The principles of remotely estimating grassland cover density in an alpine meadow soil from space lie in the synchronous collection of in situ samples with the satellite pass and statistically linking these cover dens...The principles of remotely estimating grassland cover density in an alpine meadow soil from space lie in the synchronous collection of in situ samples with the satellite pass and statistically linking these cover densities to their image properties according to their geographic coordinates. The principles and procedures for quantifying grassland cover density from satellite image data were presented with an example from Qinghai Lake, China demonstrating how quantification could be made more accurate through the integrated use of remote sensing and global positioning systems (GPS). An empirical model was applied to an entire satellite image to convert pixel values into ground cover density. Satellite data based on 68 field samples was used to produce a map of ten cover densities. After calibration a strong linear regression relationship (r2 = 0.745) between pixel values on the satellite image and in situ measured grassland cover density was established with an 89% accuracy level. However, to minimize positional uncertainty of field samples, integrated use of hyperspatial satellite data and GPS could be utilized. This integration could reduce disparity in ground and space sampling intervals, and improve future quantification accuracy even more.展开更多
The ecological concept of Plant Functional Types(PFTs), which refers to the assemblage of plants with certain functional traits, has been introduced for the study of plant responses to the environment change and hum...The ecological concept of Plant Functional Types(PFTs), which refers to the assemblage of plants with certain functional traits, has been introduced for the study of plant responses to the environment change and human disturbance. Taking the alpine meadow community in the Zoigê Plateau as a study case, this paper classified PFTs in terms of plant nutrition traits. The sequential results are as follows.(1) The main herbages in the Zoigê Plateau included 16 species in 5 families. Among the five families, Cyperaceae vegetation accounted for 81.37%of herbage area in total, while the remaining 4families occupied less than 20%. As for the species,Kobresia setchwanensis Hand.-Maizz. was dominant,accounting for 48.74% of the total area; while the remaining 51.26% was comprised of Polygonum viviparum L., Anaphalis fiavescens Hand.-Mazz.,Stipa aliena Keng and other species.(2) By using the Principal Component Analysis(PCA), the assessment of herbages nutrition was carried out based on the comprehensive multi-index evaluation model.Polygonum viviparum L. had the highest nutritional value score(1.43), and Stipa aliena Keng had the lowest(-1.40). Nutritional value of herbage species had a significantly positive correlation with altitude(P<0.01) in the Zoigê Plateau.(3) Based on the nutritional values, herbages in the Zoigê Plateau could be grouped into 3 nutrition PFTs(high, medium and low) by using the Natural Breaks(Jenks) method.展开更多
Four soil types(peat, marsh, meadow, and sandy) in the Zoige Plateau of China are associated with the severity of wetland degradation. The effects of wetland degradation on the structure and abundance of fungal commun...Four soil types(peat, marsh, meadow, and sandy) in the Zoige Plateau of China are associated with the severity of wetland degradation. The effects of wetland degradation on the structure and abundance of fungal communities and cellulase activity were assessed in these 4 soil types at 3 depths using DGGE(Denatured Gradient Gel Electrophoresis), q PCR(Quantitative Real-time PCR),and 3,5-dinitrosalicylic acid assays. Cellulase activity and abundance of the fungal community declined in parallel to the level of wetland degradation(from least to most disturbed). DGGE analysis indicated a major shift in composition of fungal communities among the4 soil types consistent with the level of degradation.Water content(WC), organic carbon(OC), total nitrogen(TN), total phosphorus(TP), available nitrogen(AN), and available phosphorus(AP) were strongly correlated with cellulase activity and the structure and abundance of the fungal community.The results indicate that soil physicochemical properties(WC, OC, TN, TP, AN, and AP), cellulase activity, and diversity and abundance of fungal communities are sensitive indicators of the relative level of wetland degradation. WC was the major factorinvolved in Zoige wetland degradation and lower WC levels contributed to declines in the abundance and diversity of the fungal community and reduction in cellulase activity.展开更多
The present reported study investigated the persistence of snow anomalies over the Tibetan Plateau(TP) from the preceding seasons to summer and the relationship between the previous snow cover anomaly and summer preci...The present reported study investigated the persistence of snow anomalies over the Tibetan Plateau(TP) from the preceding seasons to summer and the relationship between the previous snow cover anomaly and summer precipitation over East Asia. The results showed that, relative to other snow indices, such as the station observational snow depth(SOSD) index and the snow water equivalent(SWE) index, the snow cover area proportion(SCAP) index calculated from the SWE and the percentage of visible snow of the Equal-Area Scalable Earth Grids(EASE-grids) dataset has a higher persistence in interannual anomalies, particularly from May to summer. As such, the May SCAP index is significantly related to summer precipitation over the Meiyu-Baiu region. The persistence of the SCAP index can partly explain the season-delayed effect of snow cover over the TP on summer rainfall over the Meiyu-Baiu region besides the contribution of the soil moisture bridge. The preceding SST anomaly in the tropical Indian Ocean and ENSO can persist through the summer and affect the summer precipitation over the Meiyu-Baiu region. However, the May SCAP index is mostly independent of the simultaneous SSTs in the tropical Indian Ocean and the preceding ENSO and may affect the summer precipitation over the Meiyu-Baiu region independent of the effects of the SST anomalies. Therefore, the May SCAP over the TP could be regarded as an important supplementary factor in the forecasting of summer precipitation over the Meiyu-Baiu region.展开更多
