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921.
The most promising approach for studying soil moisture is the assimilation of observation data and computational modeling.However,there is much uncertainty in the assimilation process,which affects the assimilation results.This research developed a one-dimensional soil moisture assimilation scheme based on the Ensemble Kalman Filter(EnKF)and Genetic Algorithm(GA).A two-dimensional hydrologic model-Distributed Hydrology-Soil-Vegetation Model(DHSVM)was coupled with a semi-empirical backscattering model(Oh).The Advanced Synthetic Apertture Radar(ASAR)data were assimilated with this coupled model and the field observation data were used to validate this scheme in the soil moisture assimilation experiment.In order to improve the assimilation results,a cost function was set up based on the distance between the simulated backscattering coefficient from the coupled model and the observed backscattering coefficient from ASAR.The EnKF and GA were used to re-initialize and re-parameterize the simulation process,respectively.The assimilation results were compared with the free-run simulations from hydrologic model and the field observation data.The results obtained indicate that this assimilation scheme is practical and it can improve the accuracy of soil moisture estimation significantly.  相似文献   
922.
The upmost segment(Holocene series)of the Milanggouwan stratigraphic section(MGS1)in the Salawusu River valley shows 11 sedimentary cycles of dune sands and fluvio-lacustrine facies,or dune sands and paleosols.The analysis of the magnetic susceptibility of this segment suggests that there are 11 magnetic susceptibility cycles with the value alternating from low to high,in which the layers of the dune sands correspond to the lower value of the magnetic susceptibility and the layers of fluvio-lacustrine facies and paleosols correspond to the higher peaks.The study reveals that the low and high magnetic susceptibility values indicate the climate dominated by cold-arid winter monsoon and warm-humid summer monsoon of East Asia,respectively,and the study area has experienced at least 22 times of mil-lennial-centennial scales climate alternation from the cold-arid to the warm-humid during the Holocene.In terms of the time and the climate nature,the variations basically correspond to those of the North Atlantic and some records of cold-warm changes in China as well.They might be caused by the alternation of winter and summer monsoons in the Mu Us Desert induced by global climate fluctuations in the Holocene.  相似文献   
923.
Studying the carrying capacity of resources and environment of city clusters in the central China has impor-tant practical guidance significance for promoting the healthy,sustainable and stable development of this region.Ac-cording to their influencing factors and reciprocity mechanism,using system dynamics approaches,this paper built a SD model for measuring the carrying capacity of resources and environment of the city clusters in the central China,and through setting different development models,the comprehensive measurement analysis on the carrying capacity was carried out.The results show that the model of promoting socio-economic development under the protection of resources and environment is the optimal model for promoting the harmony development of resources,environment,society and economy in the city clusters.According to this model,the optimum population scale of the city clusters in2020 is 42.80×106 persons,and the moderate economic development scale is 22.055× 1012 yuan(RMB).In 1996-2020,the carrying capacity of resources and environment in the city clusters took on obvious phase-change characteristics.During the studied period,it is basically at the initial development stage,and will come through the development process from slow development to speedup development.  相似文献   
924.
Typhoon Durian (2001),which formed over the South China Sea (SCS),was simulated by using the Weather Research and Forecasting (WRF) model. The genesis of typhoon Durian which formed in the monsoon trough was reproduced by numerical simulations. The simulated results agree reasonably well with observations. Two numerical experiments in which the sea surface temperature (SST) was either decreased or increased were performed to investigate the impact of the SST on the genesis of the ty-phoon. When the SST was decreased by 5℃ uniformly for all grids in the model,the winds calculated became divergent in the lower troposphere and convergent in the upper troposphere,creating conditions in which the amount of total latent heat release (TLHR) was low and the tropical cyclone (TC) could not be formed. This simulation shows the importance of the convergence in the lower tropo-sphere and the divergence in the upper troposphere for the genesis of the initial vortex. When the SST was increased by 1℃ uni-formly for all grids,a stronger typhoon was generated in the results with an increase of about 10 m s-1 in the maximum surface wind speed. Only minor differences in intensity were noted during the first 54 h in the simulation with the warmer SST,but apparent dif-ferences in intensity occurred after 54 h when the vortex began to strengthen to typhoon strength. This experiment shows that warmer SST will speed the strengthening from tropical storm strength to typhoon strength and increase the maximum intensity reached,while only minor impact can be seen during the earlier stage of genesis before the TC reaches the tropical storm strength. The results sug-gest that the amount of TLHR may be the dominant factor in determining the formation and the intensification of the TC.  相似文献   
925.
