Revealing the topographic gradient differentiation of land use in mountainous cities is essential for optimizing land-use allocation in complex terrain regions. Taking a typical mountainous urban area Nan’an District of Chongqing as a case study, this paper examines the topographic gradient characteristics and evolutionary patterns of its land-use structure using a Topographic Position Index and a topographic distribution index(DI), based on multi-temporal Sentinel-2 imagery and DEM data. The results indicate that: (1)Land use in Nan’an District is dominated by construction land and forest land; construction land is concentrated in low topographic gradient areas, whereas forest land predominates in medium and high gradient zones. (2)Topographic gradient differentiation of land use has progressively intensified: in low-gradient areas, construction land has expanded while cultivated land has shrunk, and in medium- and high-gradient areas, forest land has maintained a stable dominance. (3)The distribution advantages and structural characteristics of land use exhibit marked spatio-temporal variation across different topographic gradient levels. (4)The correlation between topography and land-use distribution is significant and persistent,which confirms that topography is a core constraining factor shaping and driving land-use patterns and their evolution in mountainous cities.

Safe and just operating spaces (SJOS) are influenced by complex cross-scale interactions and cascading effects spanning global, regional, and local landscape scales. However, existing SJOS research has often focused on single-scale assessments, overlooking the impacts of multiscale interactions and within-region heterogeneity on urban SJOS. To address this gap, we developed a cross-scale framework for assessing urban SJOS, explicitly incorporating top-down influences from upper-level constraints and bottom-up effects from lower-level heterogeneity. This approach was applied to China's five major metropolises to examine the states and cross-scale dynamics influencing urban SJOS between 1990 and 2020. Our findings reveal that the SJOS of China's metropolises were primarily influenced by factors at national and local landscape scales, with weaker influences from the global and continental scales. A persistent trade-off between social justice and environmental safety was identified across spatiotemporal scales. For instance, Chongqing in southwestern China lagged behind the eastern four metropolises in social performance but exhibited stronger environmental safety due to its extensive natural landscapes, which mitigated the anthropogenic impacts of urban centers. Regional issues, such as the overshoot of PM2.5 and ecological footprints (EF), were primarily driven by the bottom-up accumulation of localized pressures, while the overshoot of CO2 was attributed to national policy constraints and the universal exceedance of safe thresholds across scales. Addressing urban sustainability requires avoiding adverse cascading effects from other levels by emphasizing landscape heterogeneity within metropolises and fostering coordinated collaboration across scales, particularly at the regional landscape and national levels.

Approximately 35 % of Chinese cities are situated in mountainous areas, where rapid urban expansion on slopes has led to the degradation of urban ecosystem health, marked by the loss of natural landscapes, diminished resilience, and reduced ecosystem services. However, the impact of vertical urban growth on ecosystem health, especially in terms of temporal dynamics, distribution, and underlying mechanisms, remains poorly understood. Chongqing, a typical mountainous metropolis, was selected to investigate these impacts over the past two decades. By integrating the slope spectrum (SS), climbing index (CI) of built-up land, and ecosystem health index (EHI), we explored how urban expansion has affected the EHI. Additionally, we developed a method for identifying the expansion advantage slope range (EASR), which can track dynamic slope-climbing urban expansion. Our findings revealed that the built-up land expansion in Chongqing was primarily concentrated in the central areas of the western region. From 2000 to 2010, this expansion occurred primarily in urban built-up areas and shifted to other built-up areas between 2010 and 2020. Although the Climbing Index was -0.11, the EASR results indicated an increasingly significant slope-climbing trend, with slopes of built-up land increasing from [1.17, 8.25] to [1.42, 8.48]. Notably, when expansion occurs on slopes exceeding 12 degrees, the decline in the EHI becomes significantly more pronounced, with the impact coefficient rising from 0.201 to 0.447. This study reveals the fundamental relationship between slope-climbing urban expansion and ecosystems, providing valuable insights for urban planning and sustainable development in mountainous regions.

