Search Results (120)

Accurate nitrogen dioxide (NO₂) forecasting is crucial for proactive emission control and issuing public health warnings. This study provides the first evaluation of the China Meteorological Administration’s (CMA) operational CUACE/Haze-Fog V3.0 numerical prediction system, assessing its daily NO₂ forecast accuracy against independent satellite measurements and in situ observations. We compare model forecasts with TROPOspheric Monitoring Instrument (TROPOMI) satellite column data and observations from 1677 Chinese ground monitoring stations, focusing on four key regions: the Yangtze River Delta, Pearl River Delta, Beijing–Tianjin–Hebei, and Urumqi. An optimal spatial resolution of 0.15° × 0.15° was determined for TROPOMI data processing. The results indicate a strong seasonal dependency in model performance. The model systematically underestimates NO₂ concentrations in winter but performs significantly better in summer. This systematic bias is confirmed by a Normalized Mean Bias (NMB) consistently below −20% in northern regions during the winter. In the Beijing–Tianjin–Hebei region, the Root Mean Square Error (RMSE) reached 3.57 × 10¹⁵ molec/cm² (vs. TROPOMI) and 1.09 × 10¹⁵ molec/cm³ (vs. ground stations) in winter, decreasing to 0.95 and 0.91, respectively, in summer. Critically, this winter bias pertains to pollution magnitude rather than temporal correlation; the model captures pollution trends but underestimates peak severity. Our study reveals a ‘vertical decoupling’ in the operational forecasting system. While the model utilizes surface data assimilation to correct surface pollutants, this study demonstrates that these corrections fail to propagate vertically to the total NO₂ column during winter stable boundary layer conditions. This finding has broader implications for chemical transport models (CTMs): relying solely on surface data assimilation is insufficient for constraining column burdens in regions with complex vertical stratification. We propose that future operational systems integrate satellite-based vertical constraints to resolve the systematic winter bias identified here. Full article

High-resolution in situ field measurements capturing seasonal 3D mixing dynamics at river confluences are scarce, yet this understanding is essential for effective water-quality management and pollutant-transport prediction in river–lake systems. To address this gap, this study investigates the confluence of the North and South Han Rivers in the Paldang Reservoir. We introduce and apply a novel mixing proximity index (MPI) to quantify the degree of mixing and water-mass origin based on 3D electrical conductivity and temperature data. Seasonal field campaigns, conducted with an acoustic Doppler current profiler and multi-parameter sensors, revealed distinct hydrodynamic behaviors: strong summer stratification suppressed vertical mixing; winter momentum asymmetry induced persistent flow separation despite minimal temperature differences; and spring conditions fostered rapid mixing, barring some residual unmixed deep layers. The MPI effectively delineated shear layers and identified unmixed water zones, providing an enhanced understanding of mixing dynamics beyond the capabilities of traditional tracer- or statistics-based metrics. These findings highlight the combined influence of density differences, tributary momentum, and dam operations on confluence mixing, offering practical insights for water-resource management and improving 3D hydrodynamic model validation. Full article

The central Bohai Sea (CBS) is the distribution center and wintering grounds for economically important species of fish, shrimp, and crabs migrating from the Yellow Sea and the BS. However, the frequency of hypoxia in the CBS has gradually increased, posing a threat to its ecology. Therefore, we analyzed data from an on-site investigation of the cold-water mass coverage area in the southern part of the BS in the spring, summer, and autumn of 2022. We investigated the characteristics of seasonal variation in water quality parameter, the main characteristics and leading factors affecting the distribution of bottom hypoxia using stratification data and the Nutritional Status Quality Index. The “boot-shaped” distribution of hypoxia in summer was primarily the result of the intrusion of cold and highly saline water from the northern part in the study area, as well as the intrusion of high-temperature and low-salinity water from the Yellow River estuary (YRE) and the high-salinity water in the northeast corner of the study area, which had altered the stratification effect of the region. This is also the main reason that affects the accuracy of the prediction for occurrence of hypoxia stations in summer. The results show that the cold-water mass in the northern part of the Bohai Sea invades the cold-water mass in the southern part in summer 2022. Thus, this study provides novel insights into the formation and distribution of hypoxia in the CBS. Full article

