An inventory of topographic modifications is essential to addressing their impacts on hydrological and morphological processes in human-altered watersheds.However,such inventories are generally lacking.This study pres...An inventory of topographic modifications is essential to addressing their impacts on hydrological and morphological processes in human-altered watersheds.However,such inventories are generally lacking.This study presents two workflows for semi-automatic detection of linear earthen runoff and erosion control berms in rangelands using high-resolution topographic data.The workflows consist of initial object identification by applying either morphological grayscale reconstruction(MGR)or the Geomorphon(GEO)method,followed by identification refinements through filters based on objects’horizontal and vertical information.Three sites were selected within the Altar Valley,Arizona,in the southwestern United States.One site was used for developing workflows and optimizing filter thresholds,and the other two sites were used to validate workflows.The results showed that:1)The MGR-based workflow methodology could produce final precision and detection rates of up to 92%and 75%,respectively,and take less than 5 s for a 10.1 km^(2) site;2)The workflow based on the MGR method yielded greater identification accuracy than did the GEO workflow;3)Object length,orientation,and eccentricity were important characteristics for identifying earthen berms,and are sensitive to general channel flow direction and berm shape;4)Manual interrogation of topographic data and imagery can significantly improve identification precision rates.The proposed workflows will be useful for developing inventories of runoff and erosion control structures in support of sustainable rangeland management.展开更多
CLIGEN is a stochastic weather generator that creates statistically representative timeseries of daily and sub-daily point-scale weather variables from observed monthly statistics and other parameters. CLIGEN precipit...CLIGEN is a stochastic weather generator that creates statistically representative timeseries of daily and sub-daily point-scale weather variables from observed monthly statistics and other parameters. CLIGEN precipitation timeseries are used as climate input for various risk-assessment modelling applications as an alternative to observe long-term, high temporal resolution records. Here, we queried gridded global climate datasets (TerraClimate, ERA5, GPM-IMERG, and GLDAS) to estimate various 20-year climate statistics and obtain complete CLIGEN input parameter sets with coverage of the African and South American continents at 0.25 arc degree resolution. The estimation of CLIGEN precipitation parameters was informed by a ground-based dataset of >10,000 locations worldwide. The ground observations provided target values to fit regression models that downscale CLIGEN precipitation input parameters. Aside from precipitation parameters, CLIGEN’s parameters for temperature, solar radiation, etc. were in most cases directly calculated according to the original global datasets. Cross-validation for estimated precipitation parameters quantified errors that resulted from applying the estimation approach in a predictive fashion. Based on all training data, the RMSE was 2.23 mm for the estimated monthly average single-event accumulation and 4.70 mm/hr for monthly maximum 30-min intensity. This dataset facilitates exploration of hydrological and soil erosional hypotheses across Africa and South America.展开更多
Time-series of land surface phenology (LSP) data offer insights about vegetation growth patterns. They can be generated by exploiting the temporal and spectral reflectance properties of land surface components. Inte...Time-series of land surface phenology (LSP) data offer insights about vegetation growth patterns. They can be generated by exploiting the temporal and spectral reflectance properties of land surface components. Inter- annual and seasonal LSP data are important for under- standing and predicting an ecosystem's response to variations caused by natural and anthropogenic drivers. This research examines spatio-temporal change patterns and interactions between terrestrial phenology and 28 years of climate dynamics in Central Asia. Long-term (1981-2008) LSP records such as timing of the start, peak and length of the growing season and vegetation productivity were derived from remotely sensed vegetation greenness data. The patterns were analyzed to identify and characterize the impact of climate drivers at regional scales. We explored the relationships between phenologi- cal and precipitation and temperature variables for three generalized land use types that were exposed to decade- long regional drought events and intensified land and water resource use: rainfed agriculture, irrigated agriculture, and non-agriculture. To determine whether and how LSP dynamics are associated with climate patterns, a series of simple linear regression analyses between these two variables was executed. The three land use classes showed unique phenological responses to climate variation across Central Asia. Most of the phenological response variables were shown to be positively correlated to precipitation and negatively correlated to temperature. The most substantial climate variable affecting phenological responses of all three land use classes was a spring temperature regime. These results indicate that future higher temperatures would cause earlier and longer growing seasons.展开更多