Understanding biomass allocation strategies in invasive plants is crucial for developing effective management approaches. However, the mechanisms by which plant functional traits and soil properties influence biomass allocation in invaded communities, particularly in invasion-prone riparian zones, remain poorly understood. Here, we collected data on functional traits, biomass, and soil factors from invasive (IP) and non-invasive (NP) plant communities under similar site conditions in the riparian zone of the Three Gorges Reservoir in China during 2021. We examined the roles of plant community traits and soil factors in shaping biomass allocation and evaluated the applicability of the optimal and isometric allocation theories. Results showed that biomass trade-off values for both IP and NP were greater than zero and increased with elevation, indicating that riparian plants allocate more biomass to aboveground portions to combat flooding, consistent with the optimal allocation theory. Biomass allocation in NP was primarily influenced by soil physicochemical properties (e.g., bulk density and pH), whereas in IP, it was mainly determined by dominant functional traits, such as community-weighted mean height (CWM_H). The structural equation model explained 78% and 62% of the variation in biomass trade-off for NP and IP, respectively. Furthermore, it demonstrated that functional traits (e.g., CWM_H) mediated flooding's effects on biomass allocation in invaded communities. These findings underscore distinct allocation strategies between invaded and non-invaded communities and highlight the importance of trait-based mechanisms in driving invasive plant success. This study emphasizes the need to consider dominant trait dynamics when managing invasions in flood-affected riparian systems.

China has responded to the sustainability challenges via a range of policies with evolving objectives in the Yangtze River Economic Belt (YEB) since the 1990s. However, the multi-scale analysis of YEB's comprehensive sustainability and the human -environment nexus amid policy impact remains unexplored. A comprehensive review and forecast of historical and future sustainability pathways under policy impacts are imperative. Here, we systematically examined sustainability under ten National Policies (NPs) and Regional Development Policies (RDPs), forecasting Shared Socioeconomic Pathways (SSPs) in the 21st Century using the entropy weight method and machine learning models. We found that RDPs have contributed to 1.6 times increase in human development from 2000 to 2018 across dimensions of demography, economy, and society in YEB. However, it also revealed that the west -east disparity has widened from 0.14 to 0.19 during this period. Conservation efforts and national initiatives for ecological civilization have led to environmental improvement in the YEB, especially after the RDP3 in 2014, when the eastern provinces, like Shanghai, have already surpassed the peak inverted U -shape curve of the environmental-human nexus. Among the SSPs, SSP1 shows the most sustainable scenario with the lowest ecological footprint at 6.2 hm2 per capita and the highest value of regional sustainability and environmental subsystem. To achieve SSP1, an iterative, inclusive, and context-specific Science-Policy-Practice dialogue is essential. This enables feedback loops and collaboration among policymakers, scientists, and practitioners to foster regional sustainability by studying the implications of historical and future pathways.

Dams worldwide have significantly altered the composition of riparian forests. However, research on the functional traits of dominant herbs experiencing flooding stress due to dam impoundment remains limited. Given the high plasticity of leaf traits and their susceptibility to environmental influences, this study focuses on riparian herbs along the Three Gorges Hydro-Fluctuation Zone (TGHFZ). Specifically, it investigates how six leaf physiological traits of leading herbs-carbon, nitrogen, phosphorus, and their stoichiometric ratios-adapt to periodic flooding in the TGHFZ using cluster analysis, one-way analysis of variance (ANOVA), multiple comparisons, Pearson correlation analysis, and principal component analysis (PCA). We categorized 25 dominant herb species into three plant functional types (PFTs), noting that species from the same family tended to fall into the same PFT. Notably, leaf carbon content (LCC) exhibited no significant differences across various PFTs or altitudes. Within riparian forests, different PFTs employ distinct adaptation strategies: PFT-I herbs invest in structural components to enhance stress resistance; PFT-II, mostly comprising gramineous plants, responds to prolonged flooding by rapid growth above the water; and PFT-III, encompassing nearly all Compositae and annual plants, responds to prolonged flooding with vigorous rhizome growth and seed production. Soil water content (SWC) emerges as the primary environmental factor influencing dominant herb growth in the TGHFZ. By studying the response of leaf physiological traits in dominant plants to artificial flooding, we intend to reveal the survival mechanisms of plants under adverse conditions and lay the foundation for vegetation restoration in the TGHFZ.

