictly at the endpoints of the three strategies, species formed a continuum across strategies. K-means analysis recognized six clusters of taxa that we refer to as opportunistic, equilibrium, demersal periodic, pelagic–oceanic periodic, intermediate, and salmonic strategists. Each strategy reflects a unique set of life-history and ecological attributes. The proposed life-history classification can provide a conceptual framework for multi-species fisheries management and offer important theoretical support for the scientific management of fishery resources in this region.
Petrogenic organic carbon (OC) is an important component of terrestrial organic matter and has traditionally been regarded as excluded from active regional carbon cycling. Recent studies, however, have demonstrated that petrogenic OC can undergo active oxidation in river-dominated continental margins, implying that its burial and preservation would contribute to the global carbon budget. Nevertheless, the burial processes and their controlling factors of petrogenic OC remain poorly constrained. Here, we use hopanoids as source-specific biomarkers to reconstruct a 300-year burial history of petrogenic OC in the East China Sea (ECS), revealing the two burial stages under climatic and anthropogenic forcing. Prior to the 1950s, low hopanoid maturity and dominant biological hopanoid configurations indicated natural inputs from rock weathering and petrogenic residues in soils. Despite frequent flooding during the 1840s–1920s, the petrogenic OC gradually declined, in contrast to the high-energy hydrodynamic environment. We attribute this to rapid proximal deposition, which limits offshore transport on the ECS inner shelf. The low proportion of petrogenic OC indicated that enhanced soil OC delivery further diluted the natural petrogenic OC signal. After the 1950s, hopanoid maturity increased sharply, indicating the presence of anthropogenic petroleum inputs. In addition, natural petrogenic OC persisted or even rose in recent years, likely due to the reactivation of previously deposited petrogenic OC, driven by enhanced erosion in the lower Changjiang River basin and its delta after dam construction. Overall, this record reveals a transition from a climate-dominated regime to an anthropogenic one after the 1950s. Hopanoid-based reconstruction provides new insights into the fate of petrogenic organic carbon and advances our understanding of its role in the global carbon budget and carbon cycle.
Coastal reclamation reshapes shorelines and land-use/land-cover (LULC) with significant consequences for carbon storage, yet quantitative studies that jointly link transect-scale shoreline change, LULC transitions and multi-epoch carbon stock dynamics remain limited. Here we couple multi-temporal remote sensing with the transect-scale Digital Shoreline Analysis System (DSAS) and spatial carbon accounting using the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) carbon module to quantify how reclamation-driven shoreline advance altered LULC and carbon storage in three subareas representative of reclamation in the eastern Zhoushan Archipelago. Validated shorelines and LULC maps were produced for five epochs and used to derive transect shoreline metrics, identify LULC transfers, and estimate carbon stocks. The results show that large-scale reclamation is the primary driver of wetland loss and of net declines in regional carbon storage, and that periods of pronounced shoreline advance coincide with the largest carbon losses. Donggang experienced the most intensive cumulative advance, with a mean net shoreline movement along transects of 1 017 m. Across the study area, total carbon declined from 75 373.27 Mg in 1989 to 47 681.76 Mg in 2009 and then partially recovered to 60 606.21 Mg by 2024. Correlation analysis reveals strong associations between reclaimed area and wetland reduction, and between impervious-area expansion and wetland loss; wetland loss in turn is tightly linked to reductions in total carbon storage. Nonetheless, carbon outcomes are spatially heterogeneous. In some reclaimed zones, post-reclamation trajectories such as conversion to vegetated or agricultural uses or preservation of inland wetlands produced local carbon gains or muted losses, whereas conversion to impervious cover resulted in substantial carbon declines. Our integrated DSAS–InVEST framework provides spatially explicit, multi-epoch evidence that reclamation-driven shoreline advance is a dominant mechanism for wetland loss and carbon decline, while highlighting that post-reclamation LULC trajectories determine local carbon responses. The framework supports targeted planning, carbon accounting and restoration prioritization to reduce long-term carbon loss in reclamation-prone coastal regions.