For more than a decade, the Four Comers Region has faced extensive and persistent drought conditions that have impacted vegetation communities and local water resources while exacerbating soil erosion. These persisten...For more than a decade, the Four Comers Region has faced extensive and persistent drought conditions that have impacted vegetation communities and local water resources while exacerbating soil erosion. These persistent droughts threaten ecosystem services, agriculture, and livestock activities, and expose the hypersensitivity of this region to inter-annual climate variability and change. Much of the intermountain Western United States has sparse climate and vegetation monitoring stations, making fine-scale drought assessments difficult. Remote sensing data offers the opportunity to assess the impacts of the recent droughts on vegetation productivity across these areas. Here, we propose a drought assessment approach that integrates climate and topographical data with remote sensing vegetation index time series. Multisensor Normalized Difference Vegetation Index (NDVI) time series data from 1989 to 2010 at 5.6 km were analyzed to characterize the vegetation productivity changes and responses to the ongoing drought. A multi-linear regression was applied to metrics of vegetation productivity derived from the NDVI time series to detect vegetation productivity, an ecosystem service proxy, and changes. The results show that around 60.13% of the study area is observing a general decline of greenness (p 〈 0.05), while 3.87% show an unexpected green up, with the remaining areas showing no consistent change. Vegetation in the area show a significant positive correlation with elevation and precipitation gradients. These results, while, confirming the region's vegetation decline due to drought, shed further light on the future directions and challenges to the region's already stressed ecosystems. Whereas the results provide additional insights into this isolated and vulnerable region, the drought assessment approach used in this study may be adapted for application in other regions where surfacebased climate and vegetation monitoring record is spatially and temporally limited.展开更多
AIM:To isolate and characterize solid tumor inhibitory and other constituents from a bioactive extract of Casimiroa tetrameria((Rutaceae).METHODS:A crude extract of C.tetrameria obtained from the US National Cancer In...AIM:To isolate and characterize solid tumor inhibitory and other constituents from a bioactive extract of Casimiroa tetrameria((Rutaceae).METHODS:A crude extract of C.tetrameria obtained from the US National Cancer Institute Natural Product Repository and found to exhibit selective toxicity to solid tumor cells was subjected bioactivity-guided fractionation involving solvent-solvent partitioning,gel filtration,and chromatography.The structures of all isolated compounds were elucidated by spectroscopic analysis(NMR and MS) and/or by comparison with the reported data.Compounds 1 and 4-9 were evaluated for their solid tumor selective cytotoxicity.RESULTS:Nine metabolites,including a new furanocoumarin,5-methoxy-8-(4'-acetoxy-3'-methylbut-2-eny-loxy)-psoralen(1),and the previously known compounds 2-9 were encountered.Of these the flavonoid zapotin(6),and N-benzoyltyramide derivatives 7 and 8 were found to be the active constituents.CONCLUSION:Zapotin(6) is the most potent constituent of C.tetrameria with solid tumor selectivity.展开更多
Rangeland hillslopes provide much of the sediment supplied to channel systems and their lengths exert a fundamental constraint on hillslope diffusive processes.However,information regarding lengths of rangeland hillsl...Rangeland hillslopes provide much of the sediment supplied to channel systems and their lengths exert a fundamental constraint on hillslope diffusive processes.However,information regarding lengths of rangeland hillslopes,and how best to estimate them,is limited.In this study,three groups of watersheds(10 in total)were selected from the Walnut Gulch Experimental Watershed according to their geology,soil and vegetation characteristics.Group 1 watersheds were at lower elevations dominated by shrubs,Group 3 were at high elevations dominated by grass,and Group 2 were mixed shrub and grass.Their hillslope lengths were calculated from 1 m-resolution DEMs using three methods:a flow routing algorithm,slope-area relationships,and inverted relationship with drainage density.Parameters that characterize the current watersheds,including Hack's exponent and coefficient,watershed shape coefficient,channel concavity and steepness,and surface roughness,were quantified and related to hillslope lengths.Results shows:(1)estimated hillslope lengths were different for the three methods and between the three groups of watersheds;(2)hillslope lengths that measured from the flow routing algorithm for the ten selected watersheds primarily ranged from 30 to 100 m,with a median value of 63.0 m,which was 20%e50%greater than those derived from slope-area plots or drainage densities;(3)hillslope lengths estimated from the flow routing method were greater in Group 3 watersheds than in Group 2 and then in Group 1 watersheds.We attributed these differences in hillslope lengths to the historic epeirogenic pulses,watershed and drainage network morphology,and differences in vegetation characteristics;(4)measured hillslope lengths from the flow routing algorithm were best correlated with hillslope relief,then surface roughness,channel steepness and concavity.These results would benefit the applications of hydrological and erosion models in rangelands.展开更多
