Based on the data of meteorological elements and concentration of negative ions in the county town station,Luguhe station and Yunjishan station during 2020-2024,the temporal and spatial variations in the concentration...Based on the data of meteorological elements and concentration of negative ions in the county town station,Luguhe station and Yunjishan station during 2020-2024,the temporal and spatial variations in the concentration of negative ions and their influencing factors in Xinfeng County were analyzed.The results show that the concentration of negative ions was the highest in summer,followed by spring;it was lower in autumn and the lowest in winter.In terms of diurnal variations,it was higher in the early morning and night,and lower in the noon and afternoon,which was closely related to the diurnal variations of human activities and meteorological conditions.The factors that affect the concentration of negative ions in the air are more complex.Besides meteorological factors,vegetation,altitude,human activities and other factors should be considered.展开更多
The increasing concentration of atmospheric CO_(2) since the Industrial Revolution has affected surface air temperature.However,the impact of the spatial distribution of atmospheric CO_(2) concentration on surface air...The increasing concentration of atmospheric CO_(2) since the Industrial Revolution has affected surface air temperature.However,the impact of the spatial distribution of atmospheric CO_(2) concentration on surface air temperature biases remains highly unclear.By incorporating the spatial distribution of satellite-derived atmospheric CO_(2) concentration in the Beijing Normal University Earth System Model,this study investigated the increase in surface air temperature since the Industrial Revolution in the Northern Hemisphere(NH) under historical conditions from 1976-2005.In comparison with the increase in surface temperature simulated using a uniform distribution of CO_(2),simulation with a nonuniform distribution of CO_(2)produced better agreement with the Climatic Research Unit(CRU) data in the NH under the historical condition relative to the baseline over the period 1901-30.Hemispheric June-July-August(JJA) surface air temperature increased by 1.28℃ ±0.29℃ in simulations with a uniform distribution of CO_(2),by 1.00℃±0.24℃ in simulations with a non-uniform distribution of CO_(2),and by 0.24℃ in the CRU data.The decrease in downward shortwave radiation in the non-uniform CO_(2) simulation was primarily attributable to reduced warming in Eurasia,combined with feedbacks resulting from increased leaf area index(LAI) and latent heat fluxes.These effects were more pronounced in the non-uniform CO_(2)simulation compared to the uniform CO_(2) simulation.Results indicate that consideration of the spatial distribution of CO_(2)concentration can reduce the overestimated increase in surface air temperature simulated by Earth system models.展开更多
[Objective] The aims were to understand variation characteristics of water resources and provide theoretical guidance for the formulation of agricultural irrigation methods.[Method] Taking the precipitation records du...[Objective] The aims were to understand variation characteristics of water resources and provide theoretical guidance for the formulation of agricultural irrigation methods.[Method] Taking the precipitation records during crop growing season（from April to September）observed by 177 weather stations from 1971 to 2008 in the three provinces of Northeast China（Heilongjiang,Jilin and Liaoning）as research data,annual change and spatial distribution characteristics of precipitation during crop growing season were analyzed by means of small grid interpolation and climatic trend rate.[Result] The precipitation during crop growing season general exhibited the decreasing trend and the precipitation trend rate was-8.6 mm/10a in Northeast China.In addition,there was lack of rain from 1971 to 1980 and relatively abundant of rain during 1981 and 1990 respectively.Moreover,the precipitation obviously exhibited decreasing trend from 1991 to 2008.But the decreasing trend was inconsistent in spatial distributions,that was,the precipitation slightly increased in relatively rainless areas and obviously decreased in relatively rainy areas.[Conclusion] The areas with obvious decreasing trend of precipitation during crop growing season are the main grain producing zones in Northeast China,so the problem of food production security caused by the precipitation changes should be paid enough attention.展开更多
In this paper we deduce the analytic solutions of the first- and second-order vertical derivative zero points for gravity anomalies in simple regular models with single, double, and multiple edges and analyze their sp...In this paper we deduce the analytic solutions of the first- and second-order vertical derivative zero points for gravity anomalies in simple regular models with single, double, and multiple edges and analyze their spatial variation. For another simple regular models where it is difficult to obtain the analytic expression of the zero point, we try to use the profile zero points to analyze the spatial variation. The test results show that the spatial variation laws of both first- and second-order vertical derivative zero points are almost the same but the second-order derivative zero point position is closer to the top surface edge of the geological bodies than the first-order vertical derivative and has a relatively high resolution. Moreover, with an increase in buried depth, for a single boundary model, the vertical derivative zero point location tends to move from the top surface edge to the outside of the buried body but finally converges to a fixed value. For a double boundary model, the vertical derivative zero point location tends to migrate from the top surface edge to the outside of the buried body. For multiple boundary models, the vertical derivative zero point location converges from the top surface edge to the outside of the buried body where some zero points coincide and finally vanish. Finally, the effectiveness and reliability of the proposed method is verified using real field data.展开更多
[Objective] The paper was to study the spatial variation characteristics of soil available plumbum （Pb） in vegetable bases of Urumqi City. [Method] With the vegetable base in northern suburb of Urumqi city as a typi...[Objective] The paper was to study the spatial variation characteristics of soil available plumbum （Pb） in vegetable bases of Urumqi City. [Method] With the vegetable base in northern suburb of Urumqi city as a typical area, the structure feature of soil available Pb content in suburb of oasis city in the arid area was ana- lyzed to get the spatial distribution pattern of available Pb, the origin and pollution source of this distribution pattern were also revealed. [Result] The available Pb in vegetable base of northern suburb in Urumqi City belonged to moderate variation. Semivariance model fitting showed that available Pb content could be fit with expo- nential function, which had spatial correlation within a certain range. The spatial dis- tribution pattern of available Pb content was obtained by using optimal Kriging inter- polation, and indicated that soil available Pb content was closely related to industrial activities, sewage irrigation and atmospheric dust. [Conclusion] The study provided the scientific basis for recognition, pollution risk assessment and pollution control of Pb pollution sources in the region, which have great significance on creating safe and clean production environment and selecting reasonable vegetable planting districts.展开更多
Slope spectrum has been proved to be a significant methodology in revealing geomorphological features in the study of Chinese loess terrain. The determination of critical areas in deriving slope spectra is an indispen...Slope spectrum has been proved to be a significant methodology in revealing geomorphological features in the study of Chinese loess terrain. The determination of critical areas in deriving slope spectra is an indispensable task. Along with the increase in the size of the study area, the derived spectra are becoming more and more alike, such that their dif- ferences can be ignored in favor of a standard. Subsequently, the test size is defined as the Slope Spectrum Critical Area （SSCA）. SSCA is not only the foundation of the slope spectrum calculation but also, to some extent, a reflection of geomorphological development of loess relief. High resolution DEMs are important in extracting the slope spectrum. A set of 48 DEMs with different landform areas of the Loess Plateau in northern Shaanxi province was selected for the experiment. The spatial distribution of SSCA is investigated with a geo-statistical analysis method, resulting in values ranging from 6.18 km^2 to 35.1 km^2. Primary experimental results show that the spatial distribution of SSCA is correlated with the spatial distribution of the soil erosion intensity, to a certain extent reflecting the terrain complexity. The critical area of the slope spectrum presents a spatial variation trend of weak-strong-weak from north to south. Four terrain parameters, gully density, slope skewness, terrain driving force （Td） and slope of slope （SOS）, were chosen as indicators. There exists a good exponential function relationship between SSCA and gully density, terrain driving force （Td） and SOS and a loga- rithmic function relationship between SSCA and slope skewness. Slope skewness increases, and gully density, terrain driving force and SOS decrease with increasing SSCA. SSCA can be utilized as a discriminating factor to identify loess landforms, in that spatial distributions of SSCA and the evolution of loess landforms are correlative. Following the evolution of a loess landform from tableland to gully-hilly region, this also proves that SSCA can represent the development degree of local landforms. The critical stable regions of the Loess Plateau represent the degree of development of loess landforms. Its chief significance is that the per- ception of stable areas can be used to determine the minimal geographical unit.展开更多
