The study of snow and ice melt(SIM) is important in water-scarce arid regions for the assessment of water supply and quality. These studies involve unique difficulties, especially in the calibration of hydro-models be...The study of snow and ice melt(SIM) is important in water-scarce arid regions for the assessment of water supply and quality. These studies involve unique difficulties, especially in the calibration of hydro-models because there is no direct way to continuously measure the SIM at hydrostations. The recursive digital filter(RDF) and the isotopic hydro-geochemical method(IHM) were coupled to separate the SIM from eight observed series of alpine streamflows in northwestern China.Validation of the calibrated methods suggested a good capture of the SIM characteristics with fair accuracy in both space and time. Applications of the coupled methods in the upper reaches of the Hei River Basin(HRB) suggested a double peak curve of the SIM fraction to streamflow for the multi-component recharged(MCR) rivers, while a single peak curve was suggested for the rainfall-dominant recharged(RDR)rivers. Given inter-annual statistics of the separation,both types of the alpine rivers have experienced an obvious decrease of SIM since 1960 s. In the past 10 years, the SIM in the two types of rivers has risen to the levels of the 1970 s, but has remained lower than the level of the 1960 s. The study provided a considerable evidence to quantify the alpine SIM based on the separation of observed data series at gauge stations. Application of the coupled method could be helpful in the calibration and validation of SIM-related hydro-models in alpine regions.展开更多
Spartina alterniflora is one of exotic plants along the coastal region in China. It was introduced as an important engineering approach to ecological restoration in the later 1970 s. However, owing to its good adaptab...Spartina alterniflora is one of exotic plants along the coastal region in China. It was introduced as an important engineering approach to ecological restoration in the later 1970 s. However, owing to its good adaptability and strong reproductive capacity, the introduced species is explosively spreading along the coastal region quickly and resulting in a significant impact on the health and safety of coastal wetland ecosystems. It is imperative to quantify the spatial extent and the rate of S. alterniflora sprawl in order to assess its ecological damages and economic impacts. Remote sensing techniques have been used to address these challenges but large unsuccessful due to mixed spectral properties. In this study, a hybrid method was proposed for S. alterniflora detection using medium resolution remote sensing images by integrating both spatial and spectral features of S. alterniflora. The hybrid method consists of two phases:(1) delineation of intertidal zone as the potential area of S. alterniflora distribution and(2) extraction of S. alterniflora fraction distribution with a mixture pixel analysis. The proposed method was tested at the Xiangshan Bay on the east coastal region of Zhejiang Province, China, and mapped the spatial extent of S. alterniflora with Landsat datasets in the 2003, 2009 and 2014. The results showed that, the S. alterniflora has grown exponentially over past 10 years. In 2003, the total area of S. alterniflora was about 590 hm2, but quickly reached to 1 745 hm2 in 2009, and 5 715 hm2 in 2014. With a rate of approximately 10-folds growth within a decade, the invasive species almost occupied all muddy beaches to become the most dominant coastal salt vegetation in this region. It is believed that the strong biological reproductive capacity was the primary reason for such quick spread and at the same time human reclamation activities were also believed to have facilitated the environmental conditions for S. alterniflora sprawl.展开更多
Background:Transitional economies in Southeast Asia—a distinct group of developing countries—have experienced rapid urbanization in the past several decades due to the economic transition that fundamentally changed ...Background:Transitional economies in Southeast Asia—a distinct group of developing countries—have experienced rapid urbanization in the past several decades due to the economic transition that fundamentally changed the function of their economies,societies and the environment.Myanmar,one of the least developed transitional economies in Southeast Asia,increased urbanization substantially from 25%in 1990 to 31%in 2019.However,major knowledge gaps exist in understanding the changes in urban land use and land cover and environment and their drivers in its cities.Methods:We studied Yangon,the largest city in Myanmar,for the urbanization,environmental changes,and the underlying driving forces in a radically transitioned economy in the developing world.Based on satellite imagery and historic land use maps,we quantified the expansion of urban built-up land and constructed the land conversion matrix from 1990 through 2020.We also used three air pollutants to illustrate the changes in environmental conditions.We analyzed the coupled dynamics among urbanization,economic development,and environmental changes.Through conducting a workshop with 20 local experts,we further analyzed the influence of human systems and natural systems on Yangon’s urbanization and sustainability.Results:The city of Yangon expanded urban built-up land rapidly from 1990 to 2000,slowed down from 2000 to 2010,but gained momentum again from 2010 to 2020,with most newly added urban built-up land appearing to be converted from farmland and green land in both 1990–2000 and 2010–2020.Furthermore,the air pollutant concen-tration of CO decreased,but that of NO_(2)and PM_(2.5)increased in recent years.A positive correlation exists between population and economic development and the concentration of PM_(2.5)is highly associated with population,the economy,and the number of vehicles.Finally,the expert panel also identified other potential drivers for urbanization,including the extreme climate event of Cyclone Nargis,capital relocation,and globalization.Conclusions:Our research highlights the dramatic expansion of urban land and degradation of urban environment measured by air pollutants and interdependent changes between urbanization,economic development,and environmental changes.展开更多
Previous research has explored the potential to integrate lidar and optical data in aboveground biomass(AGB)estimation,but how different data sources,vegetation types,and modeling algorithms influence AGB estimation i...Previous research has explored the potential to integrate lidar and optical data in aboveground biomass(AGB)estimation,but how different data sources,vegetation types,and modeling algorithms influence AGB estimation is poorly understood.This research conducts a comparative analysis of different data sources and modeling approaches in improving AGB estimation.RapidEye-based spectral responses and textures,lidar-derived metrics,and their combination were used to develop AGB estimation models.The results indicated that(1)overall,RapidEye data are not suitable for AGB estimation,but when AGB falls within 50–150 Mg/ha,support vector regression based on stratification of vegetation types provided good AGB estimation;(2)Lidar data provided stable and better estimations than RapidEye data;and stratification of vegetation types cannot improve estimation;(3)The combination of lidar and RapidEye data cannot provide better performance than lidar data alone;(4)AGB ranges affect the selection of the best AGB models,and a combination of different estimation results from the best model for each AGB range can improve AGB estimation;(5)This research implies that an optimal procedure for AGB estimation for a specific study exists,depending on the careful selection of data sources,modeling algorithms,forest types,and AGB ranges.展开更多