Accurate wetland delineation is the basis of wetland definition and mapping, and is of great importance for wetland management and research. The Zoige Plateau on the Qinghai-Tibet Plateau was used as a research site f...Accurate wetland delineation is the basis of wetland definition and mapping, and is of great importance for wetland management and research. The Zoige Plateau on the Qinghai-Tibet Plateau was used as a research site for research on alpine wetland delineation. Several studies have analyzed the spatiotemporal pattern and dynamics of these alpine wetlands, but none have addressed the issues of wetland boundaries. The objective of this work was to discriminate the upper boundaries of alpine wetlands by coupling ecological methods and satellite observations. The combination of Landsat 8 images and supervised classification was an effective method for rapid identification of alpine wetlands in the Zoig6 Plateau. Wet meadow was relatively stable compared with hydric soils and wetland hydrology and could be used as a primary indicator for discriminating the upper boundaries of alpine wetlands. A slope of less than 4.5° could be used as the threshold value for wetland delineation. The normalized difference vegetation index (NDVI) in 434 field sites showed that a threshold value of 0.3 could distinguish grasslands from emergent marsh and wet meadow in September. The median normalized difference water index (NDWI) of emergent marsh remained more stable than that of wet meadow and grasslands during the period from September until July of the following year. The index of mean density in wet meadow zones was higher than the emergent and upland zones. Over twice the number of species occurred in the wet meadow zone compared with the emergent zone, and close to the value of upland zone. Alpine wetlands in the three reserves in 2014 covered 1175.19 kin2 with a classification accuracy of 75.6%. The combination of ecological methods and remote sensing technology will play an important role in wetland delineation at medium and small scales. The correct differentiation between wet meadow and grasslands is the key to improving the accuracy of future wetland delineation.展开更多
Zoige Plateau wetlands are located in the northeastern corner of the Qinghai-Tibet Plateau.The landscape pattern evolution processes in the Zoige Plateau and their driving factors were identified by analyzing the dyna...Zoige Plateau wetlands are located in the northeastern corner of the Qinghai-Tibet Plateau.The landscape pattern evolution processes in the Zoige Plateau and their driving factors were identified by analyzing the dynamic changes in landscape modification and conversion and their dynamic rates of alpine wetlands over the past four decades.The results showed that the landscape conversion between wetlands and non-wetlands mainly occurred during the period from 1966 to 1986.The marsh wetland area converted from lake and river wetlands was larger because of swamping compared to other wetland landscapes.Meanwhile,the larger area of marsh wetlands was also converted to lake wetlands more than other types of wetlands.The modification processes mainly occurred among natural wetland landscapes in the first three periods.Obvious conversions were observed between wetland and nonwetland landscapes(i.e.,forestland,grassland,and other landscapes) in the Zoige Plateau.These natural wetland landscapes such as river,lake and marsh wetlands showed a net loss over the past four decades,whereas artificial wetland landscapes(i.e.,paddy field and reservoir and pond wetlands) showed a net decrease.The annual dynamic rate of the whole wetland landscape was 0.72%,in which the annual dynamic rate of river wetlands was the highest,followed by lake wetlands,while marsh wetlands had the lowest dynamic rate.The integrated landscape dynamic rate showed a decreasing trend in the first three periods.The changes in wetland landscape patterns were comprehensively controlled by natural factors and human activities,especially human activities play an important role in changing wetland landscape patterns.展开更多
Although mathematical models(e.g., De Nitrification and De Composition(DNDC) provide a powerful tool to study regional carbon budget, it is still difficult to obtain accurate simulation results because there exists la...Although mathematical models(e.g., De Nitrification and De Composition(DNDC) provide a powerful tool to study regional carbon budget, it is still difficult to obtain accurate simulation results because there exists large uncertainties in modeling regional carbon budget. Through the investigation on the sensitivity of model output parameters to the input parameters, sensitivity analysis(SA) has been proved to be able to identify the key sources of uncertainties and be helpful to reduce the model uncertainties. However, some input parameters with discrete values(e.g., land use type and soil type) and the regional effect of the sensitive parameters were rarely examined in SA. In this paper, taking the Zoige Plateau as a case area, we combined the one-factor-ata-time(OAT) with Extended Fourier Amplitude Sensitivity Test(EFAST) to conduct a SA of DNDC for simulating the regional carbon budget, including Gross Primary Productivity(GPP), Net Primary