Despite the improvement in cultivar characters and management practices, large gaps between the attainable and potential yields still exist in winter wheat of China. Quantifying the crop potential yield is essential f...Despite the improvement in cultivar characters and management practices, large gaps between the attainable and potential yields still exist in winter wheat of China. Quantifying the crop potential yield is essential for estimating the food production capacity and improving agricultural policies to ensure food security. Gradually descending models and geographic infor- mation system （GIS） technology were employed to characterize the spatial variability of potential yields and yield gaps in winter wheat across the main production region of China. The results showed that during 2000-2010, the average potential yield limited by thermal resource （YGT） was 23.2 Mg ha-1, with larger value in the northern area relative to the southern area. The potential yield limited by the water supply （YGw） generally decreased from north to south, with an average value of 1.9 Mg ha-1 across the entire study region. The highest YGw in the north sub-region （NS） implied that the irrigation and drainage conditions in this sub-region must be improved. The averaged yield loss of winter wheat from nutrient deficiency （YGH） varied between 2.1 and 3.1 Mg ha-1 in the study area, which was greater than the yield loss caused by water limitation. The potential decrease in yield from photo-thermal-water-nutrient-limited production to actual yield （YGo） was over 6.0 Mg ha-1, ranging from 4.9 to 8.3 Mg ha^-1 across the entire study region, and it was more obvious in the southern area than in the northern area. These findings suggest that across the main winter wheat production region, the highest yield gap was induced by thermal resources, followed by other factors, such as the level of farming technology, social policy and economic feasibility. Furthermore, there are opportunities to narrow the yield gaps by making full use of climatic resources and developing a reasonable production plan for winter wheat crops. Thus, meeting the challenges of food security and sustainability in the coming decades is possible but will require considerable changes in water and nutrient management and socio-economic policies.展开更多
Understanding the spatial variation in annual actual evapotranspiration （AET） and its influencing factors is crucial for a better understanding of hydrological processes and water resources management. By synthesizi...Understanding the spatial variation in annual actual evapotranspiration （AET） and its influencing factors is crucial for a better understanding of hydrological processes and water resources management. By synthesizing ecosystem-level observations of eddy-covariance flux sites in China （a total of 61 sites）, we constructed the most complete AET dataset in China up to now. Based on this dataset, we quantified the statistic characteristics of AET and water budgets （defined as the ratio of AET to annual mean precipitation （MAP）, AET/MAP） of terrestrial ecosystems in China. Results showed that AET differed significantly among both different vegetation types and climate types in China, with overall mean AET of 534.7＋232.8 mm yr1. AET/MAP also differed significantly among different climate types, but there were no distinct differences in AET/MAP values across vegetation types, with mean AET/MAP of 0.82＋0.28 for non-irrigated ecosystems. We further investigated how the main climatic factors and vegetation attributes control the spatial variation in AET. Our findings revealed that the spatial variation of AET in China was closely correlated with the geographical patterns of climate and vegetation, in which the effects of total annual net radiation （Ro）, MAP and mean annual air temperature （MAT） were dominant. Thus, we proposed an empirical equation to describe the spatial patterns of AET in China, which could explain about 84% of the spatial variation in AET of terrestrial ecosystems in China. Based on the constructed dataset, we also evaluated the uncertainties of five published global evapotranspiration products in simulating site-specific AET in China. Results showed that large biases in site-specific AET values existed for all five global evapotranspiration products, which indicated that it is necessary to involve more observation data of China in their parameterization or validation, while our AET dataset would provide a data source for it.展开更多
Sampling and testing are conducted on groundwater depth and vegetation coverage in the 670 km2 of the Sangong River Basin and semi-variance function analysis is made afterwards on the data obtained by the application ...Sampling and testing are conducted on groundwater depth and vegetation coverage in the 670 km2 of the Sangong River Basin and semi-variance function analysis is made afterwards on the data obtained by the application of geo-statistics. Results showed that the variance curve of the groundwater depth and vegetation coverage displays an exponential model. Analysis of sampling data in 2003 indicates that the groundwater depth and vegetation coverage change similarly in space in this area. The Sangong River Basin is composed of upper oasis, middle ecotone and lower sand dune. In oasis and ecotone, influenced by irrigation of the adjoining oasis, groundwater level has been raised and soil water content also increased compared with sand dune nearby, vegetation developed well. But in the lower reaches of the Sangong River Basin, because of descending of groundwater level, soil water content decreased and vegetation degenerated. From oasis to abandoned land and desert grassland, vegetation coverage and groundwater level changed greatly with significant difference respectively in spatial variation. Distinct but similar spatial variability exists among the groundwater depth and vegetation coverage in the study area, namely, the vegetation coverage decreasing (increasing) as the groundwater depth increases (decreases). This illustrates the great dependence of vegetation coverage on groundwater depth in arid regions and further implies that among the great number of factors affecting vegetation coverage in arid regions, groundwater depth turns out to be the most determinant one.展开更多
Chemometric approach based on principal component analysis（PCA） was utilized to examine the spatial variances of environmental and ecological characteristics in the Zhujiang River（Pearl River） Estuary and adjacent...Chemometric approach based on principal component analysis（PCA） was utilized to examine the spatial variances of environmental and ecological characteristics in the Zhujiang River（Pearl River） Estuary and adjacent waters（ZREAW） in the South China Sea. The PCA result shows that the ZREAW can be divided into different zones according to the principal components and geographical locations of the study stations,and indicates that there are distinct regional variances on environmental features and the corresponding phytoplankton biomass and community structures among different areas. The spatial distribution of ecological features was implied to be influenced by various degrees of the different water resources,such as the Pearl River discharges,the coastal current and the oceanic water from the South China Sea. The variation of the biomass maximum zone and the complex impacts on the spatial distributions of phytoplankton biomass and production were also evaluated.展开更多