Suspended sediment transport in large rivers is characterized by complex cross-sectional patterns. This study investigates the cross-sectional distribution of the suspended sediment concentration (SSC), based on 15 measurement campaigns at six stations along a 67 km reach of the middle Rhine in Germany. Utilizing a multi-method approach, we conducted turbidity and acoustic backscatter measurements, in situ particle size data, recorded water quality parameters such as electrical conductivity, and took 495 pump-based water samples over a period of 2.5 years. Statistical analysis of this comprehensive dataset shows that lateral differences have greater importance for the cross-sectional SSC distribution than vertical differences, suggesting that incomplete river mixing is of greater importance than vertical stratification for uncertainties in load calculations. We demonstrate that surface measurements are consistently representative for the whole water column and that applying the traditional Rouse equation for vertical extrapolation from surface measurements leads to large errors. We conclude that efficient monitoring programs should prioritize covering the lateral SSC distribution for more accurate load calculations and offer practical recommendations for improved SSC monitoring in similar conditions. Full article

The discharge of antibiotics from riverine sources into estuaries and adjacent coastal seas is an emerging environmental concern. In this study, we employ seasonal averages derived from a five-year, high-resolution, three-dimensional ocean circulation model to investigate the transport and degradation of a representative antibiotic tracer with a half-life of 31 days, released from the Yangtze River and the Qiantang River into the East China Sea. The model incorporates realistic tides, climatological winds, and seasonal runoff, enabling an examination of typical seasonal conditions. The simulated tracer remains concentrated near the estuarine outlets, with dispersion shaped by the seasonal circulation and stratification. Particle-tracking experiments show distinct pathways: Yangtze-sourced material is rapidly exported southward along the 30 m isobath, traveling about 100 km within 5–10 days, while Qiantang-sourced material exhibits much longer residence times (>30 days) within Hangzhou Bay. Vertical distributions also vary seasonally, with summer stratification confining the tracer to the surface layer and winter mixing dispersing it to deeper waters offshore. These results highlight the contrasting transport behaviors of the two river sources and illustrate how hydrodynamic conditions regulate antibiotic fate in estuarine–coastal environments. Full article

The monitoring of turbidity in estuarine environments is a challenging essential task for managing water quality and ecosystem health. This study focuses on the lower reaches of the River Mersey, Liverpool. Harmonized Sentinel-2 MSI Level-2A imagery was integrated with in situ measurements from seven Environment Agency monitoring stations for two consecutive years (January 2023–January 2025). The workflow included image preprocessing, spectral index calculation, and the application of four machine learning algorithms: Gradient Boosting Regressor, XGBoost, Support Vector Regressor, and K-Nearest Neighbors. Among these, Gradient Boosting Regressor achieved the highest predictive accuracy (R² = 0.84; RMSE = 15.0 FTU), demonstrating the suitability of ensemble tree-based methods for capturing non-linear interactions between spectral indices and water quality parameters. Residual analysis revealed systematic errors linked to tidal cycles, depth variation, and salinity-driven stratification, underscoring the limitations of purely data-driven approaches. The novelty of this study lies in demonstrating the feasibility and proof-of-concept of using machine learning to derive spatially explicit turbidity estimates under data-limited estuarine conditions. These results open opportunities for future integration with Computational Fluid Dynamics models to enhance temporal forecasting and physical realism in estuarine monitoring systems. The proposed methodology contributes to sustainable coastal management, pollution monitoring, and climate resilience, while offering a transferable framework for other estuaries worldwide. Full article

