Abstract:Wetlands have unique biogeochemical cycles with many chemical transformations and chemical transport processes that are not shared饰many other ecosystems. The construction of irrigation ditches in wetland changes the hydrology state, and thus influences the biological geochemistry circulation. In order to understand the effects of drainage ditches on the biogeochemical cycling in wetland, this paper takes the Sanjiang Plain as an example, and makes a detail introduction to the impacts of drainage ditches on the characteristics of movement, transformation, inputs and outputs of chemical elements and on the chemical mass balance. Results show that a lot of chemical elements are lost because of draining, which causes the degeneration of wetland.

Abstract:This paper computed the weight of influence factors by gray pertinence method and BP network,and as- sessed shallow groundwater resource vulnerability in the Hufu Plain in 1984 and 2000 by the integrated method. The changes in vulnerability grade and its spatial characteristics in 2000 were significant compared with those in 1984.The advices to exploit properly groundwater should be based on current groundwater resource vulnerability because of its changes with time.

Abstract:Topography index (wetness index) is a crucial kind of input data,which links the saturation deficit of a basin with the conception of variable contributing area.According to the definition of topography index,procedures of calculating the index were presented.Solutions to problems of processing grids with zero slope degree and expurgated deviations induced by the involvement of channels in computation were introduced.The index was derived from the DEM of the Lianghekou Basin with a solution of 60 m in this method,and then imported into TOP-MODEL with a suitable data set.The result of daily runoff simulation turns out to be acceptable with about 70% prediction precision.

Abstract:On the basis of the calculation of light-temperature production potential modified by the natural factors such as rainfall,soil fertility and soil quality,potentialities of land productivity and food production in North Shaanxi Province were analyzed.Furthermore,the maximum grain yield and the land supporting capacity for population in the years of 2010 and 2020 were predicted by means of the agriculture ecology zone (AEZ) method.The key to understanding the harmonious and sustainable development relationship between human being and land resources was also presented.

Abstract:The paper aims at the problems of food security,the decline in land ecological quality and the social and economical security in the process of land utilization.A system of evaluation criterions was set up based on the PRS evaluation model of land use.The weigh of all the criterions was then determined using Delphi method.Finally, quadratic function was used to work out the degree of land security.The result indicates that in terms of the land security value,the status of land security in Chongqing was better in 2004 compared with that in 1999,and now is at the beginning of a security stage.

Abstract:The distribution and dynamic change characteristics of sandy desertification lands in China were analyzed by using the monitoring data.The reasons for dynamic changes in the deserted lands were briefly discussed.Meanwhile,a controlling strategy for the deserted lands was presented.To combat the deserted lands is showed to be in a stalemate phase of controlling and destroying.It is a heavy responsibility to maintain the reversing situation of the deserted lands.

Abstract:Through considering the effects of spatiotemporal transformations as well as watershed topography on runoff routing,this paper reports the development and implementation of the new method named spatially distributed time-variable routing method.The method incorporates time-variable factors into distributed yielding and routing simulations.In this way,it can overcome the shortcomings of ignoring the changes of excess rainfall over time in the traditional methods.Inaddition,with the support of the geographical information system (GIS) and remote sensing(RS),most of the parameters in the model can be obtained by means of DEM,soil maps and/or satellite images.Among the others,only some sensitive parameters need to be determined through calibration.Although the model seems to be simple,it can reflect the physical mechanism of rainfallrunoff process.In consequence,the method can predict the runoff hydrograph in the ungauged watersheds,so that it can be extended to other areas in the future.In the combination of this method with GIS technique,stream responses to runoff events in the Jiaokou Reservoir Watershed in Zhejiang Province were predicted.Results showed that the model efficiency was high,and the simulations were approximately consistent with the observations for the shapes of runoff hydrographs when the factor for the changes of excess rainfall over time was considered in the model.Most importantly, the floods can be identified by the shapes of each peak including the major and minor ones of all floods,especially of the double-peaks or multi-peaks flood,regardless of the rainfall intensity.

