Theoretical study of the ionospheric dynamo region inside the South Atlantic Anomaly

The South Atlantic Anomaly(SAA)is a region where the geomagnetic field is significantly lower than that of the surrounding area.On the basis of the models of CHAOS-7.8,Mass Spectrometer Incoherent Scatter Model(NRLMSISE-00),and International Reference Ionosphere 2016(IRI-2016),we theoretically investigated the lower and upper boundaries of the ionospheric dynamo region inside the SAA.In the ionospheric dynamo region,electrons are coupled with magnetic field lines,whereas ions are decoupled from magnetic field lines.Our results showed that the ionospheric dynamo region inside the SAA is higher and larger than that outside the SAA.We also studied the boundary variations of the dynamo region inside the SAA depending on the seasons and solar activities.We found that the dynamo region inside the SAA is the highest and largest in the summer of the southern hemisphere at solar maximum.The larger and higher altitude range of the ionospheric dynamo region in the SAA can contribute to the stronger ionospheric currents in this region.

Characteristics of Garden Culture in Southern Region of the Five Ridges

Geographical conditions, humanistic environment and garden development history in the southern region of the Five Ridges (or Lingnan, "Ling" means "ridge", "nan" means "south") were introduced in this study, and characteristics of garden culture in this region were analyzed.

Clay mineral distribution characteristics of surface sediments in the South Mid-Atlantic Ridge

Clay minerals are usually considered as important indicators to identify sources in both terrigenous and marine sediments.In particular,clay minerals in metalliferous sediments(MS)have long been studied in global oceans except in South Mid-Atlantic Ridge(SMAR)due to limited explorations.Thus,32 MS and 34 non-MS(NMS)samples were analyzed to clarify the distribution characteristics and mineral compositions of clay minerals.All the sediments were collected along the SMAR between 12°S and 27°S.After removal of organic matter and carbonate,clay fractions(<2μm)were investigated by Xray diffraction(XRD)analysis.Results show that clay mineral assemblages of surface MS consist dominantly of smectite,less abundant illite,chlorite,and kaolinite in average weight percentage of 30%,21%,18%,and 16%,respectively.On the other hand,clay mineral assemblages in the NMS consist mainly of illite,less abundant kaolinite,chlorite,and very scarce smectite in average weight percentage of 47%,29%,24%,and 0.2%,respectively.The clay fractions in MS are mainly composed of amorphous or poorly crystallized Fe/Mn oxyhydroxides,clay mineral,quartz,and plagioclase.However,the counterparts in the NMS are mainly composed of well-crystallized clay minerals,quartz,and plagioclase without the presence of Fe/Mn oxyhydroxides.It is suggested that most of the illite,kaolinite,and chlorite in both MS and NMS are likely aeolian dust in origin from South Africa continent.In addition,the abundance of kaolinite dominates the clay mineral assemblage at low latitudes,where the intensive chemical weathering of continental source rocks facilitating the formation of kaolinite.In terms of smectite,it is indicated of authigenic origin in consideration of only smectite is available in several MS and the absence in NMS.Moreover,the MS samples with only smectite available are always accompanied by goethite.Therefore,it is assumed that most of smectite occurred in studied area is the results of interaction between hydrothermal Fe-oxyhydroxide,silica,and seawater.

Creation of "Regional Characteristic" in Planning and Design of Farmers' Residential Area at the South of Lower Reaches of the Yangtze River

After analysis of location feature of the south of lower reaches of Yangtze River and its construction of urban and rural integration,the paper pointed out harmonious combination between natural and artificial factors had been neglected in planning and design of farmers' residential area at the south of lower reaches of Yangtze River,"regional characteristic" losing,residential area in the form of "city community" and buildings in European style.In view of these problems,relevant planning and design thoughts and methods had been proposed as to how to create "regional characteristic" from the perspective of planning,architecture and landscape design.It discussed with emphasis the importance of construction base type and combination of environment with residential area construction;inspirations and design methods obtained from traditional architectures;and the content of landscape overall planning and specific design.It was hoped to enlighten designers to shoulder social and historical responsibility,make exploration unremittingly,and construct beautiful homelands for people.