The conservation and transmission of cultural heritage are enduring drivers of sustainable development. As a significant form of cultural heritage, temples play a vital role in maintaining urban historical continuity and embodying local culture. This study investigated the landscape roles of temples within the ancient city of Chongqing. Drawing primarily on sources such as the “Chongqing Fuzhi Quantu” (Complete Map of Chongqing Prefecture) from the Qing Dynasty, it identifies 79 temples in historical Chongqing. Employing Historical Geographic Information Systems (HGIS), the study reveals the multi-scale distribution characteristics of these temples and their interaction mechanisms with the urban spatial structure. The findings indicate that: (1) The development of Chongqing’s temples is closely linked to the stratification process of urban historical landscapes, serving as historical markers reflecting urban culture; (2) The distribution of temples in Qing-dynasty Chongqing exhibited significant correlations with the mountain-river environment and topography, forming clusters at key urban nodes while demonstrating spatial differentiation based on their attributes; (3) the landscape roles of temples in the ancient Chongqing city by guiding the urban landscape order, shaping city landmarks, and anchoring collective memories. Through the interrelated interactions across multiscale spaces, they collectively shaped the urban imagery. The study aims to provide practical recommendations for urban heritage conservation, cultural tourism, and sustainable development. Full article

To elaborate on the effects of hydraulic projects and physicochemical factors on the spatiotemporal distribution of phytoplankton communities, we monitored the phytoplankton communities and related water parameters in the Ganjiang River’s main channel over a five-year period. The survey revealed 65 species across six phyla, with Chlorophyta, Cyanophyta and Bacillariophyta as the most diverse groups. Phytoplankton abundance and biomass exhibited significant seasonal variations (p < 0.001), peaking in summer and autumn and reaching their lowest values in winter and spring. Spatially, phytoplankton abundance and biomass were not significantly different (p > 0.05), the abundance and biomass of Cyanophyta were higher in the two reservoir areas compared to the upstream sampling points. This suggests that the hydraulic projects altered the river’s flow and velocity, which led to a succession in phytoplankton community composition. Correlation analysis showed a strong positive association between the abundance and biomass of both Cyanophyta and Chlorophyta and water temperature (p < 0.001), but showed a significant negative relationship with nitrogen (p < 0.05). In contrast, Bacillariophyta abundance and biomass were positively and significantly correlated with ammonium nitrogen (p < 0.05). Redundancy analysis confirmed that water temperature and nitrogen are the primary environmental variables influencing the phytoplankton community’s succession. The direct alteration of river hydrodynamic characteristics by hydraulic projects, coupled with the reservoir-induced water stratification and its influence on vertical water temperature distribution, ultimately results in the profound reshaping of the phytoplankton community structure through coupled effects with nitrogen cycling. The findings from this study can scientifically inform the ecological scheduling, water quality management and water supply security of the Ganjiang River basin’s cascade reservoirs. Full article

The growth of the human population, combined with climate change, has made the provisioning of water resources to human populations one of the greatest challenges of recent decades. One commonly adopted solution has been the construction of small dams and reservoirs close to urban settlements. However, concerns have arisen that, despite their small size, small dams may have environmental impacts similar to those known for large dams. The severe water crisis observed between 2014 and 2015 led to the multiplication of small dams in southeastern Brazil, such as the one built on the Fetá stream at the Capivari River basin in the municipality of Louveira. This study aimed to contribute to the assessment of the impacts of small dam construction on water quality by monitoring basic parameters and nutrients during the filling and stabilization period of the Fetá reservoir. As expected, the interruption of water flow and the increase in water residence time led to increases in temperature, pH, electrical conductivity, dissolved oxygen and concentrations of dissolved carbon and nitrogen, as well as a reduction in turbidity. Consistent with the shallow depth of the water column, neither thermal nor chemical stratification was observed. Nevertheless, the water quality of surface and bottom layers was markedly different. Over time, water volume and water quality tended to stabilize. This research clearly demonstrates that small dams and reservoirs cause qualitatively similar environmental impacts to those of large-scale dams and reservoirs worldwide. Full article