Background:Meadow ecosystems have important ecological functions and support socioeconomic services,yet are subject to multiple stressors that can lead to rapid degradation.In the Sierra Nevada of the western USA,recr...Background:Meadow ecosystems have important ecological functions and support socioeconomic services,yet are subject to multiple stressors that can lead to rapid degradation.In the Sierra Nevada of the western USA,recreational pack stock(horses and mules)use in seasonally wet mountain meadows may lead to soil trampling and meadow degradation,especially when soil water content is high and vegetation is developing.Methods:In order to improve the ability to predict meadow vulnerability to soil disturbance from pack stock use,we measured soil resistance(SR),which is an index of vulnerability to trampling disturbance,at two spatial scales using a stratified-random sampling design.We then compared SR to several soil and vegetation explanatory variables that were also measured at the two spatial scales:plant community type(local scale)and topographic gradient class(meadow scale).Results:We found that local-scale differences in drivers of SR were contingent on the meadow scale,which is important because multiple spatial scale evaluation of ecological metrics provides a broader understanding of the potential controls on ecological processes than assessments conducted at a single spatial scale.We also found two contrasting explanatory models for drivers of SR at the local scale:(1)soil gravimetric water content effects on soil disaggregation and(2)soil bulk density and root mass influence on soil cohesion.Soil resistance was insufficient to sustain pack stock use without incurring soil deformation in wet plant communities,even when plant cover was maximal during a major drought.Conclusions:Our study provides new information on seasonally wet meadow vulnerability to trampling by pack stock animals using multi-scale drivers of SR,including the contrasting roles of soil disaggregation,friction,and cohesion.Our work aims to inform meadow management efforts in the Sierra Nevada and herbaceous ecosystems in similar regions that are subject to seasonal soil saturation and livestock use.展开更多
In its 40-year history,the science of conservation has faced unprecedented challenges in terms of environmental damage and rapid global change,and environmental problems are only increasing as greater demands are plac...In its 40-year history,the science of conservation has faced unprecedented challenges in terms of environmental damage and rapid global change,and environmental problems are only increasing as greater demands are placed on limited natural resources.Conservation science has been adapting to keep pace with these changes.Here,we highlight contemporary and emerging trends and innovations in conservation science that we believe represent the most effective responses to biodiversity threats.We focus on specific areas where conservation science has had to adjust its approach to address emerging threats to biodiversity,including habitat destruction and degradation,climate change,declining populations and invasive species.We also document changes in attitudes,norms and practices among conservation scientists.A key component to success is engaging and maintaining public support for conservation,which can be facilitated through the use of technology.These recent trends in conservation and management are innovative and will assist in optimizing conservation strategies,increasing our leverage with the general public and tackling our current environmental challenges.展开更多
Hydrologic response in a watershed is driven by precipitation.Multi-site rainfall generators can be used to model watersheds using spatially varied rainfall inputs to better analyze how the rainfall variability affect...Hydrologic response in a watershed is driven by precipitation.Multi-site rainfall generators can be used to model watersheds using spatially varied rainfall inputs to better analyze how the rainfall variability affects runoff generation.This study adopted both a single-site rainfall generator(CLIGEN)and a multi-site rainfall generator to generate two rainfall data sequences,which were then used to drive the Soil and Water Assessment Tool(SWAT)for runoff simulation.The 148-km2 Walnut Gulch Experimental Watershed and its two sub-watersheds were selected to evaluate the hydrologic response.Runoff calibration was done against measured runoff in the watershed.Statistics showed that the single-site and multi-site rainfall generators gave similar results regarding annual precipitation.However,the multi-site generator performed much better than the single-site generator in both mean summer flow and for the different return period flows.The runoff derived from the single-site generator was significantly over-estimated in all three watersheds.As for the multi-site generator,the derived runoff was satisfactorily predicted in the smaller watersheds but only overestimated in the largest watershed.This indicated that in small to medium sized watersheds,the spatial variability of rainfall could play an important role for hydrologic response because of the heterogeneity of convective rainfall in this semi-arid region,which makes the application of multi-site rainfall generator a better option than the single-site generator.展开更多