[Objective] The study of spatial-temporal variations and influencing factors of water-related ecosystem services under complex terrain in Southwest China can serve as a foundation for the ecological management and sustainable development in this region. [Methods] The annual water yield and soil erosion in Southwest China from 1992 to 2020 were evaluated to explore the multi-dimensional (including time, space and elevation) variation characteristics by the InVEST model and universal soil loss equation. In addition, the relative weight analysis method was used to quantify the relative contribution rate of climate and land use change to water-related ecosystem services. [Results] (1) From 1992 to 2020, water yield in Southwest China showed a downward trend, with a notable mutation occurring in 2002; soil erosion showed an increasing trend, with a mutation observed in 1997. (2) The water yield decreased and soil erosion increased with rising altitude. (3) The relative contribution rate of precipitation to both water yield and soil erosion in karst areas was found to be greater than that in non-karst areas. [Conclusion] Climate change has a more significant impact on water yield and soil erosion, while land use change has a less obvious impact. This study will contribute to the ecological protection in complex terrain (with different elevations and different landforms) and provide a scientific basis for land management and ecological restoration measures in karst areas.

Metropolises are pivotal places in mitigating and adapting to climate change, reducing environmental risks, and improving social justice to achieve global sustainability. Thus, here we integrated nine biophysical boundaries and nine social foundations into the Safe and Just Operating Space (SJOS) framework to examine the sustainability of China's five metropolises in 2020 and conduct a cross-scale interactions analysis in the case of Chongqing's SJOS by linking the global contexts to landscape components. We found that neither China as a whole nor the five metropolises (i.e., Beijing, Shanghai, Tianjin, Guangzhou, and Chongqing) all transgressed the environmental ceilings, especially in the aspects of carbon emissions, PM2.5, and footprints of ecology and nitrogen. Four metropolises achieved the basic requirements of social justice, except the Chongqing. However, Chongqing has better environmental conditions, spatially with increased environmental safety along the gradients of urban, rural, and natural landscapes. Taking the metropolises as the focal scale, metropolitan SJOS are affected by context-specific thresholds, top-down constraints from broader contexts, bottom-up cascading effects, governance, and anthropogenic perturbance. Operating within the metropolitan SJOS necessitates collaborations across individuals, landscapes, regions, countries, and the Earth system as a whole.

Context China’s high-speed economic development was accompanied by rapid urbanization for forty years, guided by a series of changing policies enacted by the central government. However, did China become more sustainable both economically and environmentally? Or more specifically, did it operate within or towards a safe and just space (SJS)? Although numerous relevant studies exist, these questions have not been adequately addressed, and a multi-scale landscape perspective is needed. Objectives The main objective of this study was to examine China’s urbanization trends, associated institutional changes, and their impacts on the nation’s sustainability trajectory during the past four decades. Specifically, we intended to analyze the impacts of urbanization and related policies on the spatial patterns, temporal trends, shortfalls, and complex nexus of the different dimensions of SJS across scales in China. Methods We apply the SJS framework, which integrates eight environmental ceilings and seven social justice foundations, to examine China’s urbanization, socioeconomic dynamics, and institutional changes, as well as their impacts on sustainability at multiple spatial scales. Segmented regression and correlation analysis were used to analyze the relationship of SJS with landscape urbanization and governance across China. Results Since the implementation of China’s Western Development Plan, China has faced increasing challenges of overshoots in CO 2 emissions, phosphorus and nitrogen loading, ecological footprint, and material footprint on a per capita basis. However, our analysis showed that, by 2015, China met nearly all basic social justice needs. The pattern of SJS showed geospatial gradients of increasing social justice (except material footprint), multi-footprints, and CO 2 from eastern to central, northeastern, and western regions, and from developed to developing provinces. The tradeoffs between social justice, environmental safety, and regional equality remain pronounced across heterogeneous landscapes with different levels of urbanization. The western region’s material footprint expanded enormously, but mainly for consumption in the eastern region of China. Conclusions China’s development in the past four decades is characterized by enormous economic growth, rapid urbanization, much improved living standards, highly fragmented landscapes, and increasing environmental problems. To promote sustainability, China should continue to implement the strategy of high-quality development and promote ecological civilization. Regional landscape-based approaches are needed to explicitly recognize geospatial heterogeneity and disparities, and better understand the urbanization-governance-landscape nexus for promoting a safer and more just China.