Large areas assessments of forest bioinass distribution are a challenge in heterogeneous landscapes, where variations in tree growth and species composition occur over short distances. In this study, we use statistica...Large areas assessments of forest bioinass distribution are a challenge in heterogeneous landscapes, where variations in tree growth and species composition occur over short distances. In this study, we use statistical and geospatial modeling on densely sample.d forest biomass data to analyze the relative importance of ecological and physiographic variables as determinants of spatial variation of forest biomass in the environmentally heterogeneous region of the Big Sur, California. We estimated biomass in 280 forest Plots （one plot per 2.85 km2） and meas- ured an array of ecological （vegetation community type, distance to edge, amount of surrounding non-forest vegetation, soil properties, fire history） and physiographic drivers （elevation, potential soil moisture and solar radiation, proximity to the coast） of tree growth at each plot location. Our geostatistical analyses revealed that biomass distribution is spatially structured and autocorrelated up to 3.1 kin. Regression tree （RT） models showed that both physiographic and ecological factors influenced bio- mass distribution. Across randomly selected sample densities （sample size 112 to 280）, ecological effects of vegetation community type and distance to forest edge, and physiographic effects of elevation, potential soil moisture and solar radiation were the most consistent predictors of biomass. Topographic moisture index and potential solar radiation had apositive effect on biomass, indicating the importance of topographically- mediated energy and moisture on plant growth and biomass accumula- tion. RT model explained 35% of the variation in biomass and spatially autocorrelated variation were retained in regession residuals. Regression kriging model, developed from RT combined with kriging of regression residuals, was used to map biomass across the Big Sur. This study dem- onstrates how statistical and geospatial modeling can be used to dis- criminate the relative importance of physiographic and ecologic effects on forest biomass and develop spatial models to predict and map biomass distribution across a heterogeneous landscape.展开更多
This paper reveals the temporal and spatial variations of stable isotope in precipitation of the Yarlung Zangbo River Basin based on the variations of δ^18O in precipitation at four stations （Lhaze, Nugesha, Yangcu...This paper reveals the temporal and spatial variations of stable isotope in precipitation of the Yarlung Zangbo River Basin based on the variations of δ^18O in precipitation at four stations （Lhaze, Nugesha, Yangcun and Nuxia） in 2005. The results show that δ^18O of precipitation has distinct seasonal changes in the Yarlung Zangbo River Basin. The higher value of δ^18O occurs in spring prior to monsoon precipitation, and the lower value occurs during monsoon precipitation. From the spatial variations, with the altitude-effect and rainout process during moisture transport along the Yarlung Zangbo River Valley, δ^18O of precipitation is gradually depleted. Thus, δ^18O of precipitation decreases gradually from the downstream to the upstream, and the lapse rate of δ^18O in precipitation is approximately 0.34‰/100m and 0.7%J‰/100km for the two reasons. During monsoon precipitation, spatial variation of δ^18O in precipitation is dominated by the amount effect in the large scale synoptic condition.展开更多
The limit equilibrium method （LEM） is widely used for sliding stability evaluation of concrete gravitydams. Failure is then commonly assumed to occur along the entire sliding surface simultaneously.However, the brit...The limit equilibrium method （LEM） is widely used for sliding stability evaluation of concrete gravitydams. Failure is then commonly assumed to occur along the entire sliding surface simultaneously.However, the brittle behaviour of bonded concrete-rock contacts, in combination with the varying stressover the interface, implies that the failure of bonded dam-foundation interfaces occurs progressively. Inaddition, the spatial variation in cohesion may introduce weak spots where failure can be initiated.Nonetheless, the combined effect of brittle failure and spatial variation in cohesion on the overall shearstrength of the interface has not been studied previously. In this paper, numerical analyses are used toinvestigate the effect of brittle failure in combination with spatial variation in cohesion that is taken intoaccount by random fields with different correlation lengths. The study concludes that a possible existenceof weak spots along the interface has to be considered since it significantly reduces the overallshear strength of the interface, and implications for doing so are discussed.展开更多
This study is based on meteorological observation data collected at 38 weather stations on the Tibetan Plateau over several decades. Daily reference crop evapotranspiration （ETo） was calculated with the FAO-56 stand...This study is based on meteorological observation data collected at 38 weather stations on the Tibetan Plateau over several decades. Daily reference crop evapotranspiration （ETo） was calculated with the FAO-56 standard Penman-Monteith formula. A test of normality was performed with Statistica 6.0 software, isotropic and anisotropic semi-variogram analysis was conducted with the GS＋ （geostatistics for the environmental sciences） system for Windows 7.0, and the characteristics of spatial variation of daily ETo were obtained. The following results can be obtained Daily ETo for different periods on the Tibetan Plateau are distributed normally; Except for daily ETo in the E-W （east-west） direction in the summer, which showed a slight negative correlation with distance change, the Moran＇s indexes of daily ETo for different periods in all directions on the Tibetan Plateau within a 100-km distance were positive, demonstrating a positive correlation with distance change; Variograms of daily ETo in June, the dry season, the wet season, as well as annual average daily ETo fit well with the Gaussian model; A variogram of daily ETo in December fit well with the exponential model; Variograms of daily ETo for the four seasons fit well with the linear With sill model.展开更多
The preceding and succeeding precipitation(PSP)often act together with extreme precipitation(EP),in turn,causing floods,which is an objective component that is often overlooked with regard to summer flood hazards in t...The preceding and succeeding precipitation(PSP)often act together with extreme precipitation(EP),in turn,causing floods,which is an objective component that is often overlooked with regard to summer flood hazards in the arid region of Northwest China.In this study,event-based extreme precipitation(EEP)was defined as continuous precipitation that includes at least one day of EP.We analyzed the spatiotemporal variation characteristics of four EEP types(front EEP,late EEP,balanced EEP,and single day EEP)across the Loess Plateau(LP)based on data acquired from 87 meteorological stations from 1960 to 2019.Precipitation on the LP basically maintained a spatial pattern of"low in the northwest region and high in the southeast region",and EP over the last 10 a increased significantly.The cumulative precipitation percentage of single day EEP was 34%and was dominant for 60 a,while the cumulative precipitation percentage of front,late,and balanced EEP types associated with PSP accounted for 66%,which confirms to the connotation of EEP.The cumulative frequencies of front and late EEP types were 23%and 21%,respectively,while the cumulative frequency of balanced EEP had the lowest value at only 13%.Moreover,global warming could lead to more single day EEP across the LP,and continuous EEP could increase in the northwestern region and decrease in the eastern region in the future.The concept of process-oriented EP could facilitate further exploration of disaster-causing processes associated with different types of EP,and provide a theoretical basis for deriving precipitation disaster chains and construction of disaster cluster characteristics.展开更多
Alluviation and sedimentation of the Yellow River are important factors influencing the surface soil structure and organic carbon content in its lower reaches.Selecting Kaifeng and Zhoukou as typical cases of the Yell...Alluviation and sedimentation of the Yellow River are important factors influencing the surface soil structure and organic carbon content in its lower reaches.Selecting Kaifeng and Zhoukou as typical cases of the Yellow River flooding area,the field survey,soil sample collection,laboratory experiment and Geographic Information System(GIS)spatial analysis methods were applied to study the spatial distribution characteristics and change mechanism of organic carbon components at different soil depths.The results revealed that the soil total organic carbon(TOC),active organic carbon(AOC)and nonactive organic carbon(NOC)contents ranged from 0.05–30.03 g/kg,0.01–8.86 g/kg and 0.02–23.36 g/kg,respectively.The TOC,AOC and NOC contents in the surface soil layer were obviously higher than those in the lower soil layer,and the sequence of the content and change range within a single layer was TOC>NOC>AOC.Geostatistical analysis indicated that the TOC,AOC and NOC contents were commonly influenced by structural and random factors,and the influence magnitudes of these two factors were similar.The overall spatial trends of TOC,AOC and NOC remained relatively consistent from the 0–20 cm layer to the 20–100 cm layer,and the transition between high-and low-value areas was obvious,while the spatial variance was high.The AOC and NOC contents and spatial distribution better reflected TOC spatial variation and carbon accumulation areas.The distribution and depth of the sediment,agricultural land-use type,cropping system,fertilization method,tillage process and cultivation history were the main factors impacting the spatial variation in the soil organic carbon(SOC)components.Therefore,increasing the organic matter content,straw return,applying organic manure,adding exogenous particulate matter and conservation tillage are effective measures to improve the soil quality and attain sustainable agricultural development in the alluvial/sedimentary zone of the Yellow River.展开更多