Abstract:Topographic data are critical to global changes in climate,land formations,atmospheric changes,and research in soil and water loss.Recently,NASA released SRTM DEM at 90-meter resolution covering 80% of the Earth's land surface.Prior to SRTM DEM,GTOPO30 (1 km) was the highest-resolution global DEM.As it is a new product,we have no knowledge of SRTM DEM,and so,it is necessary to assess its accuracy.The article introduces apparent accuracy and production procedure of SRTM DEM in comparison with GTOPO30.Further-more,the article analyzes and compares these two DEM datasets at 1 km resolution in Tibet.Results show that SRTM DEM has higher accuracy than GTOPO30.This research can be a good reference for applications in other areas.

Abstract:The amount of soil erosion in the Qingcheng project area was predicted using remote sensing(RS) images,Geographical information system(GIS) technology and the revised universal soil loss equation (RUSLE). The annual average amount of soil erosion in the Qingeheng project area was estimated to be about 7 058 t/km², belonging to intense erosion.Soil erosion degree map was obtained through soil erosion degree classification.The seriously eroded area(greater than 10 000 t/km²) accounted for 24.8 % of the total area,but contributed 62.2 % of sediment of the whole watershed.The amount of soil loss on the land greater than 25 degree of slope was greater than 10 168 t/km².Therefore,control of soil loss on the land is the key to the solution of soil erosion in the area. The method of soil erosion investigation will provide quick,quantitative and scientific data for strategies of both soil erosion prevention and soil protection.

Abstract:The 3S technology,an integrated technology with remote sensing,GPS and GIS,is a new high-tech means.The 3S technology was used for the investigation of soil erosion in Xiamen,and the studying method may be outlined as follows.First,the author obtained the slope data by DEM,the vegetation cover rate by interpretation of SPOT5 images,and the land use data by the digital land use map.Second,the author understood the situation of soil erosion by following the standards for soil erosion classification and gradation and using the overlaying function of GIS.Third,basing on the situation of soil erosion in the region,the author analyzed the changes and causes of soil erosion distribution.The result provides a scientific base for soil and water conservation planning and soil erosion control.

Abstract:Based on satellite operational data,basic meteorological database,agro-meteorological data and the result from the analysis of climatologic resources,a system is designed to have the functions of calculation,query,appendix and analysis of spatial attributes on the platform of the GIS software ArcGIS 8.3.The data can be accessed via the internet using the grade of purview.The system provides the basic data,data processing and images of clirnatologic resources and ecological environment and other associated technical products.It furnishes the basis databank for the study of changes in ecological environment of Northeast China.

Abstract:In terms of the impact of different land uses on soil erosion,the Xiangyanggou watershed was divided into five slope grade units with the aid of ArcGIS.Soil erosion in the units under the conditions of existed soil and water conservation measures was estimated using the universal soil loss equation,and was then contrasted to the case before adopting the measures.Results show that soil and water loss has been greatly controlled,and soil and water conservation measures have evidently plaid a relatively great role.However,the watershed is still suffering from medium erosion,and the 25°～35°slope grade unit contributes most of soil loss,followed by the 15°～25°and>35°slope grade units.Based on the analysis of estimated modulus for different slope grade units,suggestions for further soil erosion control are presented in combination with existed soil and water conservation measures.

Abstract:The serious landscape pollution in the Tai Lake district of Changzhou City is caused by abandoned quarries.The characteristic data of abandoned quarries were obtained using the GIS and RS technology.Landscape pollution was analyzed quantitatively by the landscape pollution index.The quarries which caused the serious landscape pollution were screened out.It is very important for the administrators to arrange the schedule for ecological restoration.The integrated procedure of ecological restoration engineering is established.Plants for ecological restoration in the district are chosen by field investigation.Five different ecological restoration measures are determined for the twenty-seven quarries in the district.