Global environmental challenges, including eutrophication and hypoxia in enclosed water bodies, require innovative solutions for sustainable water quality management. Lake Biwa, Japan’s largest freshwater lake, suffers from hypoxia in its bottom layers due to strong summer stratification that inhibits vertical mixing. To address this issue, the present study employed a three-dimensional hydrodynamic–ecosystem model to numerically evaluate the effectiveness of training walls (guiding dikes) at river mouths in enhancing vertical mixing and improving bottom-layer oxygenation. Simulations revealed that the installation of guiding dikes significantly altered horizontal advection and promoted vertical mixing, particularly during winter, when weakened stratification allowed snowmelt inflows to sink along the dikes. As a result, local increases in dissolved oxygen concentrations of up to 0.4 mg/L were observed in the bottom layer. These findings demonstrate that guiding dikes can effectively improve oxygen supply to hypoxic zones, especially during periods of low stratification, providing a promising strategy for lake management in temperate regions experiencing seasonal snowmelt. Full article

Historic and cultural villages in China are increasingly challenged by rapid urbanization, uneven commercial development, and fragmented preservation mechanisms. Understanding their spatiotemporal distribution and the factors shaping it is crucial for advancing the integrated development of cultural heritage conservation, ecological sustainability, and socio-economic growth. This study examines 487 historic and cultural villages using the nearest neighbor index (NNI) and kernel density analyses to reveal spatial differentiation patterns. Vector buffer analysis and the geographic detector method were further employed to identify the key drivers of village distribution. The results indicate that: (1) historic and cultural villages exhibit a distinctly clustered spatial pattern, characterized by “more in the southeast, fewer in the northwest; more in the northeast, fewer in the southwest” (NNI = 0.44, Z = –23.52, p = 0.00); (2) provincial-level spatial density demonstrates clear stratification, with high-density clusters concentrated in the Yangtze River Delta, southern Anhui, the Fujian–Zhejiang–Jiangxi junction, and along the Yellow River in Shanxi–Shaanxi–Henan. From the fifth to seventh designation batches, kernel density peaks (maximum ~0.11 × 10⁻²) increased significantly, reflecting stronger spatial clustering; and (3) the spatial distribution of villages is jointly shaped by natural geography, socio-economic conditions, transportation infrastructure, visitor markets, and tourism resources. Among these, nighttime light intensity was identified as the most influential individual factor (q = 0.6132), while the combination of slope aspect and per capita disposable income emerged as the dominant factor pair (q = 0.966). Full article

This study provides new constraints on the paleogeographic evolution of the Arctic during the Mesozoic. U–Pb geochronology of detrital zircon and rutile grains, together with (U–Th)/He zircon thermochronological data from the uppermost Middle Jurassic to Cretaceous strata of the Sverdrup well in the Kara Sea, reveals a major shift in sediment provenance. Two distinct age populations of detrital zircon define this transition: Group 1 (Middle Jurassic–Hauterivian) shows dominant Neoproterozoic–Cambrian (ca. 700–500 Ma) and Paleozoic (ca. 350–290 Ma) peaks, whereas Group 2 (Aptian–Albian) is characterized by prominent Paleoproterozoic (ca. 1980–1720 Ma), Paleozoic (ca. 350–255 Ma), and Early Mesozoic (ca. 240–115 Ma) ages. Corresponding variations in (U–Th)/He zircon ages—from a Triassic peak (~225 Ma) in Group 1 to a dominant Early Cretaceous peak (~140 Ma) in Group 2—support a switch from a proximal to more distal sediment source. We propose that the emergence of large continent-scale river systems transported clastic material from the southern margin of the Siberian Craton to the Arctic Ocean starting in the late Early Cretaceous. The development of a significant freshwater supply potentially initiated a thick low-salinity layer within the surface waters of the central Arctic Ocean, possibly leading to the onset of a strong salinity stratification of near-surface water masses as in the modern Arctic Ocean. Full article