Marine sediments serve as the major sink for global organic carbon, profoundly influencing the carbon cycle and climate change. Organic carbon (OC) stability tends to increase with sediment depth. However, the coupled geochemical mechanisms that regulate the molecular evolution and stability of OC remain poorly understood. This study systematically quantified the vertical variations in key geochemical factors, including major-element compositions, grain-size parameters, and mineral assemblages, in Yellow Sea coastal sediments. Characterized OC molecular characteristics and thermal stability based on the evidence from Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and thermogravimetric/derivative thermogravimetry-FTIR analyses. And further identified the dominant controls and coupled mechanisms by which sedimentary minerals influence OC stability and preservation. Results demonstrated that OC decreased progressively with depth. The major elements Al, Si, K, and Fe, as well as total nitrogen, total sulfur, and average particle diameter were significantly positively correlated with the OC, underscoring their substantial indicative power for characterizing and predicting organic carbon distribution in coastal sediments. In contrast, Na abundance, grain-size standard deviation, and skewness were significantly negatively correlated with total organic carbon (TOC), suggesting that finer and compositionally enriched sediments promote OC accumulation, whereas poorly sorted or coarser sediments inhibit it. In shallow oxidizing environments, clay minerals such as illite and kaolinite, along with carbonate minerals like calcite and dolomite, stabilize lipid-type organic carbon with high H/C ratios through surface adsorption. In deeper reducing environments, organic carbon is enriched with thermally stable, low-H/C-ratio aromatic compounds and mineral-bound carbon. Condensed humic substances were the dominant organic components and were likely stabilized through associations with clay minerals rich in chlorite and reduced minerals. This study elucidates the coupled regulatory mechanisms underlying various sedimentary mineral indicators of organic carbon preservation, providing a scientific foundation for understanding carbon sink evolution and potential in coastal sediments.
The turbidity maximum zone (TMZ) has a profound influence on estuarine ecosystems and socially productive activities. However, the long-term patterns of TMZ in the Zhujiang (Pearl) River Estuary (PRE) remain poorly understood. In this study, the interannual variability of TMZ in the PRE was analyzed. A total of 181 TMZ maps were generated from 1987 to 2022 by applying the Otsu method to set the threshold for total suspended sediment normalized values. The results revealed that the TMZ exhibited interannual modes of variability over the past 36 a in the PRE. The occurrence frequency of TMZ during every three years indicates that it appeared most frequently in the West Shoal and East Shoal. In addition, the extent of TMZ showed a significant decline trend from 1987 to 2022, and the high-frequency TMZ area decreased from 337.91 km2 in period 1987–1989 to 39.59 km2 in period 2020–2022, representing an 88.23
Significant changes in sea surface temperature (SST) under global warming have profoundly affected marine biodiversity and ecosystem stability. However, most existing studies on SST and its extreme characteristics have focused on the open oceans, with limited attention to coastal regions. As critical interfaces for fisheries, aquaculture, and diverse socio-economic activities, coastal waters are particularly vulnerable to extreme SST variations. Based on long-term in situ observations from marine stations, this study investigates the spatiotemporal characteristics of mean SST and SST extremes along China coast from 1960 to 2023, with emphasis on long-term trends, seasonal variations, and regional disparities. Results show that coastal mean SST has increased significantly at a rate of 0.27°C/(10 a), exceeding the global ocean average. Spatially, higher SST warming rates were observed in the coastal waters of the Bohai Sea, the Yellow Sea, and the vicinity of the Changjiang River Estuary, whereas relatively lower rates were recorded along the South China Sea coast. Significant seasonal heterogeneity is identified, with stronger warming in autumn and winter than in summer, although summer warming has accelerated in recent decades. Extreme SST events also exhibit substantial long-term changes. The total days of marine heatwaves (MHWs) increased significantly, while the total days of marine cold-spells (MCSs) decreased, with the magnitude of the decrease in MCS days being smaller than the increase in MHW days. In the last decade, MHWs have occurred year-round, with peak occurrences in winter and minima in spring. Our findings reveal the spatiotemporal complexity of SST variability along the China coast and underscore the indispensable role of long-term homogenized observations from coastal marine stations as a core benchmark for regional climate change research.