Abstract:Stream buffer strips are located between the terrestrial ecosystem and the aquatic ecosystem,which are also the important composition of stream ecosystem.This paper emphasizes the introduction of six ecological functions of buffer strips,that is,species heaven,nutrient source,river bank stabilization,water quality amelioration, landscape value and harmful impact alleviation.However,disturbances caused by human activities to stream buffer strips become serious due to a great increment in the land for construction and transportation.Therefore,there is an urgent need in scientific rehabilitation and management.For this reason,we present three basic principles of scientific management of stream buffer strips as the guidelines for the rehabilitation and construction of stream buffer strips in different grades in different areas.By taking the Nansha River located in Haidian district of Beijing for an example,we illustrate the functions of stream buffer strips and the scientific management principles.

Abstract:Through field surveys and remote sensing dynamic monitoring,reversible processes of oasis and desertification in the arid oasis region were studied by proceeding from men-earth relationship theory and taking land use change as a breakthrough point.On the basis of field survey data and evaluation of remote sensing image classification,dynamic and spatial changes in both land use and land cover in the region were analyzed.It was found that abused water and soil resources,increased population,changes in national policies and institution and other factors led to sharp contradictions between men and the earth.This has the greater impact on local economic development and the achievement of sustainable development.Accordingly,it is proposed that the only way to prevent desertification and restore oasis is to coordinate man-earth relationship and strengthen regional geographic building.

Abstract:Ecological security is the key part and base for agricultural sustainable development.A review of ecological security was given from the aspects of concepts,features,and meanings,status and methods,as well as themes of studies on ecological security at home and abroad.By taking a county as a basic unit,an integrated evaluation of agricultural ecological security in Hunan Province was made in terms of the pressure,quality,rehabilitation ability of resource-ecology-environment,using the technique of AHP.The result indicates that regional heterogeneity of security degree is distinct,which not only decreases from east to west,but also decreases from south to north, with the exception in a few areas.The quality of resource-ecology-environment is the base of spatial patterns for a- gricultural eco-security in Hu' nan Province.However,the pressure and rehabilitation ability of resource-ecology-environment also have a great impact on ecological security and influence its spatial pattern.The strategy for establishing ecological safety of agricultural sustainable development is pointed out as well.

Abstract:Through the analyses of characteristics of gully thalweg and soil erosion in upland and gully land,sediment sources in small watershed,sediment yield relationship between upland and gully and ecological functions of vegetation corridor,it is considered that vegetation corridor combined with land preparation measures may block runoff and sediment from upland and reduce the amount of soil erosion in a watershed by 54.5%～77.0 %.

Abstract:He'nan province locates in transition areas of both south climate to north climate and mountain to plain area.Influenced by special climate,geography environment and human being actions etc.,the situation of soil and water losses is serious and the productive conditions and ecological environment are fragility in these mountain areas.Basis on the analysis of harm of soil and water loss and the function of soil and water conservation to improve the productive conditions and ecological environment,the paper points out that soil and water conservation is the root to maintain agricultural sustainable development in mountain areas.The countermeasures of improve water and soil conservation and maintain agricultural sustainable development in mountain areas are prevention and protection,erosion control and construct farmland with high productivity by terracing on the slope,reinforce the projects of blocking sands and sluice and water system match on the slope,strengthen supervising and management and keep the new artificial water and soil losses within limits.

Abstract:An index system of integrated evaluation with eight indexes and the five items of sociality,resource, economics,technique and ecologic environment is established by using the fuzzy comprehensive evaluation method. The system is combined with the execution of water saving improvement of the Guanzhong irrigation districts.In addition,an integrated evaluation model is constructed.Evaluation comments are divided into the four grades of low benefit,general benefit,good benefit and very good benefit.The integrated evaluation value can be obtained by the fuzzy analysis and calculation.After water saving improvement,integrated evaluation index of the Guanzhong irrigation districts raises a grade,that is,from the general benefit to good benefit.