Search Results (110)

Based on long-term series of observations of water flow of 22 small and medium-sized rivers in the forest-steppe and steppe east of the East European Plain, an analysis of its trend changes in 1961–2022, i.e., in the time interval of the Anthropocene with the most progressive climate change in the study region, was carried out. The main quantitative hydrological parameters studied were annual average water discharge, annual maximum water discharge (Q_max), minimum water discharge (Q_min-CP) during the ice-covered period of the riverbed (cold period, mainly December–March), minimum water discharge (Q_min-WP) during the ice-free period of the riverbed (warm period, mainly April–November), as well as some of their ratios, which provide a clear idea of changes in the intra-annual variability of water flow. The principal methodological toolkit used was a standard set of statistical tests applied to time series analysis. A summary of the study results showed that statistically significant trend changes in the annual water flow of most of the analyzed rivers were not observed for the specified period. At the same time, statistically significant intra-annual changes in the flow were revealed: a significant reduction in Q_max (especially in the forest-steppe zone) and a significant increase in Q_min-CP and Q_min-WP. Thus, the ratio between Q_max and Q_min-CP (Q_min-WP) decreased between the baseline climatic periods 1961–1990 and 1991–2020 by an average of 4.1 (4.0) times in the rivers of the forest-steppe zone, and by 5.2 (5.3) times in the rivers of the steppe zone. Climate change is considered the leading cause of the observed intra-annual changes in river water flow in the study region, with the main factor being an increment in annual air temperature, especially during the cold season. Full article

The Archimedes spiral hydrokinetic turbine (ASHT), an innovative horizontal-axis design, holds significant potential for harvesting energy from localized ocean and river currents. However, prolonged operation can result in blade erosion, which reduces efficiency and may lead to operational failures. To ensure reliability and prevent damage, it is essential to accurately identify the locations and progression of wear caused by sand particle impacts. Using a CFD–DPM approach, this study systematically investigates the effects of sand concentration and particle size on erosion rates and distribution across nine ASHT configurations, along with the underlying physical mechanisms. The results indicate that erosion rate increases linearly with sand concentration due to higher particle impact frequency. Erosion zones expand from the blade tip edges toward mid-span regions and areas near the hub as concentration increases. Regarding particle size, the erosion rate increases rapidly and almost linearly for diameters below 0.6 mm, but this growth slows for larger particles due to a “momentum–quantity trade-off” effect. Blade angle also exerts a tiered influence on erosion, following the pattern medium angles > small angles > large angles. Medium angles enhance the synergy between normal and tangential impact components, maximizing erosion. Erosion primarily initiates at the blade tips and edges, with the most severe wear concentrated in these high-impact zones. The derived erosion patterns provide valuable guidance for predicting erosion, optimizing ASHT blade design, and developing effective anti-erosion strategies. Full article

An in-depth analysis of land use dynamics during the evolution of regional urban systems is crucial for understanding developmental trajectories and promoting coordinated urban growth. This study adopts a land-use perspective, examining the expansion of urban construction land while identifying its source areas. By integrating Zipf’s law and using urban construction land area as an indicator of urban scale, this research analyzes transformations within the urban system. The findings reveal the following: (1) The total area of urban construction land in the Yangtze River Delta has continued to expand over time, exhibiting an inverted U-shaped curve, with high concentration observed in riverine and coastal zones. (2) Cultivated land serves as the primary source for construction land, contributing on average 77.70% over the past 25 years, amounting to a conversion of 5664.51 square kilometers. Rural residential areas rank second, contributing an average of 11.90%. (3) The rank-size distribution of cities based on urban land area largely aligns with Zipf’s law, albeit with deviations at both ends. The Pareto index increased from 0.803 to 0.897, indicating a trend toward weaker dispersion and greater concentration in urban size distribution. In conclusion, future urban development should emphasize rational expansion grounded in sustainable practices, strengthen farmland protection to ensure food security, and effectively manage rural land transformation to promote efficient land use and ecological balance. These measures will support the balanced and coordinated development of large, medium, and small cities within the urban system. Full article

