Dongting Lake Area is a semi-closed basin opening toward the north. In this area, alluvial and lacustrine sediments mainly developed in fluvial plain, low level terrace of the rivers and modern lakebed, and Quaternary red earth is widespread in low mountains, hills and hillock. Scholars paid very little attention to the red earth in this area over a long period of time in the past. In order to reveal the genesis of the Quaternary red earth in Dongting Lake Area and its preliminary climatic implications, we did a series of work. The detailed field investigation has shown that there are several types of Quaternary red earth in Dongting Lake Area, and the major type is the red earth with homogenous structure without gravel. The intact stratigraphic profile consists of the lower reticulate red earth layer or reticulate yellow brown earth layer and the upper homogeneous red earth layer or yellow brown earth layer. Ten profiles of this type of Quaternary red earth and 122 samples were collected, and their grain-size was tested by using laser particle size analyzer Malvern 2000, a product of Malvern of the UK. The results showed that: (1) Silt (4~63 μm) is the major type of particle in all samples; clay (<4 μm) is the second major type; sand accounts for the smallest portion. Aeolian particle (10~50 μm) is the dominant particle, and the mean content ranges from 33.23% to 42.23%. These features are similar to those of the loess, Xiashu loess and aeolian red earth, but quite different from fluvial red earth from Xiangjiang Rriver terrace and the residual red earth formed with the rock weathering, indicating that aeolian red earth exists on the hilly land of the west, south and east sides of Dongting Lake Area and they all belong to aggradation red earth in Mid-subtropics. (2) All the samples can be separated into four categories: vermicular red earth, homogeneous red earth, reticulate yellow-brown earth and yellow-brown earth. In terms of grain size composition, their clay contents have a ranking order of vermicular red earth >homogeneous red earth >reticulate yellow-brown earth >yellow-brown earth, while their silt contents show an opposite ranking order. Combined with other information extracted from grain size parameters, we can speculate that sedimentation significantly strengthened during the period of yellow-brown earth, so the sediments become coarser and well sorted. However, in the period of vermicular red earth, sedimentation weakens and weathering strengthens, fine particle content increases, and the red earth are poorly sorted. This probably reflects the environmental change process in which winter monsoon strengthens and weathering weakens from the mid-Pleistocene to the late Pleistocene around Dongting Lake Area. (3) Along with the direction of the winter monsoon, the average particle size and median size (φ value) of the red earth become bigger (become smaller) southwards, but the percentages of aeolian component (10~63 μm) decrease while that of the<2 μm component increase slightly. These trend, therefore, provide aeolian evidence for the Quaternary aggradation red earth sediments and suggests that the intensity of weathering enhances southwards in the Dongting Lake Area.

In this paper, based on classification method and legend layout of published geomorphological maps of the nation at different levels and different scales and the hierarchical classification method for the digital geomorphology of China with a scale of 1:1000000, we proposed a hierarchical land classification system with the indicators in five major categories. The indicators include basic landform form, morphological characteristics of geomorphological types (including morphological assembly, micro-landform morphological entities, slope form characteristics of landform surface), basic genesis and main genetic action ways, materials and lithology, formation age or period of geomorphological types, which all combined are a comprehensive presentation of geomorphological characteristics. These indicators can be divided into three categories and nine levels: landform superclass (sub-superclass), landform class (sub-class) and landform type (sub-type), at the nine levels, such as macro morphology, terrain characteristics, main genetic condition, main genetic action ways, morphological assembly, micro-landform morphological entity, slope characteristics, material and lithology and landform formation age. The geomorphological characteristics can be expressed by means of not only continuous polygons addressing morpho-genetic types, but also discrete points, lines and polygons addressing morpho-structural types. The morpho-genetic and morpho-structural geomorphological types can be exchanged for each other based on mapping scales. Based on geomorphological characteristics, the indicators of former four grades can be mapped for 1: 4000000 geomorphological maps, and former five grades for 1:1000000 geomorphological maps, and former seven grades for 1:500000 geomorphological maps. As to 1:250000 and 1:50000 geomorphological maps, parts of morpho-structural geomorphological types can be converted to morpho-genetic geomorphological types, slope form characteristics, terrain slope position, material and lithology and formation age of micro-landforms can be highlighted in order to realize the expression for detailed geomorphological types. As to China's offshore and adjacent ocean topography and geomorphology, four hierarchical geomorphological types can be classified in terms of spatial position, water dynamic condition (ocean water depth and slope characteristics), and lithosphere types and depth change. Form-genetic types can be expressed by means of the former three classes and form-structural types can be expressed by means of fourth class.