Background:The lateral movements of mass and energy across the terrestrial-aquatic interface are being increasingly recognized for their importance in the carbon(C)balance of coastal/estuarine wetlands.We quantifed th...Background:The lateral movements of mass and energy across the terrestrial-aquatic interface are being increasingly recognized for their importance in the carbon(C)balance of coastal/estuarine wetlands.We quantifed the lateral fux of detrital C in the Yangtze estuary where invasive Spartina alternifora has substantially and extensively altered the ecosystem structure and functions.Our overall objective was to close the C budget of estuarine wetlands through feld sampling,tower-based measurements,and modeling.Methods:A lateral detrital C exchange evaluation platform was established in a case study of the Yangtze River Estuary to investigate the efect of ecosystem structural changes on lateral detrital C transfer processes.This study estimated the lateral detrital C exchange based on the gross primary production(GPP)by performing coupled modeling and feld sampling.Tower-based measurements and MODIS time series and CH4 outgassing and biomass simultaneously measured the lateral detrital C fux to characterize the relative contributions of lateral(i.e.,detritus)C fuxes to the annual marsh C budget.Results:The C pools in the plants and soil of Spartina marshes were signifcantly higher than those of the native community dominated by Phragmites australis.The GPP based on MODIS(GPPMODIS)was 472.6 g C m^(−2) year^(−1) and accounted for 73.0%of the GPP estimated from eddy covariance towers(GPPEC)(646.9±70.7 g C m^(−2) year^(−1)).We also detected a higher GPPMODIS during the pre-growing season,which exhibited a similar lateral detrital C fux magnitude.On average,25.8%of the net primary production(NPP),which ranged from 0.21 to 0.30 kg C m^(−2) year^(−1),was exported during lateral exchange.The annual C loss as CH4 was estimated to be 17.9±3.7 g C m^(−2) year^(−1),accounting for 2.8%of the GPPEC.The net positive detrital C fux(i.e.,more detritus leaving the wetlands),which could exceed 0.16 kg C m^(−2) day^(-1),was related to daily tides.However,the observed lateral detrital C fux based on monthly sampling was 73.5%higher than that based on daily sampling(i.e.,the sum of daily sampling),particularly in March and October.In addition,spatiotemporal granularities were responsible for most of the uncertainty in the lateral detrital C exchange.Conclusion:This research demonstrated that an integrated framework incorporating modeling and feld sampling can quantitatively assess lateral detrital C transport processes across the terrestrial-aquatic interface in estuarine wetlands.However,we note some limitations in the application of the light-use efciency model to tidal wetlands.Spartina invasion can turn the lateral C balance from a C source(209.0 g C m^(−2) year^(−1))of Phragmites-dominated marshes into a small C sink(-31.0 g C m^(−2) year^(−1)).Sampling over a more extended period and continuous measurements are essential for determining the contribution of diferent lateral detrital C fux processes to closing the ecosystem C budgets.The sampling spatiotemporal granularities can be key to assessing lateral detrital C transfer.展开更多
Remote sensing-based methods of aboveground biomass(AGB)estimation in forest ecosystems have gained increased attention,and substantial research has been conducted in the past three decades.This paper provides a surve...Remote sensing-based methods of aboveground biomass(AGB)estimation in forest ecosystems have gained increased attention,and substantial research has been conducted in the past three decades.This paper provides a survey of current biomass estimation methods using remote sensing data and discusses four critical issues–collection of field-based biomass reference data,extraction and selection of suitable variables from remote sensing data,identification of proper algorithms to develop biomass estimation models,and uncertainty analysis to refine the estimation procedure.Additionally,we discuss the impacts of scales on biomass estimation performance and describe a general biomass estimation procedure.Although optical sensor and radar data have been primary sources for AGB estimation,data saturation is an important factor resulting in estimation uncertainty.LIght Detection and Ranging(lidar)can remove data saturation,but limited availability of lidar data prevents its extensive application.This literature survey has indicated the limitations of using single-sensor data for biomass estimation and the importance of integrating multi-sensor/scale remote sensing data to produce accurate estimates over large areas.More research is needed to extract a vertical vegetation structure(e.g.canopy height)from interferometry synthetic aperture radar(InSAR)or optical stereo images to incorporate it into horizontal structures(e.g.canopy cover)in biomass estimation modeling.展开更多
Background:Companioned by economic development,a dietary shift toward higher meat consumption is seen in developing countries and transitional economies,where the demand for livestock production has been increasing in...Background:Companioned by economic development,a dietary shift toward higher meat consumption is seen in developing countries and transitional economies,where the demand for livestock production has been increasing in response to such a dietary shift.In the Asian Dryland Belt,approaches to meet this demand have focused on grazing intensification,cropland conversion for animal feed,and supplemental feeding.With the scarcity of water,energy,and food in the region,a key question is whether or not the current approaches are sustainable.If not,what are the pathways to increase livestock production while protecting the region’s environment for a sustainable future?We provide our reviews and discuss current approaches in response to these dietary shifts and assess their environmental resilience with a focus on the grassland ecosystems in the Asian Dryland Belt.Results:While current approaches alleviate the urgent need for short-term livestock production,they lead to longterm vulnerability in food security.Trade-offs between short gains and long-term losses,between food for humans and for animals,and between agricultural intensification and environmental degradation need to be holistically examined for the sustainable development of the region.A grassland water,energy,and food nexus framework is proposed with specific recommendations to increase livestock production while considering other ecosystem services of the dryland grassland ecosystems in the Asian Dryland Belt.Conclusions:Current practices to increase livestock production are likely to lead to long-term,large-scale ecological degradation of the grassland ecosystems in the Asian Dryland Belt and are thus unsustainable.By considering the trade-offs in the nexus of water,land,food,and livelihoods,sustainable pathways were articulated and recommended.Future pilot studies are needed for validation and adoption.展开更多