Productivity(NPP), Net Ecosystem Productivity(NEP), autotrophic respiration(Ra), soil microbial heterotrophic respiration(Rh) and ecosystem respiration(Re). The result showed that the combination of OAT and EFAST could test the contribution of the input parameters with discrete values to the output parameters. In DNDC model, land use type and soil type had a significant impact on the regional carbon budget of the Zoige Plateau, and daily temperature was also confirmed to be one of the most important parameters for carbon budget. For the other input parameters, with the change of land use type or soil type at regional scale, the sensitive parameters of carbon budget would vary accordingly. The SA results would provide scientific evidence to optimize DNDC model and they suggested that we should pay attention to the spatial/temporal effect of SA and try to use the appropriate data in simulation of the regional carbon budget.展开更多
The wetlands on the Zoige Plateau have experienced serious degradation,with most of the original marsh being converted to marsh meadow or meadow.Based on the 3 wetland degradation stages,we determined the effects of w...The wetlands on the Zoige Plateau have experienced serious degradation,with most of the original marsh being converted to marsh meadow or meadow.Based on the 3 wetland degradation stages,we determined the effects of wetland degradation on the structure and relative abundance of nitrogencycling(nitrogen-fixing,ammonia-oxidizing,and denitrifying) microbial communities in 3 soil types(intact wetland:marsh soil;early degrading wetland:marsh meadow soil;and degraded wetland:meadow soil) using 454-pyrosequencing.The structure and relative abundance of nitrogen-cycling microbial communities differed in the 3 soil types.Proteobacteria was the predominant phylum in most soil samples but the most abundant soil nitrogenfixing and denitrifying microbial bacteria differed at the class,order,family,and genus levels among the 3soil types.At the genus level,the majority of nitrogenfixing bacterium sequences related to Bradyrhizobium were from marsh and marsh meadow soils;whereas those related to Geobacter originated from meadow soil.The majority of ammonia-oxidizing bacterium sequences related to Nitrosospira were from marsh(except for the 40-60 cm layer),marsh meadow and meadow soils;whereas those related to Candidatus Solibacter originated from 40-60 cm layer of marsh soil.The majority of denitrifying bacterium sequences related to Candidatus Solibacter and Anaeromyxobacter were from marsh and meadow soils;whereas those related to Herbaspirillum originated from meadow soil.The distribution of operational taxonomic units(OTUs)and species were correlated with soil type based upon Venn and Principal Coordinates Analysis(PCoA).Changes in soil type,caused by different water regimes were the most important factors influencing compositional changes in the nitrogen-fixing,ammonia-oxidizing,and denitrifying microbial communities.展开更多
High-temperature corrosion is a serious problem for the water-wall tubes of boilers used in thermal power plants. Oxidation, sulfidation and molten salt corrosion are main corrosion ways.Thereinto, the most severe cor...High-temperature corrosion is a serious problem for the water-wall tubes of boilers used in thermal power plants. Oxidation, sulfidation and molten salt corrosion are main corrosion ways.Thereinto, the most severe corrosion occurs in molten salt corrosion environment. Materials rich in oxides formers, such as chromium and aluminum, are needed to resist corrosion in high-temperature and corrosive environment, but processability of such bulk alloys is very limited. High velocity electric arc spraying (HVAS) technology is adopted to produce coatings with high corrosion resistance. By comparison, NiCr (Ni-45Cr-4Ti) is recommended as a promising alloy coating for the water-wall tubes, which can even resist molten salt corrosion attack. In the study of corrosion mechanism, the modern material analysis methods, such as scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectrometry (EDS), are used. It is found that the corrosion resistances of NiCr and FeCrAI coatings are much better than that of 20g steel, that the NiCr coatings have the best anti-corrosion properties, and that the NiCr coatings have slightly lower pores than FeCrAI coatings.It is testified that corrosion resistance of coatings is mainly determined by chromium content, and the microstructure of a coating is as important as the chemical composition of the material. In addition, the fracture mechanisms of coatings in the cycle of heating and cooling are put forward. The difference of the thermal physical properties between coatings and base metals results in the thermal stress inside the coatings. Consequently, the coatings spall from the base metal.展开更多
Nowadays, remote sensing imagery, especially with its high spatialresolution, has become an indispensable tool to provide timely up-gradation of urban land use andland cover information, which is a prerequisite for pr...Nowadays, remote sensing imagery, especially with its high spatialresolution, has become an indispensable tool to provide timely up-gradation of urban land use andland cover information, which is a prerequisite for proper urban planning and management. Thepossible method described in the present paper to obtain urban land use types is based on theprinciple that land use can be derived from the land cover existing in a neighborhood. Here, movingwindow is used to represent the spatial pattern of land cover within a neighborhood and seven windowsizes (61mx61m, 68mx68m, 75mx75m, 87mx87m, 99mx99m, 110mx110m and 121mxl21m) are applied todetermining the most proper window size. Then, the unsupervised method of ISODATA is employed toclassify the layered land cover density maps obtained by the moving window. The results of accuracyevaluation show that the window size of 99mx99m is proper to infer urban land use categories and theproposed method has produced a land use map with a total accuracy of 85%.展开更多