Globally,the threat of endangerment and extinction of small cetaceans was highlighted after the recent extinction of the Chinese River dolphin or Baiji(Lipotes vexillifer).Species with a small population size and a li...Globally,the threat of endangerment and extinction of small cetaceans was highlighted after the recent extinction of the Chinese River dolphin or Baiji(Lipotes vexillifer).Species with a small population size and a limited geographic range,such as Ganges River dolphins(GRD),are more vulnerable to extinction.The social and behavioral needs of cetaceans have been identified as potential factors increasing their vulnerability to human disturbance.However,little is known about how GRD adapt their behaviors and diel activity patterns to spatiotemporal variation.In this paper,we examined the underwater behavior of GRDs in Nepal by collecting echolocation clicks from three spatially stratified habitats in the Sapta Koshi River system over a six-month period.Our research found that GRDs behave differently in response to spatial heterogeneity,indicating diverse environmental requirements for GRD persistence.Behavioral activity and duration varied across habitats but not across time of day,suggesting that GRD behaviors are likely to be regulated by habitat structure regardless of the time of day.However,GRD consistently exhibited nocturnal activity peaks even when diurnal activity varied substantially.This indicates that river dolphins may favor nocturnal refuges as a reaction to human disturbance in highly regulated rivers.Managing human disturbances in conjunction with habitat heterogeneity can improve the persistence of riverine cetaceans.Here,we document behavioral and ecological information pertaining to GRD,which is essential to the formation of river dolphin recovery plans that link ecological perspectives to planning and management.展开更多
文摘An inventory of topographic modifications is essential to addressing their impacts on hydrological and morphological processes in human-altered watersheds.However,such inventories are generally lacking.This study presents two workflows for semi-automatic detection of linear earthen runoff and erosion control berms in rangelands using high-resolution topographic data.The workflows consist of initial object identification by applying either morphological grayscale reconstruction(MGR)or the Geomorphon(GEO)method,followed by identification refinements through filters based on objects’horizontal and vertical information.Three sites were selected within the Altar Valley,Arizona,in the southwestern United States.One site was used for developing workflows and optimizing filter thresholds,and the other two sites were used to validate workflows.The results showed that:1)The MGR-based workflow methodology could produce final precision and detection rates of up to 92%and 75%,respectively,and take less than 5 s for a 10.1 km^(2) site;2)The workflow based on the MGR method yielded greater identification accuracy than did the GEO workflow;3)Object length,orientation,and eccentricity were important characteristics for identifying earthen berms,and are sensitive to general channel flow direction and berm shape;4)Manual interrogation of topographic data and imagery can significantly improve identification precision rates.The proposed workflows will be useful for developing inventories of runoff and erosion control structures in support of sustainable rangeland management.
文摘CLIGEN is a stochastic weather generator that creates statistically representative timeseries of daily and sub-daily point-scale weather variables from observed monthly statistics and other parameters. CLIGEN precipitation timeseries are used as climate input for various risk-assessment modelling applications as an alternative to observe long-term, high temporal resolution records. Here, we queried gridded global climate datasets (TerraClimate, ERA5, GPM-IMERG, and GLDAS) to estimate various 20-year climate statistics and obtain complete CLIGEN input parameter sets with coverage of the African and South American continents at 0.25 arc degree resolution. The estimation of CLIGEN precipitation parameters was informed by a ground-based dataset of >10,000 locations worldwide. The ground observations provided target values to fit regression models that downscale CLIGEN precipitation input parameters. Aside from precipitation parameters, CLIGEN’s parameters for temperature, solar radiation, etc. were in most cases directly calculated according to the original global datasets. Cross-validation for estimated precipitation parameters quantified errors that resulted from applying the estimation approach in a predictive fashion. Based on all training data, the RMSE was 2.23 mm for the estimated monthly average single-event accumulation and 4.70 mm/hr for monthly maximum 30-min intensity. This dataset facilitates exploration of hydrological and soil erosional hypotheses across Africa and South America.