Aims:This review was developed to introduce the essential components and variants of structural equation modeling(SEM),synthesize the common issues in SEM applications,and share our views on SEM’s future in ecologica...Aims:This review was developed to introduce the essential components and variants of structural equation modeling(SEM),synthesize the common issues in SEM applications,and share our views on SEM’s future in ecological research.Methods:We searched the Web of Science on SEM applications in ecological studies from 1999 through 2016 and summarized the potential of SEMs,with a special focus on unexplored uses in ecology.We also analyzed and discussed the common issues with SEM applications in previous publications and presented our view for its future applications.Results:We searched and found 146 relevant publications on SEM applications in ecological studies.We found that five SEM variants had not commenly been applied in ecology,including the latent growth curve model,Bayesian SEM,partial least square SEM,hierarchical SEM,and variable/model selection.We identified ten common issues in SEM applications including strength of causal assumption,specification of feedback loops,selection of models and variables,identification of models,methods of estimation,explanation of latent variables,selection of fit indices,report of results,estimation of sample size,and the fit of model.Conclusions:In previous ecological studies,measurements of latent variables,explanations of model parameters,and reports of key statistics were commonly overlooked,while several advanced uses of SEM had been ignored overall.With the increasing availability of data,the use of SEM holds immense potential for ecologists in the future.展开更多
In a case study in Tao River Basin, China, we derived a high spatial-resolution regional distribution of evapotranspiration(ET) using the single crop coefficient method and Budyko equation. We then further analyzed th...In a case study in Tao River Basin, China, we derived a high spatial-resolution regional distribution of evapotranspiration(ET) using the single crop coefficient method and Budyko equation. We then further analyzed the spatio-temporal characteristics of this diverse eco-hydrological basin from 2001–2010. The results suggest that the single crop coefficient method based on leaf area index captures better spatial and temporal dynamics of the regional ET than did the Budyko Equation method. The rising temperature was the main reason for the increasing ET in the Tao River Basin during 2001–2010. Areas with high ET efficiency were distributed mainly in the areas where the vegetation coverage was high, and a lower runoff coefficient responded. The estimated spatial patterns of ET allowed an improved understanding of the eco-hydrological processes within the Tao River Basin and the method used might be generalized as a reference for future regional-scale eco-hydrological research.展开更多
Quantitative characterization of environmental characteristics of cropland(ECC)plays an important role in maintaining sustainable development of agricultural systems and ensuring regional food security. In this study,...Quantitative characterization of environmental characteristics of cropland(ECC)plays an important role in maintaining sustainable development of agricultural systems and ensuring regional food security. In this study, the changes in ECC over the Songnen Plain, a major grain crops production region in Northeast China, were investigated for the period 1990–2015. The results revealed significant changes in climate conditions, soil physical properties and cropland use patterns with socioeconomic activities. Trends in climate parameters showed increasing temperature(+0.49°C/decade, p < 0.05) and decreasing wind speed(–0.3 m/s/decade, p < 0.01) for the growing season, while sunshine hours and precipitation exhibited non-significant trends. Four topsoil parameters including soil organic carbon(SOC), clay, bulk density and pH, indicated deteriorating soil conditions across most of the croplands, although some do exhibited slight improvement. The changing amplitude for each of the four above parameters ranged within –0.052 to 0.029 kg C/kg, –0.38 to 0.30,–0.60 to 0.39 g/cm^3, –3.29 to 2.34, respectively. Crop production significantly increased(44.0 million tons) with increasing sown area of croplands(~2.5 million ha) and fertilizer application(~2.5 million tons). The study reveals the dynamics of ECC in the Songnen Plain with intensive cultivation from 1990 to 2015. Population growth, economic development, and policy reform are shown to strongly influence the spatiotemporal changes in cropland characteristics.The study potentially provides valuable scientific information to support sustainable agroecosystem management in the context of global climate change and national socioeconomic development.展开更多
Impervious surface area(ISA)is an important parameter for many environmental or socioeconomic relevant studies.The unique characteristics of remote sensing data made it the primary data source for ISA mapping at vario...Impervious surface area(ISA)is an important parameter for many environmental or socioeconomic relevant studies.The unique characteristics of remote sensing data made it the primary data source for ISA mapping at various scales.This paper summarizes general ISA mapping procedure and major techniques and discusses impacts of scale issues on selection of remote sensing data and corresponding algorithms.Previous studies have indicated that ISA mapping remains a challenge,especially in urban–rural frontiers and in covering a large area.Effectively employing rich spatial information in high spatial resolution imagery through texture and objectbased methods is valuable.Data fusion of multi-resolution images and spectral mixture analysis are common approaches to reduce the mixed pixel problem in medium spatial resolution images such as Landsat.Coarse spatial resolution images such as MODIS and DMSP-OLS are valuable for national and global ISA mapping but more research is needed to effectively integrate multisource/scale data for improving mapping performance.Development of an optimal procedure corresponding to specific study areas and purposes is required to generate accurate ISA mapping results.展开更多