Water reservoirs play a crucial role in the environment in many aspects: hydrology, geochemistry, sediment lithology, geo- and biodiversity, landscape, etc. First of all, it is necessary to have accurate information about the spatial distribution of these objects in a given area to assess their size and functioning. Maps and contemporary spatial databases are often incomplete or outdated, especially in regard to small objects, of variable surface area and condition. This article uses the following approach: high-resolution terrain models derived from airborne laser scanning (ALS) were used for visual interpretation of extensive, flat depressions representing water body basins, thus determining the total number of objects, and classifying them as kettle holes, lakes, ponds, and other types of reservoirs (e.g., overbank basins, oxbow lakes). Using an aerial orthophotomap, the objects were subsequently verified as to how many basins are currently occupied by water bodies. The next step was to determine a number of topographic and morphometric parameters for each object in order to assess their functioning conditions. For selected objects, the assessment was expanded to include a geochemical and lithological analysis of the sediments. The study was conducted in the catchment of the Słubia River (136 km²), located in Central Europe, in northwestern Poland. In the Słubia catchment, a total of 931 water body basins were mapped. The dominant forms are kettle holes (<1 ha), representing nearly 80% of all objects. At present, kettle holes are largely devoid of water bodies and subject to a strong human impact. In addition to those, 118 lake basins were identified (>1 ha, the largest being Lake Morzycko, 360 ha), half of which are occupied by water reservoirs. Ponds and other reservoirs were represented by 37 and 47 objects, respectively. From the perspective of contemporary sediment-forming processes in the documented sedimentary basins, the most favorable conditions for biogenous sediment accumulation exist in the catchments of the upper and medium courses of the Słubia River valley. Although the lithological diversity and thickness of individual sediment types in the Słubia catchment represent local features, they corroborate the results of previous telmatologic research conducted in Myślibórz Lakeland. Full article

The rapid growth of global urbanisation has resulted in significant environmental pollution, with urban water pollution emerging as a critical factor in comprehensive urban development. The present study employs panel data from 268 Chinese cities between 2013 and 2022, utilising entropy weighting and a two-effect fixed-effects model to empirically analyse how urban water pollution control promotes comprehensive urban development. The research findings reveal that water pollution control significantly promotes comprehensive urban development, but there are differences across urban regions and scales, with greater effectiveness observed in central and western regions and medium-sized and small cities. This paper also highlights that water pollution control can promote urban development by optimising industrial structure and proposes that governments should formulate regionally differentiated water pollution control policies, establish a ‘Regional Water Environment Governance and Industrial Transformation Coordination Centre,’ and implement the ‘River and Lake Chief System+’ policy. Full article

Recent years have seen frequent heavy rainfall events in Japan, often linked to Baiu fronts and typhoons. These events are exacerbated by global warming, leading to an increased frequency and intensity. As floods represent a serious threat to sustainable urban development and community resilience, this study contributes to sustainability-focused risk reduction through integrated analysis. This study focuses on the 2 June 2023 heavy rain disaster in Toyohashi City, Japan, which caused extensive damage due to flooding from the Yagyu and Umeda Rivers. Using numerical models, this study accurately reproduces flooding patterns, revealing that high tides amplified the inundation area by 1.5 times at the Yagyu River. A resident questionnaire conducted in collaboration with Toyohashi City identifies key trends in evacuation behavior and disaster information usage. Traditional media such as TV remain dominant, but younger generations leverage electronic devices for disaster updates. These insights emphasize the need for targeted information dissemination and enhanced disaster preparedness strategies, including online materials and flexible training programs. The methods and findings presented in this study can inform local and regional governments in building adaptive disaster management policies, which contribute to a more sustainable society. Full article

This study investigates the anthropogenic transformation of small- and medium-sized river basins within the Caspian Sea catchment. The basins of seven rivers—Sunzha, Sulak, Ulluchay, Karachay, Atachay, Haraz, and Gorgan—were selected as key study areas. For both the broader Caspian region, particularly its southwestern sector, and the selected study sites, trends in land cover types were analyzed, natural resource use practices were assessed, and population density dynamics were examined. Furthermore, a range of indices were calculated to quantify the degree of anthropogenic transformation, including the coefficient of anthropogenic transformation, the land degradation index, the urbanity index, the degree of anthropogenic transformation, coefficients of absolute and relative tension of the ecological and economic balance, and the natural protection coefficient. The study was conducted using geoinformation research methods and sets of geodata databases—the global LandScan population density database, the GHS Population Grid database, the ESRI land cover type dynamics database, and OpenStreetMap (OSM) data. The analysis was performed using the geoinformation programs QGIS and ArcGIS, and a large amount of literary and statistical data was additionally analyzed. It is shown that within the studied region, there has been a decrease in the number and density of the population, as a result of which the territories of river basins are experiencing an increasing anthropogenic impact, the woody type of land cover is decreasing, and the agricultural type is increasing. The most anthropogenically transformed river basins are Karachay, Haraz, and Gorgan. Full article