Spatial variation of dissolved organic carbon(DOC) in soils of riparian wetlands and responses to hydro-geomorphologic changes in the Sanjiang Plain were analyzed through in situ collecting soil samples in the Naoli R...Spatial variation of dissolved organic carbon(DOC) in soils of riparian wetlands and responses to hydro-geomorphologic changes in the Sanjiang Plain were analyzed through in situ collecting soil samples in the Naoli River and the Bielahong River. The results showed that the average contents of DOC for soil layer of 0–100 cm were 730.6 mg/kg, 250.9 mg/kg, 423.0 mg/kg and 333.1 mg/kg respectively from riverbed to river terrace along the transverse directions of the Naoli watershed. The content of the soil DOC was the highest in the riverbed, lower in the high floodplain and much lower in the river terrace, and it was the lowest in the low floodplain. The difference in the content and vertical distribution of DOC between the riverbed and the three riparian wetlands was significant, while it was not significant among the low floodplain, the high floodplain and the river terrace. The variability of soil DOC was related to the hydrological connectivity between different landscape position of the riparian wetlands and the adjacent stream. Extremely significant correlations were observed between DOC and total organic carbon(TOC), total iron(TFe), ferrous iron(Fe(II)) whose correlation coefficients were 0.819, –0.544 and –0.709 in riparian wetlands of the Naoli River. With the increase of wetland destruction, soil p H increased and soil DOC content changed. The correlation coefficients between soil DOC and TOC, TFe, Fe(II) also changed into 0.759, –0.686 and –0.575 respectively in the Bielahong River. Under the impact of drainage ditches, the correlations between soil DOC and TFe, Fe(II) were not obvious, while the soil p H was weakly alkaline and was negatively correlated with soil DOC in the previous high floodplain. It indicates that riparian hydro-geomorphology is the main factor that could well explain this spatial variability of soil DOC, and the agricultural environmental hydraulic works like ditching also must be considered.展开更多
[ Objective] The study aimed to discuss the temporal and spatial variation of phytoplankton community and main pollution indicators in cyanophyte enrichment area of northern Dianchi Lake. [ Method ] In the cyanophyte ...[ Objective] The study aimed to discuss the temporal and spatial variation of phytoplankton community and main pollution indicators in cyanophyte enrichment area of northern Dianchi Lake. [ Method ] In the cyanophyte enrichment area of northern Dianchi Lake, phytoplankton community, chlorophyll a, total nitrogen （TN） and total phosphorus （TP） concentration had been monitored monthly from January 2007 to December 2011, and the temporal and spatial variation of phytoplankton community and main pollution indicators were analyzed. [ Result] From January 2007 to December 2011, algal diversity in the area increased slightly, and algal diversity in the alongshore region was less than that in the offshore re- gion ; chlorophyll a, TN and TP concentration decreased in the alongshore region, but it was otherwise in the offshore region; chlorophyll a, TN and TP concentration in the alongshore region were higher than those in the offshore region. [ Conclusion] The research could provide theoretical references for the control of cyanophyte bloom and achievement evaluation of each control measure in Dianchi Lake.展开更多
Rice, wheat and maize are the main staple food crops to ensure the food security in China with diversified climate condition, cropping system and environmental and socio-economic factors across provinces. Spatial vari...Rice, wheat and maize are the main staple food crops to ensure the food security in China with diversified climate condition, cropping system and environmental and socio-economic factors across provinces. Spatial variation of technical efficiency in farmers' field is helpful to understand the potential to improve farmers' yield given the inputs level and reduce the yield gap. The study is based on a large-scale farm household survey which covered 1 218 rice farmers, 3 566 wheat farmers and 2 111 maize farmers in the main producing areas. The results indicate that rice farmers are with very high technical efficiency level, nearly 0.9 on average, with little room to improve the efficiency of agricultural inputs. Similar results have been found in wheat and maize farmers' fields, although the technical efficiency levels are lower than that of rice farmers while still at a high level with obvious variation across regions. Farmers with higher yield level also achieve better technical efficiency in most locations. Both local environmental and socio-economic factors significantly affect farmers' technical efficiency. In the context of urbanization and economic development, improved and new agricultural technologies need to be prioritized and facilitated to improve cereal yield at farm level.展开更多
In order to explore the spatial distribution and variation characteristics of soil moisture in coal mining subsidence area in Mu Us sandy Land,and provide theoretical basis for the restoration of the mining area,exper...In order to explore the spatial distribution and variation characteristics of soil moisture in coal mining subsidence area in Mu Us sandy Land,and provide theoretical basis for the restoration of the mining area,experiments based on a linear sampling and classic statistical and geostatistical methods were conducted. Spatial distribution characteristics and variation of soil moisture in the typical 0 to 100 cm dune area in the subsidence area and the non-subsidence area( control) were studied. The results showed that in the typical sand dune location of nonsubsidence area( control),the probability distribution curves of soil moisture changes in all layers along vertical and horizontal directions were all normal distribution,and it was consistent with the temporal and spatial variation characteristics of soil moisture in conventional dunes in Mu Us sandy land. By contrast,two years after the coal mine collapsed,the variations of soil moisture in different layers along vertical and horizontal directions were different,and soil moisture loss was more serious than that of control dune by nearly 10% to 30%,and the standard deviation varied from 0. 54 to 1. 05,increasing by 52. 08% compared with the non-subsidence area( control). The probability of positive and negative deviation greater than 1 was over 50%,and the coefficient of variation varied from 0. 14 to 0. 28,which was 80% higher than that of nonsubsidence area( control). After collapsing,the average level of soil moisture,standard deviation,variance and variation coefficient had greatly changed,and influence of coal mining subsidence on soil moisture was the most in the middle layer( 30-70 cm),and was not obvious in the surface( 0-20 cm) and lower layer( 80-100 cm). In coal mining subsidence area,the dispersion degree of soil moisture in different layers along the vertical and horizontal direction was greatly improved,which increased spatial variation of soil moisture.展开更多
文摘Based on the data of meteorological elements and concentration of negative ions in the county town station,Luguhe station and Yunjishan station during 2020-2024,the temporal and spatial variations in the concentration of negative ions and their influencing factors in Xinfeng County were analyzed.The results show that the concentration of negative ions was the highest in summer,followed by spring;it was lower in autumn and the lowest in winter.In terms of diurnal variations,it was higher in the early morning and night,and lower in the noon and afternoon,which was closely related to the diurnal variations of human activities and meteorological conditions.The factors that affect the concentration of negative ions in the air are more complex.Besides meteorological factors,vegetation,altitude,human activities and other factors should be considered.