文摘Time-series of land surface phenology (LSP) data offer insights about vegetation growth patterns. They can be generated by exploiting the temporal and spectral reflectance properties of land surface components. Inter- annual and seasonal LSP data are important for under- standing and predicting an ecosystem's response to variations caused by natural and anthropogenic drivers. This research examines spatio-temporal change patterns and interactions between terrestrial phenology and 28 years of climate dynamics in Central Asia. Long-term (1981-2008) LSP records such as timing of the start, peak and length of the growing season and vegetation productivity were derived from remotely sensed vegetation greenness data. The patterns were analyzed to identify and characterize the impact of climate drivers at regional scales. We explored the relationships between phenologi- cal and precipitation and temperature variables for three generalized land use types that were exposed to decade- long regional drought events and intensified land and water resource use: rainfed agriculture, irrigated agriculture, and non-agriculture. To determine whether and how LSP dynamics are associated with climate patterns, a series of simple linear regression analyses between these two variables was executed. The three land use classes showed unique phenological responses to climate variation across Central Asia. Most of the phenological response variables were shown to be positively correlated to precipitation and negatively correlated to temperature. The most substantial climate variable affecting phenological responses of all three land use classes was a spring temperature regime. These results indicate that future higher temperatures would cause earlier and longer growing seasons.
文摘For more than a decade, the Four Comers Region has faced extensive and persistent drought conditions that have impacted vegetation communities and local water resources while exacerbating soil erosion. These persistent droughts threaten ecosystem services, agriculture, and livestock activities, and expose the hypersensitivity of this region to inter-annual climate variability and change. Much of the intermountain Western United States has sparse climate and vegetation monitoring stations, making fine-scale drought assessments difficult. Remote sensing data offers the opportunity to assess the impacts of the recent droughts on vegetation productivity across these areas. Here, we propose a drought assessment approach that integrates climate and topographical data with remote sensing vegetation index time series. Multisensor Normalized Difference Vegetation Index (NDVI) time series data from 1989 to 2010 at 5.6 km were analyzed to characterize the vegetation productivity changes and responses to the ongoing drought. A multi-linear regression was applied to metrics of vegetation productivity derived from the NDVI time series to detect vegetation productivity, an ecosystem service proxy, and changes. The results show that around 60.13% of the study area is observing a general decline of greenness (p 〈 0.05), while 3.87% show an unexpected green up, with the remaining areas showing no consistent change. Vegetation in the area show a significant positive correlation with elevation and precipitation gradients. These results, while, confirming the region's vegetation decline due to drought, shed further light on the future directions and challenges to the region's already stressed ecosystems. Whereas the results provide additional insights into this isolated and vulnerable region, the drought assessment approach used in this study may be adapted for application in other regions where surfacebased climate and vegetation monitoring record is spatially and temporally limited.
基金supported by the US National Institutes of Health research grant CA092143 awarded by National Cancer Institute
文摘AIM:To isolate and characterize solid tumor inhibitory and other constituents from a bioactive extract of Casimiroa tetrameria((Rutaceae).METHODS:A crude extract of C.tetrameria obtained from the US National Cancer Institute Natural Product Repository and found to exhibit selective toxicity to solid tumor cells was subjected bioactivity-guided fractionation involving solvent-solvent partitioning,gel filtration,and chromatography.The structures of all isolated compounds were elucidated by spectroscopic analysis(NMR and MS) and/or by comparison with the reported data.Compounds 1 and 4-9 were evaluated for their solid tumor selective cytotoxicity.RESULTS:Nine metabolites,including a new furanocoumarin,5-methoxy-8-(4'-acetoxy-3'-methylbut-2-eny-loxy)-psoralen(1),and the previously known compounds 2-9 were encountered.Of these the flavonoid zapotin(6),and N-benzoyltyramide derivatives 7 and 8 were found to be the active constituents.CONCLUSION:Zapotin(6) is the most potent constituent of C.tetrameria with solid tumor selectivity.