Considerable efforts have been dedicated to desertification research in the arid and semi-arid drylands of central Asia. However,there are few quantitative studies in conjunction with proper qualitative evaluation con...Considerable efforts have been dedicated to desertification research in the arid and semi-arid drylands of central Asia. However,there are few quantitative studies in conjunction with proper qualitative evaluation concerning land degradation and aeolian activity in the alpine realm. In this study,spectral information from two Landsat-5 TM scenes(04.08.1994 and 28.07.2009,respectively) was combined with reference information obtained in the field to run supervised classifications of eight landscape types for both time steps. Subsequently,the temporal and spatial patterns of the alpine wetlands/grasslands evolutions in the Zoige Basin were quantified and assessed based on these two classification maps. The most conspicuous change is the sharp increase of ~627 km^2 degraded meadow. Concerning other land-covers,shallow wetland increases ~107 km^2 and aeolian sediments(mobile dunes and sand sheets) have an increase of ~30 km^2. Considering the deterioration,an obvious decrease of ~440 km^2 degraded wetland can be observed. Likewise,decrease of deep wetland(~78 km^2),humid meadow(~80 km^2) and undisturbed meadow(~88 km^2) were determined. These entire evolution matrixes undoubtedly hint a deteriorating tendency of the Zoige Basin ecosystem,which is characterized by significantly declined proportion of intact wetlands,meadow,rangeland and a considerable increase ofdegraded meadow and larger areas of mobile dunes. In particular,not only temporal alteration of the landcover categories,the spatial and topographical characteristics of the land degradation also deserves more attention. In the alpine rangelands,the higher terraces of the river channels along with their slopes are more liable to the degradation and desertification. This tendency has significantly impeded the nomadic and agriculture activities. The set of anthropozoogenic factors encompassing enclosures,overgrazing and trampling,rodent damaging and exceedingly ditching in the wetlands are assumed to be the main controlling mechanisms for the landscape degradation. A suite of strict protection policies is urgent and indispensable for self-regulation and restoration of the alpine meadow ecosystem. Controlling the size of livestock,less ditching in the rangeland,and the launching of a more strict nature reserve management by adjacent Ruoergai,Maqu and Hongyuan Counties would be practical and efficacious in achieving these objectives.展开更多
Wetland stores substantial amount of carbon and may contribute greatly to global climate change debate. However, few researches have focused on the effects of global climate change on carbon mineralization in Zoige al...Wetland stores substantial amount of carbon and may contribute greatly to global climate change debate. However, few researches have focused on the effects of global climate change on carbon mineralization in Zoige alpine wetland, Qinghai-Tibet Plateau, which is one of the most important peatlands in China. Through incubation experiment, this paper studied the effects of temperature, soil moisture, soil type (marsh soil and peat soil) and their interactions on CO2 and CH4 emission rates in Zoige alpine wetland. Results show that when the temperature rises from 5℃ to 35℃, CO2 emission rates increase by 3.3-3.7 times and 2.4-2.6 times under non-inundation treatment, and by 2.2-2.3 times and 4.1-4.3 times under inundation treatment in marsh soil and peat soil, respectively. Compared with non-inundation treatment, CO2 emission rates decrease by 6%-44%, 20%-60% in marsh soil and peat soil, respectively, under inundation treatment. CO2 emission rate is significantly affected by the combined effects of the temperature and soil type (p 〈 0.001), and soil moisture and soil type (p 〈 0.001), and CH4 emission rate was significantly affected by the interaction of the temperature and soil moisture (p 〈 0.001). Q10 values for CO2 emission rate are higher at the range of 5 ℃-25℃ than 25 ℃-35℃, indicating that carbon mineralization is more sensitive at low temperature in Zoige alpine wetland.展开更多
基金supported by the National Basic Research Program of China (No. 2006CB400505) and the National NaturalSciences Foundation of China (Nos. 49971056 and 40171007)
文摘The principles of remotely estimating grassland cover density in an alpine meadow soil from space lie in the synchronous collection of in situ samples with the satellite pass and statistically linking these cover densities to their image properties according to their geographic coordinates. The principles and procedures for quantifying grassland cover density from satellite image data were presented with an example from Qinghai Lake, China demonstrating how quantification could be made more accurate through the integrated use of remote sensing and global positioning systems (GPS). An empirical model was applied to an entire satellite image to convert pixel values into ground cover density. Satellite data based on 68 field samples was used to produce a map of ten cover densities. After calibration a strong linear regression relationship (r2 = 0.745) between pixel values on the satellite image and in situ measured grassland cover density was established with an 89% accuracy level. However, to minimize positional uncertainty of field samples, integrated use of hyperspatial satellite data and GPS could be utilized. This integration could reduce disparity in ground and space sampling intervals, and improve future quantification accuracy even more.