Oasis evolution, one of the most obvious surface processes in arid regions, affects various aspects of the regional environment, such as hydrological processes, ecological conditions, and microclimates. In this paper,...Oasis evolution, one of the most obvious surface processes in arid regions, affects various aspects of the regional environment, such as hydrological processes, ecological conditions, and microclimates. In this paper, the historical spatio-temporal evolution of the cultivated oases in the Heihe River Basin, the second largest inland watershed in the northwest of China, was assessed using multidisciplinary methods and data from multiple sources, including historical literature, ancient sites, maps and remotely sensed images. The findings show that cultivated oases were first developed on a large scale during the Han Dynasty (121 BC-220) and then gradually decreased in extent from the Six Dynasties period (220-581) to the Sui- Tang period (581-907), reaching a minimum in the Song- Yuan period (960-1368). An abrupt revival occurred during the Ming Dynasty (1368-1644) and continued through the Qing Dynasty (1644-1911), and during the period of the Republic of China (1912-1949), oasis development reached its greatest peak of the entire historical period. The oasis areas during seven major historical periods, i.e., Hart, Six Dynasties, Sui-Tang, Song-Yuan, Ming, Qing, and Republic of China, are estimated to have been 1703 kma, 1115 km2, 629 km2, 614 km2, 964 km2, 1205 km2, and 1917 km2, respectively. The spatial distribution generally exhibited a continuous sprawl process, with the center of the oases moving gradually from the downstream region to the middle and even upstream regions. The oases along the main river remained stable during most periods, whereas those close to the terminal reaches were subject to frequent variations and even abandonment. Socio-economic factors were the main forces driving the evolution of cultivated oases in the area; among them, political and societal stability, national defense, agricultural policy, population, and technological progress were the most important.展开更多
Aims Riparian ecosystems play an important role in overall ecosystem function,including the global carbon cycle of terrestrial ecosystems,at both landscape and global scales.Yet few studies have reported in situ measu...Aims Riparian ecosystems play an important role in overall ecosystem function,including the global carbon cycle of terrestrial ecosystems,at both landscape and global scales.Yet few studies have reported in situ measurements of CO_(2) in riparian areas where flooding is a unique disturbance to carbon cycling.Methods At multiple locations across riparian zones(RZ)with different water submergences in Xiangxi Bay(XXB),we studied seasonal variations of CO_(2) exchange between this Cynodon-dominated community and the atmosphere for 2 years by using static chambers.Important Findings We found that the seasonal changes in CO_(2) fluxes were apparent and dependent on the biophysical environment.In the beginning of spring,low gross primary productivity(GPP)in lightly flooded zones(LFZ)resulted in a positive net ecosystem exchange(NEE),indicating a net CO_(2) source.With the increase in temperature,more species and vegetation abundance appeared,and the increased GPP turned the LFZ from a net CO_(2) source into a sink.This transi-tion seemed predominantly controlled by the physiological growth of vegetation.The mean NEEs,REs and the light-use efficiency(α)of the vegetation at HFZ and MFZ were significantly higher than those at LFZ and UFZ.Yet the coefficients of variation(CV)of NEE and RE at MFZ and HFZ were lower than those at LFZ and UFZ.Submergence promoted the emission and uptake of CO_(2) to the atmosphere.Elongated submergence reduced the number of spe-cies and lowered the spatial variability of the RZ,further lowering the variation of the CO_(2) exchange.展开更多
Introduction:The effects of nutrients on stream conditions within individual streams or small areas have been studied extensively,but the same effects over a large region have rarely been examined due to the difficult...Introduction:The effects of nutrients on stream conditions within individual streams or small areas have been studied extensively,but the same effects over a large region have rarely been examined due to the difficulty of applying large-scale manipulative experiments.In this study,we estimated the causal effects of nutrients within the Western United States on invertebrate richness,an important biological indicator of stream conditions,by using observational data.Methods:We used the generalized propensity score method to avoid the common problem of statistical inference using observational data,i.e.,correlation established based on observational data does not imply a causal relationship because the effects of confounding factors are not properly separated.Results:Our analysis showed a subsidy-stress relationship between nutrients and invertebrate taxon richness in the whole Western United States and in its sub-ecoregions.The magnitude of the relationship varies among these subecoregions,suggesting a varying nitrogen effect on macroinvertebrates due,in large part,to the varying natural and anthropogenic conditions from ecoregion to ecoregion.Furthermore,our analysis confirmed that causal estimation results using regression can be sensitive to the imbalance of confounding factors.Conclusions:Stratifying data into ecoregions with relatively homogeneous environmental conditions or adjusting data by generalized propensity score can improve the balance of confounding factors,thereby allowing more reliable causal inference of nutrient effects.Invertebrates respond to the same nutrient levels differently across different site conditions.展开更多
基金supported by the following grants:National Key Research and Development Program of China (Grant No. 2009CB421306)the NSFC Project (Grant Nos. 41001014, 51209119) NSFC Projects (Grant Nos. 41240002, 91225301)+1 种基金the NSFC Key Project (Grant No. 91125010)the MAIRS Project funded by the NASA LCLUC Program (Grant No. NNX08AH50G)
文摘The study of snow and ice melt(SIM) is important in water-scarce arid regions for the assessment of water supply and quality. These studies involve unique difficulties, especially in the calibration of hydro-models because there is no direct way to continuously measure the SIM at hydrostations. The recursive digital filter(RDF) and the isotopic hydro-geochemical method(IHM) were coupled to separate the SIM from eight observed series of alpine streamflows in northwestern China.Validation of the calibrated methods suggested a good capture of the SIM characteristics with fair accuracy in both space and time. Applications of the coupled methods in the upper reaches of the Hei River Basin(HRB) suggested a double peak curve of the SIM fraction to streamflow for the multi-component recharged(MCR) rivers, while a single peak curve was suggested for the rainfall-dominant recharged(RDR)rivers. Given inter-annual statistics of the separation,both types of the alpine rivers have experienced an obvious decrease of SIM since 1960 s. In the past 10 years, the SIM in the two types of rivers has risen to the levels of the 1970 s, but has remained lower than the level of the 1960 s. The study provided a considerable evidence to quantify the alpine SIM based on the separation of observed data series at gauge stations. Application of the coupled method could be helpful in the calibration and validation of SIM-related hydro-models in alpine regions.