New patterns of the tree beta diversity and its determinants in the largest savanna and wetland biomes of South America

Clear and data-driven bioregionalizations can provide a framework to test hypotheses and base biodiversity conservation.Here we used occurrence and abundance data in combination with objective analytical methods to propose two bioregionalization schemes for tree species of the Cerrado and the Pantanal in South America.We also evaluated the contribution of three sets of determinants of the occurrence-and abundance-based subregions.We compiled data on tree species composition from 894 local assemblages based on species occurrences,and from 658 local assemblages based on species abundances.We used an unconstrained community-level modelling approach and clustering techniques to identify and map tree subregions for the occurrence and the abundance data sets,separately.Hierarchical clustering analyses were conducted to investigate floristic affinities between the subregions and to map broader floristic regions.We used multinomial logistic regression models,deviance partitioning,and rank-sum tests to assess the main subregion correlates.We identified 18 occurrence-and four abundance-based subregions in the Cerrado-Pantanal.The hierarchical classifications grouped the occurrence-based subregions into nine floristic zones and abundance-based subregions into two broad floristic zones.Variation in subregions were explained mainly by environmental factors and spatial structure in both occurrence and abundance data sets.The occurrence-and abundance-based subregions are complementary approaches to disentangle macroecological patterns and to plan conservation efforts in the Cerrado and the Pantanal.Our findings based on occurrence data revealed more complex and interdigitated boundaries between subregions of tree species than previously reported.The environment,historical stability,and human effects act in a synergetic way on the distribution of the subregions.Finally,the relevance of contemporary environmental factors to the subregion patterns we found alert us to the profound impact global warming may have on the spatial organization of the Cerrado-Pantanal tree flora.

Physical characteristics of high concentrated gas hydrate reservoir in the Shenhu production test area,South China Sea

High concentrated and heterogeneous distribution of gas hydrates have been identified in the gas hydrate production test region in the Shenhu area,South China Sea.The gas hydrate-bearing sediments with high saturation locate at two ridges of submarine canyon with different thickness and saturations just above the bottom simulating reflection.The crossplots of gamma ray,acoustic impedance(P-impedance)and porosity at four sites show that the sediments can be divided into the upper and lower layers at different depths,indicating different geotechnical reservoir properties.Therefore,the depositional environments and physical properties at two ridges are analyzed and compared to show the different characteristics of hydrate reservoir.High porosity,high P-wave velocity,and coarse grain size indicate better reservoir quality and higher energy depositional environment for gas hydrate at Sites W18 and W19 than those at Sites W11 and W17.Our interpretation is that the base of canyon deposits at Sites W18 and W19 characterized by upward-coarsening units may be turbidity sand layers,thus significantly improving the reservoir quality with increasing gas hydrate saturation.The shelf and slope sliding deposits compose of the fine-grained sediments at Sites W11 and W17.The gas hydrate production test sites were conducted at the ridge of W11 and W17,mainly because of the thicker and larger area of gas hydrate-bearing reservoirs than those at Sites W18 and W19.All the results provide useful insights for assessing reservoir quality in the Shenhu area.

Moisture Transport and Associated Background Circulation for the Regional Extreme Precipitation Events over South China in Recent 40 Years

Based on the hourly precipitation data at 176 observational stations over south China and the hourly ERA5reanalysis data during the 40-yr period of 1981-2020, we analyzed the universal characteristics of moisture transport and their associated background circulations for four types of regional extreme precipitation events(REPEs) over south China. Main findings are shown as follow.(i) The wind that transported moisture for the REPEs over south China featured a notable diurnal variation, which was consistent with the variations of the precipitation.(ii) Four types of REPEs could be determined, among which the southwest type(SWT) and the southeast type(SET) accounted for ~92%and ~5.7%, respectively, ranking the first and second, respectively.(iii) Trajectory analyses showed that the air particles of the SWT-REPEs had the largest specific humidity and experienced the most intense ascending motion, and therefore their precipitation was the strongest among the four types.(iv) South China was dominated by notable moisture flux convergence for the four types of REPEs, but their moisture transport was controlled by different flow paths.(v)Composite analyses indicated that the background circulation of the four types of REPEs showed different features,particularly for the intensity, location and coverage of a western Pacific subtropical high. For the SWT-REPEs, their moisture transport was mainly driven by a lower-tropospheric strong southwesterly wind band in the low-latitude regions. Air particles for this type of REPEs mainly passed over the Indochina Peninsula and South China Sea. For the SET-REPEs, their moisture transport was mainly steered by a strong low-tropospheric southeasterly wind northeast of a transversal trough. Air particles mainly passed over the South China Sea for this type of REPEs.