基金supported by the sub topics of National Key Technology R&D Program (Grant No. 2015BAC05B05-01)
文摘The ecological concept of Plant Functional Types(PFTs), which refers to the assemblage of plants with certain functional traits, has been introduced for the study of plant responses to the environment change and human disturbance. Taking the alpine meadow community in the Zoigê Plateau as a study case, this paper classified PFTs in terms of plant nutrition traits. The sequential results are as follows.(1) The main herbages in the Zoigê Plateau included 16 species in 5 families. Among the five families, Cyperaceae vegetation accounted for 81.37%of herbage area in total, while the remaining 4families occupied less than 20%. As for the species,Kobresia setchwanensis Hand.-Maizz. was dominant,accounting for 48.74% of the total area; while the remaining 51.26% was comprised of Polygonum viviparum L., Anaphalis fiavescens Hand.-Mazz.,Stipa aliena Keng and other species.(2) By using the Principal Component Analysis(PCA), the assessment of herbages nutrition was carried out based on the comprehensive multi-index evaluation model.Polygonum viviparum L. had the highest nutritional value score(1.43), and Stipa aliena Keng had the lowest(-1.40). Nutritional value of herbage species had a significantly positive correlation with altitude(P<0.01) in the Zoigê Plateau.(3) Based on the nutritional values, herbages in the Zoigê Plateau could be grouped into 3 nutrition PFTs(high, medium and low) by using the Natural Breaks(Jenks) method.
基金financially supported by the National Key Technology R&D Program (Grant No. 2007BAC18B03)the Sichuan Provincial Key Technology R&D Program (Grant No. 2012SZ0045)
文摘Four soil types(peat, marsh, meadow, and sandy) in the Zoige Plateau of China are associated with the severity of wetland degradation. The effects of wetland degradation on the structure and abundance of fungal communities and cellulase activity were assessed in these 4 soil types at 3 depths using DGGE(Denatured Gradient Gel Electrophoresis), q PCR(Quantitative Real-time PCR),and 3,5-dinitrosalicylic acid assays. Cellulase activity and abundance of the fungal community declined in parallel to the level of wetland degradation(from least to most disturbed). DGGE analysis indicated a major shift in composition of fungal communities among the4 soil types consistent with the level of degradation.Water content(WC), organic carbon(OC), total nitrogen(TN), total phosphorus(TP), available nitrogen(AN), and available phosphorus(AP) were strongly correlated with cellulase activity and the structure and abundance of the fungal community.The results indicate that soil physicochemical properties(WC, OC, TN, TP, AN, and AP), cellulase activity, and diversity and abundance of fungal communities are sensitive indicators of the relative level of wetland degradation. WC was the major factorinvolved in Zoige wetland degradation and lower WC levels contributed to declines in the abundance and diversity of the fungal community and reduction in cellulase activity.
基金support of the National Science Foundation of China (Grant Nos. 41271434 and 41375090)the Hong Kong Research Grants Council (Grant No. CUHK403612)the Basic Research Fund of Chinese Academy of Meteorological Sciences (Grant No. 2013Z002)
文摘The present reported study investigated the persistence of snow anomalies over the Tibetan Plateau(TP) from the preceding seasons to summer and the relationship between the previous snow cover anomaly and summer precipitation over East Asia. The results showed that, relative to other snow indices, such as the station observational snow depth(SOSD) index and the snow water equivalent(SWE) index, the snow cover area proportion(SCAP) index calculated from the SWE and the percentage of visible snow of the Equal-Area Scalable Earth Grids(EASE-grids) dataset has a higher persistence in interannual anomalies, particularly from May to summer. As such, the May SCAP index is significantly related to summer precipitation over the Meiyu-Baiu region. The persistence of the SCAP index can partly explain the season-delayed effect of snow cover over the TP on summer rainfall over the Meiyu-Baiu region besides the contribution of the soil moisture bridge. The preceding SST anomaly in the tropical Indian Ocean and ENSO can persist through the summer and affect the summer precipitation over the Meiyu-Baiu region. However, the May SCAP index is mostly independent of the simultaneous SSTs in the tropical Indian Ocean and the preceding ENSO and may affect the summer precipitation over the Meiyu-Baiu region independent of the effects of the SST anomalies. Therefore, the May SCAP over the TP could be regarded as an important supplementary factor in the forecasting of summer precipitation over the Meiyu-Baiu region.