基金The National Natural Science Foundation of China under contract Nos 41201460,61375002 and 61473286the Special Research Project for the Commonwealth of the Ministry of Water Resources of the People’s Republic of China under contract No.201201092the National Science and Technology Pillar Program under contract No.2015BAJ02B01
文摘Spartina alterniflora is one of exotic plants along the coastal region in China. It was introduced as an important engineering approach to ecological restoration in the later 1970 s. However, owing to its good adaptability and strong reproductive capacity, the introduced species is explosively spreading along the coastal region quickly and resulting in a significant impact on the health and safety of coastal wetland ecosystems. It is imperative to quantify the spatial extent and the rate of S. alterniflora sprawl in order to assess its ecological damages and economic impacts. Remote sensing techniques have been used to address these challenges but large unsuccessful due to mixed spectral properties. In this study, a hybrid method was proposed for S. alterniflora detection using medium resolution remote sensing images by integrating both spatial and spectral features of S. alterniflora. The hybrid method consists of two phases:(1) delineation of intertidal zone as the potential area of S. alterniflora distribution and(2) extraction of S. alterniflora fraction distribution with a mixture pixel analysis. The proposed method was tested at the Xiangshan Bay on the east coastal region of Zhejiang Province, China, and mapped the spatial extent of S. alterniflora with Landsat datasets in the 2003, 2009 and 2014. The results showed that, the S. alterniflora has grown exponentially over past 10 years. In 2003, the total area of S. alterniflora was about 590 hm2, but quickly reached to 1 745 hm2 in 2009, and 5 715 hm2 in 2014. With a rate of approximately 10-folds growth within a decade, the invasive species almost occupied all muddy beaches to become the most dominant coastal salt vegetation in this region. It is believed that the strong biological reproductive capacity was the primary reason for such quick spread and at the same time human reclamation activities were also believed to have facilitated the environmental conditions for S. alterniflora sprawl.
基金supported by the National Aeronautics and Space Administration(NASA)(Grant numbers:NNX15AD51G,80NSSC20K0740).
文摘Background:Transitional economies in Southeast Asia—a distinct group of developing countries—have experienced rapid urbanization in the past several decades due to the economic transition that fundamentally changed the function of their economies,societies and the environment.Myanmar,one of the least developed transitional economies in Southeast Asia,increased urbanization substantially from 25%in 1990 to 31%in 2019.However,major knowledge gaps exist in understanding the changes in urban land use and land cover and environment and their drivers in its cities.Methods:We studied Yangon,the largest city in Myanmar,for the urbanization,environmental changes,and the underlying driving forces in a radically transitioned economy in the developing world.Based on satellite imagery and historic land use maps,we quantified the expansion of urban built-up land and constructed the land conversion matrix from 1990 through 2020.We also used three air pollutants to illustrate the changes in environmental conditions.We analyzed the coupled dynamics among urbanization,economic development,and environmental changes.Through conducting a workshop with 20 local experts,we further analyzed the influence of human systems and natural systems on Yangon’s urbanization and sustainability.Results:The city of Yangon expanded urban built-up land rapidly from 1990 to 2000,slowed down from 2000 to 2010,but gained momentum again from 2010 to 2020,with most newly added urban built-up land appearing to be converted from farmland and green land in both 1990–2000 and 2010–2020.Furthermore,the air pollutant concen-tration of CO decreased,but that of NO_(2)and PM_(2.5)increased in recent years.A positive correlation exists between population and economic development and the concentration of PM_(2.5)is highly associated with population,the economy,and the number of vehicles.Finally,the expert panel also identified other potential drivers for urbanization,including the extreme climate event of Cyclone Nargis,capital relocation,and globalization.Conclusions:Our research highlights the dramatic expansion of urban land and degradation of urban environment measured by air pollutants and interdependent changes between urbanization,economic development,and environmental changes.
基金supported by the National Natural Science Foundation of China(No#41571411)the Zhejiang A&F University’s Research and Development Fund for the talent startup project(No#2013FR052)+1 种基金Keller,dos-Santos,Bolfe,and Batistella acknowledge the support from the Brazilian National Council for Scientific and Tech-nological Development–CNPq(No#457927/2013-5)Data were acquired by the Sustainable Landscapes Brazil project supported by the Brazilian Agricultural Research Corporation(EMBRAPA),the US Forest Service,the USAID,and the US Department of State.
文摘Previous research has explored the potential to integrate lidar and optical data in aboveground biomass(AGB)estimation,but how different data sources,vegetation types,and modeling algorithms influence AGB estimation is poorly understood.This research conducts a comparative analysis of different data sources and modeling approaches in improving AGB estimation.RapidEye-based spectral responses and textures,lidar-derived metrics,and their combination were used to develop AGB estimation models.The results indicated that(1)overall,RapidEye data are not suitable for AGB estimation,but when AGB falls within 50–150 Mg/ha,support vector regression based on stratification of vegetation types provided good AGB estimation;(2)Lidar data provided stable and better estimations than RapidEye data;and stratification of vegetation types cannot improve estimation;(3)The combination of lidar and RapidEye data cannot provide better performance than lidar data alone;(4)AGB ranges affect the selection of the best AGB models,and a combination of different estimation results from the best model for each AGB range can improve AGB estimation;(5)This research implies that an optimal procedure for AGB estimation for a specific study exists,depending on the careful selection of data sources,modeling algorithms,forest types,and AGB ranges.
基金supported by the Open Research Fund of the State Key Laboratory of Estuarine and Coastal Research(Grant No.SKLEC-KF201912)the Foundation of Key Laboratory of Yangtze River Water Environment,Ministry of Education(Tongji University),China,(Grant No.YRWEF202105)+3 种基金the Natural Science Fund of Shanghai(Grant No.19ZR1470300)the Natural Science Foundation of China(Grant No.32071584)the Special Fund for Natural Resources Development of Jiangsu Province(Marine Science and Technology Innovation)(Grant No.JSZRHYKJ202109)the Central Public-interest Scientifc Institution Basal Research Fund,ECSFR,CAFS(Grant No.2021M04).