Based on literature and survery data of fish composition collected by bottom trawl investigation from 2006 to 2007 infour main estuaries of China southeastern coastal areas and their adjacent waters,changes of the taxonomic diversity across spatialand temporal scales of fish community were analyzed by taxonomic diversity indices.The results are as follows:a total number of1397 fish species(including some freshwater species),belonging to 2 classes,42 orders,186 families and 593 genera,were collected inthe studied sea areas.The species richness increased with lower latitudes,particularly so with Perciformes.There were 339 fish spe-cies in the Yangtze River Estuary and adjacent waters,belonging to 2 classes,31 orders,101 families and 231 genera.There were 535fish species in the Minjiang River Estuary and adjacent waters,belonging to 2 classes,33 orders,133 families and 323 genera.A totalnumber of 803 fish species were collected in the Jiulongjiang River Estuary and adjacent waters,which belonged to 2 classes,35 orders,155 families and 419 genera.And 1021 fish species which belonged to 2 classes,32 orders,153 families,and 466 genera were collectedin the Pearl River Estuary and adjacent waters.The numbers of orders and families of fish species from the northern to the southern wa-ters first increased and then decreased.The average variation in taxonomic distinctness(Λ+)gradually decreased with lower latitudes inthe four estuaries and adjacent waters.There were no significant differences in the average taxonomic distinctness(△+)among the fourestuaries and adjacent waters,and fish fauna were closely related with each other,and all of them belonged to the same zoogeographicalfauna(Indian-Malaysia fauna).Fish composition in the Minjiang River Estuary and adjacent waters was more similar to that in the Jiu-longjiang River Estuary and adjacent waters among the four estuaries.Compared with the historical data,the average taxonomic dis-tinctness of fish community showed a great decrease in the Minjiang River Estuary and the Jiulongjiang River Estuary and their adjacentwaters.  相似文献   
926.
The Zhujiang (Pearl) River Delta is one of the most developed Extended Metropolitan Regions (EMR) in China.With the rapid urbanization,the agglomeration of population and industries has emerged,which has led to dramatic changes of spatial structure and land use in this region.With data of high resolution TM remote sensing images and Google Earth maps,this paper identified and analyzed the spatial pattern of the Zhujiang River Delta EMR using Envy and ArcGIS tools.It was found that 1) the industrial land uses were expanding substantially,particularly on the bank sides of the Zhujiang River estuary;2) large-scale housing developments were concentrated in the fringe of metropolitan areas such as those of Guangzhou and Shenzhen;3) a regional transportation network with the spatial pattern of ″1 circle +2 pieces + 3 axes″ had significantly affected the location choice of manufacture enterprises.At the same time,both highly specialized land use and severely mixed land use patterns were identified.As a consequence of the latter,land use efficiency of the whole EMR areas was reduced.Moreover,ecologic and environmental problems were severe.Based on the above analysis,suggestions were given from the viewpoint of spatial safety,land use efficiency,and the reorganization of spatial structure in the Zhujiang River Delta EMR.  相似文献   
927.
Ten clonal units of Carex pseudocuraica growing in four different microhabitats (perennial flooded ditch water, perennial flooded ditch sediment, seasonal flooded ditch sediment and perennial flooded soil) of the Sanjiang Plain, Northeast China, were collected randomly for phenotypic plasticity analysis. Iron content, chemical and physical properties of substrates and the total Fe of nine plant modules were measured as well. The results show that the performance of the C. pseudocuraica is affected by the microhabitat, with the greatest performance score in perennial flooded ditch water, and the lowest in perennial flooded soil. The biomass allocation indexes indicate that much more mass is allocated to stems and roots to expand colonization area. The distribution of the total Fe in plant modules appears as pyramids from the tip to the root, while marked differences are observed in the distribution proportion of stems, tillering nodes and roots that are allometrically growing. Iron transfer from substrates to the plant is mainly controlled by the substrate type. The differences of iron distribution and transfer in the plant in different microhabitats are attributed to the iron contents of the substrates as well as the phenotypic plasticity of the plant.  相似文献   
928.
This study uses the data from a sample survey conducted in April 2007 on 1 251 rural households in 11 villages of Henan Province, the largest less developed agricultural province in China, to examine how geography affects rural household income (RHI). The quantitative analysis indicates following results. 1) The significance of the traditional geographical factors reduces as RHI rank increases. 2) The landform does not affect the RHI significantly. The per capita income of rural household in a plain area is lower than that in a mountainous area. And 3) the capital endowment and status of non-farm economic activities contribute to the increase of RHI. But the probability and intensity of non-farm economic activities of rural households in urban outskirts villages are higher than that in non-urban outskirts villages. Based on the results, the paper further concludes that geography still plays a significant role in rural development, but it is changing over time. The agricultural resources (such as per capita arable land) significantly affect RHI with the relatively lower income level, while the geographical location shows a more significant impact on RHI with the relatively high income level. Along with economic development, the proximity replaces the traditional geographical factors such as landform and physical resources as the major determining factor in RHI.  相似文献   
929.
930.
Individual participation of pollutants in the pollution load should be estimated even if roughly for the appropriate environmental management of a river basin. It is difficult to identify the sources and to quantify the load, especially in modeling nonpoint source. In this study a revised model was established by integrating point and nonpoint sources into one-dimensional Streeter-Phelps (S-P) model on the basis of real-time hydrologic data and surface water quality monitoring data in the Jilin Reach of the Songhua River Basin. Chemical oxygen demand (COD) and ammonia nitrogen (NH_3-N) loads were estimated. Results showed that COD loads of point source and nonpoint source were 134 958 t/yr and 86 209 t/yr, accounting for 61.02% and 38.98% of total loads, respectively. NH_3-N loads of point source and nonpoint source were 16 739 t/yr and 14 272 t/yr, accounting for 53.98% and 46.02%, respectively. Point source pollution was stronger than nonpoint source pollution in the study area at present. The water quality of upstream was better than that of downstream of the rivers and cities. It is indispensable to treat industrial wastewater and municipal sewage out of point sources, to adopt the best management practices to control diffuse pollutants from agricultural land and urban surface runoff in improving water quality of the Songhua River Basin. The revised S-P model can be successfully used to identify pollution source and quantify point source and nonpoint source loads by calibrating and validating.  相似文献   
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