基金Under the auspices of National Natural Science Foundation of China(No.41201445,41103041)National Science and Technology Support Program(No.2012BAJ24B01)National High Technology Research and Development Program of China(No.2009AA12200307)
文摘Accurate wetland delineation is the basis of wetland definition and mapping, and is of great importance for wetland management and research. The Zoige Plateau on the Qinghai-Tibet Plateau was used as a research site for research on alpine wetland delineation. Several studies have analyzed the spatiotemporal pattern and dynamics of these alpine wetlands, but none have addressed the issues of wetland boundaries. The objective of this work was to discriminate the upper boundaries of alpine wetlands by coupling ecological methods and satellite observations. The combination of Landsat 8 images and supervised classification was an effective method for rapid identification of alpine wetlands in the Zoig6 Plateau. Wet meadow was relatively stable compared with hydric soils and wetland hydrology and could be used as a primary indicator for discriminating the upper boundaries of alpine wetlands. A slope of less than 4.5° could be used as the threshold value for wetland delineation. The normalized difference vegetation index (NDVI) in 434 field sites showed that a threshold value of 0.3 could distinguish grasslands from emergent marsh and wet meadow in September. The median normalized difference water index (NDWI) of emergent marsh remained more stable than that of wet meadow and grasslands during the period from September until July of the following year. The index of mean density in wet meadow zones was higher than the emergent and upland zones. Over twice the number of species occurred in the wet meadow zone compared with the emergent zone, and close to the value of upland zone. Alpine wetlands in the three reserves in 2014 covered 1175.19 kin2 with a classification accuracy of 75.6%. The combination of ecological methods and remote sensing technology will play an important role in wetland delineation at medium and small scales. The correct differentiation between wet meadow and grasslands is the key to improving the accuracy of future wetland delineation.
基金financially supported by National Natural Science Foundation of China(Grant No. 51179006)China National Funds for Distinguished Young Scientists (Grant No.51125035)+2 种基金National Science Foundation for Innovative Research Group (Grant No. 51121003)the Program for New Century Excellent Talents in University (NECT-10-0235)the Fok Ying Tung Foundation (Grant No. 132009)
文摘Zoige Plateau wetlands are located in the northeastern corner of the Qinghai-Tibet Plateau.The landscape pattern evolution processes in the Zoige Plateau and their driving factors were identified by analyzing the dynamic changes in landscape modification and conversion and their dynamic rates of alpine wetlands over the past four decades.The results showed that the landscape conversion between wetlands and non-wetlands mainly occurred during the period from 1966 to 1986.The marsh wetland area converted from lake and river wetlands was larger because of swamping compared to other wetland landscapes.Meanwhile,the larger area of marsh wetlands was also converted to lake wetlands more than other types of wetlands.The modification processes mainly occurred among natural wetland landscapes in the first three periods.Obvious conversions were observed between wetland and nonwetland landscapes(i.e.,forestland,grassland,and other landscapes) in the Zoige Plateau.These natural wetland landscapes such as river,lake and marsh wetlands showed a net loss over the past four decades,whereas artificial wetland landscapes(i.e.,paddy field and reservoir and pond wetlands) showed a net decrease.The annual dynamic rate of the whole wetland landscape was 0.72%,in which the annual dynamic rate of river wetlands was the highest,followed by lake wetlands,while marsh wetlands had the lowest dynamic rate.The integrated landscape dynamic rate showed a decreasing trend in the first three periods.The changes in wetland landscape patterns were comprehensively controlled by natural factors and human activities,especially human activities play an important role in changing wetland landscape patterns.