文摘Rangeland hillslopes provide much of the sediment supplied to channel systems and their lengths exert a fundamental constraint on hillslope diffusive processes.However,information regarding lengths of rangeland hillslopes,and how best to estimate them,is limited.In this study,three groups of watersheds(10 in total)were selected from the Walnut Gulch Experimental Watershed according to their geology,soil and vegetation characteristics.Group 1 watersheds were at lower elevations dominated by shrubs,Group 3 were at high elevations dominated by grass,and Group 2 were mixed shrub and grass.Their hillslope lengths were calculated from 1 m-resolution DEMs using three methods:a flow routing algorithm,slope-area relationships,and inverted relationship with drainage density.Parameters that characterize the current watersheds,including Hack's exponent and coefficient,watershed shape coefficient,channel concavity and steepness,and surface roughness,were quantified and related to hillslope lengths.Results shows:(1)estimated hillslope lengths were different for the three methods and between the three groups of watersheds;(2)hillslope lengths that measured from the flow routing algorithm for the ten selected watersheds primarily ranged from 30 to 100 m,with a median value of 63.0 m,which was 20%e50%greater than those derived from slope-area plots or drainage densities;(3)hillslope lengths estimated from the flow routing method were greater in Group 3 watersheds than in Group 2 and then in Group 1 watersheds.We attributed these differences in hillslope lengths to the historic epeirogenic pulses,watershed and drainage network morphology,and differences in vegetation characteristics;(4)measured hillslope lengths from the flow routing algorithm were best correlated with hillslope relief,then surface roughness,channel steepness and concavity.These results would benefit the applications of hydrological and erosion models in rangelands.
基金The San Francisco Public Utilities Commission funded the field and laboratory work conducted in this study.
文摘Background:Meadow ecosystems have important ecological functions and support socioeconomic services,yet are subject to multiple stressors that can lead to rapid degradation.In the Sierra Nevada of the western USA,recreational pack stock(horses and mules)use in seasonally wet mountain meadows may lead to soil trampling and meadow degradation,especially when soil water content is high and vegetation is developing.Methods:In order to improve the ability to predict meadow vulnerability to soil disturbance from pack stock use,we measured soil resistance(SR),which is an index of vulnerability to trampling disturbance,at two spatial scales using a stratified-random sampling design.We then compared SR to several soil and vegetation explanatory variables that were also measured at the two spatial scales:plant community type(local scale)and topographic gradient class(meadow scale).Results:We found that local-scale differences in drivers of SR were contingent on the meadow scale,which is important because multiple spatial scale evaluation of ecological metrics provides a broader understanding of the potential controls on ecological processes than assessments conducted at a single spatial scale.We also found two contrasting explanatory models for drivers of SR at the local scale:(1)soil gravimetric water content effects on soil disaggregation and(2)soil bulk density and root mass influence on soil cohesion.Soil resistance was insufficient to sustain pack stock use without incurring soil deformation in wet plant communities,even when plant cover was maximal during a major drought.Conclusions:Our study provides new information on seasonally wet meadow vulnerability to trampling by pack stock animals using multi-scale drivers of SR,including the contrasting roles of soil disaggregation,friction,and cohesion.Our work aims to inform meadow management efforts in the Sierra Nevada and herbaceous ecosystems in similar regions that are subject to seasonal soil saturation and livestock use.
基金This manuscript was initiated at the Ecological Society of America’s 2012 Emerging Issues Conference entitled“Developing Ecologically Based Conservation Targets under Global Change,”in Shepherdstown,WV.We thank Brian Bowen,Nancy Green,Patricia Heglund,Mary Klein,Hilary Smith,Mary Bruce Alford,and Hannah Kohut for their assistance.