基金the National Natural Science Foundation of China (Grant Nos.42175142,42141017 and 41975112) for supporting our study。
文摘The increasing concentration of atmospheric CO_(2) since the Industrial Revolution has affected surface air temperature.However,the impact of the spatial distribution of atmospheric CO_(2) concentration on surface air temperature biases remains highly unclear.By incorporating the spatial distribution of satellite-derived atmospheric CO_(2) concentration in the Beijing Normal University Earth System Model,this study investigated the increase in surface air temperature since the Industrial Revolution in the Northern Hemisphere(NH) under historical conditions from 1976-2005.In comparison with the increase in surface temperature simulated using a uniform distribution of CO_(2),simulation with a nonuniform distribution of CO_(2)produced better agreement with the Climatic Research Unit(CRU) data in the NH under the historical condition relative to the baseline over the period 1901-30.Hemispheric June-July-August(JJA) surface air temperature increased by 1.28℃ ±0.29℃ in simulations with a uniform distribution of CO_(2),by 1.00℃±0.24℃ in simulations with a non-uniform distribution of CO_(2),and by 0.24℃ in the CRU data.The decrease in downward shortwave radiation in the non-uniform CO_(2) simulation was primarily attributable to reduced warming in Eurasia,combined with feedbacks resulting from increased leaf area index(LAI) and latent heat fluxes.These effects were more pronounced in the non-uniform CO_(2)simulation compared to the uniform CO_(2) simulation.Results indicate that consideration of the spatial distribution of CO_(2)concentration can reduce the overestimated increase in surface air temperature simulated by Earth system models.
基金Supported by Special Fund for Climate Change of China Meteorological Administration(CCSF-09-13)Special Fund for Researchof Nonprofit Sector(meteorology)(GYHY200706030)~~
文摘[Objective] The aims were to understand variation characteristics of water resources and provide theoretical guidance for the formulation of agricultural irrigation methods.[Method] Taking the precipitation records during crop growing season（from April to September）observed by 177 weather stations from 1971 to 2008 in the three provinces of Northeast China（Heilongjiang,Jilin and Liaoning）as research data,annual change and spatial distribution characteristics of precipitation during crop growing season were analyzed by means of small grid interpolation and climatic trend rate.[Result] The precipitation during crop growing season general exhibited the decreasing trend and the precipitation trend rate was-8.6 mm/10a in Northeast China.In addition,there was lack of rain from 1971 to 1980 and relatively abundant of rain during 1981 and 1990 respectively.Moreover,the precipitation obviously exhibited decreasing trend from 1991 to 2008.But the decreasing trend was inconsistent in spatial distributions,that was,the precipitation slightly increased in relatively rainless areas and obviously decreased in relatively rainy areas.[Conclusion] The areas with obvious decreasing trend of precipitation during crop growing season are the main grain producing zones in Northeast China,so the problem of food production security caused by the precipitation changes should be paid enough attention.
基金jointly supported by the National Major Science and Technology Program (No. 2008ZX05025)the National 973 Program (Grant No. 2009CB219400)
文摘In this paper we deduce the analytic solutions of the first- and second-order vertical derivative zero points for gravity anomalies in simple regular models with single, double, and multiple edges and analyze their spatial variation. For another simple regular models where it is difficult to obtain the analytic expression of the zero point, we try to use the profile zero points to analyze the spatial variation. The test results show that the spatial variation laws of both first- and second-order vertical derivative zero points are almost the same but the second-order derivative zero point position is closer to the top surface edge of the geological bodies than the first-order vertical derivative and has a relatively high resolution. Moreover, with an increase in buried depth, for a single boundary model, the vertical derivative zero point location tends to move from the top surface edge to the outside of the buried body but finally converges to a fixed value. For a double boundary model, the vertical derivative zero point location tends to migrate from the top surface edge to the outside of the buried body. For multiple boundary models, the vertical derivative zero point location converges from the top surface edge to the outside of the buried body where some zero points coincide and finally vanish. Finally, the effectiveness and reliability of the proposed method is verified using real field data.
基金Supported by Scientific Research Project for Universitie in Xinjiang Uygur Autonomous Region(XJEDU2005I08)China-Italian Cooperation Projects for Environmental Protection~~
文摘[Objective] The paper was to study the spatial variation characteristics of soil available plumbum （Pb） in vegetable bases of Urumqi City. [Method] With the vegetable base in northern suburb of Urumqi city as a typical area, the structure feature of soil available Pb content in suburb of oasis city in the arid area was ana- lyzed to get the spatial distribution pattern of available Pb, the origin and pollution source of this distribution pattern were also revealed. [Result] The available Pb in vegetable base of northern suburb in Urumqi City belonged to moderate variation. Semivariance model fitting showed that available Pb content could be fit with expo- nential function, which had spatial correlation within a certain range. The spatial dis- tribution pattern of available Pb content was obtained by using optimal Kriging inter- polation, and indicated that soil available Pb content was closely related to industrial activities, sewage irrigation and atmospheric dust. [Conclusion] The study provided the scientific basis for recognition, pollution risk assessment and pollution control of Pb pollution sources in the region, which have great significance on creating safe and clean production environment and selecting reasonable vegetable planting districts.