Internal tides serve as an important carrier for the transfer, propagation, and dissipation of barotropic tidal energy in the South China Sea (SCS), and their variability is strongly modulated by multi-scale dynamic processes. Using the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM), we developed a high-resolution three-dimensional circulation model for simulating temperature, salinity, and currents in the SCS from January 2021 to January 2022. Through barotropic/baroclinic separation, harmonic analysis, and vertical mode decomposition, we systematically investigated the seasonal and spatial variability of incoherent diurnal internal tides (ICIT), and explored their underlying generation and modulation mechanisms. The results reveal pronounced seasonal variability in diurnal internal tide energy, with higher energy levels in winter/summer, and weaker in spring/autumn. The Luzon Strait, Dongsha Islands, the southern coast of Hainan Island, and the southwestern waters of the Nansha Islands are identified as the major high-energy regions for diurnal internal tides. In contrast, ICIT dominate over the northwestern continental slope, eastern Hainan waters, and the southwestern basin. ICIT are primarily modulated by multi-scale dynamic forcings, including monsoons, typhoons, and local upwelling. Results from the vertical mode decomposition indicate distinct seasonal differences in modal energy partitioning. The first mode dominates in autumn, accompanied by substantially enhanced higher-mode contributions, whereas the second mode predominates in winter (68.96 J/m3, 51.2
Strong alongshore currents generate considerable instabilities due to the cross-shore velocity gradient of the mean alongshore current. However, the precise impact of these instabilities on the temporal and spatial evolution of turbulent stress and the mean longshore current in the surf zone remains unclear, and experimental validation in this regard is even more limited. This study investigates the spatiotemporal variability of turbulent stress and the mean longshore current driven by shear instabilities in the surf zone through a series of controlled laboratory experiments. The experiments were conducted in a 55 m × 34 m × 1 m deep wave basin with a plane beach slope of 1:100, subjected to monochromatic, unidirectional, and obliquely incident waves with a large incident angle of 30°. Nine wave conditions were tested, covering a range of wave heights from 2.4 cm to 5.0 cm and periods from 1.0 s to 2.0 s, with wave steepness ranging from 0.004 8 to 0.028 8. The results indicate that shear instabilities significantly influence the very low frequency (VLF) turbulent stress and the cross-shore velocity profiles of alongshore currents in both spatial and temporal domains. The maximum VLF turbulent stress values were observed near the breaker line, highlighting this region as a hotspot for significant mixing. The spatiotemporal variations of turbulent stress and mean alongshore currents were found to be the primary drivers for eddy generation and development. The study provides the experimental validation of the synchronization between shear instability induced turbulent stress variations and eddy formation in the surf zone. The maximum alongshore current velocity increased over time, with significant adjustments observed in the rear shear region of the velocity profile.
Antarctic coastal polynyas are among the most productive regions in the Southern Ocean, playing a crucial role in maintaining ecosystem stability and sequestering atmospheric CO2. To support high primary production, glacial meltwater (GMW) significantly contributes iron (Fe) to these coastal polynyas. However, the flux of exported Fe is poorly constrained due to the rapid recycling of Fe in the euphotic zone. In this study, we investigate the utilization of 228Ra as a tracer for GMW-derived Fe inputs in Antarctic coastal polynyas. Our results show that 228Ra exhibits significantly higher activities [(0.17 ± 0.06) Bq/m3]within the coastal polynyas compared to those outside [(0.04 ± 0.04) Bq/m3]. The elevated 228Ra activities suggest GMW inputs within the polynyas, consistent with the distribution of δ18O. Stimulated by GMW-derived Fe, primary production was enhanced. Moreover, chlorophyll a (Chl a) concentrations positively correlate with 228Ra activities in the polynyas, indicating that GMW contributed Fe and 228Ra in a fixed ratio. Based on these findings, our study highlights the potential of 228Ra as a proxy for quantifying the inputs of Fe derived from GMW in Antarctica.