Aims: Siberian crane (Grus leucogeranus) is a migratory, endangered species that uses the Songnen Plain as a main stopover area.Traditionally a wetland species, today most populations of Siberian cranes feed and rest during migratory stopovers in fields of corn (Zea mays).By examining the causes of this change in stopover habitat use, we can provide better protection for and potentially recovery of this declining species.Methods: We recorded the numbers of Siberian cranes and both food resource and habitat usage on stopover sites on the Songnen Plain from September 2020 to November 2021 in the study area.These data were collected and analyzed using Google Earth, ArcGIS 10.7.Results: Of the total number of Siberian cranes we observed, 72.7% were feeding on farmland, which was 2.66 times more than that of wetland habitats.Farmland has become the main feeding habitat for Siberian cranes.The total energy provided by farmland was 1.24-2.79times as much as that provided by wetlands based on different harvesting methods, and the energy intake of Siberian cranes in farmland was about 1.56 times that of wetland.The daily feeding budget of Siberian cranes in farmland was 53.5% of their total time, which was 1.67 times more than that in wetlands.The feeding

The ecosystem services (ESs) provided by mountain regions can bring about benefits to people living in and around the mountains. Ecosystems in mountain areas are fragile and sensitive to anthropogenic disturbance. Understanding the effect of land use change on ESs and their relationships can lead to sustainable land use management in mountain regions with complex topography. Chongqing, as a typical mountain region, was selected as the site of this research. The long-term impacts of land use change on four key ESs (i.e., water yield (WY), soil conservation (SC), carbon storage (CS), and habitat quality (HQ)) and their relationships were assessed from the past to the future (at five-year intervals, 1995–2050). Three future scenarios were constructed to represent the ecological restoration policy and different socioeconomic developments. From 1995 to 2015, WY and SC experienced overall increases. CS and HQ increased slightly at first and then decreased significantly. A scenario analysis suggested that, if the urban area continues to increase at low altitudes, by 2050, CS and HQ are predicted to decrease moderately. However, great improvements in SC, HQ, and CS are expected to be achieved by the middle of the century if the government continues to make efforts towards vegetation restoration on the steep slopes.

Landscape urbanization has profound influences in the structure, function, and dynamics of the coupled human-environmental systems (CHESs). However, due to the spatial heterogeneity of urban landscape and its socioeconomic attributes, there are many limitations in our understanding of how to render urban systems more sustainable across different administrative levels and geospatial scales. Place-based and cross-level research must be conducted to provide realistic and context-specific pathways to regional sustainability. Thus, the main objectives of this study were to investigate the multiscale spatiotemporal patterns, divers, and sustainability impacts of landscape urbanization at the levels of nation, economic development zones, urban agglomerations (UAs), and cities, with a focus on the Yangtze River Economic Belt (YREB). We explored the linkages among the landscape urbanization, national development plans, and regional sustainability from the hierarchical landscape perspective, using landscape metrics and bivariate regressions. Our main findings include: (1) the YREB's built-up area expanded from 9000 to 40,000 km(2) during 1990-2015, and the general spatiotemporal patterns of landscape urbanization were similar to those in other major urban regions worldwide; (2) influenced by national development plans, the east-west disparities of landscape urbanization continued to widen in the YREB and China as a whole during 1990-2015; (3) the overall landscape urbanization pattern of the YREB was characterized by an east-west gradient interwoven with hierarchies of UAs and cities that were influenced mainly by geography, demography, and top-down governmental policies; (4) positive feedbacks between landscape urbanization and socioeconomic development underpinned rapid urbanization, resulting in insufficient public green space, deteriorated air quality, freshwater shortages and pollution, and inadequate infrastructure development, especially in the coastal urban agglomerations (UAs), megacities and super megacities. To achieve sustainability of the YREB region, future policies need to address the geospatial disparities and minimize the gradients of socioeconomic development. The hierarchical landscape approach provides new insights for improving regional landscape planning and management for sustainability.