基金financial support from National Natural Science Foundation of China(Grants No.41271433,41571373,41301385)the International Cooperation Key Project of CAS(Grant No.GJHZ201320)+3 种基金the International Cooperation Partner Program of Innovative Team,CAS(Grant No.KZZD-EW-TZ-06)STS-Network Plan,CAS(KFJ-EW-STS-020-02)the Strategic Leader Science and Technology project(XDA05050105)“Hundred Talents”Project of Chinese Academy of Sciences
文摘Although mathematical models(e.g., De Nitrification and De Composition(DNDC) provide a powerful tool to study regional carbon budget, it is still difficult to obtain accurate simulation results because there exists large uncertainties in modeling regional carbon budget. Through the investigation on the sensitivity of model output parameters to the input parameters, sensitivity analysis(SA) has been proved to be able to identify the key sources of uncertainties and be helpful to reduce the model uncertainties. However, some input parameters with discrete values(e.g., land use type and soil type) and the regional effect of the sensitive parameters were rarely examined in SA. In this paper, taking the Zoige Plateau as a case area, we combined the one-factor-ata-time(OAT) with Extended Fourier Amplitude Sensitivity Test(EFAST) to conduct a SA of DNDC for simulating the regional carbon budget, including Gross Primary Productivity(GPP), Net Primary Productivity(NPP), Net Ecosystem Productivity(NEP), autotrophic respiration(Ra), soil microbial heterotrophic respiration(Rh) and ecosystem respiration(Re). The result showed that the combination of OAT and EFAST could test the contribution of the input parameters with discrete values to the output parameters. In DNDC model, land use type and soil type had a significant impact on the regional carbon budget of the Zoige Plateau, and daily temperature was also confirmed to be one of the most important parameters for carbon budget. For the other input parameters, with the change of land use type or soil type at regional scale, the sensitive parameters of carbon budget would vary accordingly. The SA results would provide scientific evidence to optimize DNDC model and they suggested that we should pay attention to the spatial/temporal effect of SA and try to use the appropriate data in simulation of the regional carbon budget.
基金financially supported by the 11th Five Years Key Programs for Science and Technology Development of China (Grant No.2007BAC18B03)
文摘The wetlands on the Zoige Plateau have experienced serious degradation,with most of the original marsh being converted to marsh meadow or meadow.Based on the 3 wetland degradation stages,we determined the effects of wetland degradation on the structure and relative abundance of nitrogencycling(nitrogen-fixing,ammonia-oxidizing,and denitrifying) microbial communities in 3 soil types(intact wetland:marsh soil;early degrading wetland:marsh meadow soil;and degraded wetland:meadow soil) using 454-pyrosequencing.The structure and relative abundance of nitrogen-cycling microbial communities differed in the 3 soil types.Proteobacteria was the predominant phylum in most soil samples but the most abundant soil nitrogenfixing and denitrifying microbial bacteria differed at the class,order,family,and genus levels among the 3soil types.At the genus level,the majority of nitrogenfixing bacterium sequences related to Bradyrhizobium were from marsh and marsh meadow soils;whereas those related to Geobacter originated from meadow soil.The majority of ammonia-oxidizing bacterium sequences related to Nitrosospira were from marsh(except for the 40-60 cm layer),marsh meadow and meadow soils;whereas those related to Candidatus Solibacter originated from 40-60 cm layer of marsh soil.The majority of denitrifying bacterium sequences related to Candidatus Solibacter and Anaeromyxobacter were from marsh and meadow soils;whereas those related to Herbaspirillum originated from meadow soil.The distribution of operational taxonomic units(OTUs)and species were correlated with soil type based upon Venn and Principal Coordinates Analysis(PCoA).Changes in soil type,caused by different water regimes were the most important factors influencing compositional changes in the nitrogen-fixing,ammonia-oxidizing,and denitrifying microbial communities.
文摘High-temperature corrosion is a serious problem for the water-wall tubes of boilers used in thermal power plants. Oxidation, sulfidation and molten salt corrosion are main corrosion ways.Thereinto, the most severe corrosion occurs in molten salt corrosion environment. Materials rich in oxides formers, such as chromium and aluminum, are needed to resist corrosion in high-temperature and corrosive environment, but processability of such bulk alloys is very limited. High velocity electric arc spraying (HVAS) technology is adopted to produce coatings with high corrosion resistance. By comparison, NiCr (Ni-45Cr-4Ti) is recommended as a promising alloy coating for the water-wall tubes, which can even resist molten salt corrosion attack. In the study of corrosion mechanism, the modern material analysis methods, such as scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectrometry (EDS), are used. It is found that the corrosion resistances of NiCr and FeCrAI coatings are much better than that of 20g steel, that the NiCr coatings have the best anti-corrosion properties, and that the NiCr coatings have slightly lower pores than FeCrAI coatings.It is testified that corrosion resistance of coatings is mainly determined by chromium content, and the microstructure of a coating is as important as the chemical composition of the material. In addition, the fracture mechanisms of coatings in the cycle of heating and cooling are put forward. The difference of the thermal physical properties between coatings and base metals results in the thermal stress inside the coatings. Consequently, the coatings spall from the base metal.