From Basin Black Shales to Platform Carbonate Rocks:A Study on Sequence Stratigraphy for the Lower Cambrian of the Upper-Yangtze Region in South China

In the Upper-Yangtze region, especially in Guizhou Province and its adjacent areas, the Lower Cambrian is well developed and is marked by a succession from black shales of the basin facies to carbonate rocks of the platform facies. The drowning event of the platform occurring at the turn from Sinian to Cambrian resulted in a set of black shales, i.e. the Niutitang Formation, which makes up the bottom part of the Lower Cambrian. With the shoaling of the sedimentary environment, a set of carbonate rocks, i.e. the Qingxudong Formation, was formed in the top part of the Lower Cambrian. Thus, the Lower Cambrian in the study area makes up one second-order sequence that can be further subdivided into five third-order sequences, and forms a regularly cyclic succession of transgression-regression. There is a regularly vertical stacking pattern for the third-order sequences in the second-order sequence. From bottom to top, the succession of the ＂CS （condensed section） ＋HST （high-stand system tract）＂ of the third-order sequences is changed into the succession of the ＂TST （transgressive system tract）＋CS＋HST＂. Correspondingly, the drowning-type sequence boundary is changed into the exposure-type one. Therefore, both the second-order and the third-order sequences have similar sedimentary-facies architectures. A concomitant with these temporal changes, the Lower Cambrian with a thickness of 1000 m that contains five third-order sequences is changed into a condensed succession that cannot identify third-order sequences toward the southeast with the deepening of the sedimentary environment. According to the elementary features of the third-order sequences, i.e. the regularity o sedimentary-facies successions in space and the synchronism of sedimentary-environment changes in time, the detailed division of the third-order sequences at main logged sections in different paleogeographical background becomes the basis to establish the sequence-stratigraphic framework that can demonstrate two types of facies-changing surface and two types of diachronism in the stratigraphic records. This sequence-stratigraphic framework shows a growing process of the carbonate platform from the base of the condensed succession formed by black shales of basin facies. Resulting from the rapid transgression at the turn from Sinian to Cambrian the ecological space became open, which formed the antecedent condition of paleogeographical setting for ＂the Cambrian Biological Explosion＂. Ultimately, the genetic relationship between the depositional events and the biological-diversity events is very complex and there remain lots of problems that need further research in the future.

The Late Triassic Sequence-Stratigraphic Framework of the Upper Yangtze Region,South China

In the transitional period between the Middle and the Late Triassic, the Indochina orogeny caused two tectonic events in South China：（1） the formation and uplift of the Qinling-Dabie orogenic belt along the northern margin of the South China Plate, due to its collision with the North China Plate; and 2） the development of a 1300-km-wide intra-continental orogen in the southeastern part of the South China Plate, which led to a northwestward movement of the foreland thrust-fold zone. These tectonic events resulted in the ending of the Yangtze Platform, and were a stable paleogeographic factor from the Eidacaran to the end of the Middle Triassic. This platform was characterized by the widespread development of shallow-water carbonates. After the end of the Yangtze Platform, the upper Yangtze foreland basin（or Sichuan foreland basin） was formed during the Late Triassic and became a accumulation site of fluvial deposits that are composed of related strata of the Xujiahe Formation. In western Sichuan Province, the Xujiahe Formation overlies the Maantang Formation shallow-water carbonate rocks of the Xiaotangzi Formation siliciclastic rocks（from shelf shales to littoral facies）. The sequence-stratigraphic framework of the Upper Triassic in the upper Yangtze foreland basin indicates a particular alluvial architecture, characterized by sequences composed of（1） successions of low-energy fluvial deposits of high-accommodation phases, including coal seams, and（2） high-energy fluvial deposits of low-accommodation phases, including amalgamated river-channel sandstones. The spatial distribution of these fluvial deposits belonging to the Xujiahe Formation and its relative strata is characterized by gradual thinning-out, overlapping, and pinching-out toward both the east and south. This sedimentary record therefore expresses a particular sequence-stratigraphic succession of fluvial deposits within the filling succession of the foreland basin. The sequence-stratigraphic framework for the Upper Triassic in the Upper Yangtze region provides a record of the end of the Yangtze Platform and the formation of the upper Yangtze foreland basin.