文摘Background:The lateral movements of mass and energy across the terrestrial-aquatic interface are being increasingly recognized for their importance in the carbon(C)balance of coastal/estuarine wetlands.We quantifed the lateral fux of detrital C in the Yangtze estuary where invasive Spartina alternifora has substantially and extensively altered the ecosystem structure and functions.Our overall objective was to close the C budget of estuarine wetlands through feld sampling,tower-based measurements,and modeling.Methods:A lateral detrital C exchange evaluation platform was established in a case study of the Yangtze River Estuary to investigate the efect of ecosystem structural changes on lateral detrital C transfer processes.This study estimated the lateral detrital C exchange based on the gross primary production(GPP)by performing coupled modeling and feld sampling.Tower-based measurements and MODIS time series and CH4 outgassing and biomass simultaneously measured the lateral detrital C fux to characterize the relative contributions of lateral(i.e.,detritus)C fuxes to the annual marsh C budget.Results:The C pools in the plants and soil of Spartina marshes were signifcantly higher than those of the native community dominated by Phragmites australis.The GPP based on MODIS(GPPMODIS)was 472.6 g C m^(−2) year^(−1) and accounted for 73.0%of the GPP estimated from eddy covariance towers(GPPEC)(646.9±70.7 g C m^(−2) year^(−1)).We also detected a higher GPPMODIS during the pre-growing season,which exhibited a similar lateral detrital C fux magnitude.On average,25.8%of the net primary production(NPP),which ranged from 0.21 to 0.30 kg C m^(−2) year^(−1),was exported during lateral exchange.The annual C loss as CH4 was estimated to be 17.9±3.7 g C m^(−2) year^(−1),accounting for 2.8%of the GPPEC.The net positive detrital C fux(i.e.,more detritus leaving the wetlands),which could exceed 0.16 kg C m^(−2) day^(-1),was related to daily tides.However,the observed lateral detrital C fux based on monthly sampling was 73.5%higher than that based on daily sampling(i.e.,the sum of daily sampling),particularly in March and October.In addition,spatiotemporal granularities were responsible for most of the uncertainty in the lateral detrital C exchange.Conclusion:This research demonstrated that an integrated framework incorporating modeling and feld sampling can quantitatively assess lateral detrital C transport processes across the terrestrial-aquatic interface in estuarine wetlands.However,we note some limitations in the application of the light-use efciency model to tidal wetlands.Spartina invasion can turn the lateral C balance from a C source(209.0 g C m^(−2) year^(−1))of Phragmites-dominated marshes into a small C sink(-31.0 g C m^(−2) year^(−1)).Sampling over a more extended period and continuous measurements are essential for determining the contribution of diferent lateral detrital C fux processes to closing the ecosystem C budgets.The sampling spatiotemporal granularities can be key to assessing lateral detrital C transfer.
基金a grant from Research Center of Agricultural and Forestry Carbon Sinks and Ecological Environmental Remediation,Zhejiang A&F University.
文摘Remote sensing-based methods of aboveground biomass(AGB)estimation in forest ecosystems have gained increased attention,and substantial research has been conducted in the past three decades.This paper provides a survey of current biomass estimation methods using remote sensing data and discusses four critical issues–collection of field-based biomass reference data,extraction and selection of suitable variables from remote sensing data,identification of proper algorithms to develop biomass estimation models,and uncertainty analysis to refine the estimation procedure.Additionally,we discuss the impacts of scales on biomass estimation performance and describe a general biomass estimation procedure.Although optical sensor and radar data have been primary sources for AGB estimation,data saturation is an important factor resulting in estimation uncertainty.LIght Detection and Ranging(lidar)can remove data saturation,but limited availability of lidar data prevents its extensive application.This literature survey has indicated the limitations of using single-sensor data for biomass estimation and the importance of integrating multi-sensor/scale remote sensing data to produce accurate estimates over large areas.More research is needed to extract a vertical vegetation structure(e.g.canopy height)from interferometry synthetic aperture radar(InSAR)or optical stereo images to incorporate it into horizontal structures(e.g.canopy cover)in biomass estimation modeling.
基金This study was supported by the NSF Belmont forum(1531086)the National Aeronautics and Space Administration Land Cover Land Use Change program(NASA LCLUC)(#NNX15AD51G)+1 种基金the Monsoon Integrated Regional Studies,with funding from USDA through AgBioResearch(#MICL02264)at Michigan State University,and the“Dynamics of Coupled Natural and Human Systems(CNH)”Program of the NSF(#1313761)We thank Gabriela Shirkey for editing the language and format of the manuscript.
文摘Background:Companioned by economic development,a dietary shift toward higher meat consumption is seen in developing countries and transitional economies,where the demand for livestock production has been increasing in response to such a dietary shift.In the Asian Dryland Belt,approaches to meet this demand have focused on grazing intensification,cropland conversion for animal feed,and supplemental feeding.With the scarcity of water,energy,and food in the region,a key question is whether or not the current approaches are sustainable.If not,what are the pathways to increase livestock production while protecting the region’s environment for a sustainable future?We provide our reviews and discuss current approaches in response to these dietary shifts and assess their environmental resilience with a focus on the grassland ecosystems in the Asian Dryland Belt.Results:While current approaches alleviate the urgent need for short-term livestock production,they lead to longterm vulnerability in food security.Trade-offs between short gains and long-term losses,between food for humans and for animals,and between agricultural intensification and environmental degradation need to be holistically examined for the sustainable development of the region.A grassland water,energy,and food nexus framework is proposed with specific recommendations to increase livestock production while considering other ecosystem services of the dryland grassland ecosystems in the Asian Dryland Belt.Conclusions:Current practices to increase livestock production are likely to lead to long-term,large-scale ecological degradation of the grassland ecosystems in the Asian Dryland Belt and are thus unsustainable.By considering the trade-offs in the nexus of water,land,food,and livelihoods,sustainable pathways were articulated and recommended.Future pilot studies are needed for validation and adoption.