Cumulative probability curve of particle granularities is one of the methods to study the sediments. However, the sediments in the studies were mainly sands/sandstone and silts/siltstone, and granule at most in the past. Recently the rivers with large gravel bed materials including pebbles, cobbles and boulders in mountainous regions have been studied more and more. But the distribution pattern of the granularities of coarse gravels such as pebbles, cobbles and boulders has yet to be well studied. In this study, taking the modern gravel sediments of the mountainous Ganxi Stream in Zhangjiajie scenic spot as an example, the cumulative probability curves of gravel granularity were studied for the sampling on the channel bed, mid-channel bar and channel bank. The granularities of these gravel sediments ranged from 23 mm to 663 mm, with most of them being pebbles, cobbles and boulders. The results showed that these fluvial gravel sediments followed a statistical pattern very well and exhibited a spatial variation trend that reflected the river flow hydrodynamics. For each sample the gravel granularities could be expressed by a cumulative probability curve clearly with two or three sections. The gravels in different sections reflected different fluvial power in different flooding stages. Granularity parameters showed that the gravel sediments have higher degree of sortability and sphericity. The median diameters of the gravels on channel bed have a decreasing trend downstream, reflecting the decrease of stream power in that direction. The reason for the various kurtosis of the gravels is that the blocks that fell to the river from the cliffs of "the sandstone forest" had not been modified sufficiently by the stream flow. The fine gravels intercepted in the apertures of cobbles and boulders in low flooding stages resulted in negative deflection of granularity distribution of the channel gravel sediments. By comparing the sphericity among different lithological gravels one can find that the gravels composed of carbonate rocks have the highest level of sphericity while the gravels composed of quartzose sandstone have lower level of sphericity. This phenomenon suggests that the quartzose sandstone gravels have higher ability to resist the flow erosion while the carbonate rock gravels have lower ability. This work is a useful attempt to study the distribution pattern of fluvial gravels including boulders, and has a revelatory significance to the quantitative studies of the coarse gravel sediments such as cobbles and boulders in mountainous fluvial rivers with steep gradients.

DEM-based terrain analysis has been widely used in geomorphology. Currently most researches are qualitative or semi-quantitative, whereas quantitative analyses of large areas based on a variety of parameters are few and far between, and most studies use artificial field measurement with a small scale in the aspect of the relative age of the landscape entity. So, in this article, by using 30 m ASTER-GDEM, GIS and digital terrain analysis method, we extracted morphological parameters of a wide range of the areas of loess tablelands and determined their relative ages. We tried to provide basic knowledge of multi scale representation of the loess tablelands and fine landforms, achieved quantitative descriptions of the similarities and differences among the loess tablelands, and calibrated their developmental stages. First, we extracted positive landforms less than 15° in the Loess Plateau. Then, we acquired the top surface of the loess tableland using two parameters: gradient and waviness. We determined 1106 loess tablelands based on the subtraction between positive landform layer and the top surface layer. We selected 106 loess tablelands as samples to calculate average slope, axial ratio of top surface, gully density, top and bottom area ratio, percentage of negative terrain. The geometric mean of these five parameters was used as an index to estimate the relative age of the loess tableland. The index (abbreviated to I) was categorized into three levels: early development (I<1.74), middle development (1.74≤I<2.12) and late development (I≥2.12). The results showed that: (1) the morphological parameters of loess tablelands are different from one another in different developmental stages; (2) developmental stages are also inconsistent for the subtypes; (3) transitional type exhibits the characteristics more similar to the type of the previous stage. After calculating I of each subtype, we found that from early to late stages of the loess tablelands, I value increases gradually, which is consistent with other researchers' conclusions on the developmental stages of loess landforms.

Due to the scale effect of changing resolution for grid-based digital terrain analysis, it is important to determine an appropriate resolution (or a range of appropriate resolutions) for gridded digital elevation model (DEM) in practice. The commonly-used approach to determining appropriate resolutions is based on a scale effect curve characterized by certain types of statistics (the mean of local variance is commonly used), which is calculated on the multi-resolution dataset of a specific topographic attribute derived from the gridded DEMs with a series of spatial resolutions. The resolution with the highest value of the mean of local variance is considered to be an appropriate DEM resolution. Although several topographic attributes (such as slope gradient and curvature) have been used in this approach, there are few researches on the effects of different topographic attributes on the results from this approach. In this paper, we used an experiment to compare the effects of three types of topographic attributes (i.e., slope gradient, profile curvature, and horizontal curvature) applied to determining appropriate DEM resolutions. The experiment was conducted in three study areas with different terrain conditions, i.e. Xuancheng area with low relief, Coweeta area with high relief, and Kaixian area with more complex terrain conditions. The tested topographic attributes were calculated from the DEMs with a series of spatial resolutions (i.e., 5, 10, 15, 20, 25, 30, 50, 100, 150, 200, 300 m). For each topographic attribute, two widely-used algorithms were tested. One is proposed by Wood (1996), and the other is the one implemented in Arc-GIS software. The appropriate DEM resolution for a study area had the highest value of the mean of local variance derived from each tested topographic attribute, respectively. Experimental results showed that the effects of slope gradient and curvature are different on the results of the appropriate DEM resolution, while there is little difference between the results from profile curvature and horizontal curvature. The appropriate resolutions based on slope gradient information (i.e., 15, 50, and 100 m for Xuancheng area, Kaixian area, and Coweeta area, respectively) are coarser than those based on curvature information (i.e., 5, 10~15, and 5 m for Xuancheng area, Kaixian area, and Coweeta area, respectively), while the difference between them is less for the study areas with low relief. When slope gradient information was used, the appropriate resolution results for the study area with high relief are coarser than those for the area with low relief. When curvature information was used, the appropriate resolution results for the study areas with simple terrain conditions (such as Xuancheng area with low relief, and Coweeta area with high relief) are finer than those for the study area with complex terrain conditions. The range of appropriate resolutions from each topographic attribute for the study areas with simple terrain conditions is much wider than that for the study areas with complex terrain conditions. For each specific topographic attribute there is no difference between the effects of the tested algorithms of topographic attribute on the results of appropriate resolutions.