Developing an autonomous multi-layer coupling model is of great significance for enhancing China’s independent support capability for the natural environment. Focusing on the newly developed Mass Conservation Ocean Model (MaCOM), this study constructs a fully autonomous global ocean-atmosphere coupled model based on the Yin-He Global Spectral Model (YHGSM) and the Community Coupler (C-Coupler). The coupled model effectively addresses the parallel control issue of independent I/O processes in the MaCOM model, thereby providing a methodological reference for the coupling control of other analogous numerical models. Experimental results show that the newly developed ocean-atmosphere coupled model achieves high parallel efficiency and reasonable forecast performance. In the simulation of Super Typhoon Hinnamnor (2022), it performs significantly better than the standalone atmospheric model in terms of intensity prediction.
Swash zones are characterized by high hydrodynamic activity and complex sediment transport. However, limitations of observational instruments prevent a deeper understanding of this zone. Based on field observations at Yueliangwan Beach, western Guangdong Province, China, this study used large-scale particle image velocimetry (LSPIV) to analyze motion in the swash zone and assessed the accuracy of measurements at different time steps with different interrogation areas. We also examined the hydrodynamic features in the swash zone, and evaluated preliminary trends in beach evolution. The main findings were as follows. The LSPIV-derived results align closely with observed values. The accuracy of the calculated results, such as longshore velocity, onshore/offshore velocity, may be influenced by limitations in video recording coverage, complex swash motion and the chosen calculation parameters. The instantaneous flow field at high tide can be divided into three hydrodynamic regions: the initial uprush of the last wave break, the backwash region, and the residual uprush from the previous wave break. At low tide, two additional regions are the second uprush and a turbulence zone between the initial and second uprushes. In a high-tide profile, there is a peak velocity at the initial uprush. At low tide, three velocity peaks are observed, corresponding to the three uprush phases. The differences between high and low tide are correlated with the beach landform and slope as well as the incident wave conditions. The paper can provide a reference for the application of LSPIV method into a survey and analysis of swash zone dynamics.
Saltwater intrusion poses a significant threat to the security of freshwater resources in the Zhujiang (Pearl) River Delta, a region of immense economic and social importance. Effective water resource management requires predictive tools that are both accurate and practical. This study validates a one-dimensional analytical model for saltwater intrusion in the Modaomen Estuary, the primary distributary of the Zhujiang River. The model is tested against a comprehensive dataset covering ten tidal events during the 2025 dry season, a period of high intrusion risk. By assuming a Van der Burgh’s coefficient (K) of 0.5, a value appropriate for partially mixed estuaries, the model is simplified to require the calibration of only a single parameter: the longitudinal dispersion coefficient at the inflection point (D0). The results demonstrate an excellent agreement between the simulated and observed longitudinal salinity profiles under high water slack and low water slack conditions, confirming the model’s applicability. Based on the calibrated D0 values from the ten events, a new site-specific predictive equation for the dispersion coefficient is developed. Furthermore, sensitivity analyses indicate that the predictive framework is relatively insensitive to moderate uncertainties in tidal excursion length and freshwater discharge inputs. This validated analytical model, combined with the site-specific predictive equation, provides a simple yet practical tool for forecasting saltwater intrusion, offering crucial support for water resource management decisions, such as regulating freshwater releases and planning water intake locations in the Modaomen Estuary.