基金Foundation： National Natural Science Foundation of China, No.41171299, No.41171320, No.41401237
文摘Slope spectrum has been proved to be a significant methodology in revealing geomorphological features in the study of Chinese loess terrain. The determination of critical areas in deriving slope spectra is an indispensable task. Along with the increase in the size of the study area, the derived spectra are becoming more and more alike, such that their dif- ferences can be ignored in favor of a standard. Subsequently, the test size is defined as the Slope Spectrum Critical Area （SSCA）. SSCA is not only the foundation of the slope spectrum calculation but also, to some extent, a reflection of geomorphological development of loess relief. High resolution DEMs are important in extracting the slope spectrum. A set of 48 DEMs with different landform areas of the Loess Plateau in northern Shaanxi province was selected for the experiment. The spatial distribution of SSCA is investigated with a geo-statistical analysis method, resulting in values ranging from 6.18 km^2 to 35.1 km^2. Primary experimental results show that the spatial distribution of SSCA is correlated with the spatial distribution of the soil erosion intensity, to a certain extent reflecting the terrain complexity. The critical area of the slope spectrum presents a spatial variation trend of weak-strong-weak from north to south. Four terrain parameters, gully density, slope skewness, terrain driving force （Td） and slope of slope （SOS）, were chosen as indicators. There exists a good exponential function relationship between SSCA and gully density, terrain driving force （Td） and SOS and a loga- rithmic function relationship between SSCA and slope skewness. Slope skewness increases, and gully density, terrain driving force and SOS decrease with increasing SSCA. SSCA can be utilized as a discriminating factor to identify loess landforms, in that spatial distributions of SSCA and the evolution of loess landforms are correlative. Following the evolution of a loess landform from tableland to gully-hilly region, this also proves that SSCA can represent the development degree of local landforms. The critical stable regions of the Loess Plateau represent the degree of development of loess landforms. Its chief significance is that the per- ception of stable areas can be used to determine the minimal geographical unit.
基金supported by the National High-Tech R&D Program of China(863 Program,2013AA100404)the National Natural Science Foundation of China(31301234 and 31271616)+1 种基金the National Research Foundation for the Doctoral Program of Higher Education of China(20120097110042)the Priority Academic Program Development of Jiangsu Higher Education Institutions,China(PAPD)
文摘Despite the improvement in cultivar characters and management practices, large gaps between the attainable and potential yields still exist in winter wheat of China. Quantifying the crop potential yield is essential for estimating the food production capacity and improving agricultural policies to ensure food security. Gradually descending models and geographic infor- mation system （GIS） technology were employed to characterize the spatial variability of potential yields and yield gaps in winter wheat across the main production region of China. The results showed that during 2000-2010, the average potential yield limited by thermal resource （YGT） was 23.2 Mg ha-1, with larger value in the northern area relative to the southern area. The potential yield limited by the water supply （YGw） generally decreased from north to south, with an average value of 1.9 Mg ha-1 across the entire study region. The highest YGw in the north sub-region （NS） implied that the irrigation and drainage conditions in this sub-region must be improved. The averaged yield loss of winter wheat from nutrient deficiency （YGH） varied between 2.1 and 3.1 Mg ha-1 in the study area, which was greater than the yield loss caused by water limitation. The potential decrease in yield from photo-thermal-water-nutrient-limited production to actual yield （YGo） was over 6.0 Mg ha-1, ranging from 4.9 to 8.3 Mg ha^-1 across the entire study region, and it was more obvious in the southern area than in the northern area. These findings suggest that across the main winter wheat production region, the highest yield gap was induced by thermal resources, followed by other factors, such as the level of farming technology, social policy and economic feasibility. Furthermore, there are opportunities to narrow the yield gaps by making full use of climatic resources and developing a reasonable production plan for winter wheat crops. Thus, meeting the challenges of food security and sustainability in the coming decades is possible but will require considerable changes in water and nutrient management and socio-economic policies.
基金National Natural Science Foundation of China,No.31290221,No.31420103917
文摘Understanding the spatial variation in annual actual evapotranspiration （AET） and its influencing factors is crucial for a better understanding of hydrological processes and water resources management. By synthesizing ecosystem-level observations of eddy-covariance flux sites in China （a total of 61 sites）, we constructed the most complete AET dataset in China up to now. Based on this dataset, we quantified the statistic characteristics of AET and water budgets （defined as the ratio of AET to annual mean precipitation （MAP）, AET/MAP） of terrestrial ecosystems in China. Results showed that AET differed significantly among both different vegetation types and climate types in China, with overall mean AET of 534.7＋232.8 mm yr1. AET/MAP also differed significantly among different climate types, but there were no distinct differences in AET/MAP values across vegetation types, with mean AET/MAP of 0.82＋0.28 for non-irrigated ecosystems. We further investigated how the main climatic factors and vegetation attributes control the spatial variation in AET. Our findings revealed that the spatial variation of AET in China was closely correlated with the geographical patterns of climate and vegetation, in which the effects of total annual net radiation （Ro）, MAP and mean annual air temperature （MAT） were dominant. Thus, we proposed an empirical equation to describe the spatial patterns of AET in China, which could explain about 84% of the spatial variation in AET of terrestrial ecosystems in China. Based on the constructed dataset, we also evaluated the uncertainties of five published global evapotranspiration products in simulating site-specific AET in China. Results showed that large biases in site-specific AET values existed for all five global evapotranspiration products, which indicated that it is necessary to involve more observation data of China in their parameterization or validation, while our AET dataset would provide a data source for it.
基金National 973 Program for Basic Research No.G1999043506
文摘Sampling and testing are conducted on groundwater depth and vegetation coverage in the 670 km2 of the Sangong River Basin and semi-variance function analysis is made afterwards on the data obtained by the application of geo-statistics. Results showed that the variance curve of the groundwater depth and vegetation coverage displays an exponential model. Analysis of sampling data in 2003 indicates that the groundwater depth and vegetation coverage change similarly in space in this area. The Sangong River Basin is composed of upper oasis, middle ecotone and lower sand dune. In oasis and ecotone, influenced by irrigation of the adjoining oasis, groundwater level has been raised and soil water content also increased compared with sand dune nearby, vegetation developed well. But in the lower reaches of the Sangong River Basin, because of descending of groundwater level, soil water content decreased and vegetation degenerated. From oasis to abandoned land and desert grassland, vegetation coverage and groundwater level changed greatly with significant difference respectively in spatial variation. Distinct but similar spatial variability exists among the groundwater depth and vegetation coverage in the study area, namely, the vegetation coverage decreasing (increasing) as the groundwater depth increases (decreases). This illustrates the great dependence of vegetation coverage on groundwater depth in arid regions and further implies that among the great number of factors affecting vegetation coverage in arid regions, groundwater depth turns out to be the most determinant one.
基金The Knowledge Innovation Project of Chinese Academy of Sciences under contract Nos KZCX2-YW-Q07, KZCX2-YW-T001, KZCX2-YW-213 and SQ200805the National Natural Science Foundation of China under contract Nos U0633007, 40906057 and 40531006
文摘Chemometric approach based on principal component analysis（PCA） was utilized to examine the spatial variances of environmental and ecological characteristics in the Zhujiang River（Pearl River） Estuary and adjacent waters（ZREAW） in the South China Sea. The PCA result shows that the ZREAW can be divided into different zones according to the principal components and geographical locations of the study stations,and indicates that there are distinct regional variances on environmental features and the corresponding phytoplankton biomass and community structures among different areas. The spatial distribution of ecological features was implied to be influenced by various degrees of the different water resources,such as the Pearl River discharges,the coastal current and the oceanic water from the South China Sea. The variation of the biomass maximum zone and the complex impacts on the spatial distributions of phytoplankton biomass and production were also evaluated.