Building specific sediment yield map is important for planning of soil and water conservation. While the traditional method to build a specific sediment yield map usually ignored the scale effect on specific sediment yield, namely, the influence of drainage area on specific sediment yield, many researches have proved there is a functional relation between specific sediment yield and drainage area. Therefore, the scale effect should be considered when building specific sediment yield. In this paper, the scale effect of specific sediment yield is studied in the Haihe River Basin. Following the principles of integrity of river basin and the similarity of topography, the Haihe River Basin is divided into 9 sub-regions. The scale effects of all sub-regionson specific sediment yield could be classified into three regional trends: (1) a flat trend; (2) a decreasing trend; (3) an increasing trend. Scale effect for each sub-region is explained based on location, topology, geomorphology, and land use forms. Sub-regions with flat trends are mainly located in the areas of mountainous upper reaches and limited flood plains of lower reaches. Soil erosion is severe in mountainous area, and sediment has little chance to silt down on flood plains. Sub-regions with decreasing trends are mainly located in the areas of limited mountainous upper reaches and large flood plains of lower reaches, where sediment transported from mountains have more chance to silt down. There is only one sub-region with increasing trend, located in the upper reaches of the Baihe River Basin and extended from grassland with slightly soil erosion to the loess covered area with severe soil erosion. Equations are used to offset the influence of drainage area on specific sediment yield, and specific sediment yields of all hydro-stations are all calculated under a standard area. Kriging interpolation is used to create specific sediment yield maps on standard area of 1000 km² using equation of each sub-region. The pattern of specific sediment yield map shows strong soil erosion in the west and low erosion in the east, consistent with topographic distributions of the Haihe River Basin, with mountains in the west dominated by erosion and plains in the east dominated by deposition. There are two high specific sediment yield areas. One is located in the upper reaches of the Yongdinghe River Basin, Daqinghe River Basin, and Fuyanghe River Basin, with underlying surfacecovered by loess. The other one is located in the middle reaches of the Luanhe River Basin, expanding from loess to earth-rocky mountainous area. Those high value areas are the key areas for planning soil and water conservation.

The surface runoff of some rivers in the world has decreased significantly with global or regional climate changes and increasing human activities, which has caused severe eco-environmental problems. The Songhua River is a large river in Asia and its basin is an important bread basket in China. The runoff of the whole river basin and in different sections has experienced dramatic changes over the last few decades. It is necessary to study the trend of the runoff changes and quantify the influencing factors on the changes. Based on annual runoff data at 4 gauging stations in the mainstream of the river and annual precipitation data from 61 meteorological stations in and around the river basin during 1955-2010, a decreasing trend of annual runoff and precipitation for four sections (above Jiangqiao, Jiangqiao-Dalai, Dalai-Haerbin and Haerbin-Jiamusi) was revealed using the linear trend method. The cumulative anomaly was employed to detect the abrupt changes of each runoff series. Three inflexion years for the runoff incremental changes were detected and they divided the entire period into four parts: above Jiangqiao (1963, 1982 and 1998), Jiangqiao-Dalai (1962, 1985 and 1998), Haerbin-Jiamusi (1966, 1980 and 1998), and only one turning year (1988) was found in Dalai-Haerbin section. The first period (T₁) is regarded as the baseline period; the others are measurement periods. Without considering the effect of evapotranspiration, the slope change ratio of cumulative quantity (SCRCQ) was adopted to estimate the impacts of precipitation and human activities on runoff changes for the sections. In above Jiangqiao (T₂: 1964-1982, T₃: 1983-1998), Jiangqiao-Dalai (T₂: 1963-1985, T₃: 1986-1998) and Haerbin-Jiamusi (T₂: 1967-1980, T₃: 1981-1998) sections, the impacts of human activities on runoff incremental decrease were 71%~88%, 94%~97% and 72%~85%, respectively, while those of precipitation were 12%~29%, 3%~6% and 15%~28%, respectively, for the measurement periods of T₂, T₃ and T₄ (1999-2010) compared with T₁. In the measurement period (1989-2010), the impact of human activities on runoff changes in Dalai-Haerbin section was 75%, while that of precipitation was 25%. Obviously, the human activities were the most important factor causing runoff yield reduction in the later three periods for different sections of this study area. In addition, the impacts of human activities on runoff yield changes reached the maximum in the 1980s and 1990s. Although the runoff yield for different sections showed different variation characteristics, the reduction is mainly due to population increase and construction of water conservation projects.