Loess-like sediments are widely distributed in the northern subtropics of China, stretching beyond the traditional boundary of typical loess. Compared with well-researched typical loess, loess-like sediments are much less studied and their origin (eolian or fluvial) and movement pathways under evolving environments remain unclear. Micromorphology offers novel insights into explaining sediment-forming mechanisms through reconstructing the sedimentary history. To examine the debates comprehensively, multiple micromorphological metrics were systematically analyzed, and three main results were derived from the analysis: (a) Hanjiang loess-like sediment can be directly diagnosed as eolian loess based on its differences from fluvial sediment with regard to particle composition and quartz roundness; (b) combined analyses of quartz configurations with the distribution patterns of modern winter winds/dust storms indicated that a portion of the small particles were transported by upper flow in the East Asian winter monsoon from the northwestern Gobi Desert, whereas coarse grains were mainly derived from the adjacent floodplain by creep and saltation; and (c) vertical heterogeneity of configurations and compositions among layers was mainly caused by different degrees of chemical/biological/physical weathering since the latest glaciation. All measurements showed the weathering intensity of sediments decreased in the order of S-0/T-s, L-t, L-0, L-1, meaning that the East Asian summer monsoon weakened in this order during different formation periods. In summary, these metrics reconstructed the formation process and evolutionary history of monsoons in subtropical China excellently and would rival traditional indexes, but are easier to observe.

Ecological restoration programs, which mainly affect land use distribution, may eventually alter the supply of ecosystem services (ESs). Although some positive results have been achieved, the sustainability and long-term effects of ecological restoration program on ecosystem service still remain uncertain. To compare the ES outcomes of ecological restoration programs, the design of alternative land use scenarios is critical for ecological management. This paper presents a case study aiming to explore how the implementation of the Plains Afforestation Program (PAP) and alternative land use scenarios affect the provision of a set of ecosystem services in an urbanizing watershed. We selected 7 ESs, including three water-related services and four ecosystem services (food production (FP), carbon storage (CS), habitat quality (HQ), and air pollution removal(APR)). And the comprehensive ecosystem service (CES) index was adopted to reflect the total provision of multiple ESs. The trade-offs among various ESs through correlation analysis were further conducted. Finally, four alternative scenarios were designed to provide insights into the future design and implementation of ecological restoration programs. The results indicated that the PAP implementation enhanced regulating services (SC, WP, CS, and APR) and supporting services (HQ) and reduced provisioning services (WY and FP). Converting cropland to forestland could not simultaneously lead to an enhancement in all ecosystem services. Our results also showed synergies between supporting (HQ) and regulating services (CS, WP, and APR). It is worth noting that soil conservation showed trade-offs between supporting (HQ) and regulating services (CS, WP). The region with a large proportion of woodland improved habitat quality, water purification and carbon storage, but it failed to enhance soil conservation effectively because of its steeper slopes. After the implementation of PAP, no transition occurred in the relationships among the ecosystem services, whereas the trade-offs between water yield and other supporting services and regulating services have been weakened. After the land use scenarios were analyzed, the RB-400 scenario with the highest CES value of all the scenarios can be considered the optimal option because it showed the largest increase in water purification (34%) and habitat quality (3%). Moreover, water purification and habitat quality account for greater proportions of weight in our research area. This scenario provided policy implications for the land-use planning.