基金financially supported by the National Science Foundation (EF-0622770 and EF-0622677)the USDA Forest Service–Pacific Southwest Research Stationthe Gordon & Betty Moore Foundation
文摘Large areas assessments of forest bioinass distribution are a challenge in heterogeneous landscapes, where variations in tree growth and species composition occur over short distances. In this study, we use statistical and geospatial modeling on densely sample.d forest biomass data to analyze the relative importance of ecological and physiographic variables as determinants of spatial variation of forest biomass in the environmentally heterogeneous region of the Big Sur, California. We estimated biomass in 280 forest Plots （one plot per 2.85 km2） and meas- ured an array of ecological （vegetation community type, distance to edge, amount of surrounding non-forest vegetation, soil properties, fire history） and physiographic drivers （elevation, potential soil moisture and solar radiation, proximity to the coast） of tree growth at each plot location. Our geostatistical analyses revealed that biomass distribution is spatially structured and autocorrelated up to 3.1 kin. Regression tree （RT） models showed that both physiographic and ecological factors influenced bio- mass distribution. Across randomly selected sample densities （sample size 112 to 280）, ecological effects of vegetation community type and distance to forest edge, and physiographic effects of elevation, potential soil moisture and solar radiation were the most consistent predictors of biomass. Topographic moisture index and potential solar radiation had apositive effect on biomass, indicating the importance of topographically- mediated energy and moisture on plant growth and biomass accumula- tion. RT model explained 35% of the variation in biomass and spatially autocorrelated variation were retained in regession residuals. Regression kriging model, developed from RT combined with kriging of regression residuals, was used to map biomass across the Big Sur. This study dem- onstrates how statistical and geospatial modeling can be used to dis- criminate the relative importance of physiographic and ecologic effects on forest biomass and develop spatial models to predict and map biomass distribution across a heterogeneous landscape.
基金National Natural Science Foundation of China, No.40121101 No.40671043+2 种基金 No.40571039 National Basic Research Program of China, No.2005CB422002 Knowledge Innovation Program of the Chinese Academy of Sciences, No.KZCX3- SW-339
文摘This paper reveals the temporal and spatial variations of stable isotope in precipitation of the Yarlung Zangbo River Basin based on the variations of δ^18O in precipitation at four stations （Lhaze, Nugesha, Yangcun and Nuxia） in 2005. The results show that δ^18O of precipitation has distinct seasonal changes in the Yarlung Zangbo River Basin. The higher value of δ^18O occurs in spring prior to monsoon precipitation, and the lower value occurs during monsoon precipitation. From the spatial variations, with the altitude-effect and rainout process during moisture transport along the Yarlung Zangbo River Valley, δ^18O of precipitation is gradually depleted. Thus, δ^18O of precipitation decreases gradually from the downstream to the upstream, and the lapse rate of δ^18O in precipitation is approximately 0.34‰/100m and 0.7%J‰/100km for the two reasons. During monsoon precipitation, spatial variation of δ^18O in precipitation is dominated by the amount effect in the large scale synoptic condition.
文摘The limit equilibrium method （LEM） is widely used for sliding stability evaluation of concrete gravitydams. Failure is then commonly assumed to occur along the entire sliding surface simultaneously.However, the brittle behaviour of bonded concrete-rock contacts, in combination with the varying stressover the interface, implies that the failure of bonded dam-foundation interfaces occurs progressively. Inaddition, the spatial variation in cohesion may introduce weak spots where failure can be initiated.Nonetheless, the combined effect of brittle failure and spatial variation in cohesion on the overall shearstrength of the interface has not been studied previously. In this paper, numerical analyses are used toinvestigate the effect of brittle failure in combination with spatial variation in cohesion that is taken intoaccount by random fields with different correlation lengths. The study concludes that a possible existenceof weak spots along the interface has to be considered since it significantly reduces the overallshear strength of the interface, and implications for doing so are discussed.
基金supported by the Natural Science Foundation for Youths of Tibet Autonomous Region of China (Grant No. XZ-20080383)
文摘This study is based on meteorological observation data collected at 38 weather stations on the Tibetan Plateau over several decades. Daily reference crop evapotranspiration （ETo） was calculated with the FAO-56 standard Penman-Monteith formula. A test of normality was performed with Statistica 6.0 software, isotropic and anisotropic semi-variogram analysis was conducted with the GS＋ （geostatistics for the environmental sciences） system for Windows 7.0, and the characteristics of spatial variation of daily ETo were obtained. The following results can be obtained Daily ETo for different periods on the Tibetan Plateau are distributed normally; Except for daily ETo in the E-W （east-west） direction in the summer, which showed a slight negative correlation with distance change, the Moran＇s indexes of daily ETo for different periods in all directions on the Tibetan Plateau within a 100-km distance were positive, demonstrating a positive correlation with distance change; Variograms of daily ETo in June, the dry season, the wet season, as well as annual average daily ETo fit well with the Gaussian model; A variogram of daily ETo in December fit well with the exponential model; Variograms of daily ETo for the four seasons fit well with the linear With sill model.
基金This research was supported by the National Natural Science Foundation of China(52022081)the Technology Project Funded by Clean Energy and Ecological Water Conservancy Engineering Research Center of China(QNZX-2019-03).
文摘The preceding and succeeding precipitation(PSP)often act together with extreme precipitation(EP),in turn,causing floods,which is an objective component that is often overlooked with regard to summer flood hazards in the arid region of Northwest China.In this study,event-based extreme precipitation(EEP)was defined as continuous precipitation that includes at least one day of EP.We analyzed the spatiotemporal variation characteristics of four EEP types(front EEP,late EEP,balanced EEP,and single day EEP)across the Loess Plateau(LP)based on data acquired from 87 meteorological stations from 1960 to 2019.Precipitation on the LP basically maintained a spatial pattern of"low in the northwest region and high in the southeast region",and EP over the last 10 a increased significantly.The cumulative precipitation percentage of single day EEP was 34%and was dominant for 60 a,while the cumulative precipitation percentage of front,late,and balanced EEP types associated with PSP accounted for 66%,which confirms to the connotation of EEP.The cumulative frequencies of front and late EEP types were 23%and 21%,respectively,while the cumulative frequency of balanced EEP had the lowest value at only 13%.Moreover,global warming could lead to more single day EEP across the LP,and continuous EEP could increase in the northwestern region and decrease in the eastern region in the future.The concept of process-oriented EP could facilitate further exploration of disaster-causing processes associated with different types of EP,and provide a theoretical basis for deriving precipitation disaster chains and construction of disaster cluster characteristics.