Effects of collapsing gully erosion on soil qualities of farm fields in the hilly granitic region of South China

Collapsing gully erosion is a specific form of soil erosion types in the hilly granitic region of tropical and subtropical South China, and can result in extremely rapid water and soil loss. Knowledge of the soil physical and chemical properties of farmland influenced by collapsing gully erosion is important in understanding the development of soil quality. This study was conducted at the Wuli Watershed of the Tongcheng County, south of Hubei Province, China. The aim is to investigate soil physical and chemical properties of three soil layers （0-20, 20-40 and 40-60 cm） for two farmland types （paddy field and upland field） in three regions influenced by collapsing gully erosion. The three regions are described as follows： strongly influenced region （SIR）, weakly influenced region （WIR） and non-influenced region （NIR）. The results show that collapsing gully erosion significantly increased the soil gravel and sand content in paddy and upland fields, especially the surface soil in the SIR and WIR. In the 0-20 cm layer of the paddy field, the highest gravel content （250.94 g kg-1） was in the SIR and the lowest （78.67 g kg-1） was in the NIR, but in the upland filed, the surface soil （0-20 cm） of the SIR and the 40-60 cm soil layer for the NIR had the highest （177.13 g kg-1） and the lowest （59.96 g kg-1） values of gravel content, respectively. The distribution of gravel and sand decreased with depth in the three influenced regions, but silt and clay showed the inverse change. In the paddy field, the average of sand content decreased from 58.6 （in the SIR） to 49.0% （in the NIR）, but the silt content was in a reverse order, increasing from 27.9 to 36.9%, and the average of the clay content of three regions showed no significant variation （P〈0.05）. But in the upland filed, the sand, silt and clay fluctuated in the NIR and the WIR. Soils in the paddy and upland field were highly acidic （pH〈5.2） in the SIR and WIR; moreover lower nutrient contents （soil organic matter （SOM）, total N and available N, P, K） existed in the SIR. In the 0-20 cm soil layer of the paddy field, compared with the NIR and the WIR, collapsing gully erosion caused a very sharp decrease in the SOM and total N of the SIR （5.23 and 0.56 g kg-1, respectively）. But in the surface soil （0-20 cm） of the upland field, the highest SOM, total N, available N, available P and available K occurred in the NIR, and the lowest ones were in the SIR. Compared with the NIR, the cation exchange capacity （CEC） in the SIR and WIR was found to be relatively lower. These results suggest that collapsing gully erosion seriously affect the soil physical and chemical properties of farmland, lead to coarse particles accumulation in the field and decrease pH and nutrient levels.

Controlling Factors of Organic Nanopore Development: A Case Study on Marine Shale in the Middle and Upper Yangtze Region, South China

The Upper Ordovician Wufeng-Lower Silurian Longmaxi and the Lower Cambrian Qiongzhusi shales are the major targets for shale gas exploration and development in China.Although the two organic-rich shales share similar distribution ranges and thicknesses,they exhibit substantially different exploration and development results.This work analyzed the nanopore structures of the shale reservoirs in this region.Pore development of 51 shale samples collected from various formations and locations was compared using the petromineralogical,geochemical,structural geological and reservoir geological methods.The results indicate that the reservoir space in these shales is dominated by organic pores and the total pore volume of micropores,mesopores,macropores in different tectonic areas and formations show different trends with the increase of TOC.It is suggested that organic pores of shale can be well preserved in areas with simple structure and suitable preservation conditions,and the shale with smaller maximum ancient burial depth and later hydrocarbongeneration-end-time is also more conducive to pore preservation.Organic pore evolution models are established,and they are as follows:①Organic matter pore development stage,②Early stage of organic matter pore destruction,and③late stage of organic matter pore destruction.The areas conducive to pore development are favorable for shale gas development.Research results can effectively guide the optimization and evaluation of favorable areas of shale gas.