Dissolved organic matter (DOM) is a crucial driver of various biogeochemical processes in aquatic systems. Thus, many lakes and streams have been investigated in the past several decades. However, fewer studies have sought to understand the changes in DOM characteristics in the waters of the Three Gorges Reservoir (TGR) areas, which are the largest artificial reservoir areas in the world. Thus, a field investigation of dissolved organic carbon (DOC) concentrations and of chromophoric dissolved organic matter (CDOM) properties was conducted from 2013 to 2015 to track the spatial-temporal variability of DOM properties in the TGR areas. The results showed that the alternations of wet and dry periods due to hydrological management have a substantial effect on the quantity and quality of aquatic DOM in TGR areas. Increases in DOC concentrations in the wet period show an apparent “dilution effect” that decreases CDOM compounds with relatively lower aromaticity (i.e., SUVA254) and molecular weight (i.e., SR). In contrast to the obvious temporal variations of DOM, significant spatial variability was not observed in this study. Additionally, DOM showed more terrigenous characteristics in the dry period but weak terrigenous characteristics in the wet period. Furthermore, the positive correlation between SUVA254 and CDOM suggests that the aromatic component controls the CDOM dynamics in TGR areas. The first attempt to investigate the DOM dynamics in TGR areas since the Three Gorges Dam was conducted in 2012, and the unique patterns of spatial-temporal variations in DOM that are highlighted in this study might provide a new insight for understanding the role of DOM in the fates of contaminants and may help in the further management of flow loads and water quality in the TGR area.

Because of heterogeneous properties, dissolved organic matter (DOM) is known to control the environmental fate of a variety of organic pollutants and trace metals in aquatic systems. Here we report absorptive and fluorescence properties of DOM, in concurrence with concentrations of dissolved mercury (Hg), along the Xiaoqing River-Laizhou Bay estuary system located in the Bohai Sea of China. A mixing model consisting of the two end-members terrestrial and aquatic DOM demonstrated that terrestrial signatures decreased significantly from the river into the estuary. Quasi-conservative mixing behavior of DOM sources suggests that the variations in the average DOM composition were governed by physical processes (e.g., dilution) rather than by new production and/or degradation processes. In contrast to some previous studies of river-estuary systems, the Xiaoqing River-Laizhou Bay estuary system displayed a non-significant correlation between DOM and Hg quantities. Based on this and the variation of Hg concentration along the salinity gradient, we concluded that Hg showed a non-conservative mixing behavior of suggested end-member sources. Thus, rather than mixing, Hg concentration variations seemed to be controlled by biogeochemical processes.

应用三维荧光光谱技术(3D-EEM),研究了两个典型水库型湖泊(长寿湖和大洪海)水体中溶解性有机质(DOM)的荧光光谱特征,结合沿岸生态系统差异,讨论其对两个湖泊中DOM性质及来源的影响.结果表明,沿岸生态系统的差异性(尤其是人为干扰)是导致两个水体DOM地球化学特征存在明显差异的重要原因.两湖水体中DOM均存在4个荧光峰,且长寿湖样本中类蛋白物质含量更高;而大洪海水体中腐殖化程度较高的组分(C峰)含量较高.相关性分析表明,两湖DOM样本中类蛋白和类腐殖组分来源不同,而A、C峰代表的类腐殖组分存在共源性.通过荧光参数分析显示,沿岸以森林系统为主的大洪海水体DOM陆源性更强,腐殖化程度高;而长寿湖受两岸农田、果园的输入以及人为排放影响,其水体DOM具有明显的自生源特征,新生DOM含量较高,其荧光特征也反映了该区域水体受人为干扰较大.与其他不同湖泊对比,进一步表明沿岸生态系统类型及人为土地利用是决定水体DOM来源和特性的关键因素.