This study investigated the hydrochemical characteristics, solute sources, and controlling factors of the Qujiang River, a vital tributary of the Qiantangjiang River, on the basis of 61 surface water samples collected from July to September 2019. A multi-method framework integrating ArcGIS spatial analysis, a Piper trilinear diagram, a Gibbs diagram, ion ratio analysis, and principal component analysis (PCA) was systematically applied. The results demonstrate significant spatial heterogeneity in pH values (6.39–7.15 in the upper reaches, 6.31–8.83 in the middle reaches, and 6.85–8.1 in the lower reaches), with hydrochemical facies dominated by Ca-HCO₃ types (87% frequency) in the upper–middle reaches, transitioning to SO₄·Cl-Na and SO₄·Cl-Na·Ca mixed types downstream. Source apportionment indicates that carbonate weathering and atmospheric precipitation are the primary controls on hydrochemistry in the upper and middle reaches, whereas industrial effluents, evidenced by a 2.3-fold increase in SO₄²⁻ concentration, and domestic sewage, with Cl⁻ levels reaching 16.07 mg/L, are the dominant influences in the lower reaches. This study’s innovation lies in the quantitative separation of natural weathering (68% contribution) and anthropogenic activities (32%) through an integrated methodological approach, offering a basin-scale understanding of longitudinal hydrochemical evolution. These results provide valuable insights for the management and ecological conservation of medium- to small-sized basins. Full article

In the context of high-quality economic development, the empowering effect of regional integration policies on urban green and low-carbon development has significantly strengthened, playing a crucial strategic role in achieving the coordinated development of the economy and ecology. This study uses the expansion of the Yangtze River Delta urban agglomeration as a quasi-natural experimental scenario, analyzing the pathways and mechanisms through which regional integration policies influence urban green and low-carbon development based on panel data from Chinese cities between 2004 and 2022, using a multi-period Difference-in-Differences (DID) model. The empirical results show the following: ① Regional integration policies significantly enhance the efficiency of urban green and low-carbon development, a conclusion that remains robust after a series of robustness tests, including PSM-DID estimation, placebo tests, instrumental variable methods, indicator reconstruction, and policy interference exclusion. ② Mechanism tests reveal that regional integration policies mainly drive the green and low-carbon transformation through three channels: innovation investment, industrial upgrading, and talent aggregation. ③ Heterogeneity analysis indicates that the positive impact of regional integration policies on the green and low-carbon development of cities is more significant in eastern regions, resource-based cities, small and medium-sized cities, and old industrial cities. Spatial effect tests show that regional integration development has a significant spatial spillover effect on urban green and low-carbon transformation. Based on these findings, it is recommended that, in the future, in global efforts should be made to continuously improve the regional collaborative governance system, strengthen multi-dimensional linkage mechanisms in urban agglomerations, and build a policy support framework that drives innovation and optimizes the allocation of factors. This study not only provides empirical support for the green efficiency enhancement mechanisms of regional integration policies but also offers decision-making references for promoting regional coordinated development and achieving green economic growth in the digital economy era. Full article

Exploring the characteristics of changes in cropland function trade-off and the influencing factors in highly urbanized areas can promote the synergistic development of urbanization and fine cropland management. Taking the Yangtze River Delta region as the study area, this paper developed a cropland function evaluation system from the production–ecology–living perspective, identified the spatial and temporal changes in cropland function trade-offs through Wavelet analysis and Root mean square error, and explored the driving factors of the trade-offs by using GeoDetector. The results indicated the following: (1) The cropland function in the Yangtze River Delta region has undergone a transition from a single production function to a composite function integrating ecology and life in conjunction with urbanization. The trade-offs between cropland functions are weakened, and the rate of decline from 2010 to 2023 is significantly higher than that from 2000 to 2010, and the characterization of cropland in different types of cities is revealed. (2) The turning points of cropland function trade-off changes in cities of different scales diverge, with the inflection points of small and medium-sized cities and large cities shrinking toward the center (decreasing from 42–48 km to 30–36 km), and metropolises showing an obvious trend of outward expansion (expanding from 42 km to 60 km). (3) The influence of natural and socioeconomic factors on cropland function trade-off intensity generally increases over time, with socioeconomic factors increasingly becoming significant drivers of the trade-off intensities. It is recommended that the study area focus on developing cropland characterization in different types of cities in the future, and continue to improve the degree of sharing the integration of profits from cropland functions, so as to promote optimal development. Full article