基金supported by the Sustainable Energy Pathways(CHE)Program(#1230246)the Dynamics of Coupled Natural and Human Systems(CNH)Program(#1313761)of the US National Science Foundation(NSF)。
文摘Aims:This review was developed to introduce the essential components and variants of structural equation modeling(SEM),synthesize the common issues in SEM applications,and share our views on SEM’s future in ecological research.Methods:We searched the Web of Science on SEM applications in ecological studies from 1999 through 2016 and summarized the potential of SEMs,with a special focus on unexplored uses in ecology.We also analyzed and discussed the common issues with SEM applications in previous publications and presented our view for its future applications.Results:We searched and found 146 relevant publications on SEM applications in ecological studies.We found that five SEM variants had not commenly been applied in ecology,including the latent growth curve model,Bayesian SEM,partial least square SEM,hierarchical SEM,and variable/model selection.We identified ten common issues in SEM applications including strength of causal assumption,specification of feedback loops,selection of models and variables,identification of models,methods of estimation,explanation of latent variables,selection of fit indices,report of results,estimation of sample size,and the fit of model.Conclusions:In previous ecological studies,measurements of latent variables,explanations of model parameters,and reports of key statistics were commonly overlooked,while several advanced uses of SEM had been ignored overall.With the increasing availability of data,the use of SEM holds immense potential for ecologists in the future.
基金supported by the Doctoral Program of China’s Higher Education Research Fund(Grant No.20110211110011)the National Natural Science Foundation of China(Grant Nos.41001014,41240002,51209119)
文摘In a case study in Tao River Basin, China, we derived a high spatial-resolution regional distribution of evapotranspiration(ET) using the single crop coefficient method and Budyko equation. We then further analyzed the spatio-temporal characteristics of this diverse eco-hydrological basin from 2001–2010. The results suggest that the single crop coefficient method based on leaf area index captures better spatial and temporal dynamics of the regional ET than did the Budyko Equation method. The rising temperature was the main reason for the increasing ET in the Tao River Basin during 2001–2010. Areas with high ET efficiency were distributed mainly in the areas where the vegetation coverage was high, and a lower runoff coefficient responded. The estimated spatial patterns of ET allowed an improved understanding of the eco-hydrological processes within the Tao River Basin and the method used might be generalized as a reference for future regional-scale eco-hydrological research.
基金National Natural Science Foundation of China,No.41571410,No.41571199,No.41401589
文摘Quantitative characterization of environmental characteristics of cropland(ECC)plays an important role in maintaining sustainable development of agricultural systems and ensuring regional food security. In this study, the changes in ECC over the Songnen Plain, a major grain crops production region in Northeast China, were investigated for the period 1990–2015. The results revealed significant changes in climate conditions, soil physical properties and cropland use patterns with socioeconomic activities. Trends in climate parameters showed increasing temperature(+0.49°C/decade, p < 0.05) and decreasing wind speed(–0.3 m/s/decade, p < 0.01) for the growing season, while sunshine hours and precipitation exhibited non-significant trends. Four topsoil parameters including soil organic carbon(SOC), clay, bulk density and pH, indicated deteriorating soil conditions across most of the croplands, although some do exhibited slight improvement. The changing amplitude for each of the four above parameters ranged within –0.052 to 0.029 kg C/kg, –0.38 to 0.30,–0.60 to 0.39 g/cm^3, –3.29 to 2.34, respectively. Crop production significantly increased(44.0 million tons) with increasing sown area of croplands(~2.5 million ha) and fertilizer application(~2.5 million tons). The study reveals the dynamics of ECC in the Songnen Plain with intensive cultivation from 1990 to 2015. Population growth, economic development, and policy reform are shown to strongly influence the spatiotemporal changes in cropland characteristics.The study potentially provides valuable scientific information to support sustainable agroecosystem management in the context of global climate change and national socioeconomic development.
基金The authors acknowledge supports from the Zhejiang A&F University’s Research and Development Fund-talent startup project(2013FR052)Zhejiang Provincial Key Laboratory of Carbon Cycling in Forest Ecosystems and Carbon Sequestration,School of Environmental and Resource Sciences,Zhejiang A&F University and Center for Global Change and Earth Observations,Michigan State University.
文摘Impervious surface area(ISA)is an important parameter for many environmental or socioeconomic relevant studies.The unique characteristics of remote sensing data made it the primary data source for ISA mapping at various scales.This paper summarizes general ISA mapping procedure and major techniques and discusses impacts of scale issues on selection of remote sensing data and corresponding algorithms.Previous studies have indicated that ISA mapping remains a challenge,especially in urban–rural frontiers and in covering a large area.Effectively employing rich spatial information in high spatial resolution imagery through texture and objectbased methods is valuable.Data fusion of multi-resolution images and spectral mixture analysis are common approaches to reduce the mixed pixel problem in medium spatial resolution images such as Landsat.Coarse spatial resolution images such as MODIS and DMSP-OLS are valuable for national and global ISA mapping but more research is needed to effectively integrate multisource/scale data for improving mapping performance.Development of an optimal procedure corresponding to specific study areas and purposes is required to generate accurate ISA mapping results.
文摘Oasis evolution, one of the most obvious surface processes in arid regions, affects various aspects of the regional environment, such as hydrological processes, ecological conditions, and microclimates. In this paper, the historical spatio-temporal evolution of the cultivated oases in the Heihe River Basin, the second largest inland watershed in the northwest of China, was assessed using multidisciplinary methods and data from multiple sources, including historical literature, ancient sites, maps and remotely sensed images. The findings show that cultivated oases were first developed on a large scale during the Han Dynasty (121 BC-220) and then gradually decreased in extent from the Six Dynasties period (220-581) to the Sui- Tang period (581-907), reaching a minimum in the Song- Yuan period (960-1368). An abrupt revival occurred during the Ming Dynasty (1368-1644) and continued through the Qing Dynasty (1644-1911), and during the period of the Republic of China (1912-1949), oasis development reached its greatest peak of the entire historical period. The oasis areas during seven major historical periods, i.e., Hart, Six Dynasties, Sui-Tang, Song-Yuan, Ming, Qing, and Republic of China, are estimated to have been 1703 kma, 1115 km2, 629 km2, 614 km2, 964 km2, 1205 km2, and 1917 km2, respectively. The spatial distribution generally exhibited a continuous sprawl process, with the center of the oases moving gradually from the downstream region to the middle and even upstream regions. The oases along the main river remained stable during most periods, whereas those close to the terminal reaches were subject to frequent variations and even abandonment. Socio-economic factors were the main forces driving the evolution of cultivated oases in the area; among them, political and societal stability, national defense, agricultural policy, population, and technological progress were the most important.
