To investigate the spatiotemporal variations and influencing factors of carbon sources/sinks across dif-ferent ecosystem types on the Loess Plateau region,this study estimated NEP of seven ecosystem types in the re-gion from 2001 to 2024.Ridge regression,Theil-Sen median trend analysis,Mann-Kendall significance test,and centroid shift analysis were used to explore the spatiotemporal changes in NEP and the contributions of influenc-ing factors.The results showed that from 2001 to 2024,NEP on Loess Plateau exhibited an overall upward trend,with higher values in the southeast and lower values in the northwest.NEP increased significantly across all eco-systems,with the forest ecosystem showing the largest increase at a rate of 5.61 g C·m-2.The normalized differ-ence vegetation index and LAI were identified as the dominant factors influencing NEP on the Loess Plateau.The relative contribution of normalized difference vegetation index to NEP exceeded 49％across all ecosystem types,whereas the LAI contributed more than 18％.Precipitation,evapotranspiration,and temperature had relatively mi-nor impacts(relative contributions 5.96％,4.71％and 4.23％,respectively).In summary,significant differences exist in the NEP trends and the contributions of influencing factors among different ecosystem types on the Loess Plateau.NDVI and LAI are the dominant drivers,while the contributions of precipitation,evapotranspiration,and temperature are relatively limited.
Against the backdrop of rapid urbanization,ecological and environmental pressures are intensifying,making the coordination between economic development and ecological conservation a critical issue for regional sustainability.As a key ecological security barrier and economic growth corridor in Northwest China,the ecologi-cal condition of the urban agglomeration in the northern slope of the Tianshan Mountains is of great significance for regional sustainable development.Existing studies have primarily focused on ecological value accounting in agro-pastoral transition zones,while research at the scale of oasis-based urban agglomerations in arid regions re-mains limited,particularly in capturing the spatial heterogeneity of vegetation.To address this gap,this study inte-grates agricultural production statistics with actual regional vegetation characteristics to revise ecosystem service value(ESV)equivalent factors.Net primary productivity(NPP)and the normalized difference vegetation index(NDVI)are further incorporated for secondary refinement.Based on these improvements,priority areas for eco-logical compensation are identified.The results show that:(1)the comprehensive land-use dynamics in the study area exhibited an overall declining trend from 2000 to 2020,characterized by reductions in bare land and grass-land,alongside increases in other land-use types.(2)the ecosystem service value of the urban agglomeration in the northern slope of the Tianshan Mountains demonstrated a general upward trend over the past 20 years,with an average value of 1176×108 yuan,and high-value areas mainly concentrated in high-altitude forest regions.(3)areas with higher priority for ecological compensation are primarily located in Dabancheng District,Mulei Ka-zakh Autonomous County,and Urumqi County.These findings provide a scientific basis for delineating priority ecological compensation zones and promoting the coordinated advancement of ecological conservation and high-quality development in the urban agglomeration in the northern slope of the Tianshan Mountains.
To address the accuracy limitations of conventional remote sensing approaches for water body extrac-tion in desert environments,which are commonly affected by mixed pixels and boundary blurring,this study pro-poses a desert water extraction model that integrates the normalized suspended material index(NSMI)with the multi-index collaborative water extraction method(MICWE),termed MICWE-NSMI.The Ulan Buh Desert was selected as the study area,and Landsat 8 OLI surface reflectance imagery from 2020 was used.Image preprocess-ing,including cloud removal,radiometric calibration,atmospheric correction,maximum value compositing,and index calculation,was performed on the Google Earth Engine platform.A 30 m buffer zone was constructed along the preliminary water boundaries extracted by MICWE,within which turbid water bodies were further re-fined by combining inverted NSMI with Otsu adaptive threshold segmentation.A comparison with Sentinel 2 im-agery validation results indicates that the proposed MICWE-NSMI model significantly improved the boundary in-tegrity and connectivity of highly turbid waters,narrow tributaries,and flowing water bodies,with an overall ac-curacy of 93.7%and a Kappa coefficient of 0.82.Compared with conventional index-based methods,the deep learning-based ResUNet model,and the Joint Research Centre global surface water dataset,the proposed model effectively reduces water body fragmentation and misclassification in complex scenarios,including lakes in des-ert hinterlands,irrigation tributaries,and the Yellow River channel.By integrating conventional water body indi-ces with the spatial heterogeneity of suspended sediment,this study expands the methodological framework for remote sensing identification of highly turbid,fragmented,narrow,and dynamic water bodies,providing a new technical pathway for desert and arid-region water resource monitoring.
The characteristics of desert plantcommunities are comprehensively influenced byfactors such as arid environment,soil conditions,and groundwater depth,presenting unique structural and functional traits.Through field quadrat surveys and diversity index analysis,this study reveals the response mechanism of desert plant com-munity characteristics to groundwater depth and their ecological thresholds.The results show that:(1)The con-structive species,Tamarix and Populus,have the highest occurrence frequencies across different groundwater depths,accounting for 34%and 19%respectively.Within the groundwater depth range of 3.77-5.99 m,the aver-age coverage of the shrub layer reaches 42.7%,which is significantly higher than that in other intervals(P<0.05).(2)The Shannon-Wiener index reaches its peak value of 0.76 in this interval;meanwhile,the Simpson dominance index of the perennial herb layer decreases.This indicates that the groundwater depth of 4 m is the critical thresh-old for the community structure to shift from a"single arbor"pattern to a"arbor-shrub-herb"tripartite symbiotic pattern.(3)The community-weighted mean(CWM)of the average height of shrubs shows a non-linear decreas-ing trend with increasing groundwater depth,dropping from 2.7 m to 1.0 m.This phenomenon suggests that plants achieve morphological adaptation to water stress by adjusting their height.(4)Soil physical and chemical properties,together with groundwater depth,jointly affect the community characteristics.Among them,herbs are significantly influenced by soil physical and chemical properties(P<0.05).
Understanding the mechanisms by which vegetation-change trends respond to their driving factors is important for environmental resource management,particularly in ecologically fragile regions.In this study,vege-tation cover on the Loess Plateau is analyzed in terms of the normalized difference vegetation index(NDVI),us-ing precipitation and temperature as the climatic factors.Land use,nighttime light remote sensing,and population density data are integrated to establish a human activity intensity(HAI)index.Trend analysis and partial deriva-tives revealed the spatiotemporal characteristics of NDVI changes on the Loess Plateau from 2001 to 2022 in dif-ferent ecological subregions and on the regional scale.The precipitation,temperature,and HAI contributions to the NDVI changes were quantified and the dominant factors driving the vegetation cover changes were explored.The key findings reveal that(1)the NDVI has been steadily increasing at 0.0049 per year,indicating good vegeta-tion recovery on the Loess Plateau over the past 22 years.(2)The precipitation,temperature,and HAI contributed(on average)0.0947%·a-1,0.0643%·a-1,and 0.1083%·a-1 to the NDVI changes,respectively,in the study area.(3)The NDVI increase on the Loess Plateau is primarily driven by the combined effects of climate and human ac-tivity,with climate factors playing a secondary role.Monitoring the impact of climate change on vegetation and strengthening the management of human activities are essential for promoting sustainable ecological restoration and environmental protection strategies on the Loess Plateau.