Meiofauna play essential roles in matter cycling and energy transmission, making them vital to the mangrove environment. In September 2022, sediment and water samples were collected from the bay and creek zones of the Coringa mangroves. We investigated the benthic meiofaunal assemblages and diversity concerning the environmental variables from mangroves. Seven meiofaunal groups including free-living nematodes, benthic harpacticoid copepods, polychaetes, ostracods, kinorhyncha, foraminifera, and amphipods were reported. The meiofauna abundance ranged between 734 ± 75 and 5 741 ± 224 individuals per 10 cm2 [ind./(10 cm2)]. Although, nematodes are indicators that measure the ecological state of mangroves on the basis of a range of pressures. Nematoda dominated the creek zone of the mangrove, whereas harpacticoids dominated the bay zone. Eighteen genera from 12 families, including the most prevalent Xyalidae, Desmodoridae, and Linhomoeidae, represented nematodes. The taxa Monhystera paludicola, Daptonema orientale, and Terschellingia longicaudata were prevalent in the silt-dominated zones of mangroves. Several pollution indicator nematode species, including M. paludicola, Sabatieria punctata, and D. orientale, have also been found in the bay zone. In terms of the nematode feeding guilds, epigrowth feeders were dominant, followed by nonselective deposit feeders. Variations in salinity, organic carbon, and sediment texture have a direct impact on the distribution and abundance of meiobenthic organisms, indicating a strong ecological link between habitat conditions and organismal responses. The results highlight the need for more studies on the distribution of meiofauna and their contributions to ecosystem services while offering insights into the dynamics of meiofauna in the Coringa mangrove.
Understanding the spatial variability of sea level distributions is essential for revealing tidal dynamics. However, the statistical structures and physical drivers underlying this spatial variability remains unclear. Here, we apply the bimodal-coupling general unit hydrograph (BC-GUH) model to tide-gauge records from Global Extreme Sea Level Analysis (GESLA-3) and satellite altimetry data from TOPEX/Poseidon-Jason missions, and extract four physically interpretable parameters: modal dominance, modal location, scale, and shape to quantify the probabilities of low-water-level (LWL) and high-water-level (HWL) events in the northern South China Sea (NSCS). The analysis reveals that sea level distributions across the NSCS exhibit coherent but regionally distinct patterns. Specifically, the probabilities of LWL and HWL are systematically organized by tidal propagation pathways, shoreline confinement, and basin resonance. In narrow straits such as the Taiwan Strait, exceptionally large tidal ranges sustain HWL dominance, whereas in the Zhujiang River (Pearl River) Estuary, river-tide interaction may compress the modal range and enhance asymmetry toward persistent HWL events. By contrast, the Beibu Gulf shows amplified LWL dominance due to semi-enclosed basin resonance, while offshore basins are characterized by weak but stable LWL modes that may be locally reorganized by reefs and typhoon forcing. These findings demonstrate that the BC-GUH framework directly links statistical parameters to physical tidal dynamics by explicitly relating their spatial variability to distinct tidal propagation pathways, geomorphological confinement, and basin-scale resonance regimes, offering a unified description of bimodal sea level variability. The approach provides new insights into how geomorphology and hydrodynamic setting shape the probability of extreme events, thereby improving the capacity to assess coastal and estuarine risks under changing environmental conditions.
In recent decades, intense anthropogenic perturbations have considerably affected the Zhujiang River (Pearl River) Estuary. However, the sedimentary records of human activities remain unclear because of the large spatial and temporal variation of sediments in this estuary. In this study, two 210Pb-dated sediment cores were retrieved from the western and eastern parts of Lingdingyang Bay (LDB) to determine grain size, total organic carbon (TOC) and total nitrogen (TN) contents, TOC/TN ratio and stable isotope (δ13Corg) of organic carbon (OC). The two cores exhibited opposite change trends in grain size and δ13Corg value. The western and eastern cores exhibited coarse-to-fine and fine-to-coarse trends, respectively, responding well to decreased sediment load and stronger tidal current. These hydrodynamics changes resulted from human activities, including dam construction, coastal reclamation and channel dredging. The δ13Corg values strongly correlated with eutrophication and hydrodynamic changes. The increase trend of δ13Corg values in western cores likely resulted from enhanced marine primary productivity owing to elevated wastewater inputs. In contrast, the declining trend in eastern cores may be attributed to the selective preservation of terrestrial OC in high-energy tidal settings. This study suggests that the spatial and temporal variation of sediment in LDB responds to various human activities, further improving our understanding of hydrodynamic and carbon cycling processes in highly disturbed estuarine ecosystems.