基金Under the auspices of Jiangsu Provincial Natural ScienceFoundation(No .BK2002420 )
文摘Nowadays, remote sensing imagery, especially with its high spatialresolution, has become an indispensable tool to provide timely up-gradation of urban land use andland cover information, which is a prerequisite for proper urban planning and management. Thepossible method described in the present paper to obtain urban land use types is based on theprinciple that land use can be derived from the land cover existing in a neighborhood. Here, movingwindow is used to represent the spatial pattern of land cover within a neighborhood and seven windowsizes (61mx61m, 68mx68m, 75mx75m, 87mx87m, 99mx99m, 110mx110m and 121mxl21m) are applied todetermining the most proper window size. Then, the unsupervised method of ISODATA is employed toclassify the layered land cover density maps obtained by the moving window. The results of accuracyevaluation show that the window size of 99mx99m is proper to infer urban land use categories and theproposed method has produced a land use map with a total accuracy of 85%.
基金funded by the German Research Foundation (DFG) for the fieldwork and China Scholarship Council (201306190112)
文摘Considerable efforts have been dedicated to desertification research in the arid and semi-arid drylands of central Asia. However,there are few quantitative studies in conjunction with proper qualitative evaluation concerning land degradation and aeolian activity in the alpine realm. In this study,spectral information from two Landsat-5 TM scenes(04.08.1994 and 28.07.2009,respectively) was combined with reference information obtained in the field to run supervised classifications of eight landscape types for both time steps. Subsequently,the temporal and spatial patterns of the alpine wetlands/grasslands evolutions in the Zoige Basin were quantified and assessed based on these two classification maps. The most conspicuous change is the sharp increase of ~627 km^2 degraded meadow. Concerning other land-covers,shallow wetland increases ~107 km^2 and aeolian sediments(mobile dunes and sand sheets) have an increase of ~30 km^2. Considering the deterioration,an obvious decrease of ~440 km^2 degraded wetland can be observed. Likewise,decrease of deep wetland(~78 km^2),humid meadow(~80 km^2) and undisturbed meadow(~88 km^2) were determined. These entire evolution matrixes undoubtedly hint a deteriorating tendency of the Zoige Basin ecosystem,which is characterized by significantly declined proportion of intact wetlands,meadow,rangeland and a considerable increase ofdegraded meadow and larger areas of mobile dunes. In particular,not only temporal alteration of the landcover categories,the spatial and topographical characteristics of the land degradation also deserves more attention. In the alpine rangelands,the higher terraces of the river channels along with their slopes are more liable to the degradation and desertification. This tendency has significantly impeded the nomadic and agriculture activities. The set of anthropozoogenic factors encompassing enclosures,overgrazing and trampling,rodent damaging and exceedingly ditching in the wetlands are assumed to be the main controlling mechanisms for the landscape degradation. A suite of strict protection policies is urgent and indispensable for self-regulation and restoration of the alpine meadow ecosystem. Controlling the size of livestock,less ditching in the rangeland,and the launching of a more strict nature reserve management by adjacent Ruoergai,Maqu and Hongyuan Counties would be practical and efficacious in achieving these objectives.
基金Under the auspices of Fundamental Research Funds for the Central Universities (No. BLYX200932)National Natural Science Foundation of China (No. 30700108, 41071329)Forestry Commonweal Program (No. 200804005)
文摘Wetland stores substantial amount of carbon and may contribute greatly to global climate change debate. However, few researches have focused on the effects of global climate change on carbon mineralization in Zoige alpine wetland, Qinghai-Tibet Plateau, which is one of the most important peatlands in China. Through incubation experiment, this paper studied the effects of temperature, soil moisture, soil type (marsh soil and peat soil) and their interactions on CO2 and CH4 emission rates in Zoige alpine wetland. Results show that when the temperature rises from 5℃ to 35℃, CO2 emission rates increase by 3.3-3.7 times and 2.4-2.6 times under non-inundation treatment, and by 2.2-2.3 times and 4.1-4.3 times under inundation treatment in marsh soil and peat soil, respectively. Compared with non-inundation treatment, CO2 emission rates decrease by 6%-44%, 20%-60% in marsh soil and peat soil, respectively, under inundation treatment. CO2 emission rate is significantly affected by the combined effects of the temperature and soil type (p 〈 0.001), and soil moisture and soil type (p 〈 0.001), and CH4 emission rate was significantly affected by the interaction of the temperature and soil moisture (p 〈 0.001). Q10 values for CO2 emission rate are higher at the range of 5 ℃-25℃ than 25 ℃-35℃, indicating that carbon mineralization is more sensitive at low temperature in Zoige alpine wetland.