TEM investigations of South Atlantic Ridge 13.2°S hydrothermal area

According to the exploration contract about polymetallic sulfides in the SWIR （Southwest Indian Ridge） signed by China with the International Seabed Authority, to delineate sulfide minerals and estimate resource quantity are urgent tasks. We independently developed our first coincident loop Transient Electromagnetic Method （TEM） device in 2010, and gained the TEM data for seafloor sulfide at South Atlantic Ridge 13.2°S in June 2011. In contrast with the widely applied CSEM （Marine controlled-source electromagnetic） method, whose goal is to explore hydrocarbons （oil/gas） of higher resistivity than seawater from 102 to 103 m below the sea floor, the TEM is for low resistivity minerals, and the target depth is from 0 to 100 m below the sea floor. Based on the development of complex sulfide geoelectrial models, this paper analyzed the TEM data obtained, proposing a new method for seafloor sulfide detection. We present the preliminary trial results, in the form of apparent resistivity sections for both half-space and full-space conditions. The results cor- respond well with the observations of the actual hydrothermal vent area, and the detection depth reached 50-100m below the bed, which verified the capability of the equipment.

Characteristics of Upper Mantle Activity in the South China Sea Region and the Indochina Mantle Plume

Abstract According to computed results of the mantle traction field beneath the lithosphere based on satellite-modelled gravity anomalies of different degrees, it has been revealed that the three types of mantle convection on different scales existing in the South China Sea region is the key factor controlling the geodynamics. The mantle convection models on large and middle scales have been proved by natural seismic S-wave tomographic data and interpreted by using the present mantle plume concept. In consideration of other relevant geological and geophysical data, the authors put emphasis on discussing the expression form, origin and age of the Indochina mantle plume and its important effect on the conversion of organic matter and hydrocarbon accumulation in Cenozoic basins.

Abundance and Distribution of Fatty Acids in Sediments of the South Mid-Atlantic Ridge

Sediment samples obtained from the South Mid-Atlantic Ridge were studies by gas chromatography-mass spectrometer （GC-MS） for the abundance and distributions of total fatty acids （TFAs）. Approximately 34 fatty acids were identified, with the chain-lengths ranging from C12 to C30. The total concentrations of TFAs （∑TFA） ranged from 7.15 to 30.09 μgg-l dry sediment, and ∑TFA was weakly correlated with bitumen content （R2=0.69）. The ∑TFA of samples around hydrothermal areas were significantly higher than that of samples away from hydrothermal areas, indicating intense primary production and large biomass in the hydro- thermal areas, and suggesting a close relationship between hydrothermal activity and ∑TFA of samples. The characteristics of the TFA composition in the present study are rich in monounsaturated fatty acids and lacking in polyunsaturated fatty acids, and the ra- tios between the concentrations of monounsaturated fatty acids and ∑TFAs in samples close to the hydrothermal areas, are about 0.8, but for samples far from the hydrothermal areas, they are only about 0.5. Several fatty acids （e.g., a/iC15：0 and C16：1co7）, which are signature biomarkers for sulfur-metabolizing bacteria, show the same distribution trend as ∑TFA of samples, further highlighting the close relationship between fatty acid content and hydrothermal activity and/or hydrothermal communities. The metabolic activities of hydrothermal communities, especially those of microorganisms, are likely the main source of fatty acids in samples.

Component characteristics of polycyclic aromatic compounds in sediments of the South Mid-Atlantic Ridge

10 samples of sediments obtained from the South Mid-Atlantic Ridge were measured for the abundances and distributions of polycyclic aromatic compounds（PAHs）. The total concentrations of PAHs（∑PAHs） ranged from 2.768 to 9.826 μg/g dry sediment. The ∑PAHs was higher in sample 22V-TVG10 and sample 26V-TVG05 which were close to hydrothermal fields, with the lowest value in sample 22V-TVG14 which was farthest from hydrothermal fields, suggesting a probable hydrothermal origin of ∑PAHs of samples. Approximately nine kinds of PAHs were identified, and low molecular mass tricyclic and tetracyclic aromatic compounds were predominant in the samples. The concentrations of fluoranthene which were typical as hydrothermal alteration compounds were the highest among PAHs with dry weight between 0.913–3.157 μg/g. The phenanthrene homologue was most abundant in the samples, and the ratios between parent phenanthrene and methylphenanthrene which probably reflected the degree of hydrothermal alteration ranged from 0.097 to 1.602. The sample 22V-TVG10 possessing a maximum ratio value showed the intense influence of the hydrothermal alteration on this sample, which might further imply that PAHs in sediments were mainly derived from the hydrothermal alteration.