The medium river basins (MRBs) in Nepal originate from mid-hills. These medium-range rivers are typically non-snow-fed, relying on rain and other water sources. These rivers are typically small, and the sizes of medium river basins vary between 500 and 5000 km². These MRBs are often used for irrigation and other agricultural purposes. In this analysis, we first set up, calibrated, and validated three hydrological models (i.e., HBV, HEC HMS, and SWAT) at the Kankai River Basin (one MRB in eastern Nepal). Then, the best-performing SWAT hydrological model was forced with cutting-edge climate models (CMs) using thirteen CMIP6 models under four shared socioeconomic pathways (SSPs). We employed ten bias correction (BC) methods to capture local spatial variability in precipitation and temperature. Finally, the likely streamflow alteration during two future periods, i.e., the near-term timeframe (NF), spanning from 2031 to 2060, and the long-term timeframe (FF), covering the years 2071 to 2100, were evaluated against the historical period (baseline: 1986–2014), considering the uncertainties associated with the choice of CMs, BC methods, or/and SSPs. The study results confirm that there will not be any noticeable shifts in seasonal variations in the future. However, the magnitude is projected to alter substantially. Overall, the streamflow is estimated to upsurge during upcoming periods. We observed that less deviation is expected in April, i.e., around +5 to +7% more than the baseline period. Notably, a higher percentage increment is projected during the monsoon season (June–August). During the NF (FF) period, the flow alteration will be around +20% (+40%) under lower SSPs, whereas the flow alteration will be around +30% (+60%) under higher SSPs during high flow season. Thus, the likelihoods of flooding, inundation, and higher discharge are projected to be quite high in the coming years. Full article

Phosphorus is the primary contributor to eutrophication in water bodies, and identifying phosphorus sources in rivers is crucial for controlling phosphorus pollution and subsequent eutrophication. Although phosphate oxygen isotopes (δ¹⁸O_P) have the capacity to trace phosphorus sources and cycling in water and sediments, they have not been used in small- to medium-sized watersheds, such as the Xiaodongjiang River (XDJ), which is located in an agricultural watershed, source–complex region of southern China. This study employed phosphate oxygen isotope techniques in combination with a land-use-based mixed end-member model and the MixSIAR Bayesian mixing model to quantitatively determine potential phosphorus sources in surface water and sediments. The δ¹⁸O_P values of the surface water ranged from 5.72‰ to 15.02‰, while those of sediment ranged from 10.41‰ to 16.80‰. In the downstream section, the δ¹⁸O_P values of the surface water and sediment were similar, suggesting that phosphate in the downstream water was primarily influenced by endogenous sediment control. The results of the land-use–source mixing model and Bayesian model framework demonstrated that controlling phosphorus inputs from fertilizers is essential for reducing phosphorus emissions in the XDJ watershed. Furthermore, ongoing rural sewage treatment, manure management, and the resource utilization of aquaculture substrates contributed to reduced phosphorus pollution. This study showed that isotope techniques, combined with multi-model approaches, effectively assessed phosphorus sources in complex watersheds, offering a theoretical basis for phosphorus pollution management to prevent eutrophication. Full article