文摘In its 40-year history,the science of conservation has faced unprecedented challenges in terms of environmental damage and rapid global change,and environmental problems are only increasing as greater demands are placed on limited natural resources.Conservation science has been adapting to keep pace with these changes.Here,we highlight contemporary and emerging trends and innovations in conservation science that we believe represent the most effective responses to biodiversity threats.We focus on specific areas where conservation science has had to adjust its approach to address emerging threats to biodiversity,including habitat destruction and degradation,climate change,declining populations and invasive species.We also document changes in attitudes,norms and practices among conservation scientists.A key component to success is engaging and maintaining public support for conservation,which can be facilitated through the use of technology.These recent trends in conservation and management are innovative and will assist in optimizing conservation strategies,increasing our leverage with the general public and tackling our current environmental challenges.
基金Specific Cooperative Agreement between the USDA Agricultural Research Service(Agreement number 58-53424-018)the University of Arizona(Agreement number 2022-13610-012-22S)+1 种基金the Independent research project of State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin(Grant No.SKL2020TS10)the Research&Development Support Program of China Institute of Water Resources and Hydropower Research(grant number SC0145B012021).
文摘Hydrologic response in a watershed is driven by precipitation.Multi-site rainfall generators can be used to model watersheds using spatially varied rainfall inputs to better analyze how the rainfall variability affects runoff generation.This study adopted both a single-site rainfall generator(CLIGEN)and a multi-site rainfall generator to generate two rainfall data sequences,which were then used to drive the Soil and Water Assessment Tool(SWAT)for runoff simulation.The 148-km2 Walnut Gulch Experimental Watershed and its two sub-watersheds were selected to evaluate the hydrologic response.Runoff calibration was done against measured runoff in the watershed.Statistics showed that the single-site and multi-site rainfall generators gave similar results regarding annual precipitation.However,the multi-site generator performed much better than the single-site generator in both mean summer flow and for the different return period flows.The runoff derived from the single-site generator was significantly over-estimated in all three watersheds.As for the multi-site generator,the derived runoff was satisfactorily predicted in the smaller watersheds but only overestimated in the largest watershed.This indicated that in small to medium sized watersheds,the spatial variability of rainfall could play an important role for hydrologic response because of the heterogeneity of convective rainfall in this semi-arid region,which makes the application of multi-site rainfall generator a better option than the single-site generator.
基金supported by the National Natural Science Foundation of China(42030508,41988101)the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(2019QZKK0301)+1 种基金funding from the European Research Council(ERC-SyG-2013-610028 IMBALANCE-P)funding from the project “Inside out”(#POIR.04.04.00-00-5F85/18-00)funded by the HOMING programme of the Foundation for Polish Science co-financed by the European Union under the European Regional Development Fund。
基金This study was supported by the National Key Research and Development Program of China(2016YFC0500503 and 2016YFC0500501)by the Department of Science and Technology of Inner Mongolia Autonomous Region for studying steppe ecosystems on the Mongolian Plateau(20140409 and 201503001).
文摘Globally,the threat of endangerment and extinction of small cetaceans was highlighted after the recent extinction of the Chinese River dolphin or Baiji(Lipotes vexillifer).Species with a small population size and a limited geographic range,such as Ganges River dolphins(GRD),are more vulnerable to extinction.The social and behavioral needs of cetaceans have been identified as potential factors increasing their vulnerability to human disturbance.However,little is known about how GRD adapt their behaviors and diel activity patterns to spatiotemporal variation.In this paper,we examined the underwater behavior of GRDs in Nepal by collecting echolocation clicks from three spatially stratified habitats in the Sapta Koshi River system over a six-month period.Our research found that GRDs behave differently in response to spatial heterogeneity,indicating diverse environmental requirements for GRD persistence.Behavioral activity and duration varied across habitats but not across time of day,suggesting that GRD behaviors are likely to be regulated by habitat structure regardless of the time of day.However,GRD consistently exhibited nocturnal activity peaks even when diurnal activity varied substantially.This indicates that river dolphins may favor nocturnal refuges as a reaction to human disturbance in highly regulated rivers.Managing human disturbances in conjunction with habitat heterogeneity can improve the persistence of riverine cetaceans.Here,we document behavioral and ecological information pertaining to GRD,which is essential to the formation of river dolphin recovery plans that link ecological perspectives to planning and management.