Water Resources of the South Asian Region in a Warmer Atmosphere

The global mean surface temperature may rise by about 0.3t per decade during the next few decades as a result o f anthropogenic greenhouse gas emissions in the earth's atmosphere. The data generated in the greenhouse warming simulations (Business-as-Usual scenario of IPCC) with the climate models developed at Max Planck Institute for Meteorology, Hamburg have been used to assess future plausible hydrological scenario for the South Asian region.The model results indicate enhanced surface warming (2.7) for summer and 3.6℃ for winter) over the land reginos of South Asia during the next hundred years. While there is no significant change in the precipitation over most of the land regions during winter, substantial increase in precipitation is likely to occur during summer. As a result, an increase in soil moisture is likely over central india, Bangladesh and South China during summer but a statistically significant decline in soil moisture is expected over central China in winter. A moderate decrease in surface runoff may occur over large areas of central China during winter while the flood prone areas of NE--India, Bangladesh and South China are likely to have an increase ill surface runoff during summer by the end of next century.

Mathematical model of wave transformation over radial sand ridge field on continental shelf of South Yellow Sea

According to a deformed mild-slope equation derived by Guang-wen Hong and an enhanced numerical method, a wave refraction-diffraction nonlinear mathematical model that takes tidal level change and the high-order bathymetry factor into account has been developed. The deformed mild-slope equation is used to eliminate the restriction of wave length on calculation steps. Using the hard disk to record data during the calculation process, the enhanced numerical method can save computer memory space to a certain extent, so that a large-scale sea area can be calculated with high-resolution grids. This model was applied to wave field integral calculation over a radial sand ridge field in the South Yellow Sea. The results demonstrate some features of the wave field： （1） the wave-height contour lines are arc-shaped near the shore; （2） waves break many times when they propagate toward the shore; （3） wave field characteristics on the northern and southern sides of Huangshayang are different; and （4） the characteristics of wave distribution match the terrain features. The application of this model in the region of the radial sand ridge field suggests that it is a feasible way to analyze wave refraction-diffraction effects under natural sea conditions.

The distribution and composition of hydrocarbons in sediments of the South Mid-Atlantic Ridge

Sediment samples obtained from the South Mid-Atlantic Ridge are analyzed by a gas chromatography-mass spectrometer（GC-MS） for the abundances and distributions of hydrocarbons. The hydrocarbons in the samples exhibit a bimodal distribution of n-alkanes and are rich in 3-methylalkanes, 8-methylalkanes and 2, 4,（n-1）-trimethylalkanes, which may be the result of metabolic activity of benthic microorganism. Terpanes, hopanes and steranes are all enriched in the samples, which also support the microbial origin of hydrocarbons in samples.Bitumen and hydrocarbons in the samples show a trend that the contents are the highest in the Samples 22V-TVG10 and 26V-TVG05 collected near hydrothermal areas, and the lowest in samples 22IV-TVG01, 22V-TVG11,and 22V-TVG14 collected far from the hydrothermal areas, which suggest the possible influence on the samples by hydrothermal activity.

Interpretation of the west segment of the coastal fault zone in the coastal region of South China based on the gravity data

By systemic processing, comprehensive analysis, and interpretation of gravity data, we confirmed the existence of the west segment of the coastal fault zone(west of Yangjiang to Beibu Bay) in the coastal region of South China. This showed an apparent high gravity gradient in the NEE direction, and worse linearity and less compactness than that in the Pearl River month. This also revealed a relatively large curvature and a complicated gravity structure. In the finding images processed by the gravity data system, each fault was well reflected and primarily characterized by isolines or thick black stripes with a cutting depth greater than 30 km. Though mutually cut by NW-trending and NE-trending faults, the apparent NEE stripe-shaped structure of the west segment of the coastal fault zone remained unchanged,with good continuity and an activity strength higher than that of NW and NE-trending faults. Moreover,we determined that the west segment of the coastal fault zone is the major seismogenic structure responsible for strong earthquakes in the coastal region in the border area of Guangdong, Guangxi, and Hainan.

Land degradation in the subtropical hilly andmountain regions of South China

Land degradation, caused by water erosion. closely related to inherent vulnerabilities of itseco-environment in South China. Spatial variation of land degradation from top to foot of a slope wasmainly induced by differentiation of surface materials and their erodibility, nutrient and moisture dueto downslope variation of land erosion. It was showed by comparing maps of land degradationbetween the 1950s and the 1980s that changes of land degradation varied from one area to anotherbecause of differences of human activities, including land reclamation and vegetation depletion.