基金Support for this research was provided by the Great Lakes Bioenergy Research Center,U.S.Department of Energy,Office of Science,Office of Biological and Environmental Research(Awards DE-SC0018409 and DE-FCO2-07ER64494)by the National Science Foundation Long-term Ecological Research Program(DEB 1832042)at the Kellogg Biological Station,and by Michigan State University AgBioResearch.
文摘对于土地用途转为种植生物燃料作物后的根系产量,还很少进行过长期的测定。为了评价此前的土地用途对地下生物量积累的影响,我们在“美国休耕保护项目”(Conservation Reserve Program,CPR)下生长了22年的草地(CRP草地)和使用期超过50年的农业用地(AGR农地)转为种植生物燃料作物玉米(Zea mays,Corn,C)、柳枝稷(Panicum virgatum,Switchgrass,Sw)和恢复性草原植被(Prairie,Pr)。我们将一块CPR草地维持为对照。我们的假设是土地利用历史和作物类型对根系密度有显著的影响;其中,原CRP草地上种植的多年生作物具有较高的根系生产力,而在原农业用地上种植的玉米的根系生产力最低。通过内生长土芯法对内生长根系生物量进行了原位测定,同时对地上净初级生产力(ANPP)进行了测量。包括气温、生长季长度和降水量在内的辅助测量则被用来考查它们对根系生产量的影响。根系生产力在未转变的CRP草地最高(1716 g m?2 yr?1),而在玉米田中最低(526 g m?2 yr?1)。由CRP草地和AGR农田转变而来的多年生作物种植地在第一年都具有较低的根系生物量和ANPP,但柳枝稷在2011年达到峰值,恢复后的草原植被也在一年后达到峰值。恢复后的草原生态系统稳定性较高(AGR-Pr:4.3±0.11;CRP-Pr:4.1±0.10),而仅种植单一作物的生态系统稳定性都较低。根系生产量与ANPP呈正相关性(R2=0.40)。总体而言,对生物燃料作物大规模种植过程中的根系生物量积累应予以重视,因为这是固碳的一种主要来源。
基金This research was a part of the project funded by the National Natural Science Foundation of China(NSFC)(NO.30900196 and NO.51278281)to Three Georges UniversityIt was also funded by Natural Science Foundation of Hubei Province(2015CFC834)+1 种基金Provincial Department of Education Scientific research projects(Q20151209)the Key Laboratory of Aquatic Botany and Watershed Ecology at the Chinese Academy of Sciences,and Engineering Research Center of Eco-environment in Three Gorges Reservoir Region,Ministry of Education(KF2016-03).
文摘Aims Riparian ecosystems play an important role in overall ecosystem function,including the global carbon cycle of terrestrial ecosystems,at both landscape and global scales.Yet few studies have reported in situ measurements of CO_(2) in riparian areas where flooding is a unique disturbance to carbon cycling.Methods At multiple locations across riparian zones(RZ)with different water submergences in Xiangxi Bay(XXB),we studied seasonal variations of CO_(2) exchange between this Cynodon-dominated community and the atmosphere for 2 years by using static chambers.Important Findings We found that the seasonal changes in CO_(2) fluxes were apparent and dependent on the biophysical environment.In the beginning of spring,low gross primary productivity(GPP)in lightly flooded zones(LFZ)resulted in a positive net ecosystem exchange(NEE),indicating a net CO_(2) source.With the increase in temperature,more species and vegetation abundance appeared,and the increased GPP turned the LFZ from a net CO_(2) source into a sink.This transi-tion seemed predominantly controlled by the physiological growth of vegetation.The mean NEEs,REs and the light-use efficiency(α)of the vegetation at HFZ and MFZ were significantly higher than those at LFZ and UFZ.Yet the coefficients of variation(CV)of NEE and RE at MFZ and HFZ were lower than those at LFZ and UFZ.Submergence promoted the emission and uptake of CO_(2) to the atmosphere.Elongated submergence reduced the number of spe-cies and lowered the spatial variability of the RZ,further lowering the variation of the CO_(2) exchange.
基金The first author receives financial support from the National Aeronautics and Space Administration(NASA)’s Land Cover and Land Use Program through their grant to Michigan State University(NNX15AD51G).
文摘Introduction:The effects of nutrients on stream conditions within individual streams or small areas have been studied extensively,but the same effects over a large region have rarely been examined due to the difficulty of applying large-scale manipulative experiments.In this study,we estimated the causal effects of nutrients within the Western United States on invertebrate richness,an important biological indicator of stream conditions,by using observational data.Methods:We used the generalized propensity score method to avoid the common problem of statistical inference using observational data,i.e.,correlation established based on observational data does not imply a causal relationship because the effects of confounding factors are not properly separated.Results:Our analysis showed a subsidy-stress relationship between nutrients and invertebrate taxon richness in the whole Western United States and in its sub-ecoregions.The magnitude of the relationship varies among these subecoregions,suggesting a varying nitrogen effect on macroinvertebrates due,in large part,to the varying natural and anthropogenic conditions from ecoregion to ecoregion.Furthermore,our analysis confirmed that causal estimation results using regression can be sensitive to the imbalance of confounding factors.Conclusions:Stratifying data into ecoregions with relatively homogeneous environmental conditions or adjusting data by generalized propensity score can improve the balance of confounding factors,thereby allowing more reliable causal inference of nutrient effects.Invertebrates respond to the same nutrient levels differently across different site conditions.