Historically, the Wei River has served as part of the Yongji Canal section of the Grand Canal, playing a crucial role in connecting northern and southern China. However, with the acceleration of urbanization in China, issues such as excessive land development and ecological landscape fragmentation have emerged. Exploring the mechanisms of landscape fragmentation evolution in the Wei River basin and proposing optimization strategies is of significant importance for land use and ecological stability within small- to medium-sized river basins. This study selected land use data from the Weihe River basin between 2000 and 2020, using landscape pattern indices to analyze the trend of landscape fragmentation. The principal component analysis (PCA) and geographical detector methods were employed to explore the distribution characteristics and driving factors of landscape fragmentation. The research results indicate that: (1) The degree of landscape fragmentation in the Wei River basin has progressively intensified over time. The edge density index (ED), the landscape division index (DIVISION), the landscape shape index (LSI), and the Shannon diversity index (SHDI) have increased annually, while the contagion index (CONTAG) and area-weighted mean patch size (Area_AM) have continuously decreased; (2) Landscape fragmentation in the Wei River basin is characterized by stable changes in the source and tributary fragmentation areas, a concentrated distribution of fragmentation in the tributaries, and a significant increase in fragmentation in the main stream; (3) The analysis using the geographic detector method indicates that vegetation coverage (FVC), human activity intensity (HAI), and land use/land cover change (LUCC) are the main driving factors of landscape fragmentation in the Wei River basin. The findings explore the mechanisms of landscape fragmentation in the basin and provide a reference for land use planning and ecological restoration in the region. Full article

This investigation endeavors to demarcate the boundaries of small- and medium-sized river catchments within the Caspian Sea drainage basin, with a specific focus on the Northeastern Caucasus, Azerbaijan, and Iran regions. A multi-faceted approach was employed, incorporating various remote sensing methods to select key areas, including the catchments of the Sunzha, Sulak, Ulluchay, Karachay, Atachay, Haraz, and Gorgan rivers. Subsequently, geoinformation systems (GISs) and topographic maps were utilized to determine the morphometric characteristics of these catchments, accompanied by an assessment of the accuracy of remote sensing data. The aim of this study is to evaluate the accuracy and suitability of digital elevation models (DEMs) with a spatial resolution of 30 m per pixel (including ASTER DEM, ALOS DEM, NASADEM, Copernicus 30 m DEM, and SRTM 30 m DEM) and 90 m per pixel (Copernicus 90 m DEM and SRTM 90 m DEM) for delineating small- and medium-sized Caspian Sea basin river catchments. For the DEMs that successfully and accurately delineated watershed boundaries, the morphometric characteristics of the river basins were calculated. This research has yielded novel findings regarding the morphometric characteristics (area, perimeter, ruggedness of the catchment line (roundness coefficient), maximum height, minimum height, average height of the river basin, maximum slope of the surface, average slope of the surface, length of the main watercourse, basin shape parameter (catchment elongation coefficient), shape coefficient, length of the river basin, average river basin slope, and average width of the basin) of individual mountainous small- and medium-sized rivers in the Northeastern Caucasus, Azerbaijan, and Iran, with the catchments of the aforementioned rivers serving as exemplars. The practical significance of these results lies in the fact that such detailed morphometric characteristics of catchments have been obtained for the first time, and their boundaries have been clarified (burned out according to various DEMs), which can serve as a basis for decision-making processes and contribute to the development of operational environmental monitoring of the state of rivers and their catchments. Full article

Between 1995 and 2022, 19 measuring points in small and medium sized streams in the Harz National Park, Germany, were sampled. The samples were evaluated in terms of their macroinvertebrate (MI) biology and hydrochemistry. Nearly all streams showed a natural hydromorphology, and low values of biological oxygen demand (BOD) characteristic for rivers not contaminated by organic matter. Nevertheless, in the 1990s, most streams were still only settled by a small number of MI species. However, by 2022, the MI species number had doubled or tripled in most cases, with a maximum increase from 14 to 52. There is a clear correlation between species number and pH. At 15 of the 19 sampling sites, the acidity class has gotten better by at least one value. Thus, acid-sensitive species, mainly from the taxonomic orders Trichoptera, Plecoptera, and Ephemeroptera, have been able to settle higher altitudes, as well as formerly acidic reaches. In general, the streams contain a very specific macroinvertebrate fauna that emphasizes the conservation value of the Harz National Park. Attenuation of acidification has not only influenced the MI diversity. Along with the increase in pH, fish populations have recovered, and formerly fish-free stream sections have been recolonised. The biological recovery of the streams has also been fostered by the breakdown of spruce forest monocultures in the surroundings, the natural development of deciduous trees on the banks, and increasing levels of DOC (dissolved organic carbon). Full article