基金National Natural Science Foundation of China,No.41101088,No.U1404401Natural Science Foundation of Henan Province,No.182300410129New Interdisciplinary and Characteristic Subject Cultivation Project of Henan University,No.XXJC20140003。
文摘Alluviation and sedimentation of the Yellow River are important factors influencing the surface soil structure and organic carbon content in its lower reaches.Selecting Kaifeng and Zhoukou as typical cases of the Yellow River flooding area,the field survey,soil sample collection,laboratory experiment and Geographic Information System(GIS)spatial analysis methods were applied to study the spatial distribution characteristics and change mechanism of organic carbon components at different soil depths.The results revealed that the soil total organic carbon(TOC),active organic carbon(AOC)and nonactive organic carbon(NOC)contents ranged from 0.05–30.03 g/kg,0.01–8.86 g/kg and 0.02–23.36 g/kg,respectively.The TOC,AOC and NOC contents in the surface soil layer were obviously higher than those in the lower soil layer,and the sequence of the content and change range within a single layer was TOC>NOC>AOC.Geostatistical analysis indicated that the TOC,AOC and NOC contents were commonly influenced by structural and random factors,and the influence magnitudes of these two factors were similar.The overall spatial trends of TOC,AOC and NOC remained relatively consistent from the 0–20 cm layer to the 20–100 cm layer,and the transition between high-and low-value areas was obvious,while the spatial variance was high.The AOC and NOC contents and spatial distribution better reflected TOC spatial variation and carbon accumulation areas.The distribution and depth of the sediment,agricultural land-use type,cropping system,fertilization method,tillage process and cultivation history were the main factors impacting the spatial variation in the soil organic carbon(SOC)components.Therefore,increasing the organic matter content,straw return,applying organic manure,adding exogenous particulate matter and conservation tillage are effective measures to improve the soil quality and attain sustainable agricultural development in the alluvial/sedimentary zone of the Yellow River.
基金Under the auspices of National Natural Science Foundation of China(No.41101080,41171047)Natural Science Foundation of Shandong Province(No.ZR2014DQ028)
文摘Spatial variation of dissolved organic carbon(DOC) in soils of riparian wetlands and responses to hydro-geomorphologic changes in the Sanjiang Plain were analyzed through in situ collecting soil samples in the Naoli River and the Bielahong River. The results showed that the average contents of DOC for soil layer of 0–100 cm were 730.6 mg/kg, 250.9 mg/kg, 423.0 mg/kg and 333.1 mg/kg respectively from riverbed to river terrace along the transverse directions of the Naoli watershed. The content of the soil DOC was the highest in the riverbed, lower in the high floodplain and much lower in the river terrace, and it was the lowest in the low floodplain. The difference in the content and vertical distribution of DOC between the riverbed and the three riparian wetlands was significant, while it was not significant among the low floodplain, the high floodplain and the river terrace. The variability of soil DOC was related to the hydrological connectivity between different landscape position of the riparian wetlands and the adjacent stream. Extremely significant correlations were observed between DOC and total organic carbon(TOC), total iron(TFe), ferrous iron(Fe(II)) whose correlation coefficients were 0.819, –0.544 and –0.709 in riparian wetlands of the Naoli River. With the increase of wetland destruction, soil p H increased and soil DOC content changed. The correlation coefficients between soil DOC and TOC, TFe, Fe(II) also changed into 0.759, –0.686 and –0.575 respectively in the Bielahong River. Under the impact of drainage ditches, the correlations between soil DOC and TFe, Fe(II) were not obvious, while the soil p H was weakly alkaline and was negatively correlated with soil DOC in the previous high floodplain. It indicates that riparian hydro-geomorphology is the main factor that could well explain this spatial variability of soil DOC, and the agricultural environmental hydraulic works like ditching also must be considered.
基金Supported by the National Science and Technology Project of Water Pollution Control and Management (2009ZX07317-006-003)
文摘[ Objective] The study aimed to discuss the temporal and spatial variation of phytoplankton community and main pollution indicators in cyanophyte enrichment area of northern Dianchi Lake. [ Method ] In the cyanophyte enrichment area of northern Dianchi Lake, phytoplankton community, chlorophyll a, total nitrogen （TN） and total phosphorus （TP） concentration had been monitored monthly from January 2007 to December 2011, and the temporal and spatial variation of phytoplankton community and main pollution indicators were analyzed. [ Result] From January 2007 to December 2011, algal diversity in the area increased slightly, and algal diversity in the alongshore region was less than that in the offshore re- gion ; chlorophyll a, TN and TP concentration decreased in the alongshore region, but it was otherwise in the offshore region; chlorophyll a, TN and TP concentration in the alongshore region were higher than those in the offshore region. [ Conclusion] The research could provide theoretical references for the control of cyanophyte bloom and achievement evaluation of each control measure in Dianchi Lake.
基金funded by the grants from the National Key Research and Development Program China(2016YFD0300100)。
文摘Rice, wheat and maize are the main staple food crops to ensure the food security in China with diversified climate condition, cropping system and environmental and socio-economic factors across provinces. Spatial variation of technical efficiency in farmers' field is helpful to understand the potential to improve farmers' yield given the inputs level and reduce the yield gap. The study is based on a large-scale farm household survey which covered 1 218 rice farmers, 3 566 wheat farmers and 2 111 maize farmers in the main producing areas. The results indicate that rice farmers are with very high technical efficiency level, nearly 0.9 on average, with little room to improve the efficiency of agricultural inputs. Similar results have been found in wheat and maize farmers' fields, although the technical efficiency levels are lower than that of rice farmers while still at a high level with obvious variation across regions. Farmers with higher yield level also achieve better technical efficiency in most locations. Both local environmental and socio-economic factors significantly affect farmers' technical efficiency. In the context of urbanization and economic development, improved and new agricultural technologies need to be prioritized and facilitated to improve cereal yield at farm level.
基金Supported by National Natural Science Foundation of China(41661062)Shaanxi Provincial Science and Technology Research and Development Plan Project(2014KJXX-21)Shaanxi Provincial Natural Science Fund Project(2014jm5126)
文摘In order to explore the spatial distribution and variation characteristics of soil moisture in coal mining subsidence area in Mu Us sandy Land,and provide theoretical basis for the restoration of the mining area,experiments based on a linear sampling and classic statistical and geostatistical methods were conducted. Spatial distribution characteristics and variation of soil moisture in the typical 0 to 100 cm dune area in the subsidence area and the non-subsidence area( control) were studied. The results showed that in the typical sand dune location of nonsubsidence area( control),the probability distribution curves of soil moisture changes in all layers along vertical and horizontal directions were all normal distribution,and it was consistent with the temporal and spatial variation characteristics of soil moisture in conventional dunes in Mu Us sandy land. By contrast,two years after the coal mine collapsed,the variations of soil moisture in different layers along vertical and horizontal directions were different,and soil moisture loss was more serious than that of control dune by nearly 10% to 30%,and the standard deviation varied from 0. 54 to 1. 05,increasing by 52. 08% compared with the non-subsidence area( control). The probability of positive and negative deviation greater than 1 was over 50%,and the coefficient of variation varied from 0. 14 to 0. 28,which was 80% higher than that of nonsubsidence area( control). After collapsing,the average level of soil moisture,standard deviation,variance and variation coefficient had greatly changed,and influence of coal mining subsidence on soil moisture was the most in the middle layer( 30-70 cm),and was not obvious in the surface( 0-20 cm) and lower layer( 80-100 cm). In coal mining subsidence area,the dispersion degree of soil moisture in different layers along the vertical and horizontal direction was greatly improved,which increased spatial variation of soil moisture.