Understanding mixing behavior at river confluences is essential for effective watershed management in response to increasing environmental issues such as algal blooms and chemical pollution. This study focused on the confluence of the Nakdong and Geumho Rivers, employing high-resolution field measurements using an ADCP (M9) and YSI EXO sensors. Water temperature (°C) and electrical conductivity (μS/cm) data were collected under three representative conditions, including flow ratios of 0.91, 0.45, and 0.29, as well as 0.05, with a maximum temperature difference of up to 6 °C. Mixing behavior was three-dimensionally analyzed by integrating cross-sectional and longitudinal data, and the accuracy of visualization was evaluated using IDW and Kriging spatial interpolation techniques. The analysis revealed that under low flow ratio conditions, vertical mixing was delayed; the thermal stratification persisted up to approximately 3 km downstream from the confluence (Line 3), and complete mixing was not achieved until about 7 km downstream (Line 5) due to density currents. Quantitative comparison indicated that IDW (R² = 0.901, RMSE = 31.522) outperformed Kriging (R² = 0.79, RMSE = 35.458). This study provides a quantitative criterion for identifying the mixing completion zone, thereby addressing the limitations of previous studies that relied on numerical models or limited field data, and offering practical evidence for water quality monitoring and sustainable river management. Full article

Urban particulate matter (PM) pollution critically impacts public health and climate. However, traditional ground-based monitoring fails to resolve vertical PM distribution, limiting understanding of transport and stratification-coupled mechanisms. Vertical profiles collected by an unmanned aerial vehicle (UAV) over Hangzhou, a core megacity in China’s Yangtze River Delta, reveal the spatiotemporal heterogeneity and multi-scale drivers of regional PM pollution during two intensive ten-day campaigns capturing peak pollution scenarios (winter: 17–26 January 2019; summer: 21–30 August 2019). Results show stark seasonal differences: winter PM₁ and PM_2.5 averages were 2.6- and 2.7-fold higher (p < 0.0001) than summer. Diurnal patterns were bimodal in winter and unimodal (single valley) in summer. Vertically consistent PM₁ and PM_2.5 distributions featured sharp morning (08:00) concentration increases within specific layers (winter: 250–325 m; summer: 350–425 m). Analysis demonstrates multi-scale coupling of synoptic systems, boundary layer processes, and vertical wind structure governing pollution. Key mechanisms include a winter “Transport-Accumulation-Reactivation” cycle driven by cold air, and summer typhoon circulation influences. We identify hygroscopic growth triggered by inversion-high humidity coupling and sea-breeze-driven secondary aerosol formation. Leveraging UAV-based vertical profiling over Hangzhou, this study pioneers a three-dimensional dissection of layer-coupled PM dynamics in the Yangtze River Delta, offering a scalable paradigm for aerial–ground networks to achieve precision stratified control strategies in megacities. Full article

Massachusetts Bay in the northeastern United States is highly vulnerable to ocean acidification (OA) due to reduced buffering capacity from significant freshwater inputs. We hypothesize that acidification varies across temporal and spatial scales, with short-term variability driven by seasonal biological respiration, precipitation–evaporation balance, and river discharge, and long-term changes linked to global warming and river flux shifts. These patterns arise from complex nonlinear interactions between physical and biogeochemical processes. To investigate OA variability, we applied the Northeast Biogeochemistry and Ecosystem Model (NeBEM), a fully coupled three-dimensional physical–biogeochemical system, to Massachusetts Bay and Boston Harbor. Numerical simulation was performed for 2016. Assimilating satellite-derived sea surface temperature and sea surface height improved NeBEM’s ability to reproduce observed seasonal and spatial variability in stratification, mixing, and circulation. The model accurately simulated seasonal changes in nutrients, chlorophyll-a, dissolved oxygen, and pH. The model results suggest that nearshore areas were consistently more susceptible to OA, especially during winter and spring. Mechanistic analysis revealed contrasting processes between shallow inner and deeper outer bay waters. In the inner bay, partial pressure of pCO₂ (pCO₂) and aragonite saturation (Ω_a) were influenced by sea temperature, dissolved inorganic carbon (DIC), and total alkalinity (TA). TA variability was driven by nitrification and denitrification, while DIC was shaped by advection and net community production (NCP). In the outer bay, pCO₂ was controlled by temperature and DIC, and Ω_a was primarily determined by DIC variability. TA changes were linked to NCP and nitrification–denitrification, with DIC also influenced by air–sea gas exchange. Full article