Karst rocky desertification is the third severe land degradation in China, following desertification in the north and soil and water loss in the Loess Plateau. This paper reviewed the progress and problems in the studies of Karst rocky desertification, and proposed a new method, which is temporal trajectory analysis based on high-resolution remote sensing data. At present, we have achieved great progress in the fields such as karst geology and geomorphology, restoration and reconstruction of Karst ecosystem, spatial pattern and dynamic changes of rocky desertification, evolution mechanism of karst rocky desertification as well as monitoring methods based on remote sensing. However, there are still a number of problemsin the studies of evolutional process of karst rocky desertification: (1) Current studies are mainly focusing on the spatial pattern of the rocky desertification based on remote sensing data and have successfully described the degree of severity of land degradation, but few of them are concerning the evolutional process of karst rocky desertification; (2) Most of the studies on the evolutional mechanism of Karst rocky desertification are qualitative descriptions and few of them are quantitative analyses; (3) The remote sensing monitoring methods normally are the double temporal variation detection method based on the "two time cycle" scales; only the information of "change/no change" or "what changes from what" can be acquired. Therefore, a new method, temporal trajectory analysis based on middle/high resolution remote sensing data, is introduced in this paper. This methodfocuses on "continuous" variations in a long time scale, and it is concerning not only what has changed between two time points, but also "where" and "how" the changes happened. By the temporal trajectory analysis method, the rocky desertification process in a long time series can be investigated, and the development of rocky desertification can be quantitatively and spatiallytracked, so that we can know where, how and why the rocky desertification has happened. Temporal trajectory analysis method has advantages in discovering the evolutional process of rocky desertification. Moreover, quantitative analysis ofthe pattern, process and evolutional mechanism of Karst rocky desertification will be the trend in the future.

Currently, many different erosion and sediment transport models are available. They are important tools to predict soil erosion and sediment yield under different conditions. The most commonly used models include Universal Soil Loss Equation (USLE), Revised Universal Soil Loss Equation (RUSLE), Water Erosion Predict Project (WEPP), Soil and Water Assessment Tool (SWAT), and the Limburg Soil Erosion Model (LISEM), et al. The physical distributed soil models can be well used in other regions once they were built in a given region. Therefore, physical soil erosion model hasreceived more attentionover the decades. However, the structures of the physical erosion models are usually complex and a lot of parameters are required to run them, which to some extent limits their applications. The Water and Tillage Erosion Model and Sediment Delivery Model (WaTEM/SEDEM) developed at the Physical and Regional Geography Research Group, KU Leuven University, Belgium, is a spatially distributed soil erosion and sediment delivery model. Unlike other more sophisticated dynamic models, this model requires minimal basis data input and the model structure is simple, similar to RUSLE model. Although WaTEM/SEDEM has data requirement almost similar to RUSLE model, it can assess both water and tillage erosion simultaneously. Mostly importantly,WaTEM/SEDEM can spatially model soil erosion and sediment deposition rates as well as the soil redistribution patterns. This model also allows incorporation of landscape structure or the spatial organization of different land units and the connectivity, and can then be used to delineate sediment source areas in an agricultural landscape, and to simulate the impact of various scenarios of an integrated catchment management on the rates and patterns of soil loss and sediment delivery. Therefore, WaTEM/SEDEM can provide useful information for land managers to implement rational management to control soil loss. Up to date, the model has been successfully used in Europe and other regions around the world. However, few studieshave been conducted in China using this model. In this paper, the model structure, the algorithms used to calculate soil erosion and sediment transport, the model input and output, and its applications were systematically introduced. A case study in Shuangfengtan catchment, Hunan Province was also reported in this paper to verify its usefulness. Besides the advantages mentioned above, the disadvantages of this model were also pointed out. For example, WaTEM/SEDEM does not predict sediment transport within a river, bank erosion or floodplain sediment deposition. At the end of this paper, the prospect of the application of WaTEM/ SEDEM in the data-limited regions was discussed.